(190-V-NAM, 3rd Ed., October 2002) 502–95 

Background

Small grain equivalents (SGe) expresses the effectiveness of residue or growing crops in resisting wind erosion, as compared 

with a reference condition. Agricultural Research Service has established benchmark SGe values for several common crops by 

wind tunnel testing. The research indicates that effectiveness of vegetative material is the result of vegetative roughness and is 

a function of residue weight, average stalk diameter, specific weight of stalk, orientation relative to the ground surface (standing or flat), and spatial distribution. Spatial distribution relates to plant population, row spacing, and row direction relative to 

wind flow. 

Conservation planners frequently need to estimate the effectiveness of vegetation or residue for which small grain equivalence 

has not been determined. In the absence of wind tunnel tests or predictive equations, it may be desirable for NRCS to develop 

interim best judgment SGe curves based on judgment and field experience as a basis for consistent estimates. This can be 

done with confidence when the relationships are understood. The general principles are: 

• Standing residue is more effective than an equal weight of flat residue. 

• Fine residue is more effective, pound for pound, than coarse residue. 

• Given equal diameter and equal pounds per acre, residue that has low specific weight (density) is more effective than 

residue with high density. 

• Rows perpendicular to wind are more effective than rows parallel to wind. 

• Dense stands are more effective than thin stands. 

Several of the SGe curve charts in exhibit 502–10 were developed using the procedure described below. The footnotes with 

each figure identify which curves are best judgments by NRCS and which are from published sources resulting from wind tunnel research by ARS. Interim curves developed using similar procedures are to be submitted to the national agronomist or to 

an NRCS Cooperating Scientist located at an ARS Research Unit, for technical review and approval for trial use. 

Procedure

1. Use only the SGe curves developed and published by ARS in exhibits 502–10, figures a–1 through d–8 as benchmark values. 

2. Select one or more benchmark crops having physical characteristics similar to the crop in question. For purposes of 

comparison, give preference to SGe curves from published sources and minimize use of curves based on best judgment estimates. 

3. Array the selected crop and the benchmark crops in order of apparent effectiveness on a pound-for-pound basis. Use 

comparative physical characteristics such as stalk diameter and 

density for guidance. If possible, bracket the crop in question between two benchmark crops. 

4. By interpolation from benchmark curves, estimate and plot a curve for the crop in question. Estimate at least two 

SGe values, representing low and high levels of residue, to establish the slope of the curve. 

Example (This procedure was used to develop the SGe curve for standing flax, figure b-9.): 

Exhibit 502-11 Estimating small grain equivalents for

untested vegetation
502–96 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Crop

Flax, standing stubble

Benchmark crops with similar characteristics—winter wheat; other similar crops that have curves available for comparison—millet. 

Comparative characteristics and effectiveness: flax stubble (6-inch height) is assumed to be finer and denser than 

small grains and millet. Standing flax is assumed less effective than standing millet (4-inch height) because of stubble 

height that relates to thinner stands (pound for pound). 

Estimated small grain equivalents SGe value (by interpolation):

Pounds residue SGe, Winter wheat SGe, Flax (estimated) SGe, Millet 

 (figure a-1) (figure a-7) 

200 750 480 360 

500 1,800 1,200 850 

2,000 7,000 4,400 3,200 

Additional note

Some predictive equations have been developed to estimate the SGe of vegetative material. To use these equations, 

diameter and specific weight must be known, as well as the amount and orientation of the material. Contact the state 

or national agronomist for assistance in using these procedures. 
(190-V-NAM, 3rd Ed., October 2002) 502–97 

Background

When the wind tunnel is used to determine small grain equivalents of vegetative cover, the material tested is usually uniform 

in size, density, and orientation. Vegetative cover found in the field, however, frequently includes two or more components 

that are not alike. Common combinations are (l) part standing and part flat, (2) part course and part fine, or (3) part growing

and part dead. 

SGe values for mixed cover can be determined in the wind tunnel. However, there are too many possible combinations for development of practical field guides. When SGe conversion curves represent uniform components, the reference values can be 

combined to estimate SGe for any mixture of vegetative cover. 

The following procedure is recommended for estimating SGe of mixed vegetative cover. 

Procedure

1. Describe each major type of vegetative cover and estimate the percentage of total air-dry weight made up of each 

component. 

2. Using the appropriate conversion curve, and total air-dry weight of all the vegetative cover, determine the SGe value 

of each component cover type. 

3. Multiply the SGe value of each component by that component’s percentage of total air-dry weight. 

4. Add the products. The sum of the products is the weighted SGe for the mixed cover. 

Example crop:

Winter wheat, 2,500 lb residue (air-dry weight) after harvest. 1,500 lb (60 percent) is standing stubble and 1,000 lb (40 percent) is flat randomly distributed straw. 

Calculation: 

Standing winter wheat: 

2,500 lb = 8,500 lb SGe x 0.60 = 5,100 lb 

Flat winter wheat: 

2,500 lb = 3,300 lb SGe x 0.40 = 1,320 lb 

Weighted average: 

SGe = 6,420 lb 

Exhibit 502-12 Estimating small grain equivalents of

mixed vegetative cover that has two or

more components
502–98 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Exhibit 502–13 Crop yield — residue conversions

(This section reserved, to be developed) 

Exhibit 502–14 Residue reduction by tillage

(This section reserved, to be developed) 

Exhibit 502–15 E Tables: Soil loss from wind erosion

in tons per acre per year

(Insert appropriate E tables for local values of the climatic factor, C) 

Exhibit 502–16 Wind physics

(This section reserved, to be developed) 

Exhibit 502–17 Wind erosion control exhibits

(This section reserved, to be developed) 
(190-V-NAM, 3rd Ed., October 2002) 502–99 

National 

Agronomy 

Manual 

Part 502 Wind Erosion

Subpart 502G References

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Manual 

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Chepil, W.S. 1960. How to determine required width of 

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farm fields. Jour. Soil and Water Conserv. 17(4):162- 

165. 

Chepil, W.S. and N.P. Woodruff. 1954. Estimations of 

wind erodibility of field surfaces. Jour. Soil and Water Conserv. 9:257-265, 285. 

Chepil, W.S., N.P. Woodruff, F.H. Siddoway, D.W. 

Fryrear, and D.V. Armbrust. 1963. Vegetative and 

nonvegetative materials to control wind and water 

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Chepil, W.S., N.P. Woodruff, and A.W. Zingg. 1955. Field 

study of wind erosion in western Texas. USDA, 

SCS-TP-125. 

Cole, George W. 1984. A stochastic formulation of soil erosion caused by wind. Trans. Amer. Soc. Agr. Engin. 

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Durar, A.A., J.L. Steiner, S.R. Evett, and E.L. Skidmore. 

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Downes, J.D., D.W. Fryrear, R.L. Wilson, and C.M. 

Sabota. 1977. Influence of wind erosion on growing 

plants. Trans. Amer. Soc. Agr. Engin. 20:885-889. 

Fisher, P.S. and E.L. Skidmore. 1970. WEROS: A FORTRAN IV program to solve the wind erosion 

equation. USDA, ARS 41-174, 13 pp. 

Fryrear, D.W. 1969. Reducing wind erosion in the southern 

Great Plains. Tex. Agr. Expt. Sta., Misc. Publ. 929, 

pp. 1-10. (Technical Report) 

Fryrear, D.W. 1971. Survival and growth of cotton plants 

damaged by windblown sand. Agron. Jour. 

63(4):638-642. 

Fryrear, D.W. 1981. Tillage influences monthly wind erodibility of dryland sandy soils. In Crop production with 

conservation tillage. Amer. Soc. Agr. Engin. Publ. 

#7-81, pp. 153-163. 

Fryrear, D.W., D.V. Armbrust, and J.D. Downes. 1975. 

Plant response to wind-erosion damage. Proc. 30th

Annual Meeting of Soil Conserv. Soc. Amer., Aug. 

10-13, 1975, San Antonio, Texas, pp. 144-146. 

Fryrear, D.W., and J.D. Downes. 1975. Consider the plant 

in planning wind erosion control systems. Trans. 

Amer. Soc. Agr. Engin. 18:1070-1072. 

Fryrear, D.W., and P.T. Koshi. 1971. Conservation of 

sandy soils with a surface mulch. Trans. Amer. Soc. 

Agr. Engin. 14(3):492-495, 499. 

Fryrear, D.W., C.A. Krammes, D.L. Williamson, and T.M. 

Zobeck. 1994. Computing the wind erodible fraction 

of soils. Jour. Soil and Water Cons. 49(2):183-188. 

Fryrear, D.W., J. Stubbendieck, and W.G. McCully. 1973. 

Grass seedling response to wind and windblown sand. 

Crop Sci. 13(6):622-625. 
(190-V-NAM, 3rd Ed., October 2002) 502–101 

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Manual 

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Hagen, L.J. 1976. Windbreak design for optimum wind erosion control. In Proc. of the Symposium “Shelterbelts 

on the Great Plains,” Great Plains Agr. Council Publ. 

No. 78, pp. 31-36. 

Hagen, L.J. 1991. A wind erosion prediction system to meet 

user needs. Jour. Soil and Water Conserv. 46(2):105- 

111. 

Hagen, L.J. 1995. Erosion submodel. In Wind erosion prediction system technical description. Proc. of WEPP/ 

WEPS Symposium, Soil and Water Conservation Society, Ankeny, IA. 

Hagen, L.J. 1995. Wind erosion: emission rates and transport capacities on rough surfaces. Amer. Soc. Agric. 

Engin. Paper No. 91-2082, St. Joseph, Michigan. (Society Proceedings) 

Hagen, L.J. and D.V. Armbrust. 1992. Aerodynamic roughness and saltation trapping efficiency of tillage ridges. 

Trans. Amer. Soc. Agric. Engin. 35(5):1179-1184. 

Hagen, L.J., E.L. Skidmore, and J.D. Dickerson. 1972. Designing narrow strip barrier systems to control wind 

erosion. Jour. Soil and Water Conserv. 

27(6):269-272. 

Hagen, L.J., E.L. Skidmore, P.L. Miller, and J.E. Kipp. 

1981. Simulation of effect of wind barriers on airflow. Trans. Amer. Soc. Agr. Engin. 

24(4):1002-1008. 

Hagen, L.J., and N.P. Woodruff. 1975. Particulate loads 

caused by wind erosion in the Great Plains. APCA 

Jour. 25(8):860-861. 

Lyles, L. 1980. The U.S. wind erosion problem. Amer. Soc. 

Agr. Engin. Publication 7-81, Proc. of the ASAE 

Conf. on Crop Production with Conservation in the 

80s, December 1-2, 1980, Chicago, Illinois, pp. 

16-24. 

Lyles, L. 1981. Equivalent wind-erosion protection from selected crop residues. Trans. Amer. Soc. Agr. Engin. 

24(2):405-408. 

Lyles, L. 1983. Erosive wind energy distributions and climatic factors for the West. Jour. Soil and Water 

Conserv. 38(2):106-109. 

Lyles, L. 1983. Improved wind erosion prediction. Paper 

presented at 1984 ARS Erosion Workshop, Purdue 

University, West Lafayette, Indiana, November 1983. 

Lyles, L. 1985. Predicting and controlling wind erosion. 

Agric. History 59(2):205-214. 

Lyles, L. and Bruce E. Allison. 1980. Range grasses and 

their small grain equivalents for wind erosion control. 

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Lyles, L. and R.K. Krauss. 1971. Threshold velocities and 

initial particle motion as influenced by air turbulence. 

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Lyles, L. and N.P. Swanson. 1976. Advances in wind and 

water erosion control. Proc. of Conservation Tillage 

Workshop, August 10-12, 1976, Fort Collins, Colorado. Great Plains Agr. Council Publ. No. 77, pp. 

13-32. 

Lyles, L., and J. Tatarko. 1982. Emergency tillage to control wind erosion: Influences on winter wheat yields. 

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windblown soil on plant seedlings. Agron. Jour. 

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Lyles, L., N.F. Schmeidler, and N.P. Woodruff. 1973. 

Stubble requirements in field strips to trap windblown 

soil. Kans. Agr. Expt. Sta. Res. Pub. 164, 22 pp. 

Mech, S.J., and N.P. Woodruff. 1967. Wind erosion on irrigated lands. Agron. Monograph No. 11, Irrigation of 

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964-973. 

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22-69. 

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(Lycopersicon esculentum L.). Jour. Amer. Soc. Hort. 

Sci. 103(3):351-355. 
502–102 (190-V-NAM, 3rd Ed., October 2002) 

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Part 502 Wind Erosion

Renard, K.G., G.R. Foster, G.S. Weesies, D.K. McCool, 

and D.C. Yoder, coordinators. 1997. Predicting Soil 

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wind erosion control. Trans. Amer. Soc. Agr. Engin. 

8(3):327-331. 

Skidmore, E.L. 1965. Assessing wind erosion forces: directions and relative magnitudes. Soil Sci. Soc. Amer. 

Proc. 29(5):587-590. 

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green beans. Agron. Jour. 58:311-315. 

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Symposium Series 38, Atmosphere- Surface Exchange of Particulate and Gaseous Pollutants (1974), 

pp. 452-465. 

Skidmore, E.L. 1983. Wind erosion calculator: revision of 

residue table. Jour. Soil and Water Conserv. 

38(2):110-112. 

Skidmore, E.L. 1984. Wind climatic erosivity. Paper presented at ASA meeting, Las Vegas, Nevada. 

Skidmore, E.L. 1987. Wind erosion direction factors as influenced by field shape and wind preponderance. Soil 

Sci. Soc. of America Jour. 51(1):198-202. 

Skidmore, E.L., and L. Dahl. 1978. Surface Soil Drying: 

Simulation Experiment. Abstracts for commission papers, 11th Congress. Int. Soc. Soil Sci., Edmonton, 

AB. 19-27 June 1978. 

Skidmore, E.L., and L.J. Hagen. 1977. Reducing wind erosion with barriers. Trans. Amer. Soc. Agr. Engin. 

20(5):911-915. 

Skidmore, E.L., and N.P. Woodruff. 1968. Wind erosion 

forces in the United States and their use in predicting 

soil loss. USDA, Agricultural Research Service, Agriculture Handbook No. 346 42 pp. 

Skidmore, E.L., P.S. Fisher, and N.P. Woodruff. 1970. 

Wind erosion equation: computer solution and application. Soil Sci. Soc. Amer. Proc. 34(5):931-935. 

Skidmore, E.L., M. Kumar, and W.E. Larson. 1979. Crop 

residue management for wind erosion control in the 

Great Plains. Jour. Soil and Water Conserv. 

34(2):90-96. 

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Soil Conservation Service; SCS-TP-108. 

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field environment and crops: a guide for determining 

design and orientation. USDA, Forest Service, Production Research Report No. 62. 

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21:633-655. 

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Organization, Geneva, Switzerland. 

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shelter angle and surface roughness and cumulative 

sheltered storage depth. In J. Karacsony and G. Szalai 

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(Conference Proceedings) 

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factor for applying the wind erosion equation on irrigated land. USDA, Soil Conservation Service. 

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(EPIC). Unpublished draft. 

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present, and future. Proc. of 30th Annual Meeting of 

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Antonio, Texas, pp. 147-152. 
(190-V-NAM, 3rd Ed., October 2002) 502–103 

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Manual 

Part 502 Wind Erosion

Woodruff, N.P., and D.V. Armbrust. 1968. A monthly climatic factor for the wind erosion equation. Jour. Soil 

and Water Conserv. 23(3):103-104. 

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equation. Soil Sci. Soc. Amer. Proc. 29(5):602-608. 

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control. Proc. of the National Conservation Tillage 

Conference, Des Moines, Iowa, March 28-30, 1973, 

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wind erosion control. Agr. Engin. 37:751-754, 758. 

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29(3):127-129. 

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Fryrear. 1972. How to control wind erosion. USDA, 

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22 pp. 

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and M.C. Lundquist. 1976. Selected trees and shrubs 

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43:191-193. 
(190-V-NAM, 3rd Ed., October 2002) 503–i 

Crop Production

Contents: 

Part 503

Subpart 503A Crop rotation 503–1

503.00 Definition .......................................................................................................... 503–1 

503.01 Benefits of crop rotations .................................................................................. 503–1 

Subpart 503B Tillage systems 503–2

503.10 Introduction ...................................................................................................... 503–2 

503.11 Conservation tillage .......................................................................................... 503–2 

Subpart 503C Nutrient management (Under development) 503–5

Subpart 503D Pest management (Under development) 503–5

Subpart 503E Crop residue 503–6

503.40 Benefits of managing crop residue ................................................................... 503–6 

503.41 Crop residue production (Under development) ................................................ 503–6 

503.42 Crop residue retention (Under development) ................................................... 503–6 

503.43 Estimating crop residue cover ........................................................................... 503–6 

503.44 Determining the weight of standing vegetative cover ....................................... 503–7 

Subpart 503F References 503–8

Figures Figure 503–1 Acceptable orientations for residue measurement lines 503–6 

Figure 503–2 Counting residue pieces along a line transect 503–7 

Exhibits Exhibit 503–1 Example worksheet for recording crop residue measurement 503–8 

Exhibit 503–2 Example worksheet for recording crop residue measurement 503–9 
503–ii (190-V-NAM, 3rd Ed., October 2002) 
 190-V-NAM, 3rd Ed., October 2002) 503–1 

Subpart 503A Crop rotation

503.00 Definition

A crop rotation is a sequence of different crops grown in a 

recurrent sequence over a given number of years. In some 

rotations a crop may occupy the land two years in succession. Crop rotations can vary in one or more of the following ways (Beck 1990): 

• Plant family – grass vs. broadleaf 

• Life cycle – annual vs. biennial vs. perennial 

• Season of growth – winter annual vs. spring/summer 

annual 

• Rooting depth – shallow vs. moderate vs. deep 

• Residue production – light vs. heavy 

• Residue type – fragile vs. non-fragile 

• Water use efficiency – high vs. low 

To realize the greatest benefits, a crop rotation should not 

have the same annual crop grown 2 years in succession and 

should alternate plant families. This minimizes the potential 

for build-up and carryover of insect and disease populations, and maintains some degree of diversity in the cropping system. 

503.01 Benefits of crop rotations

Properly designed crop rotations provide many benefits, 

and give producers more management options for their 

cropping systems. Conservation planners, when working 

with producers to develop a conservation management system, should emphasize the importance of maintaining the 

planned sequence of crops in the rotation. The benefits that 

accrue from the rotation, such as erosion reduction and pest 

management, depend on the crops being grown in the designated order. Crop rotations can help address the following 

resource concerns: 

Pest management — Rotations can reduce the incidence 

and severity of weeds, insects, and diseases in a cropping 

system. When a different crop is grown each year, a different host crop is present that is usually not compatible with 

pest problems that may have carried over from the previous 

year. Because of this, the levels of any given pest are kept 

at levels that make them easier to manage. A crop rotation 

allows the use of different management strategies for pest 

problems. Herbicides and insecticides with differing modes 

of action can be used, reducing the possibility that some 

Part 503 Crop Production 

species will become resistant to chemical control. Different 

crops each year may allow tillage to be used to control 

pests, further reducing the need for chemical controls 

(Sprague and Triplett 1986). 

Erosion control — Cropping systems that consist of continuous row crops and excessive tillage have a higher potential for wind or water erosion than rotations that include 

closely-spaced row crops or perennial crops. Different 

crops have different growth and development periods so 

that one crop may provide protection from erosive forces 

during a period of the year that another may not. Closelyspaced row crops, such as small grains or narrow-row soybeans, or perennial crops provide more canopy and surface 

cover than wide-row crops and reduce the potential for erosion. 

Surface residue — Surface residue is one of the most effective erosion reduction measures available. High residueproducing crops following low residue-producing crops 

help maintain higher levels of crop residue on the soil surface. Residue management practices, such as mulch tillage 

or no-till, can help maximize the amount of crop residue on 

the soil surface during critical erosion periods. 

Soil quality — Cropping sequences that include hay or pasture crops in rotation produce greater soil aggregate stability than systems that have continuous grain crops. In systems that have all grain crops, greater aggregate stability 

occurs with crops that produce higher amounts of residue. 

For example, rotations that alternate sorghum with soybeans 

result in greater organic carbon levels in the soil than with 

continuous soybeans (Unger 1994). 

Nutrient management — Crop rotations that have forage 

legumes or legume cover crops preceding grain crops can 

reduce the need for nitrogen (N) fertilizer for the grain crop. 

Average corn yields of 160 bushels per acre have been obtained with corn following alfalfa (Triplett et al. 1979). Leguminous cover crops can provide an estimated 60 to 70 

pounds of N per acre (Hargrove 1986). Small grain crops 

following legumes can scavenge the nitrogen fixed by the 

legume, reducing the potential for N losses by leaching. 

Water management – Dryland cropping systems can take 

advantage of stored soil moisture by alternating shallow and 

deep-rooted crops. For example, many areas in the Great 

Plains alternate winter wheat, a shallow-rooted crop, with 

safflower, a deep-rooted crop. 
503–2 (190-V-NAM, 3rd Ed., October 2002) 

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Livestock feed production – For livestock operations, crop 

rotations that include hay and pasture can provide a major 

portion, and in some cases, all of the livestock forage and 

feed. Additional information on planning crop rotations for 

livestock operations is in the National Range and Pasture 

Handbook, chapter 5, section 2. 

Subpart 503B Tillage systems

503.10 Introduction

The tillage system is an integral part of the cropping management system for a farm. The type, number, and timing of 

tillage operations have a profound effect on soil, water and 

air quality. Tillage systems vary widely depending on the 

crops, climate, and soils. The impacts of tillage on crop 

residue vary greatly depending on inplements used, implement adjustments and the number of tillage trips. NRCS 

planners should be familiar with the tillage systems in their 

area, and how the application of these systems affects the 

resources. 

503.11 Conservation tillage

Conservation tillage as defined by the Conservation Technology Information Center is any tillage and planting system with 30 percent or more residure cover remaining on 

the soil surface after planting to reduce soil erosion by water. Where soil erosion by wind is the primary concern, at 

least 1,000 pounds per acre of flat small-grain residue 

equivalent are left on the soil surface during the critical 

wind erosion period. 

(a) Residue management practices

Residue management practices that typically meet the conservation tillage definition include: 

No-till and strip-till — No-till and strip-till systems manage 

the amount, orientation, and distribution of crop and other 

plant residues on the soil surface year-round, while growing 

crops in narrow slots, or tilled or residue-free strips in soil 

previously untilled by full-width inversion implements. The 

soil is left undisturbed from harvest to planting except for 

nutrient injection. Seeds are placed in a narrow seedbed or 

slot made by coulter(s), row cleaners, disk openers, in-row 

chisels, or rototillers, where no more than one third of the 

row width is disturbed. Weeds are controlled primarily with 

herbicides. Row cultivation for emergency weed control 

should utilize undercutting implements that minimize residue burial. 

Ridge-till — Managing the amount, orientation, and distribution of crop and other plant residues on the soil surface 

year-round, while growing crops on preformed ridges alternated with furrows protected by crop residue. The soil is 
(190-V-NAM, 3rd Ed., October 2002) 503–3 

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left undisturbed from harvest to planting except for nutrient 

injection. Planting is done in a seedbed prepared on ridges 

with sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between ridges. Weed control is 

done with herbicides or cultivation or both. Ridges are rebuilt during row cultivation. 

Mulch-till — Managing the amount, orientation, and distribution of crop and other plant residue on the soil surface 

year-round, while growing crops where the entire field surface is tilled prior to planting. Tillage tools such as chisels, 

field cultivators, disks, sweeps, or blades are used. Weed 

control is done with herbicides or cultivation, or both. 

(b) Crop residue management

Despite considerable acceptance of these definitions there 

is still some confusion as to the meaning of conservation 

tillage. Crop residue management is defined as: 

Any tillage and planting system that uses no-till, 

ridge-till, mulch-till, or other systems designed to 

retain all or a portion of the previous crop’s residue 

on the soil surface. The amount required depends on 

other conservation practices applied to the field and 

the farmer’s objectives. 

Tillage systems, whether a conservation tillage system or 

some other system that retains little if any residue, is an important part of a crop production system. Crop response to 

various tillage systems is variable and the variability if often difficult to explain because so many aspects of crop production are influenced by tillage. In addition, weather variability is an additional factor which influences crop production from one year to the next. Items to consider in designing a conservation tillage system include the following: 

Soil temperature — Crop residue insulates the soil surface 

from the sun’s energy. This may be a plus at planting time 

or may delay planting and/or lead to poorer germination. If 

this is a concern, the use of planter attachments to remove 

residue from the row area will improve the situation. Later 

in the growing season crop residue on the soil surface may 

lower the soil temperature, resulting in increased crop 

growth and yield. 

Allelopathy — This refers to toxic effects on a crop because of decaying residue from the same crop or closely related crop. Crop rotation can eliminate this problem. The 

use of planter attachments to remove the residue from the 

row area may reduce the problem. 

Allelopathic effects can also be beneficial by reducing competition from some weeds. 

Moisture — When crop residue is on the soil surface, 

evaporation is reduced and water infiltration is increased. 

Although this may be a disadvantage at planting time in 

some areas, the extra soil moisture may increase yields if a 

dry period is encountered later in the growing season. Notill systems often have more water than conventional systems available for transpiration later in the growing season, 

resulting in increased yields. 

Organic matter — Soil organic matter tends to stabilize at 

a certain level for a specific tillage and cropping system. 

Each tillage pass aerates the soil, resulting in the oxidation 

of decaying residues and organic matter. Crop residue left 

on the soil surface, in no-till or ridge-till systems, decomposes slower, resulting in increased organic matter levels in 

the upper few inches. 

Soil density — All tillage systems have some effect on soil 

density. Systems that disturb the plow layer by inversion 

tillage or mixing and stirring temporarily decrease soil density. However, after the soil is loosened by tillage, the density gradually increases due to wetting and drying, wheel 

traffic, and secondary tillage operations. By harvest the soil 

density has returned to almost the same density as before 

tillage operations started. Cropping management systems 

that use several tillage operations can create a compacted 

layer at the bottom of the plow layer. If the compaction is 

excessive, then drainage is impeded, plant root growth is restricted, there is reduced soil aeration, herbicide injury may 

increase, and nutrient uptake may be restricted. 

No-till systems have a higher soil density at planting time 

than other systems because the plow layer is not disturbed 

to form a seedbed. This higher density seldom has any effect on germination, emergence and subsequent crop 

growth. Many times the crop will benefit from this because 

these soils retain more available moisture. 

Stand establishment — Regardless of tillage system uniform planting depth, good seed to soil contact, and proper 

seed coverage is needed to obtain a good stand. Coulter 

and/or row cleaners may be needed to ensure a good stand 

in a no-till system. In addition, extra weight and heavy-duty 

down-pressure springs may be needed for the planter or 

drill to penetrate undisturbed soil, especially under less than 

ideal moisture conditions. 
503–4 (190-V-NAM, 3rd Ed., October 2002) 

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Fertilizer placement — Starter fertilizer (nitrogen and 

phosphorus) is generally recommended to help overcome 

the affects of lower soil temperatures at planting time. If 

fertility levels (P, K, and pH) are at maintenance levels before switching to a conservation tillage system, fertility 

should not be a problem. In a no-till system surface application of phosphorus and lime will result in stratification of 

these nutrients, but this has not shown to affect crop yield. 

It is generally recommended that nitrogen be knifed into the 

soil in a no-till system, or a nitrogen stabilizer be used. Surface-applied nitrogen may volatilize and be lost if a rain 

does not move the nitrogen into the soil profile shortly after 

application. 

Weed control — Controlling weeds is essential for profitable production systems. With less tillage, herbicides and 

crop rotations become more important in obtaining adequate weed control. Weed identification, herbicide selection, application rate, and timing are important. A burndown may be needed in no-till and ridge-till systems. A 

change in weed species can be expected in no-till and ridgetill systems. Perennials may become more evident but usually can be controlled with good management. The combination of post-applied herbicides and bioengineered crops 

has made weed control much easier, even in a no-till system. 

Insect management — Regardless of tillage system, effective insect-management guidelines and tactics are available. 

Different tillage systems may affect potential insect pressure, but management addresses this. 

Disease control — Residue on the soil surface offers the 

potential for increased disease problems. However, there 

are numerous strategies to overcome this problem. Crop rotation or the selection of disease-resistant hybrids may nullify this potential problem. 

Crop yields — Weather has more affect on crop yields than 

the tillage system. Crop yields generally are better when a 

crop rotation is utilized, especially in no-till system. 

Production costs — All of the related costs associated with 

various tillage systems must be analyzed to evaluate the 

profitability. 

Machinery and labor costs — Total cost for machinery and 

labor per acre usually decrease as the amount of tillage is 

reduced. If the size of the power units can be decreased (notill system) then the savings can be even more dramatic. 

No-till equipment (planters, drills, nutrient injection equipment) may be more expensive than that needed for conventional equipment. No-till producers have been able to farm 

more acres than conventional tillage producers without additional labor because of the increased efficiency. 
(190-V-NAM, 3rd Ed., October 2002) 503–5 

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Part 503 Crop Production 

Subpart 503C Nutrient

management

(Under development) 

Subpart 503D Pest management

(Under development) 
503–6 (190-V-NAM, 3rd Ed., October 2002) 

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Subpart 503E Crop residue

503.40 Benefits of managing crop residue

Crop residue management is paramount to improving soil 

health. Without residue left on or only partially incorporated in the soil surface, there will be continued degradation of soil organic matter levels and soil health will not be 

maximized. Lower soil organic matter leads to lower cation exchange capacity, lower pH, lower water holding capacity, greater susceptibility to soil erosion, and poorer 

soil structure. Poor soil structure results in less pore space, 

decreased infiltration, and increased surface runoff. 

Soil organic matter is an extremely important component 

of a productive soil. Because organic matter has many exchange sites it is capable of buffering many soil reactions. 

For example, by holding hydrogen ions, their content is reduced in soil solution that results in less soil acidity. At a 

pH near neutral (pH 7.0), plant nutrients are most available. In addition, organic matter increases soil aggregate 

stability and thereby reduces detachment by falling raindrops and surface runoff. Declining levels of soil organic 

matter over time is a strong indicator of declining soil 

health. 

Research in Morris, Minnesota, (Riecosky 1995) reported 

that as much carbon (C) was lost to the atmosphere as CO2

in just 19 days after moldboard plowing wheat residue as 

was produced by the crop. Carbon is the key component of 

soil organic matter and serves as an energy source for microbial activity. 

Tillage stirs the soil similar to poking a fire that results in 

more rapid loss of carbon. Therefore, the primary reason 

organic matter levels of continuous cultivated soils have 

declined to less than half of their original level is directly 

related to tillage and the resulting loss of carbon to the atmosphere. To increase organic matter levels of the soil, 

crops that produce large amounts of residue should be 

grown with a significant reduction in tillage. Undisturbed 

root systems are the main contributor to increased soil carbon levels. 

503.41 Crop residue production

(Under development) 

503.42 Crop residue retention

(Under development) 

503.43 Estimating crop residue cover

The line transect method — The line transect method has 

been proven effective in estimating the percent of the 

ground surface covered by plant residue at any time during 

the year. 

Estimates of percent cover are used for determining the impact of residue on sheet and rill erosion. They cannot be 

used directly for determining the impact of residue on wind 

erosion. 

Estimates of percent cover obtained using the line transect 

method to evaluate the impact of residue on sheet and rill 

erosion are most accurate when the residue is lying flat on 

the soil surface and is evenly distributed across the field. 

The following is the recommended procedure for using the 

line transect method: 

1. Use a commercially available 50- or 100-foot long 

cable, tape measure, or any other line that has 100 

equally spaced beads, knots, or other gradations 

(marks) at which to sight. 

2. Select an area that is representative of the field as a 

whole and stretch the line out across the crop rows. 

The line may be oriented perpendicular to the rows, 

or in a direction that is at least 45 degrees off the row 

direction (fig. 503–1). 

Figure 503–1 Acceptable orientations for residue measurement lines 

Row

Direction
(190-V-NAM, 3rd Ed., October 2002) 503–7 

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Part 503 Crop Production 

The locations in the field where the line is stretched 

out to make measurements should be selected randomly from among the areas of the field that are 

typical of the entire field. End rows, field borders, 

and parts of the field that appear different are probably not typical of the entire field and should be 

avoided. 

3. Walk along the line, stopping at each mark. Position 

the eye directly over the mark, and look down at it. 

When sighting, do not look at the entire mark. Rather 

look at a single point on each mark. 

A point has an area about like the end of a needle. On 

commonly used equipment, the knots, beads, or 

gradations have much larger areas than the end of a 

needle. A measurement is not based on whether or not 

some portion of a mark is over the residue. It is based 

on whether or not a specific point associated with the 

mark is over residue. 

If using a commercially available beaded line, one 

way to accomplish the above is to select as the point 

of reference the place along the line where a bead 

begins. 

4. Determine the percent residue cover by counting the 

number of points at each mark along the line under 

which residue is seen. Count only from one side of 

the line for the single, selected point count at each 

mark. Do not move the line while counting. 

Count only that residue that is large enough to intercept raindrops. A rule of thumb is to count only 

residue that is 3/32 inch in diameter or larger (fig. 

503–2). When using a line with 100 points, the 

percent residue cover is equal to the number of points 

under which residue is seen. 

5. Three to five transects should be done in each field, 

using the procedure described in steps 1 through 4. 

Five transects are recommended. 

With five measurements, estimates of percent residue 

cover are accurate to within ±15 percent of the mean. 

Three measurements will give estimates accurate to 

within ± 32 percent of the mean. 

For example, if the mean of five measurements was 

50 percent cover, you could be confident (at the 95% 

confidence level) that the true mean was between 42 

percent and 57 percent cover. For a 30 percent cover 

average based on five measurements, you could be 

confident that the true value was between 25 percent 

and 34 percent cover. 

6. The documentation of individual transects and computations made to determine average percent residue 

amounts should be done in a professional manner. 

Documentation should be done in a way that permits easy 

tracking from the field measurements to the final answer. 

The development and use of a documentation worksheet is 

recommended. Example worksheet formats are illustrated at 

the end of this section. 

Converting pounds of residue to percent cover—For some 

applications, the weight of the crop residue needs to be 

known rather than the percent cover. Figure 503-3 illustrates the relationship between residue weight and percent 

residue cover for various crops. It also illustrates the procedure for estimating the amount of surface cover provided by 

a known weight of residue. 

503.44 Determining the weight of standing

vegetative cover

In many instances, the amount of above-ground biomass 

needs to be known. The procedures for estimating and measuring the weight of standing vegetation are given in the 

National Range and Pasture Handbook, Part 600.0401(c). 

Figure 503–2 Counting residue pieces along a line transect 

Does not count as

a point of residue

Counts as a point

of residue
503–8 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 503 Crop Production 

Subpart 503F References

Beck, D.L., 1990. Rotational systems: The key to successful 

no-till. Unpublished paper. 

Hargrove, W.L. 1986. Winter legumes as a nitrogen source 

for no-till grain sorghum. Agron. J. 78: 70. 

Laflen, J.M., M. Amenlya, and E.A. Hintz, 1981. Measuring crop residue cover, Jour. of Soil and Water 

Conservation, Vol. 36, No. 6, pp. 341-343. 

Reicosky, D.C., and M.J. Lindstrom. 1995. Fall tillage 

method: Effect on short-term carbon dioxide flux 

from soil. Agron. J. 85(6) 1237-1243. 

Richards, B.K., M.F. Walter, and R.E. Muck, 1984. Variation in line transect measurements of crop residue 

cover, Jour. of Soil and Water Conservation, Vol. 39, 

No. 1, pp. 60-61. 

Sprague, Milton A., and G.B. Triplett, Eds. 1986. No-tillage and surface-tillage agriculture. John A. Wiley & 

Sons, New York. 

Triplett, G.B., Jr., F. Haghiri, and D.M. Van Doren., Jr. 

1979. Plowing effects on corn yield response to nitrogen following alfalfa. Agron. J. 71:801 – 803. 

Unger, P.W., Ed., 1994. Managing agricultural residues. 

Lewis Publishers, Boca Raton, FL. 

U.S. Department of Agriculture. 1997. National Range and 

Pasture Handbook, Natural Resources Conservation 

Service. 

Figure 503–3 Relationship of residue weight to percent residue cover for various crops. Dashed lines with arrows illustrate the 

procedure to convert residue weight to percent residue cover. 
 190-V-NAM, 3rd Ed., October 2002) 503–9 

Exhibit 503–1 Example worksheet for recording crop

residue measurement

Crop residue measurement worksheet

(for use with the line transect method)

State _______________________________

Field no. ________ Planned residue level _______ percent Residue type _______________

Field no. ________ Planned residue level _______ percent Residue type _______________

Land user ___________________________ Opid ____________________ Tract _________

County __________________

Transect

number

Total number

of points 1/

Number of points

with residue 2/

Percent residue

this transect

Average percent residue for field

Average percent residue for field

1

2

3

4

5

Transect

number

Total number

of points 1/

Number of points

with residue 2/

Percent residue

this transect

1

2

3

4

5

1/ To achieve the degree of accuracy quoted in the NAM-recommended procedure for using the line transect method, each

 transect must be based on looking at a total of at least 100 points.

2/ Attach a map or sketch showing the location of each line transect within the field. All measurements shall be made using the

 line transect procedure contained in the National Agronomy Manual.

Data collector Title Date
503–10 (190-V-NAM, 3rd Ed., October 2002) 

Exhibit 503–2 Example worksheet for recording crop

residue measurement

Crop residue measurement worksheet

(for use with the line transect method)

1/ To achieve the degree of accuracy quoted in the NAM-recommended procedure for using the line transect method, each

 transect must be based on looking at a total of at least 100 points.

2/ Attach a map or sketch showing the location of each line transect within the field. All measurements shall be made using the

 line transect procedure contained in the National Agronomy Manual.

State _______________________________

Field no. ________ Planned residue level _______ percent Residue type _______________

Land user ___________________________ Opid ____________________ Tract _________

County __________________

Field no.

Field no. Transect number

(record number of counts with residue)

Average

residue for

field

crop Residue kind Planned tillage system Planned amount

Residue field measurements 1/ 2/

Data collector Title Date

1 2345
 190-V-NAM, 3rd Ed., October 2002) 504–i 

Water Management

Contents: Subpart 504A Managing soil moisture on nonirrigated lands 504–1

504.00 Soil moisture management overview ........................................................... 504–1 

504.01 Soil characteristics ....................................................................................... 504–1 

504.02 Crop characteristics ...................................................................................... 504–6 

504.03 Methods for determining crop evapotranspiration ....................................... 504–7 

504.04 Tillage systems effect on water conservation ............................................. 504–11 

504.05 Saline seeps ................................................................................................ 504–17 

Subpart 504B References 504–20 

Figures Figure 504-1 The USDA textural triangle describes the proportions of sand, silt, 504–1 

and clay in the basic textural classes 

Figure 504-2 Relationship of soil moisture content and water availability to crops 504–3 

Part 504
504–ii (190-V-NAM, 3rd Ed., October 2002) 

.........................................................................................................

Tables Table 504-1 Available Water Capacity (AWC) by soil texture 504–4 

Table 504-2 Available water capacity adjustments because of salinity 1/ 504–6 

Table 504-3 Critical periods for plant moisture stress 504–9 

Table 504-4 Depth to which roots of mature crops will extract available water 504–11 

from a deep, uniform, well-drained soil under average unrestricted 

conditions (depths shown are for 80% of the roots) 

Table 504-5 Maximum rooting depth of mature crops seeded on fallow from 504–11 

1976 to 1979 at Fort Benton, MT 

Table 504-6 Effect of tillage and corn residue on infiltration using simulated 504–13 

rainfall 

Table 504-7 Net soil-water gain at the end of fallow as influenced by straw mulch 504–14 

rates at four Great Plains locations 

Table 504-8 Water use efficiency of 3-year no-till cropping systems and 504–16 

continuous spring wheat as compared with no-till spring wheat and winter 

wheat-fallow systems at various locations across the Great Plains 

Table 504-9 Salt tolerance of selected crops 504–18 

National 

Agronomy 

Manual 

Part 504 Water Management 
 190-V-NAM, 3rd Ed., October 2002) 504–1 

Part 504 Water Management 

Subpart 504A Managing soil moisture on nonirrigated lands

504.00 Soil moisture management overview

Soil moisture management in dryland agriculture is an integral factor in producing a viable crop production system. 

Climatic factors, crop selection, rotational influences, tillage system as well as inherent soil characteristics all interrelate in assessing the availability of adequate water necessary for a selected crop rotation. 

504.01 Soil characteristics

Physical soil characteristics have a major impact on the infiltration, movement, and storage of water within the soil 

profile. These characteristics include soil texture, bulk density, structure, pore space, organic matter content, salinity, 

and sodicity as well as other inherent soil characteristics. 

(a) Water infiltration

Water infiltration is the process of water entering the soil 

from the soil surface. Infiltration rates are affected by tillage practices, amounts of surface residue, soil water content, surface sealing, soil organic matter, soil macropore development, salinity, and sodicity. Infiltration rates change 

during a rainfall event and typically become slower over 

time. They typically also decrease over the growing season 

because of cultivation and harvest equipment. This is especially true if operations are done at higher soil-water levels. 

Macropores, or preferential flow paths, such as cracks or 

wormholes, substantially influence infiltration, and the internal soil drainage. Infiltration rates are also affected by 

water quality; for example, suspended sediment, temperature, 

salinity, and sodicity all affect water surface tension. 

(b) Soil texture

Soil texture refers to the weight proportion of the soil separates (sand, silt, and clay) for analysis. It defines the fineness or coarseness of a soil. Particle sizes larger than 2 mm 

are considered rock fragments, and those that are less than 2 

mm are the fine earth fraction. The fine earth fraction is determined from a laboratory particle-size distribution. The 

fraction classed as rock or coarse fragments is determined 

by the proportion of the soil volume they occupy. Rock 

fragment classes are used to modify soil textures. Mediumtextured soils with a high clay and silt content hold the most 

water, while fine-textured soils generally hold more water 

than coarse-textured soils. Water in clay soils can be held at 

a greater tension that reduces its availability to plants. 

Figure 504-1 displays what is commonly referred to as the 

USDA textural triangle. It describes the proportions of 

sand, silt, and clay in the basic textural classes. Texture determines the amount of surface area on the soil particles 

within the soil mass. Clay and humus both exist in colloidal 

state and have an extremely large surface area per unit 

weight. They carry surface electrical charges to which ions 

and water are attracted. 

(c) Soil structure

Soil structure is the arrangement and organization of soil 

particles into natural units of aggregation. Weakness planes 

that persist through cycles of wetting and drying and cycles 

of freezing and thawing separate these units. Structure influences air and water movement, root development, and nutrient supply. 

Figure 504-1 The USDA textural triangle describes the 

proportions of sand, silt, and clay in the basic 

textural classes 

Silt ( % )

Clay ( % )

Sand ( % )

sandy clay

loam

sandy loam

loamy

 sand

sand

sandy

clay

clay loam

loam

silt loam

silt

silty clay

loam

silty clay

clay
504–2 (190-V-NAM, 3rd Ed., October 2002) 

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Structure type refers to the particular kind of grouping that 

predominates in a soil horizon. Single-grained and massive 

soils are structureless. In single-grained soil, such as loose 

sand, water percolates rapidly. Water moves slowly through 

most clay soil. A more favorable water relationship occurs 

in soil that has prismatic, blocky, and granular structure. 

Platy structure in fine and medium soils impedes the downward movement of water. 

Structure can be improved with cultural practices, such as 

reducing tillage, improving internal drainage, liming or adding sulfur to soil, using grasses or deep rooted crops in rotation, incorporating crop residue, and adding organic material or soil amendments. Structure can be destroyed by 

heavy tillage equipment or excess operations. 

Texture, root activity, clay mineralogy, percent organic 

matter, microbial activity, and the freeze-thaw cycle all play 

a part in aggregate formation and stability. Some aggregates 

are quite stable upon wetting, and others disperse readily. 

Soil aggregation helps maintain stability when wet, resist 

dispersion caused by the impact from rain, maintain soil intake rate, and resist surface water and wind erosion. 

(d) Soil bulk density

Bulk density is the weight per unit volume of dry soil, 

which includes the volume of solids and pore space. Units 

are expressed as the weight at oven-dry and volume at field 

capacity water content, expressed as grams per cubic centimeter (g/cc) or pounds per cubic foot (lb/ft3). Bulk density 

is used to convert water measurements from a weight basis 

to a volume basis. Other factors affecting soil bulk density 

include freeze/thaw process, plant root growth and decay, 

wormholes, and organic matter. 

(e) Organic matter

Soil organic matter is the organic fraction of the soil. It includes plant and animal residue at various stages of decomposition, and cells and tissues of soil organisms. Organic 

matter directly influences soil structure, soil condition, soil 

bulk density, water infiltration, plant growth and root development, permeability, total water holding capacity, biological activity, oxygen availability, nutrient availability, and 

tilth, as well as many other factors that make the soil a 

healthy natural resource for plant growth. Organic matter 

has a high cation adsorption capacity, and its decomposition 

releases plant nutrients including nitrogen, phosphorous, 

and sulfur. Site specific organic matter values should always be used for planning and managing cropping systems. 

Published values often are from sites that were managed 

quite differently. 

(f) Soil water holding capacity

The potential for a soil to hold water is an important factor 

in designing a crop production system. Total water held by 

a soil is called water-holding capacity. However, not all soil 

water is available for extraction by plant roots. The volume 

of water available to plants that a soil can store is referred 

to as available water capacity (AWC). Figure 504-2 is a 

general illustration of soil water content and availability for 

a loam soil. 

Available water capacity is the traditional term used to express the amount of water held in the soil available for use 

by most plants. It is dependent on crop rooting depth and 

several soil characteristics. Units of measure are expressed 

in various terms: 

• Volume unit as inches of water per inch or per foot of 

soil depth 

• Gravimetric percent by weight 

• Percent on a volume basis 

In fine textured soils and soils affected by salinity, sodicity, 

or other chemicals, a considerable volume of soil water may 

not be available for plant use. 

Soil-water potential, more correctly, defines water available to plants. It is the amount of work required per unit 

quantity of water to transport water in soil. The concept of 

soil-water potential replaces arbitrary terms such as gravitational, capillary, and hygroscopic water. 

In the soil, water moves continuously in the direction of decreasing potential energy or from higher water content to 

lower water content. As a plant takes up water from the soil, 

the concentration of water in the soil immediately adjacent 

to its roots is reduced. Water from the surrounding soil then 

moves into the soil around the roots. 

For practical reasons, the terms and concepts of field capacity and permanent wilting point are normally used. Units of 

megapascals [MPA (metric units)] or bars or atmospheres 

(English units) are generally used to express soil water potential. One megapascal is equal to ten bars or atmospheres. 

Field capacity—The field capacity of a well-drained soil is 

the amount of water a held by that soil after free water has 

drained because of gravity. For coarse textured soil, drainage occurs soon after a rain event because of relatively 

large pores and low soil particle surface tension. In fine textured soil, drainage takes much longer because of smaller 

pores and their horizontal shape. Major soil properties that 

affect field capacity are texture, organic matter content, 
(190-V-NAM, 3rd Ed., October 2002) 504–3 

National 

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Manual 

Part 504 Water Management 

structure, bulk density, and strata within the profile that restrict water movement. Generally, fine textured soil holds 

more water than coarse textured soil. Some soils, such as 

some volcanic and organic soils, are unique in that they can 

retain significant volumes of water at tensions less than onetenth bar, thereby giving them a larger available water capacity. 

An approximation of field capacity soil-water content level 

can be identified in the laboratory. It is the water retained in 

a soil when subjected to a tension of -0.01 mPa [-0.1 atmosphere (bar)] for sandy soils and -0.03 mPa for other finer 

textured soils. 

Field capacity water content level can be estimated in the 

field immediately following a rain, after free water has 

drained through the soil profile. Some judgment is necessary to determine when free water has drained and field capacity has been reached. Free water in coarse textured soil 

(sandy) can drain in a few hours. Medium textured (loamy) 

soil takes about 24 hours, and fine textured (clayey) soil 

may take several days. 

Permanent wilting point—This is the soil-water content at 

which most plants cannot obtain sufficient water to prevent 

permanent tissue damage. The lower limit to the available 

water capacity has been reached for a given plant when it 

has so exhausted the soil moisture around its roots as to 

have irrecoverable tissue damage, thus yield and biomass 

are severely and permanently affected. The water content in 

the soil is then said to be the permanent wilting percentage 

for the plant concerned. 

Experimental evidence shows that this water content point 

does not correspond to a unique tension of 1.5 megapascals 

(MPa) for all plants and soils. The quantity of water a plant 

can extract at tensions greater than this figure appears to 

vary considerably with plant species, root distribution, and 

soil characteristics. Some plants show temporary plant 

moisture stress during hot daytime periods and yet have adequate soil moisture. In the laboratory, permanent wilting 

point is determined at 1.5 MPa tension. Unless plant specific data are known, any water remaining in a soil at 

greater than 1.5 MPa tension is considered unavailable for 

plant use. 

Figure 504-2 Relationship of soil moisture content and water availability to crops. 
504–4 (190-V-NAM, 3rd Ed., October 2002) 

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but this water may not be available for plant use because of 

the restricted root penetration and limited capillary water 

movement. Adjustment to the available water capacity 

based upon this additional field information should be 

made. 

Different soils hold and release water differently. When 

soil-water content is high, very little effort is required by 

plant roots to extract moisture. As each unit of moisture is 

extracted, the next unit requires more energy. This relationship is referred to as a soil moisture release characteristic. 

The tension in the plant root must be greater than that in the 

soil at any water content to extract the soil water. Typically 

with most field crops, soil moisture is not the limiting factor 

for crop yield when water is available at less than -0.5 MPa 

(-5 atmospheres) in medium or fine textured soils. At soilwater tensions of more than about 0.5 MPa, plant yield or 

biomass is reduced in medium to fine textured soils. 

Major soil characteristics affecting the available water capacity are texture, structure, bulk density, salinity, sodicity, 

mineralogy, soil chemistry, and organic matter content. Of 

these, texture is the predominant factor in mineral soil. Because of the particle configuration in certain volcanic ash 

soil, the soil can contain very high water content at field capacity levels. This provides a high available water capacity 

value. Table 504–1 displays average available water capacity based on soil texture. 

The available water capacity value shown in soil survey reports, the Field Office Technical Guide, or the National Soil 

Survey Information System account for the estimated volume of coarse fragments for the specific soil series. However, in an onsite investigation any additional coarse fragments found in the soil profile must be accounted for. 

Coarse fragments of volcanic material, such as pumice and 

cinders, can contain water within the fragments themselves, 

Table 504-1 Available Water Capacity (AWC) by soil texture 

Texture Texture AWC range AWC range Estimated typical 

symbol (in/in) (in/ft) AWC (in/ft) 

COS Coarse sand 0.01 - 0.03 0.1 - 0.4 0.25 

S Sand 0.01 - 0.03 0.1 - 0.4 0.25 

FS Fine sand 0.05 - 0.07 0.6 - 0.8 0.75 

VFS Very fine sand 0.05 - 0.07 0.6 - 0.8 0.75 

LCOS Loamy coarse sand 0.06 - 0.08 0.7 - 1.0 0.85 

LS Loamy sand 0.06 - 0.08 0.7 - 1.0 0.85 

LFS Loamy fine sand 0.09- 0.11 1.1 - 1.3 1.25 

LVFS Loamy very fine sand 0.10 - 0.12 1.0 - 1.4 1.25 

COSL Coarse sandy loam 0.10 - 0.12 1.2 - 1.4 1.3 

SL Sandy loam 0.11 - 0.13 1.3 - 1.6 1.45 

FSL Fine sandy loam 0.13 - 0.15 1.6 - 1.8 1.7 

VFSL Very fine sandy loam 0.15 - 0.17 1.8 - 2.0 1.9 

L Loam 0.16 - 0.18 1.9 - 2.2 2.0 

SIL Silt loam 0.19 - 0.22 2.3 - 2.6 2.45 

SI Silt 0.16 - 0.18 1.9 - 2.2 2.0 

SCL Sandy clay loam 0.14 - 0.16 1.7 - 1.9 1.8 

CL Clay loam 0.15 - 0.17 1.8 - 2.0 1.9 

SICL Silty clay loam 0.17 - 0.19 2.0 - 2.3 2.15 

SC Sandy clay 0.15 - 0.17 1.8 - 2.0 1.9 

SIC Silty clay 0.15 - 0.17 1.8 - 2.0 1.9 

C Clay 0.14 - 0.16 1.7 - 1.9 1.8 
(190-V-NAM, 3rd Ed., October 2002) 504–5 

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(g) Soil pore space

Soil is composed of soil particles, organic matter, water, 

and air. Pore space allows the movement of water, air, and 

roots. Dense soil has a low AWC because of decreased pore 

space. Density can make AWC differences of -50 percent to 

+30 percent compared to average densities. Sandy soils 

generally have bulk densities greater than soils with high clay 

content. Sandy soils have less total pore space than silt and 

clay soils. Gravitational water flows through sandy soils 

much faster because the pores are much larger. Clayey soils 

hold more water than sandy soils because clay soils have a 

larger volume of small, flat-shaped pore spaces that hold 

more capillary water. Clay soil particles are flattened or 

plate-like in shape, thus, soil-water tension is also higher for 

a given volume of water. When the percent clay in a soil increases over about 40 percent, AWC is reduced even 

though total soil-water content may be greater. Permeability 

and drainability of soil are directly related to the volume, 

size and shape of pore space. 

Uniform plant root development and water movement in 

soil occurs when the soil profile bulk density is uniform, a 

condition that seldom exists in the field. Generally, soil 

compaction occurs in all soils where tillage implements and 

wheel traffic are used. Compaction decreases pore space, 

decreasing root development, oxygen content, water movement and availability. 

(h) Soil depth

Soil depth is the dimension from the soil surface to bedrock, hardpan, or water table; to a specified soil depth; or to 

a root growth restrictive layer. The deeper the soil and plant 

roots, the more soil-water storage is available for plant use. 

Crop rooting depth and the resulting total AWC control the 

length of time plants can go between rainfall events before 

reaching moisture stress. Equipment compaction layers or 

naturally-occurring impervious layers restrict the downward 

movement of water and root penetration. 

An abrupt change in soil texture with depth can restrict 

downward water movement. For example, coarse sand underlying medium or fine textured soil requires saturation at 

the textural interface before substantial amounts of water 

will move into the coarser soil below. When a coarse textured soil abruptly changes to a medium or fine textured 

soil, a temporary perched water table develops above the 

less permeable soil. Stratified soils or shallow soils over 

hardpans or bedrock can also hold excess gravitational water at the interface. The excess water can move upward because of the increased soil particle surface tension as the 

soil water in the upper profile is used by plants or capillary 

action resulting from surface evaporation. Thus, an otherwise shallow soil with low total AWC can have characteristics of a deeper soil. 

(i) Water tables

Water tables can be a barrier for root development because 

of restricted oxygen availability. Providing artificial drainage of poorly drained soils increases soil depth for potential 

root development. Adequate soil drainage must be present 

for sustained growth of most plants. 

In other situations, where water tables are not a barrier to 

root development, planned water table control and management of shallow ground water can supply all or part of the 

seasonal crop water needs. The water must be high quality, 

salt free, and held at or near a constant elevation. The water 

table level should be controlled to provide water according 

to crop needs. 

(j) Chemical properties

The physical and chemical weathering of materials on the 

Earth’s surface form soil. These materials may have been 

rock, or they may have been other materials that were transported from somewhere else and deposited over rock. Exposure of the surface to water, oxygen, organic matter, and 

carbon dioxide brings about chemical alterations to the material. Oxidation, reduction, hydration, hydrolysis, and carbonation contribute to chemical and physical changes in the 

surface material. If it is rock, the material gradually breaks 

down into smaller particles, forming a mineral soil. If it is a 

transported material, such as glacial till or loess, weathering 

can affect soil chemistry and mineralogy. The chemical and 

mineralogical composition of the soil varies with respect to 

depth or horizon. Weathering intensity decreases with depth 

from the surface. The longer the weathering has proceeded, 

the thicker the weathered layer and the greater the dissimilarity from the original material. In mineral soils, organic 

matter content generally decreases with depth. 

The colloidal fraction (diameter less than 0.001 mm) of the 

soil plays an important part in the chemistry of the soil. Microbiological activity is greatest near the surface where oxygen, organic matter content, and temperature are the highest. 
504–6 (190-V-NAM, 3rd Ed., October 2002) 

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Cation exchange capacity (CEC) is the total amount of cations held in a soil in such a way that they can be removed 

by exchanging with another cation in the natural soil solution, expressed in milliequivalents per 100 grams of ovendry soil (meq/100 gm). The cation exchange capacity is a 

measure of the ability of a soil to retain cations, some of 

which are plant nutrients. It is affected primarily by the kind 

and amount of clay and organic matter. Soils that have low 

CEC hold fewer cations and may require more frequent applications of fertilizers than soils with high CEC. See Soil 

survey reports, the Field Office Technical Guide, or the National Soil Survey Information System for CEC estimates 

for specific soil series. 

(k) Saline soil effects

Salt-affected soils are generally classified as follows, using 

electrical conductivity of the soil-water extract, ECe, as the 

basis: 

Salinity ECe

Nonsaline 0–2 dS/m 

Very Slight 2 - 4 dS/m 

Slight 4 - 8 dS/m 

Moderate 8 - 16 dS/m 

Strong > 16 dS/m 

Salts in the soil-water solution decrease the amount of water 

available for plant uptake. Table 504–2 displays AWC values adjusting for effect of salinity versus texture. ECe is defined as the electrical conductivity of the soil-water extract 

corrected to 77 °F (25 °C). Units are expressed in millimhos per centimeter (mmho/cm) or decisiemens per meter 

(dS/m); 1 mmho/cm = 1 dS/m. As water is evaporated from 

the soil surface or used by plants, salt within the soil-water 

solution are left behind either on the ground surface or 

within the soil profile. Leaching with excess water through 

the soil profile can reduce accumulated saline salts. 

504.02 Crop characteristics

(a) Response to water, crop yield, and quality

Crop response to available water is dependent not only on 

the genetic characteristics and requirements of the plant but 

also on the environmental constraints to which it is subjected. Soil moisture is only one component needed to 

achieve desired crop yield and quality. Soil water within a 

desirable depletion range (preferably less than 5 bars tension) generally provides the expected yield and quality. The 

Table 504-2 Available water capacity adjustments because of salinity 1/

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Electrical conductivity (ECe x103) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

0 2 4 6 8 10 12 14 

Soil texture 

 - - - - - - - - - - - - - - - - - - - - Available water capacity (in/in) 2/ - - - - - - - - - - - - - - - - - - - - - - 

Clay .14 - .16 .13 - .15 .12 - .14 .11 - .13 .10 - .12 .09 - .11 .07 - .08 .04 - .05 

Silty clay .15 - .17 .14 - .16 .13 - .15 .12 - .14 .11 - .12 .09 - .11 .07 - .08 .04 - .05 

Sandy clay .15 - .17 .14 - .16 .13 - .15 .12 - .14 .11 - .12 .09 - .11 .07 - .08 .04 - .05 

Silty clay loam .19 - .21 .18 - .20 .17 - .18 .15 - .17 .14 - .15 .12 - .13 .09 - .10 .06 - .07 

Clay loam .19 - .21 .18 - .20 .17 - .18 .15 - .17 .14 - .15 .12 - .13 .09 - .10 .06 - .07 

Sandy clay loam .14 - .16 .13 - .15 .12 - .14 .11 - .13 .10 - .12 .09 - .11 .07 - .08 .04 - .05 

Silt loam .19 - .21 .18 - .20 .17 - .18 .15 - .17 .14 - .15 .12 - .13 .09 - .10 .06 - .07 

Loam .16 - .18 .15 - .17 .14 - .16 .13 - .15 .12 - .13 .10 - .11 .08 - .09 .05 - .06 

Very fine sandy loam .15 - .17 .14 - .16 .13 - .15 .12 - .14 .11 - .12 .09 - .11 .07 - .08 .04 - .05 

Fine sandy loam .13 - .15 .12 - .14 .11 - .13 .11 - .12 .09 - .11 .08 - .09 .06 - .07 .04 - .05 

Sandy loam .11 - .13 .10 - .12 .10 - .11 .09 - .11 .08 - .09 .07 - .08 .05 - .06 .03 - .04 

Loamy very fine sand .10 - .12 .10 - .11 .09 - .11 .08 - .09 .07 - .08 .06 - .07 .04 - .05 .02 - .03 

Loamy fine sand .09 - .11 .09 - .10 .08 - .10 .07 - .09 .06 - .08 .06 - .07 .04 - .05 .03 - .04 

Loamy sand .06 - .08 .06 - .08 .06 - .07 .05 - .06 .04 - .06 .04 - .05 .03 - .04 .02 - .03 

 Fine sand .05 - .07 .05 - .07 .05 - .06 .04 - .06 .04 - .05 .03 - .04 .02 - .03 .02 

1/ Compiled by NRCS, National Soil Survey Laboratory, Lincoln, NE 

2/ 15 mmhos conductivity results in a 75-95% reduction in available water capacity 
(190-V-NAM, 3rd Ed., October 2002) 504–7 

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effect on yield and quality depends on how severe and during which period of crop growth water deficit occurs. In addition, some crops require less water to initially produce a 

minimum yield, are more efficient at utilizing available water, or go through their growth cycle during periods of reduced environmental stress. Brown and Carlson (1990) relate that barley was more productive, under the same environmental conditions as winter wheat, spring wheat, oats, 

and safflower. Barley was more efficient than other crops at 

converting plant available water to grain because of its water to grain conversion efficiency, its lower water requirements to initially produce the first unit of yield, and its early 

season maturity, avoiding environmental stresses that reduce yield potential. 

Other management factors that limit maximum productivity 

are crop selection, previous crop, weed problems, soil fertility, and planting date also limit the crops ability to use 

available water. 

(b) Crop water requirements

Crop evapotranspiration (ETc), sometimes called crop consumptive use, is the amount of water that plants use in transpiration and building cell tissue plus water evaporated 

from an adjacent soil surface. Crop evapotranspiration is influenced by several major factors: plant temperature, ambient air temperature, solar radiation (sunshine duration/intensity), wind speed/movement, relative humidity/vapor pressure, and soil-water availability. Seasonal local crop water 

use requirements are essential for planning crop production 

systems. 

504.03 Methods for determining

crop evapotranspiration

(a) Direct measurement of crop evapotranspiration

Direct measurement methods for ETc include 

• aerodynamic method, 

• detailed soil moisture monitoring, 

• lysimetry, 

• plant porometers, and 

• regional inflow-outflow measurements. 

All these methods require localized and detailed measurements of plant water use. Detailed soil moisture monitoring 

in controlled and self-contained devices (lysimeters) is 

probably the most commonly used. Little long-term historical data outside of a few ARS and university research stations are available. 

(b) Estimated crop evapotranspiration (ETc)

More than 20 methods have been developed to estimate the 

rate of crop ET based on local climate factors. The simplest 

methods are equations that generally use only mean air temperature. The more complex methods are described as energy equations. They require real time measurements of solar radiation, ambient air temperature, wind speed/movement, and relative humidity/vapor pressure. These equations have been adjusted for reference crop ET with lysimeter data. Selection of the method used for determining local crop ET depends on 

• location, type, reliability, timeliness, and duration of 

climatic data; 

• natural pattern of evapotranspiration during the year; 

and 

• intended use intensity of crop evapotranspiration 

estimates. 

Although any crop can be used as the reference crop, 

clipped grass is the reference crop of choice. Some earlier 

reference crop research, mainly in the West, used 2-yearold alfalfa (ETr

). With grass reference crop (ETo) known, 

ET estimates for any crop at any stage of growth can be calculated by multiplying ETo by the appropriate crop growth 

stage coefficient (kc), usually displayed as a curve or table. 

The resulting value is called crop evapotranspiration (ETc). 

The following methods and equations used to estimate reference crop evapotranspiration (ETo). ETo methods and 
504–8 (190-V-NAM, 3rd Ed., October 2002) 

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equations are described in detail in the Engineering Field 

Handbook, Part 623, Chapter 2, Irrigation Water Requirements (1990). The reference crop used is clipped grass. 

Crop coefficients are based on local or regional growth 

characteristics. The Natural Resources Conservation Service (NRCS) recommends the following methods: 

Temperature method 

• FAO Modified Blaney-Criddle (FAO Paper 24) 

• Modified Blaney-Criddle (SCS Technical Release 

No. 21) 

Energy method 

• Penman-Monteith method 

Radiation method 

• FAO Radiation method (FAO Paper 24) 

Evaporation pan method

The FAO Modified Blaney-Criddle, Penman-Monteith, and 

FAO Radiation equations represent the most accurate equations for these specific methods. They are most accurately 

transferable over a wide range of climate conditions. 

The intended use, reliability, and availability of local climatic data may be the deciding factor as to which equation 

or method is used. 

For estimation of monthly and seasonal crop water needs, a 

temperature-based method generally proves to be quite satisfactory. The FAO Modified Blaney-Criddle equation uses 

long-term mean temperature data with input of estimates of 

relative humidity, wind movement, and sunlight duration. 

This method also includes an adjustment for elevation. The 

FAO Radiation method uses locally measured solar radiation and air temperature. 

Crop ET and related tables and maps can be included to replace or simplify crop ET calculations. These maps and 

tables would be locally developed, as needed. 

(c) Critical growth periods

Plants must have ample moisture throughout the growing 

season for optimum production and the most efficient use of 

water. This is most important during critical periods of 

growth and development. Most crops are sensitive to water 

stress during one or more critical growth periods in their 

growing season. Moisture stress during a critical period can 

cause an irreversible loss of yield or product quality. Critical periods must be considered with caution because they 

depend on plant species as well as variety. Some crops can 

be moderately stressed during noncritical periods with no 

adverse effect on yields. Other plants require mild stress to 

set and develop fruit for optimum harvest time (weather or 

market). Critical water periods for most crops are displayed 

in table 504-3. 
(190-V-NAM, 3rd Ed., October 2002) 504–9 

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Table 504-3 Critical periods for plant moisture stress 

Crop Critical period Comments 

Alfalfa At seedling stage for new seedlings, just after Any moisture stress during growth period 

cutting for hay, and at start of flowering stage reduces yield. Soil moisture is generally 

for seed production. reduced immediately before and during 

cutting, drying, and hay collecting. 

Beans, dry Flowering through pod formation. 

Broccoli During head formation and enlargement. 

Cabbage During head formation and enlargement. 

Cauliflower During entire growing season. 

Cane berries Blossom through harvest. 

Citrus During entire growing season. Blossom and next season fruit set occurs 

during harvest of the previous crop. 

Corn, grain From tasseling through silk stage and Needs adequate moisture from germination until kernels become firm. to dent stage for maximum production. Depletion of 

80% or more of AWC can occur during final ripening 

period without impacting yield. 

Corn, silage From tasseling through silk stage and Needs adequate moisture from germination until kernels become firm. to dent stage for maximum production. 

Corn, sweet From tasseling through silk stage and 

until kernels become firm. 

Cotton First blossom through boll maturing stage. Any moisture stress, even temporary, ceases blossom 

formation and boll set for at least 15 days after moisture again becomes available. 

Cranberries Blossom through fruit sizing. 

Fruit trees During the initiation and early development Stone fruits are especially sensitive to moisperiod of flower buds, the flowering and fruit ture stress during last two weeks before harvest. 

setting period (may be the previous year), 

the fruit growing and enlarging period, and 

the pre-harvest period. 

Grain, small During boot, bloom, milk stage, early head Critical period for malting barley is at soft 

development and early ripening stages. dough stage to maintain a quality kernel. 

Grapes All growth periods, especially during See vine crops. 

fruit filling. 

Peanuts Full season. 

Lettuce Head enlargement to harvest. Water shortage results in a sour and 

strong lettuce. 
504–10 (190-V-NAM, 3rd Ed., October 2002) 

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Table 504-3 Critical periods for plant moisture stress—Continued 

Crop Critical period Comments 

Melons Blossom through harvest. 

Milo Secondary rooting and tillering to boot 

stage, heading, flowering, and grain formation 

through filling. 

Onions, dry During bulb formation, near harvest. 

Onions, green Blossom through harvest Strong and hot onions can result from moisture. 

stress. 

Nut trees During flower initiation period, fruit set, Pre-harvest period is not critical because nuts 

and mid-season growth. form during mid-season period. 

Pasture During establishment and boot stage 

to head formation. 

Peas, dry At start of flowering and when pods 

are swelling. 

Peas, green Blossom through harvest. 

Peppers At flowering stage and when peppers 

are swelling. 

Potato Flowering and tuber formation to harvest. Low-quality tubers result if moisture stress 

during tuber development and growth. 

Radish During period of root enlargement. Hot radishes can be the result of moisture stress. 

Sunflower Flowering to seed development. 

Sorghum, grain Secondary rooting and tillering to boot 

stage, heading, flowering, and grain 

formation through filling. 

Soybeans Flowering and fruiting stage. 

Strawberries Fruit development through harvest. 

Sugar beets At time of plant emergence, following Temporary leaf wilt on hot days is common 

thinning, and 1 month after emergence. even with adequate soil water content. 

Sugarcane During period of maximum vegetative 

growth. 

Tobacco Knee high to blossoming. 

Tomatoes When flowers are forming, fruit is setting, 

and fruits are rapidly enlarging. 

Turnips When size of edible root increases Strong tasting turnips can be the result of 

rapidly up to harvest. moisture stress. 

Vine crops Blossom through harvest. 

Watermelon Blossom through harvest. 
(190-V-NAM, 3rd Ed., October 2002) 504–11 

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Table 504-4 Depth to which roots of mature crops will extract 

available water from a deep, uniform, welldrained soil under average unrestricted conditions (depths shown are for 80% of the roots) 

Crop Depth Crop Depth 

(ft) (ft) 

Alfalfa 5 Milo 2 - 4 

Asparagus 5 Mustard 2 

Bananas 5 Onions 1 - 2 

Beans, dry 2 - 3 Parsnips 2 - 3 

Beans, green 2 - 3 Peanuts 2 - 3 

Beets, table 2 - 3 Peas 2 - 3 

Broccoli 2 Peppers 1 - 2 

Berries, blue 4 - 5 Potatoes, Irish 2 - 3 

Berries, cane 4 - 5 Potatoes, sweet 2 - 3 

Brussels sprouts 2 Pumpkins 3 - 4 

Cabbage 2 Radishes 1 

Cantaloupes 3 Safflower 4 

Carrots 2 Sorghum 4 

Cauliflower 2 Spinach 1 - 2 

Celery 1 - 2 Squash 3 - 4 

Chard 1 - 2 Strawberries 1 - 2 

Clover, Ladino 2 - 3 Sudan grass 3 - 4 

Cranberries 1 Sugar beets 4 - 5 

Corn, sweet 2 - 3 Sugarcane 4 - 5 

Corn, grain 3 - 4 Sunflower 4 - 5 

Corn, seed 3 - 4 Tobacco 3 - 4 

Corn, silage 3 - 4 Tomato 3 

Cotton 4 - 5 Turnips 2 - 3 

Cucumber 1 - 2 Watermelon 3 - 4 

Eggplant 2 Wheat 4 

Garlic 1 - 2 

Grains & flax 3 - 4 

Grapes 5 Trees

Grass pasture/hay 2 - 4 Fruit 4 - 5 

Grass seed 3 - 4 Citrus 3 - 4 

Lettuce 1 - 2 Nut 4 - 5 

Melons 2 - 3 

(d) Rooting depth

The soil is a storehouse for plant nutrients, an environment 

for biological activity, an anchorage for plants, and a reservoir for water to sustain plant growth. The amount of water 

a soil can hold available for plant use is determined by its 

physical and chemical properties. 

Table 504-5 Maximum rooting depth of mature crops seeded 

on fallow from 1976 to 1979 at Fort Benton, 

MT 

Crop Root depth (Feet) 

Alfalfa, vernal 20 

Argentine rape 4 

Barley 5 

Flax 5 

Mustard, yellow 4 

Safflower 7 

Sunflower 6 

Wheat, winter 6 

Wheatgrass 9 

The type of root system a plant has is fixed by genetic factors. Some plants have taproots that penetrate deeply into 

the soil, while others develop many shallow lateral roots. 

The depth of the soil reservoir that holds water available to 

a plant is determined by that plant’s rooting characteristics 

and soil characteristics including compaction layers and water management. The distribution of the plant roots determines its moisture extraction pattern. Typical rooting 

depths for various crops grown on a deep, well drained soil 

with good water and soil management are listed in table 

504-4. With good soil management and growing conditions, 

crops can root much deeper (table 504–5). 

For annual crops, rooting depths vary by stage of growth 

and should be considered in determining the amount of soil 

water available. 

For most plants, the concentration of moisture absorbing 

roots is greatest in the upper part of the root zone (usually 

in the top quarter). Extraction is most rapid in the zone of 

greatest root concentration and where the most favorable 

conditions of aeration, biological activity, temperature, and 

nutrient availability occur. Water also evaporates from the 

upper few inches of the soil; therefore, water is diminished 

most rapidly from the upper part of the soil. This creates a 

high soil-water potential gradient. 
504–12 (190-V-NAM, 3rd Ed., October 2002) 

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In uniform soils that are at field capacity, plants use water 

rapidly from the upper part of the root zone and more 

slowly from the lower parts. About 70 percent of available 

soil water comes from the upper half of a uniform soil profile. Any layer or area within the root zone that has a low 

AWC or increased bulk density affects root development 

and may be the controlling factor for soil moisture availability. 

Variations and inclusions are in most soil map units, thus 

uniformity should not be assumed. Field investigation is required to confirm or determine onsite soil characteristics including surface texture, depth, slope, and potential and actual plant root zone depths. 

Soil texture, structure, and condition help determine the 

available supply of water in the soil for plant use and root 

development. Unlike texture, structure and condition of the 

surface soil can be changed with management. 

Very thin tillage pans can restrict root development in an 

otherwise homogenous soil. Never assume a plant root 

zone. Observe root development of present or former crops. 

Numerous soil factors may limit the plant’s genetic capabilities for root development. The most important factors 

are: 

• soil density and pore size or configuration, 

• depth to restrictive or confining layers, 

• soil-water status, 

• soil aeration, 

• nutrient availability, 

• water table, 

• salt concentrations, and 

• soil-borne organisms that damage or destroy plant 

root system. 

Root penetration can be extremely limited into dry soil, a 

water table, bedrock, high salt concentration zones, equipment and tillage compaction layers, dense fine texture soils, 

and hardpans. When root development is restricted, it reduces plant available soil-water use and consequent storage, 

which in turn limits crop production. 

High soil densities that can result from tillage and farm 

equipment seriously affect root penetration. Severe compacted layers can result from heavy farm equipment, tillage 

during higher soil moisture level periods, and from the total 

number of operations during the crop growing season. In 

many medium to fine textured soils, a compacted layer at a 

uniform tillage depth causes roots to be confined above the 

compacted layer at depths usually less than 6 to 10 inches 

from the surface. Roots seek the path of least resistance, 

thus do not penetrate a compacted dense layer except 

through cracks. Every tillage operation causes some compaction. Even very thin tillage pans restrict root development and can confine roots to a shallow depth, thereby limiting the depth for water extraction. This is probably most 

common with row crops where many field operations occur 

and with hayland when soils are at high moisture levels during harvest. 

Subsoiling when the soil is dry can fracture compacted layers. However, unless the cause of compaction (typically tillage equipment itself), the number of operations, and the 

method and timing of the equipment’s use are changed, 

compaction layers will again develop. Only those field operations essential to successfully growing a crop should be 

used. Extra field operations require extra energy (tractor 

fuel), labor, and cost because of the additional wear and 

tear on equipment. Necessary tillage operations should only 

be performed when the soil surface from 0 to 2 inches or 0 

to 3 inches in depth is dry enough not to cause soil smearing or compaction. The lightest equipment with the fewest 

operations necessary to do the job should be used. 

For site specific planning and design, never assume a plant 

root zone depth. Use a shovel or auger to observe actual 

root development pattern and depth with cultural practices 

and management used. The previous crops or even weeds 

will generally show root development pattern restrictions. 
(190-V-NAM, 3rd Ed., October 2002) 504–13 

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504.04 Tillage systems effect on

water conservation

(a) Comparisons of water conservation under

different residue management systems

Tillage practices influence soil moisture throughout the 

growing season. Reduced-tillage or no-till systems decrease 

evaporation losses, if the residue remains on the soil surface. Both surface roughness and residue slow water runoff, 

allowing more time for infiltration. In addition, surface residue prevents soil surface sealing, thus increasing infiltration 

and soil water stored. The net effect of tillage systems that 

leave surface residue is less variation in soil water during 

the summer months and more plant available water. 

Evaporation—a primary source of water loss during the 

first half of the growing season before the crop canopy 

closes. Crop residue on the soil surface shades the soil surface and reduces the amount of solar energy absorbed, 

thereby reducing soil temperatures and evaporation. Residue also reduce air velocity at the soil surface, slowing the 

rate at which evaporation occurs. Residue cover offers the 

greatest reduction in evaporation when the soil is moist and 

not yet shaded by the crop. Unger and Parker (1968) reported that the cumulative evaporation after 16 weeks was 

57 percent less when wheat residue remained on the surface 

rather than mixed into the soil. 

The difference in cumulative evaporation between bare soil 

and soil with a residue cover is related to the frequency and 

amount of rainfall. For small, infrequent rainfall events, the 

two soil surfaces show little difference in cumulative evaporation. However, with larger more frequent rains, less 

evaporation occurs from soil protected by surface residue 

than from bare soil. In stubble covered wheat field, evaporation ranges from 60-75 percent of that occurring from 

bare soil. Evaporation from the soil depends on water rising 

to the surface by capillary action as the soil dries. Shallow 

incorporation of residue reduces this capillary action however; leaving residue on the soil surface generally reduces 

evaporation more than shallow incorporation. 

Water infiltration—the process of water entering the soil at 

the soil/air interface. Crop residue affects soil infiltration by 

intercepting raindrop energy and the associated soil sealing 

or ponding that occurs thereby increasing infiltration and 

reducing the amount of runoff. Simulated rainfall studies in 

Ohio show that infiltration increases with surface residue 

(table 504-6). Although the infiltration rate was initially 

greater on the plowed field than the bare no-till field, the 

residue in the no-till field enabled faster water infiltration. 

Runoff—tillage systems that leave crop residue on the soil 

surface generally reduce runoff. The factors that influence 

the differences in runoff are soil characteristics, weather 

patterns, the presence of macropores, management, and the 

amount and kind of residue. The residue characteristics that 

affect water infiltration also affect runoff by increasing the 

time to initiation of runoff and lowering runoff rates. Residue on the soil surface increases the surface roughness of 

the soil, reduces runoff velocities, and causes ponding that 

further delays runoff. In addition, surface residue obstructs 

and diverts runoff, increasing the length of time in the 

downslope flow path allowing more time for infiltration. 

Another important point is the effect of having both standing and flat residues present. The presence of standing and 

flat residues reduces the likelihood that small localized flow 

areas will combine into larger networks, and decreases the 

velocity and overall transport of runoff from the field. If the 

climate and soil conditions exclude macropore development 

and traffic causes unrelieved reductions in infiltration, runoff rates can increase even with high residue crop production systems such as no-till, particularly in the early years of 

the systems before surface organic matter has time to accumulate. 

Table 504-6 Effect of tillage and corn residue on infiltration 

using simulated rainfall 

(Triplett et al. 1968) 

- - - - - - - - - - -Total infiltration after 1 hour (inches) - - - - - - - - - - - 

Treatment Initial run Wet run 1/

Plowed, bare 0.71 0.41 

No-tillage, bare 2/

 0.48 0.25 

No-tillage, 40% cover 0.92 0.53 

No-tillage, 80% cover 1.73 1.37 

1 Wet run took place 24 hr after initial run. 

2 Residue cover was removed for research purposes. 
504–14 (190-V-NAM, 3rd Ed., October 2002) 

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Gilley (1986, 1987) and co-workers conducted a series of 

studies evaluating the effect of different types and amounts 

of residue on runoff rates. Five rates of corn residue were 

spread on the soil surface at 0, 10, 31, 51, and 83 percent 

ground cover (0, 1, 1.12, 3.36, 6.73, and 13.45 mg/ha). 

Rainfall was applied at a rate of 28 millimeters per hour on 

days 1, 2, and 3 of the study. Average runoff rates were 

15.6, 10.7, 6.0, 1.8, and 0 millimeters per hour for the 0, 10, 

31, 51, and 83 percent residue covers, respectively. Runoff 

rates were also studied for sorghum and soybean residues at 

a rainfall rate of 48 millimeters per hour. The runoff rate for 

soybean decreased by 68 percent as residue cover increased 

from 0 to 56 percent; the runoff rate for sorghum decreased 

by 73 percent as residue cover increased from 0 to 44 percent. 

Snow catch—Maximizing snow catch is a vital conservation measure in the northern Great Plains, since snow constitutes 20 to 25 percent of the annual precipitation. Stubble 

height management is a tool used to maximize snow catch. 

Taller stubble retains more snow, increasing soil water content. Bauer and Black (1990) in a 12 year study reported 

that increasing small grain stubble height from 2 to 15 

inches increased soil water content to a depth of 5 feet by 

1.6 inches. Increasing the snow catch on a field can also increase spring melt runoff depending on the early spring soil 

infiltration characteristics. However, in soils on which annual crops are grown, infiltration of snowmelt occurs 80 to 

90 percent of the time because the soil is usually frozen 

while dry or not frozen as deeply due to the snow coverage 

to permit infiltration. Greb (1979) reported that the efficiency of storing meltwater is often double that of storing 

water received as rain. 

Water storage—Soil moisture savings is of great importance in regions of low rain fall and high evapotranspiration, on soil low in water holding capacity, and in years 

with below normal rainfall. In the Corn Belt, excessive soil 

moisture in the spring months often has a negative effect on 

crop growth since it slows soil warming and delays planting. However, on soils where drought stress often occurs 

during the summer months, having more available water 

during crop pollination and seed filling usually offsets these 

early season negative effects. Seed zone soil moisture also 

aids in plant establishment and growth in dry areas of the 

United States. For a high percentage of the farmland, moisture savings should be a primary reason for producers to consider reduced tillage systems. 

Research on the effects of reducing tillage and increasing 

surface residue have indicated that high amounts of surface 

residue results in increased soil water stored. Unger (1978) 

reported that high wheat residue levels resulted in increased 

water storage during the fallow period and the increased 

subsequent grain sorghum the following year. Similar results of water storage under high residue conditions, shown 

in table 504-7, summarized by Greb (1983) for 20 cropyears from four locations. 

Management changes in the Great Plains since 1916 have 

improved soil water storage, fallow efficiency (percentage 

of the precipitation received during the fallow period and 

stored as soil water), and small grain yields. However, fallow efficiencies up to 40 percent were reported in the 

1970’s and have not improved beyond this value. Furthermore, subsequent research in the Great Plains with modern 

no-till wheat-fallow systems indicates that most of the 

moisture received is stored early in the year, after crop harvest, and very little soil water is stored beyond the first of 

July. This information indicates that reducing or eliminating 

fallow from the rotation, intensifying the cropping pattern, 

and utilizing the soil moisture stored through the rotation is 

a means of taking advantage of our increased capability to 

store water earlier in the cropping cycle with high residue 

crop production systems. 

Excessive soil water—Soil properties that affect water infiltration, permeability, and drainage must always be properly 

assessed when making residue management decisions. Research in the Corn Belt has shown that no-till management 

systems on some poorly drained soils has resulted in lower 

yields compared to the yields of conventionally tilled systems. Continued research has shown, however after 18 

years of continued no-till that yields are now equal or 

Table 504-7 Net soil-water gain at the end of fallow as 

influenced by straw mulch rates at four Great 

Plains locations 

Location Years - - - - Mulch rate (mg/ha) - - - - 

reported 0 2.2 4.4 6.6 

Bushland, TX 3 7.1 9.9 9.9 10.7 

Akron, CO 6 13.4 15.0 16.5 18.5 

North Platte, NE 7 16.5 19.3 21.6 23.4 

Sidney, MT 4 5.3 6.9 9.4 10.2 

Mean 10.7 12.7 14.5 15.7 

Gain with mulch 2.0 3.8 5.0 

Note: Soil water gain units = centimeter. 
(190-V-NAM, 3rd Ed., October 2002) 504–15 

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greater than conventionally tilled systems. The initial yield 

reductions on these poorly drained soils may have been attributed to a number of factors. The positive yield response 

after continuous no-till on these soils may be attributed to 

the development of internal drainage characteristics such 

macropores, increases in organic matter, better surface soil 

structure, and the use of disease resistant cultivars. 

When dealing with heavier residue amounts from the preceding crop it may be necessary in no-till situations to use 

residue managers that move the residue to the side of the 

seed trench. Poorly drained soils are not easily adapted to 

high residue systems and may need to be managed with limited till systems such as ridge-till or fall and spring strip-till 

methods. Some warm-season species such as corn or sunflower respond to warm, clean seedbed conditions. This 

may also be accomplished including crops in the rotation 

that produce lower amounts of dark colored residue or the 

inclusion of cover crop. (Refer to Subpart 506B, Suitability 

for crop production systems.) 

(b) Cropping system intensity

Improving the relative efficiency of water use in crop production systems has been a major goal in achieving more 

productive modern crop production systems. Reducing water losses in cropping systems by changes in tillage systems, residue management, crop selection and sequence has 

achieved more intense rotations and greater water use efficiency (WUE). 

Water use efficiency can be defined as the dry matter produced divided by the growing season evapotranspiration 

(ET) and expressed in units of dry matter per unit of water 

for a given crop in that system. Since water losses in a system such as runoff and drainage are often unknowns, ET is 

replaced by a value comprised of soil water used during the 

growing season plus growing season precipitation. This relationship can be shown in the equation below. 

The result of the calculation is not exactly identical to situations where true ET is known because not all the precipitation received during the growing season does enter or stay 

in the soil. This overestimate of water available to the plant, 

however is valuable to quantify the efficiency of crops 

grown on a systems basis for a given climate. 

Changes in cropping systems by decreasing tillage, increasing surface residues, making conscious decisions on residue 

orientation, as well as, strategically placing crops in rotations have produced these changes in water use efficiency. 

Cropping system intensification has improved the WUE, 

and has increased the productivity of crop production systems in the Great Plains. Three-year systems increased 

WUE in every climate regime in Texas, Kansas, and Colorado (table 504-8). The WUE for the 3-year rotation winter 

wheat-corn-fallow averaged 196 pounds per acre per inch, 

compared with an average WUE of 140 pounds per acre per 

inch for winter wheat-fallow. 

Continuous cropping may be a viable option for producers 

in areas where fallow has traditionally been a part of a cropping sequence. With high residue management the inclusion 

of annual forages, such as sorghums, millet, field peas, or 

small grains, would increase the producers flexibility to 

maximize WUE. Crop choice affects WUE of the crop production system because each species has a different potential for production. Optimizing WUE in a particular crop 

production system requires choosing crops with the highest 

potential WUE for your particular environment. 

Several predictive tools (water-use-production functions) 

have been developed to assist producers in crop selection in 

several environments across the Great Plains. Black et al. 

(1981) suggested that a flexible cropping strategy would 

provide efficient water use to control saline seeps in the 

northern Great Plains. Flexible cropping is defined as seeding a crop when stored soil water and rainfall probabilities 

are favorable for satisfactory yield, or fallowing when prospects are unfavorable. Available soil water can be estimated 

by measuring moist soil depth with a soil moisture probe or 

other soil sampling equipment. Brown et al. (1981) have 

developed soil water guidelines and precipitation probabilities for barley and spring wheat for flexible cropping systems 

in Montana and North Dakota. 

When considering a flexible cropping system a producer 

should evaluate the amount of plant-available soil water at 

seeding time, the precipitation probabilities for the seasonal 

needs of a given crop, and management factors such as variety, crop rotation, weed and insect problems, soil fertility, 

and planting date. Current information in the Great Plains at 

WUE = Dry matter yield

(( ) Soil water at planting - Soil water at harvest growing season precipitation + )
504–16 (190-V-NAM, 3rd Ed., October 2002) 

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various locations includes yield water-use-production functions for winter wheat, spring wheat, barley, oats, millet, 

corn, sunflower, dry beans, canola, crambe, soybean, and 

safflower given soil moisture and rainfall-probability information (Brown and Carlson 1990; Vigil et al. 1995; Nielson 

1995). This information can assist a producer in crop selection in a given year, however users of these water use/yield 

relationships need to understand that the final crop yield is 

influenced by the timing of precipitation as well as the 

amount of water used. 

Table 504-8 Water use efficiency of 3-year no-till cropping systems and continuous spring wheat as compared with no-till spring 

wheat and winter wheat-fallow systems at various locations across the Great Plains (Peterson et al. 1996) 

System WUE, Location 

lb/acre per in 

Spring wheat/Fallow 130 Minot, ND 

Cont. spring wheat 119 Do. 

Spring wheat/Fallow 78 Williston, ND 

Cont. spring wheat 125 Do. 

Winter wheat/ Fallow 155 Sterling and Stratton, CO 

Winter wheat/ Corn/ Fallow 202 Do. 

Winter wheat/ Fallow 156 Akron, CO 

Winter wheat/ Corn/ Fallow 250 Do. 

Winter wheat/Fallow 144 Tribune, KS 

Winter wheat/Sorghum/ Fallow 201 Do. 

Winter wheat/ Fallow 128 Walsh, CO 

Winter wheat/ Sorghum/ Fallow 148 Do. 

Winter wheat/Fallow 87 Bushland, TX 

Winter wheat/Sorghum/Fallow 156 Do. 

Spring wheat/Fallow 104 Average 

Winter wheat/Fallow 140 Average 

Cont. spring wheat 122 Average 

Winter wheat/Corn/Fallow 196 Average 

Wheat/Sorghum/Fallow 181 Average 
(190-V-NAM, 3rd Ed., October 2002) 504–17 

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504.05 Saline seeps

(a) Development of saline seeps

Saline seep describes a salinization process accelerated by 

dryland farming practices. Saline seep is an intermittent or 

continuous saline water discharge at or near the soil surface 

downslope from a recharge area under dryland farming conditions that reduces or eliminates crop growth in the affected area because of increased soluble salt concentration 

in the root zone. Saline seeps are differentiated from other 

saline soil conditions by their recent and local origin, saturated root zone in the soil profile, shallow perched water 

table, and sensitivity to precipitation and cropping systems. 

In the recharge area, water percolates to zones of low hydrologic conductivity at depths of 2 to 60 feet below the 

soil surface and flows internally downslope to emerge at the 

point where the transport layer approaches the soil surface 

or soil permeability is reduced. 

The saline-seep problem stems from surface geology, 

above-normal precipitation periods, and farming practices 

that allow water to move beyond the root zone. 

Under native vegetation, grasses and forbs used most of the 

water before it had a chance to percolate below the root 

zone to the water table. With sod plow-up, subsoils became 

wetter and fallow kept the land relatively free of vegetation 

for months at a time. Beginning in the forties, soil water 

storage efficiency during fallow improved with the advent 

of large tractors, good tillage equipment, effective herbicides, and timely tillage operations. This extra water filled 

the root zone to field capacity and allowed some water to 

move to the water table and downslope to emerge as a saline seep. 

Several factors that may individually or in combination contribute water to shallow water tables include: fallow, high 

precipitation periods, poor surface drainage, gravelly and 

sandy soils, drainageways, constructed ponds and dugouts, 

snow accumulation, roadways across natural drainageways, 

artesian water, and crop failures resulting in low use of 

stored soil water. Saline-seep formation begins with a root 

zone filled to its water-holding capacity. Some of this water 

runs off the surface, some evaporates, and the rest moves 

into the soil. Once the soil is filled to field capacity, any additional water that moves through the root zone may contribute to saline seepage. 

Water percolating through salt-laden strata dissolves salts 

and eventually forms a saline water table above an impermeable or slowly permeable layer. The underground saline 

water migrates downslope and dissolves more salts, adding 

to the perched water table at the site of the seep. Whenever, 

the water table rises to within 3 feet of the surface the water 

plus dissolved salts then move to the soil surface by capillary action were the discharge water evaporates, concentrating salt on or near the soil surface. As a result, crop growth 

in the affected area is reduced or eliminated and the soil is 

too wet to be farmed. 

(b) Identification of saline seeps

Early detection and diagnosis of a saline-seep problem are 

important in designing and implementing control and reclamation practices to prevent further damage. By early detection, a producer may be able to change his or her cropping 

system to minimize the damage. Detection of discharge areas may be accomplished by visual or by electrical conductivity detection. Visual symptoms of an impending saline 

seep may include 

• vigorous growth of kochia or foxtail barley in small 

areas where the soil would normally be too dry to 

support weed growth, 

• scattered salt crystals on the soil surface, 

• prolonged periods of soil surface wetness in small 

areas, 

• poor seed germination or rank wheat or barley growth 

accompanied by lodging in localized areas, 

• stunted trees in a shelterbelt accompanied by leaf 

chlorosis, or 

• a sloughed hillside in native vegetation adjacent to a 

cultivated field. 

Soil electrical conductivity (EC), which is proportional to 

soil salinity, can be determined in the field using resistivity. 

This technique can be used to identify and confirm an encroaching or developing saline seep. Soil salinity in the discharge area may be low near the soil surface, but increases 

considerably with depth. Once the discharge area is identified, the next step is to locate the recharge area. Most remedial treatments for controlling the seep must be applied to 

the recharge area, which is always at a higher elevation than 

the discharge area. The approximate size of the recharge 

area must be determined to be successful. Most recharge areas are within 2,000 feet and many are within 100 to 600 

feet of the discharge area, depending on the geology involved. 
504–18 (190-V-NAM, 3rd Ed., October 2002) 

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Several procedures for identifying the recharge area include: visual, soil probing, soil surveys, drilling, soil resistivity, and electromagnetic techniques. Even if the previously mentioned equipment is not available, a visual approximation of the recharge area can be made, and strategies implemented to correct the saline-seep problem. 

Some facts to remember are that the recharge areas are 

higher in elevation than the seep or discharge area, the recharge areas are generally within 2,000 feet of the discharge areas, and that seeps in glacial till areas expand 

downslope, laterally, and upslope toward the recharge 

area. Saline seeps in non-glaciated areas tend to expand 

downslope, away from the discharge area. After the recharge area has been located, a management plan should 

be designed to control the saline-seep problem. 

(c) Effects of salinity on yields

Saline soil is a term used to characterize soil containing 

sufficient salts to adversely affect the growth of most crop 

plants. One or more of the following may cause these adverse effects: 

• Direct physical effects of salts in preventing soil 

water uptake by the plant roots because of increased 

osmotic tension. 

• Direct chemical effects of salt in disrupting the 

nutritional and metabolic processes of the plant. 

• Indirect effect of salt in altering soil structure, 

permeability, and aeration. 

Agricultural crops differ significantly in their response to 

excessive concentrations of soluble salts in the root zone. 

This ability of the plant to produce economic yields in a saline environment is termed salt tolerance. Crop selection is 

one of the primary options available to growers to maximize productivity under saline conditions. Table 504-9 lists 

the salinity threshold and yield decrease of several selected 

agricultural crops. The threshold salinity level is the maximum allowable salinity that does not reduce yield below 

that of non-saline conditions. The yield decrease is reported 

as a percent yield reduction for every whole unit increase in 

salinity measured as electrical conductivity (EC) mmho/cm. 

For example, alfalfa yields decrease about 7.3 percent per 

unit of salinity increase above 2.0 mmho/cm. Therefore, at 

a soil salinity of 5.4 mmho/cm, alfalfa yield would be 25 

percent lower than at soil salinity levels less than 2.0 mmho/ 

cm. 

Crop production has been reduced on approximately 

2 million dryland acres in the northern Great Plains of the 

United States and Canada. Brown (1982) reported that this 

production loss on 2 million acres in the northern Great 

Plains could be translated into $120 million in lost annual 

farm income. 

(d) Management practices for control of saline seeps

Saline-seeps are caused by water moving below the root 

zone in the recharge area. Because of this movement of water though the recharge area, there will be no permanent solution to the saline-seep problem unless control measures 

Table 504-9 Salt tolerance of selected crops 1/

Common Botanical Salt tolerance Yield decline 

name name threshold (% per 

 (mmhos/cm) mmhos/cm) 

Alfalfa Medicago sativa 2.0 7.3 

Barley Hordeum vulgare 8.0 5.0 

Sorghum Sorghum bicolor 6.8 16.0 

Soybean Glycine max 5.0 20.0 

Wheat Triticum aestivum 6.0 7.1 

Wheatgrass, tall Agropyron elongatum 7.5 4.2 

Wildrye, beardless Leymus triticoides 2.7 6.0 

1/ Maas and Hoffman (1977) and Maas (1990) 
(190-V-NAM, 3rd Ed., October 2002) 504–19 

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are applied to the recharge area. These measures vary according to the soil texture and underlying geologic material, 

water table fluctuations, depth to the low hydraulic conductivity zone, occurrences of potholes and poorly drained areas, and annual precipitation and frequency of high precipitation periods. 

Two general procedures are available for managing salineseeps: either make agronomic use of the water for crop production before it percolates below the root zone; or mechanically drain either surface or subsurface water before it 

reaches the discharge area. Mechanical drainage is generally not performed either because of current farm bill legislation or because of constraint that subsurface water is excessively contaminated with salts and downstream disposal 

is difficult because of physical or legal limitations. However, before any control measures are implemented an 

evaluation of the land capability class should be determined. All control measures should be compatible with the 

land capability class involved. 

The most effective solution to the saline-seep problem is to 

use as much of the current precipitation as possible for crop 

or forage production before it percolates beyond the root 

zone. Forage crops, such as alfalfa, use more water than cereal grains and oil crops because they have deep root systems, are perennial, and have longer growing seasons. 

Planting alfalfa in the recharge area of a saline seep is often 

the most effective way to draw down stored subsoil moisture and stop water flow to a saline-seep. Alfalfa can use all 

current precipitation plus a substantial amount of water 

from the deep subsoil. Halvorson and Reule (1976), (1980) 

found that alfalfa growing on approximately 80 percent of 

the recharge area effectively controlled several saline seeps. 

They also found that a narrow buffer strip of alfalfa (occupying less than 20 percent of the recharge area) on the immediate upslope side of a seep did not effectively control 

the water in the discharge area. Grasses may also effectively 

draw down subsurface water if the depth to the low hydraulic conductivity zone is less than 15 feet. After terminating 

alfalfa or grass production, the recharge area should be 

farmed using a flexible cropping system. 

Flexible cropping is defined as seeding a crop when stored 

soil water and rainfall probabilities are favorable for satisfactory yield or fallowing when prospects are unfavorable. 

Available soil water can be estimated by measuring moist 

soil depth with a soil moisture probe or other soil sampling 

equipment. Black et al. (1981) suggested that this cropping 

strategy would provide efficient water use to control saline 

seeps in the northern Great Plains. Brown et al. (1981) have 

developed soil water guidelines and precipitation probabilities for barley and spring wheat for flexible cropping systems in Montana and North Dakota. 

When considering a flexible cropping system a producer 

should evaluate the amount of plant-available soil water at 

seeding time, the precipitation probabilities for the seasonal 

need of a given crop, and management factors such as variety, crop rotation, weed and insect problems, soil fertility, 

and planting date. Current information in the northern Great 

Plains at various locations includes yield water-use-production functions for winter wheat, spring wheat, barley, oats, 

millet, corn, sunflower, dry beans, canola, crambe, soybean, 

and safflower, given soil moisture and precipitation information. Oilseeds such as safflower or sunflower included in 

the rotation utilize residual subsoil moisture below the normal rooting depth of small grains while disrupting disease 

and pest cycles associated with cereal grain production. After successful application of control measures to the recharge area, the seep area and surrounding area can then be 

seeded to a grass or grass/legume mixture tolerant to the saline conditions present in the discharge area. A return to a 

cropping system that does not adequately utilize stored soil 

water in the recharge area may reactivate the seep. 

Once the water flow from the recharge area to the seep has 

been stopped or controlled and the water table in the seep 

has dropped enough to permit cultivation, cropping in the 

seep area can begin. Crop selection is important when initiating crop production on the discharge area. In the northern 

Great Plains, six-row barley is the most salinity-tolerant cereal available, and it is normally the first crop seeded. As 

the reclamation processes continues, comparing yields in 

and outside the seep area can be used to monitor progress. 

The water table depth should be closely monitored during 

the reclamation period. 
504–20 (190-V-NAM, 3rd Ed., October 2002) 

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Another approach that can be used on discharge areas is to 

manage salt-tolerant grasses seeded on the area. If the water 

table is above 4 feet the grasses should be mowed and completely removed to prevent excess snow accumulation and 

the subsequent rise in the water table. If the water table is 

below 4 feet, the grass can be left to catch snow. The resulting snowmelt will leach the salt downward into the soil and 

improve subsequent grass growth. Snow trapping using 

grass strips or crop stubble will enhance water movement 

through the profile in the discharge area and hasten the reclamation process. These practices will not be effective until 

hydrologic control is achieved in the recharge area and the 

water table is significantly lowered in the discharge area. 

Research and farmer experience have shown that yields will 

generally return to normal in 3 to 5 years. 

In saline-seep areas, observation wells are useful for monitoring water table levels during the control, reclamation, 

and post-reclamation periods. Water tables fluctuate seasonally and annually. Reclaimed saline seeps may be reactivated by a significant rise in the water table, which persists 

for several weeks or months. If a saline water table is less 

than 3 feet below the soil surface, saline water can move to 

the surface by capillary rise and create a salt problem. To 

alleviate this problem, monitoring wells at least 10 feet in 

depth should be installed in discharge areas, along drainage-ways, and in recharge areas. Ideally, the water table 

should be at least 6 feet in depth. Water table levels should 

be monitored monthly, especially during and after snowmelt, and rainy seasons. A rising water table that persists 

into the summer months indicates that cropping practices 

should be intensified to increase soil water use. 

Subpart 504B References

Arshad, M.A., K.S. Gill, and G.R. Coy. 1995. Barley, 

canola, and weed growth with decreasing tillage in a 

cold, semiarid climate. Agron. Jour. 87:49-55. 

Bauer, A. and A.L. Black. 1990. Effects of annual vegetative barriers on water storage and agronomic 

characteristics of spring wheat. North Dakota Agric. 

Exp. Stn. Res. Rpt. No. 112. 16 p. 

Black, A.L. 1973. Crop residue, soil water, and soil fertility 

related to spring wheat production and quality after 

fallow. Soil Sci. Soc. Amer. Proc., Vol. 37. 

Black, A.L. 1994. Managing seed zone soil water. Crop 

residue management to reduce erosion and improve 

soil quality. (Northern Great Plains) W.C. 

Moldenhauer, Managing Editor A.L.Black, Regional 

Editor. USDA-ARS Conservation Research Report 

Number 38. 

Black, A.L., P.L. Brown, A.D. Halvorson, and F.H. 

Siddoway. 1981. Dryland cropping strategies for efficient water-use to control saline seeps in the Northern 

Great Plains, U.S.A. Agric. Water Manage., (4):295- 

311. 

Brown, P.L., A.D. Halvorson, F.H. Siddoway, H.F. 

Mayland, and M.R. Miller. 1982. Saline-seep diagnosis, control, and reclamation. U.S. Department of 

Agriculture, Conservation Research Report No. 30, 

22 p., illus. 

Brown, T.A., A.L. Black, C.M. Smith, and others. 1981. 

Soil water guidelines and precipitation probabilities 

for barley and spring wheat in flexible cropping systems in Montana and North Dakota. Montana 

Cooperative Extension Service Bulletin No. 356, 30 

p. 

Brown, T.A., and Carlson, G.R. 1990. Grain yields related 

to stored soil water and growing season rainfall. Montana State University Agricultural Experiment Station 

Special Report 35, 22 p. 
(190-V-NAM, 3rd Ed., October 2002) 504–21 

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Gilley, J.E., S.C. Finker, R.G. Spomer, and L.N. Mielke. 

1986. Runoff and erosion as affected by corn residue. 

I. Total losses. Trans. Am. Soc. Agric. Eng., 29, 157. 

Gilley, J.E., S.C. Finker, R.G. Spomer, and L.N. Mielke. 

1986. Runoff and erosion as affected by corn residue. 

II. Rill and interrill components. Trans. Am. Soc. 

Agric. Eng., 29, 161. 

Gilley, J.E., S.C. Finker, and G.E. Varvel. 1986. Runoff 

and erosion as affected by sorghum and soybean residue. Trans. Am. Soc. Agric. Eng., 29, 1605. 

Gilley, J.E., S.C. Finker, and G.E. Varvel. 1987 Slope 

length and surface residue influences on runoff and 

erosion. Trans. Am. Soc. Agric. Eng., 30, 148. 

Greb, B.W. 1979. Reducing drought effects on croplands in 

the west-central Great Plains. U.S. Department of Agriculture, Agriculture Information Bulletin No. 420. 

Greb, B.W. 1983. Water Conservation: Central Great 

Plains. In Dryland Agriculture, Dregne, H.E., and 

Willis, W.O., Eds/ Agronomy Monogr. 23, Amer. 

Soc. of Agron., Madison, Wis. 

Lyon, D.J., F. Boa, and T.J. Arkebauer. 1995. Water-yield 

relations of several spring-planted dryland crops following winter wheat. Jour. Prod. Agric., Vol. 8, no. 2. 

Maas, E.V. 1990. Crop salt tolerance. Agricultural salinity 

assessment and management, Amer. Soc. Civil Eng. 

Man. and Rep. No. 71, 

pp. 262-304. 

Maas, E.V., and G.J. Hoffman. 1977. Crop salt tolerance– 

Current assessment. Jour. Irrig. and Drain. Div., 

Amer. Soc. Civil Eng., 103(IR2):115-134. 

Nielson, D.C. 1995. Water use/yield relationships for Central Great Plains Crops. Conservation Tillage Fact 

Sheet no. 2-95. U.S. Dept. Agric., ARS and NRCS; 

and Colorado Conservation Tillage Association. 

Nielson, D.C. 1996. Estimating corn yields from precipitation records. Conservation Tillage Fact Sheet 2-96. 

U.S. Dept. Agric., ARS and NRCS; and Colorado 

Conservation Tillage Association. 

Nielson, D.C. 1997. Water use and yield of Canola under 

dryland conditions in the Central Great Plains Jour. 

Prod. Agric., Vol. 10, no. 2. 

Peterson, G.A. 1994. Interactions of surface residues with 

soil and climate. Crop residue management to reduce 

erosion and improve soil quality. (Northern Great 

Plains) W.C. Moldenhauer, Managing Editor A.L. 

Black, Regional Editor. U.S. Dept. Agric., ARS, Conservation Research Report Number 38. 

Peterson, G.A., A.J. Schlegel, D.L. Tanaka, and O.R. Jones. 

1996. Precipitation use efficiency as affected by cropping and tillage system. Jour. Prod. Agric., Vol. 9, no. 

2. 

Pikul, Jr., J.L., and J.F. Zuzel. 1994. Soil crusting and water 

infiltration affected by long-term tillage and residue 

management. Soil Sci. Soc. Am. Jour. 58:1524-1530. 

Richards, L.A. 1954. Diagnosis and improvement of saline 

soils. USDA , United States Salinity Laboratory Staff. 

Agric. Handbook 60. 

Steiner, J.L. 1989. Tillage and surface residue effects on 

evaporation from soils. Soil Sci. Soc. Am. Jour. 

53:911-916. 

Steiner, J.L. 1994. Crop residue effect on water conservation. Managing agricultural residues. Ed. P.W. Unger 

Tanaka, D.L. 1989. Spring wheat plant parameters as affected by fallow methods in the northern great plains. 

Soil Sci. Soc. Am. Jour. 

53:1506-1511. 

Triplett, Jr., G.B., D.M. Van Doren, Jr., and B.L. Schmidt. 

1968. Effect of corn stover mulch on no-tillage corn 

yield and water infiltration. Agronomy Jour. 60:236- 

239. 

Unger, P.W. and J.J. Parker, Jr. 1968. Residue placement 

effects on decomposition, evaporation, and soil moisture distribution. Agron. Jour. 60:469-472. 

Unger, P.W. 1978. Straw-mulch rate effect on soil water 

storage and sorghum yield. Soil Sci. Soc. Am. Jour. 

42:486. 
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Unger, P.W., and A. F. Wiese. 1979. Managing irrigated 

winter wheat residues for water storage and subsequent dryland grain sorghum production. Soil Sci. 

Soc. Am. Jour., Vol. 43. 

Unger, P.W. 1986. Wheat residue management effects on 

soil water storage and corn production. Soil Sci. Soc. 

Am. Jour., Vol. 50. 

Unger, P.W. 1994. Residue management for winter wheat 

and grain sorghum production with limited irrigation. 

Soil Sci. Soc. Am. Jour. 58:537-542. 

Vigil, M.F., D.C. Nielson, R. Anderson, and R. Bowman. 

1995. Taking advantage of the benefits of no-till with 

rainfall probability distributions. Conservation Tillage 

Fact Sheet 4-95. U.S. Dept. Agric., ARS and NRCS. 
(190-V-NAM, 3rd Ed., October 2002) 506–i 

Plant Attributes

Contents:

Part 506

Subpart 506A Vegetative stabilization 506–1

506.00 Structures ..................................................................................................... 506–1 

506.01 General considerations ................................................................................. 506–1 

506.02 Seeding and planting process ....................................................................... 506–2 

506.03 Seed, plant, and amendment application rates ............................................. 506–2 

506.04 Disturbed land .............................................................................................. 506–5 

Subpart 506B Suitability for crop production systems 506–6

506.20 Suitability for crop production ..................................................................... 506–6 

Table Table 506-1 Common mulch material 506–4 

(190-V-NAM, 3rd Ed., October 2002) 506–1 

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Agronomy 

Manual 

Part 506 Plant Attributes Part 506 Plant Attributes 

Subpart 506A Vegetative stabilization

506.00 Structures

Structures are engineered earthen water retention, conveyance, or other conservation practice components. This section deals with establishing vegetation on typical erosion 

control structures such as Public Law 566 dams, diversions, 

waterways, emergency watershed program structures, and 

others. These structures are designed and constructed for 

soil and slope stability with vegetative treatment to protect 

and maintain the integrity of the structure. 

506.01 General considerations

Plants—Protecting structures is typically accomplished 

with grasses enhanced by a legume component for some nitrogen generation. Landscaping with shrubs and trees blend 

structures into surrounding landforms. Species and cultivar 

selection and effective planting techniques are key to successful establishment. Select plants to meet the existing site 

conditions including internal soil drainage, soil texture and 

percent fine particles present, organic matter, density, pH 

and nutrients available from the soil, exposure and aspect, 

temperature zone, and plant hardiness factors. Recommended plant lists are available in each state. 

Proper plant selection to meet the existing and future site 

use will minimize future maintenance. Cultivars that have 

been released through the NRCS Plant Materials program 

should receive first consideration. Consider using native 

plants if they are known to be effective. Avoid using plants 

known to be invasive, such as kudzu, multiflora rose, or 

phragmites. 

Soil—Soil is the medium in which seeds germinate and 

roots grow. The condition of the soil may well determine 

the success or failure of seedings or plantings. Soil texture, 

structure, tilth, organic matter, drainage, and chemical composition need to be reviewed to be certain that compatible 

plants have been selected. Soil amendments should be 

specified to meet site and plant needs. 

If topsoil is salvaged onsite, use it on the most sensitive 

area(s) of the structure, such as emergency spillways or 

faces of dams. Blend the topsoil into the surface of the 

structure to avoid a sharp contrast between compacted fill 

material and the topsoil. 

Water and wind management—Potential erosion problems 

need to be considered when selecting appropriate species 

and establishment techniques. Water as rainfall or snowmelt, spring ice flows in streams, surface runoff, or seepage 

areas may require special attention. Diversions and waterways may need to be established to manage excess surface 

water, or subsurface drains may need to be installed to dry 

out seeps. Exposed areas subject to wind should be treated 

with adequate protection to insure establishment of the 

planting. This may include mulch anchoring, temporary 

windbreaks or using wind barrier plants. 

Combinations of geotextiles, soil bioengineering (live 

fascines, brush mattresses) and biotechnical stabilization 

may be desirable to handle special conditions of erosive 

water velocities or areas of temporary high flows. 

Land use—Land use surrounding the structure(s) should be 

evaluated to blend the disturbed area into as natural setting 

as possible. Plantings should be planned based on anticipated growth and appearance of the species. Blending structures with the environment will enhance the visual appearance and present a positive effect to the public. 

Geology—Geologic investigations include the overburden 

material and the underlying parent material. Bedrock, 

changes of soil texture at various depths, and saline areas 

can be addressed early in the planning process when identified from the geologic review. 

Existing vegetation—Existing vegetation can be a source 

of potential species that should be included in the seeding 

of constructed structures. It may be desirable to select species from several successional stages to include in the 

revegetation plan. Using species that grow on surrounding 

areas will help blend the structure into the landscape. Caution is needed when doing this, because local species may 

not tolerate tranplanting or may not perform well on disturbed sites. Local ecotypes, where available commercially, 

would be preferred sources of plant material. 
506–2 (190-V-NAM, 3rd Ed., October 2002) 

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Present and proposed use—Consideration of the proposed 

future use of the structure is important in species selection. 

If people and vehicles will be using the area, traffic patterns 

should be planned. Paths should be designed to minimize 

erosion potential. Plants that impede recreational activities, 

such as vines or dense, tangled growth, should be avoided. 

Select vegetation that will enhance the long-term use of the 

area as well as provide erosion control cover needed. For 

example, if fishing will be allowed after a large dam is constructed, leave some grass areas without shrubs at the 

water’s edge. Where recreational abuse of the site causes 

soil erosion, select plant species that will discourage the use 

of these areas. 

Climate—Select species for the local climate — Rainfall 

and temperature vary greatly within a state. Exposure to 

wind may create a sandblasting problem on the plants or 

may result in desiccation of the plants. Site aspect (north 

facing slopes) may result in several degrees difference in 

temperature. The USDA Plant Hardiness Zone Map, Misc. 

Pub. No. 1475, 1990, can serve as a general guide for selecting plants. The Plant Zone map may be veiwed on-line 

at 

http://www.usna.usda.gov/Hardzone/

However, local conditions may offer protection or may create exposure that will influence the plant performance. 

Shade tolerance—Where structures will be shaded for part 

or all day, be sure the species are tolerant for the anticipated 

condition. If canopy cover closure is anticipated in the future, then include appropriate ground cover species to meet 

the future site condition. 

Site preparation—The area before construction should be 

reviewed to select and preserve any highly desirable plants 

or section of plants near the perimeter or edge of the construction zone. Endangered, threatened, or declining species 

considerations must be met before construction. Install any 

temporary wind or water control measures. If topsoil or 

other organic matter is available onsite, salvage as much as 

is economically feasible. Do not waste it by burial or other 

loss. 

506.02 Seeding and planting process

Seeding should be done as construction is completed or at 

intervals during construction. Daily or regular time interval 

seedings may be mandatory where site location or local 

laws require this. Frequently, daily seedings are planned for 

temporary erosion control until the work for the entire 

project is completed. Then the areas will be reseeded to 

permanent vegetation at an appropriate planting date. 

Seedbed preparation—The objective in seedbed preparation is to create a condition where seed can be planted, 

emerging seedlings will have a favorable microenvironment, and the surface area will be such as to allow the type 

of maintenance required to support protective vegetative 

cover. 

During this operation, soil amendments such as lime, gypsum, or fertilizer should be applied. Also, remove large 

stones (generally greater than 1 to 2 inches in diameter for 

areas that will be lawns or parks, and greater than 4 to 6 

inches in diameter for other areas) and debris that will 

hinder seeding or planting and future operations and maintenance. 

Seedbed scarification may be required unless seeding is accomplished within 24 hours of final grading. Sand and 

gravel (sites with less than 20% fines passing a 200 mesh) 

do not require scarification as long as moisture is adequate. 

When the surface soil is powdery, the soil is too dry for 

seeding. If clumps of mud stick to the planting equipment, 

the soil is too wet unless a hydroseeder or other suitable 

equipment is used. 

Areas of compaction should be identified and ripped or 

scarified to a depth of at least 9 to 12 inches to create a 

more favorable rooting zone. Topsoil (if available) should 

be applied and blended with the surface of the structure. All 

tillage operations should be performed on or as close to the 

contour as possible. The balance of the area should be 

scarified or loosened to a minimum of 3 inches to allow 

good soil to seed contact. Scarification may be waived if 

the seeding is accomplished immediately after the final 

grading is finished and site conditions warrant this approach. 
(190-V-NAM, 3rd Ed., October 2002) 506–3 

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506.03 Seed, plant, and amendment application rates

Seed and plant rates—General seeding rates and planting 

quantities of adapted species or mixtures are available in 

the NRCS Field Office Technical Guide (FOTG), Section 

IV, Critical Area Planting Standard 342. 

Seed or plant specifications, or both—To insure the quality all planting material, specify genus, species, cultivar (if 

applicable), specific inoculant, and percent pure live seed 

or minimum seed germination. All seeds should meet Federal and state seed laws for proper labeling and noxious 

weed content. Criteria for shrub and tree quality, size and 

type of plant material should be based on standards in the 

publication American Standards for Nursery Stock, developed by the American Association of Nurserymen. 

Time of seeding or planting—Specify appropriate planting 

dates. Spring seedings may be adequate where normal rainfall is available. However, the effect of annual weeds and 

midsummer droughts should be considered. Fall seedings in 

many parts of the country have the advantage of more reliable precipitation and favorable temperatures. In addition, 

in the northern states, the annual weeds are generally winter 

killed. 

Cool-season grasses generally do best when seeded in the 

fall. However, construction will often be completed during 

periods of the year when seedings should not be made. In 

these cases, temporary seeding or mulching should be done 

and the permanent seeding made at the optimum time of 

year for the species used. 

Warm-season grasses are normally seeded in the spring. 

Some fall seedings are successful providing weather conditions remain cold and the seed remains dormant. In general, 

warm-season grasses should have about 100 days of growing season remaining after planting. 

Where soil or site conditions limit available moisture, such 

as sandy or rocky soils, a temporary irrigation systems can 

help insure adequate establishment of vegetative cover. Irrigation can be used on earth-fill structures if care is taken to 

apply only amounts necessary. If the system is not operated 

properly, irrigation water induced erosion can occur. Steep 

slopes (3:1 or steeper) are generally too hazardous on 

which to set irrigation pipe, plus the erosion potential is too 

great. 

Soil amendments—The desired soil pH will depend on the 

plant species selected and long-term goal of species composition. Acid soil should generally have the pH adjusted to 

5.5 or higher for grasses and 6.0 if legumes are to be used. 

This will allow the rhizobium bacteria associated with legume roots to function. Ground agricultural limestone, either calcitic (high Ca) or dolomitic (high Mg) is used. The 

most desirable ratio is a Ca:Mg ratio of 10:1; however 

wider ratios are acceptable. High pH or saline soil may require gypsum (CaSO4.2H2O) application. A detailed soil 

analysis should be used to determine the type and amount of 

nutrients needed. Usually high levels of some elements may 

be toxic, and special steps may be needed to amend these 

areas. Add only the amount of nutrients required to produce 

adequate vegetative cover. 

Method of seeding or planting—Many techniques are 

available that have proven successful. Site conditions will 

dictate options. 

Steep slopes on which regular seeding equipment cannot be 

safely operated must be seeded by broadcasting the seed, 

blowing it on, or by hydroseeding (applying seed, and 

sometimes soil amendments and mulch, in a water slurry or 

suspension). For hydroseeders, coverage is limited by the 

size of equipment, wind conditions, and stream load. Centrifugal seeding equipment requires dry weather conditions 

and limited wind interference. High-velocity blowers are 

normally used for sites where it is difficult to hold seed in 

place, or sites that are inaccessible by large equipment. 

These blowers will force some of the seed into the soil and 

crevices for germination. For this method to work properly, 

the soil must be moist. Some delicate seeded species may 

experience seed damage. 

Calibration of hydroseeders or blowers is difficult. Experienced operators usually will be able to uniformly apply seed 

by estimating the land area and applying tank loads at acceptable rates. Hydroseeders frequently add colored mulch 

to mark the area covered. 

Another technique for steep slopes is to use a track type 

bulldozer to incorporate seed and amendments. Operate the 

bulldozer up and down the slope. The cleat tracks create areas in which seed may be trapped. Soil migrating down the 

slope will cover the seed and the indentations in the bank 

hold additional moisture. This works well on sands and 

gravel. 
506–4 (190-V-NAM, 3rd Ed., October 2002) 

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On flatter areas, additional equipment is available to better 

place the seed into the soil and in arid regions, to better take 

advantage of soil moisture. 

Imprinting works well to allow for deep placement of seed, 

This allows for access to moisture and affords the germinating seedling some wind protection. 

Special grass drills with packing wheels and other special 

features are available. Warm season grass boxes are available to handle the fluffy prairie grass seed. These units have 

devices within the boxes to prevent the bridging of seed, resulting in even seed flow. 

Broadcast seeding with an airflow spreader is an acceptable 

seeding method for some species and purposes. 

Herbaceous planting material, such as bermudagrass sprigs, 

American beachgrass cuttings or trees requires special 

knowledge and handling. Internal heating of this material 

frequently occurs during shipping and storage. The damage 

to the growing points may go undetected by an untrained 

person until the plants do not grow. During delivery and 

planting, every effort should be made to keep the plants 

cool and moist to insure good survival and growth. 

Mulching — Mulching is an important process in establishing vegetation (especially cool-season grasses) on structures 

or other critical areas. Mulch cover will help maintain favorable moisture conditions, prevent soil erosion by water 

or wind, hold seed in place, and maintain cooler, more constant soil temperatures. Mulch should be applied immediately after seeding (within a few hours or less). It should be 

uniformly applied at the specified rate. 

Mulch material (table 506–1) is not all equal in providing 

the optimum conditions for germinating seeds. Small grain 

straw is the preferred material for most sites. This material 

generally has few weed seeds and provides the best results 

of any tested material. Grass or mixed legume and grass hay 

is good but frequently has weed and hay seeds that may also 

grow and compete with the desired seeded species for moisture, nutrients, and light. This is a problem with warm-season grass plantings. It does not make much sense to use cerTable 506-1 Common mulch material 

Mulch material Quality standard Application rate Remarks 

Hay, small grain straw Air-dried; free of mold; 2 tons per acre. Subject to wind blowing unless 

free of noxious weeds. anchored; cover about 90% of soil 

surface. 

Wood excelsior Green or air-dried 2 tons per acre. Decomposes slowly; subject to 

burred wood fiber. blowing unless anchored; pack 

aged in 80-90 lb bales. 

Wood fiber cellulose Partially digested wood 2,000 lb per acre. Apply with hydroseeder; used as an 

fiber; usually with green anchoring material for mulches subject 

dye and a dispersing agent. to blowing. 

Jute mat - twisted yarn Undyed, unbleached plain 48 in x 50 yd or Use without additional mulch; secure 

weave; warp 78 ends/yd; 48 in x 75 yd. as per manufacturers’ specification. 

weft 41 ends/yd; 60–90 lb 

rolls. 

Excelsior wood fiber Interlocking web of 48- x 100-inch Use without additional mulch; secure 

mats excelsior fibers with 2-sided plastic or as per manufacturers’ specification. 

photodegradable 48- x 180-inch 

plastic netting. 1-sided plastic. 

Straw or coconut Photodegradable plastic 6.5 x 83.5 ft, Designed to withstand fiber individually 

or combined mats net on one or two sides. 81 rolls per acre. specific water velocities. 
(190-V-NAM, 3rd Ed., October 2002) 506–5 

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tified seed and then throw weedy mulch over the seeding. 

Other fibrous material such as coconut fiber, excelsior fiber 

and wood fiber all may be used. Economics will sometimes 

dictate which mulch material is used. Many latex compounds and commercial products will control erosion and 

hold seed in place under some moisture and temperature regimes. 

Competition is a problem with warm-season grass 

plantings. Consider alternatives to mulching when warmseason grasses are seeded in northern regions. An oat cover 

crop, seeded in the fall, will grow enough to protect the soil. 

Because it will winter kill, the residue will be present in the 

spring to prevent erosion, but not compete with the warmseason grass seedlings. 

Mulch material can be selected from the list below. Use appropriate materials for the location. The optimum mulch 

material for cool season grasses and legumes is small grain 

straw at 4,000 pounds per acre, anchored with 500 to 750 

pounds wood fiber hydromulch. This will provide optimum 

conditions for rapid germination and establishment. 

Mulch anchoring—Once mulch is applied, it must remain 

in place. Few if any of the seeded species will establish in 

bare areas from which the mulch has moved. On critical 

sites that are droughty and wind swept, mulch anchoring 

must be performed to obtain uniform establishment. The 

cost of establishing erosion control cover is frequently justified, and reducing the area needing reseeding offsets this 

cost. Mulch anchoring material selection and application 

rate is important to establish some species. 

Material for anchoring fibrous material ranges from wood 

fiber hydromulch to latex compounds to asphalt emulsion, 

to mesh netting, to mulch blankets. All are excellent for 

specific situations. Follow manufactures recommendations 

for use. Selection is dependent on the intended use, cost, and 

available labor or equipment. 

A wide assortment of implements is available to anchor 

mulch by incorporating some of the mulch into the soil surface. 

Ultimately, the local growing conditions will dictate the 

outcome of the seeding. If a short-term drought occurs as 

the seed is germinating, allowing the mulch to be blown 

around or removed from the site during this time may result 

in a seeding failure. This is especially critical on droughty 

soils and for spring seedings. 

506.04 Disturbed land

(a) Planning principles

Vegetative treatment of disturbed land areas requires some 

planning to overcome many potential problems. These include water and wind management concerns, sedimentation, 

potential limiting or excess elements on site, intended land 

use, length of time the area or partial area must be exposed 

for continued construction, existing slope and planned slope 

and slope length, and presence or absence of vegetation. 

The kind of soil and drainage class will influence the type 

of plant desired. 

Water and wind erosion concerns must be dealt with before 

establishing vegetation. Plants tolerant to wind may be used 

to protect areas before establishing more permanent and desirable species, or temporary wind breaks (wind fence) may 

be used. Plants tolerant of inundation or wetness may be required along with regrading or shaping portions of the site to 

divert or retain water. If the site requiers grading and leveling, salvage as much topsoil and existing as possible. 

Shape and grade for intended future use. Areas planned for 

sports or other types of recreation require considerably 

more attention and detail than an area being reclaimed for 

wildlife habitat. 

If a site is barren of vegetation, or nearly so, the cause 

needs to be determined before trying to establish vegetation. Past use or history of industry may provide clues to the 

lack of vegetation. Old garage areas or motor pool areas 

may have petroleum contamination or battery acid spills. 

Mining operations or industrial sites may have dumps associated with them, in which chemicals associated with the industry were disposed. By asking questions about the past 

use, the planner can then begin piecing the puzzle together. 

Testing for residual material or chemicals is the only way to 

confirm what is present. 

Soil physical barriers such as restrictive or compacted layers in the rooting zone need to be identified and corrected. 

Soil sample analysis for particle size distribution may be required. Several plants may be available for use on soil that 

has 40 percent fines but fewer are suitable if the fines are 

less than 15 percent. Select plants for the long term, not 

ones that will grow well for 1 or 2 years. For example, use 

of ryegrass and cool season grasses on sand and gravel areas will grow and provide temporary cover. However, when 

the fertilizer is depleted and moisture becomes deficient, 

the cool-season plants will die off. If switchgrass and other 

warm-season grasses are used, they will persist for more 

than 20 years while natural succession occurs. 
506–6 (190-V-NAM, 3rd Ed., October 2002) 

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Fertility levels need to be assessed before selecting the appropriate plants. Percent organic matter, potentially toxic 

levels of elements, and pH are interrelated, and they need to 

be quantified before treatment. 

The natural plant succession for the area should be considered, especially when selecting species to use. It may be 

desirable to select species from several successional stages 

to include in the revegetation plan. Use plants that blend to 

the surrounding areas. Avoid selecting invasive species. 

Biotechnical or soil bioengineering options should be 

evaluated for unstable slopes. The use of live fascines or 

brush layering techniques should be considered in lieu of 

more expensive stone gabion baskets and riprap. Chapters 

16 and 18 of the Engineering Field Handbook detail these 

techniques. 

(b) Unique critical areas

Strip-mined areas—Strip mining is the removal of overburden to gain access to some mineral or fuel. The spreading 

or dumping of this overburden material frequently exposes 

contaminants. Coal mining in the Appalachian Mountains 

frequently exposes sulfur and iron, the oxidation of which 

results in the formation of acid materials. The best solution 

is to cover this acid-forming material during the mining process. If left exposed, the soil pH can become extremely low, 

causing any aluminum in the soil to become available for 

plant uptake. When this occurs, the plants selected must be 

tolerant to potential aluminum toxicity. Because of exposure, slope, and rock, these sites are frequently very 

droughty. 

The sequence of mining operations can be the best management practice and provide for minimizing future toxic areas 

through proper closing of mined areas. This requires saving 

the overburden and replacing it on the surface in proper sequence before vegetating the area. 

Mine tailings—Areas covered with waste material from 

mining operations may be high in heavy metals, or have 

other chemical or physical conditions that make vegetative 

establishment difficult or impossible. Covering this material 

with a minimum of six inches of borrow material from surrounding areas may be necessary to establish vegetation, 

stabilize the site and help insure the long-term survival of 

desirable vegetation. 

Coastal and inland sands and sand dunes—Areas of 

blowing sand need wind erosion control measures. This 

may be accomplished using plants such as American 

beachgrass or with windbreaks or other physical structures. 

On inland sands, planting single or double rows of American beachgrass or other appropriate plants, perpendicular to 

the prevailing wind erosion direction, will provide protection for establishing more permanent vegetation. Spacing 

between rows should be ten times the anticipated height of 

the plants after one growing season. Wait one year before 

seeding the permanent vegetation. 
(190-V-NAM, 3rd Ed., October 2002) 506–7 

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Subpart 506B Suitability for crop

production systems

506.20 Suitability for crop production

Crop selection in a properly designed rotation is critical to 

maximize rotational benefits. A properly designed crop rotation provides an excellent tool in breaking insect, weed 

and disease cycles (Refer to Part 503, Subpart A, Crop rotation). 

In the past 10 years there has been a major shift in agriculture toward crop production systems using higher amounts 

of surface residue. In the United States between 1989 and 

1997, there has been a 13.5 percent increase in cropland 

acres involved in some form of residue management. During this same time period the acres in no-till crop production systems have increased 10.1 percent. One of the consequences of this change in crop production systems is that 

less seedbed modification though tillage is occurring while 

placing greater reliance on crop selection and variety or hybrid characteristics. Conservation tillage or no-till methods 

require changes in machinery, fertility programs, and pesticide use. In addition, crop and seed selection must also be 

reevaluated. Selecting a more desirable variety or hybrid 

should not be a substitution for properly designed crop rotation. 

After a proper rotation has been designed, two primary areas of crop selection need to be evaluated in depth: variety 

or hybrid performance and after-harvest seedbed characteristics for the next crop in the rotation. 

(a) Variety or hybrid performance

characteristics

In crop production systems using higher amounts of surface 

residue, the importance of desirable variety or hybrid characteristics varies among crops. Some important common 

characteristics to consider are high-quality seed, the right 

maturity for the geographic area, good early season emergence, good early season seedling vigor, consistent performance across soil types, vigorous root development and 

disease and insect resistance. 

Of these characteristics, choosing high-quality seed, those 

with the right maturity for the geographic area, and that 

consistent performance are not just characteristics for high 

residue situations but are universal among tillage systems. 

However, because of the cooler and wetter seedbeds normally encountered in high residue situations, these characteristics are not only important but may also need to be 

modified. An example would be a warm-season grass such 

as corn. Selecting hybrids 5 to 10 days earlier in maturity 

may be necessary when planting into heavy residues. In addition, consistent performance across various soil types is 

important, because it is a sign that the hybrid can withstand 

stress under varied environmental conditions. 

Early season emergence and seedling vigor become of 

greater importance specifically with warm-season crop species when cooler, wetter soil conditions are the rule. Selecting varieties or hybrids with good early emergence and 

early seedling vigor is necessary where soil conditions that 

have more stored soil moisture and will be cooler and wetter. Crops under these conditions must germinate quickly 

and have good early season growth potential to provide the 

necessary competitive edge required against early weed 

competition. Treating crop seeds with fungicides can help 

offset these potenial negative effects of planting in high 

residue conditions. 

The selection of varieties or hybrids that can develop vigorous root systems without the help from conventional cultivation is also a very important characteristic for reduce till 

or no-till system. Some hybrids or varieties also produce a 

stronger stem or stalk that translates into consistent performance and may contribute to a more durable residue cover 

following harvest. When selecting varieties and hybrids for 

superior root and stem characteristics, inquire whether these 

characteristics have been evaluated under reduced tillage or 

no-till conditions. 

Tolerance to common insect and disease can be important 

depending on the area and crop rotation. This can be especially true when the crop to be planted is closely related to 

the preceding crop in the rotation, such a cool-season grass 

planted into a cool-season grass. Another example might be 

planting soybeans in field with heavy surface residues and 

poorly drained soils. Selecting soybean varieties for 

phytophthora root rot resistance may be a major advantage 

in these fields. An important point to mention again is that 

the selection of varieties with insect or disease tolerance is 

not a substitution for rotation. 
506–8 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 506 Plant Attributes 

(b) After harvest seedbed characteristics for the

next crop in the rotation

Previously, modifying the seedbed in preparation for the 

next crop was done with tillage, either conventional (plow, 

disk, arrow), or in recent years, by building ridges (ridge 

till), or fall and spring strip till methods. In high-residue 

cropping systems, residue characteristics such as the 

amount, color, resistance to decay, and stubble height of 

residue left after harvest can affect the seedbed characteristics for the next crop. These characteristics can be an advantage if properly managed, or they can be an obstacle to 

good production advantage or can be an obstacle if not 

properly incorporated into a cropping system. 

Residue levels and residue color affect soil temperatures. 

High levels of residue keep the soil cool longer because the 

residue absorbs or reflects the sun's energy. After crops 

such as corn or grain sorghum, which can produce high levels of surface sover, the soil will warm up slower. When 

dealin with heavier amounts of residue from the preceding 

crop, it may e necessary in no-till situations to use residue 

managers that move the residue off to the side of the seed 

slot. Dark-colored residue, such as that produced by oilseed 

and legume crops, absorbs the sun's energy and transfers it 

to the soil, causing it to warm up faster then if the residue 

was lighter colored. 

Warm- season species such as corn or sunflower respond to 

warm, clean seedbed conditions. These conditions can be 

obtained by managing the type and amount of residue from 

the preceding crop. For example, soybeans produce relatively low amounts of residue that is dark colored. After 

soybeans, the seedbed for subsequent crops will be mellow, 

warm, and very conducive to fast, uniform emergence. 

Other crop species may benefit from the micro-environmental conditions produced by high amounts of surface residue. 

Cool soil conditions are not a concern when seeding winter 

wheat. However surface moisture and sufficient standing 

stubble to catch snow are important factors to consider. Surface residue helps prevent the soil from drying out or cooling down too rapidly, extending the fall growing period for 

winter wheat. For another example, soybeans are sensitive 

to heat, drought, and high soil temperatures. Heavier surface residue levels improve soybean performance under 

these conditions. 

When higher amounts of surface residues are desirable for 

crop production, the inclusion of a crop with more durable 

residue characteristics may be necessary. As surface residues increase, microbial populations in the upper one or 

two inches of soil also increase, which increases the rate of 

decay of these residues. Including a crop residue is more resistant to decay, such as corn, sorghum, or sunflowers, will 

help increase surface residue levels. 

Stubble height of previous crop residues can be very beneficial in increasing soil moisture and can increase the survival 

of fall-planted crops. In the northern Great Plains, increasing stubble height traps more snow on the field, increasing 

the available water for crop production. Stubble height can 

be increased by setting the combine header higher, or by using stripper headers to harvest grain. 

Taller stubble heights can also moderate air and soil temperatures, improving the survival of winter wheat and increasing the effective range of the crop further north. The 

maximum winter wheat hardiness is obtained with winter 

wheat planted into standing small grain stubble. However, 

when winter wheat is planted following another small grain, 

varieties with tolerance to leaf spotting diseases should be 

considered in some environments. Managing stubble height 

coupled with selecting disease-tolerant varieties allows 

higher yielding varieties with less winter hardiness to be 

planted further north than was previously possible. 
(190-V-NAM, 3rd Ed., October 2002) 506–9 

National 

Agronomy 

Manual 

Part 506 Plant Attributes 

Subpart 506C References

American Nursery and Landscape Association. American 

Standard for Nursery Stock. 1997.57pp. 

(190-V-NAM, 3rd Ed., October 2002) 507–i 

Cropland Conservation

Management Systems

Contents:

Part 507

Subpart 507A Major cropland practices 507–1

507.00 Cropland conservation management systems ................................................. 507–1 

507.10 Cropland conservation management systems—humid east ............................ 507–1 

507.11 Typical cropland resource concerns ................................................................507–1 

507.12 Purposes, effects, and impacts of the major cropland conservation ............... 507–1 

management systems 

507.13 Economics of the major agronomic practices/treatments ............................... 507–2 

507.20 Resource concerns and effects-dryland regions of the Great Plains ............... 507–4 

and western United States 

507.21 Defining and describing dryland regions ........................................................ 507–5 

507.22 Regional resource settings of dryland cropping areas of the United States ....507–5 

507.23 Principles and guidelines of dryland conservation Management systems ......507–5 

507.24 Factors in planning dryland cropping systems ................................................ 507–8 

507.25 Major cropping systems and technologies for the dryland regions ................. 507–8 

of the United States 

Subpart 507B References 507–10 

Table Table 507-1 Example of major purposes and expected effects of commonly 507–3 

used conservation practices/treatments on cropland 

Table 507-2 Climatic zone delineation 507–5 

Table 507–3 Major cropping systems and water and soil conservation management 507–9 

technologies for U.S. dryland agricultural regions 

 (190-V-NAM, 3rd Ed., October 2002) 507–1 

Part 507 Cropland Conservation Management

Systems

Subpart 507A Major cropland

practices

507.00 Cropland conservation management

systems

The development of sustainable cropland conservation 

management systems involves effective conservation planning. This conservation planning process views the agroecosystem as an integration of complex natural physical, 

chemical, and biological functions. Our look back at history 

should convince us that undertakings to manage agro-ecosystems as a natural resource must consider the entire system rather than just the parts. Nothing less than managing 

for the whole or health of the agro-ecosystem is acceptable. 

Managing for the health of the agro-ecosystem requires acceptance of a holistic approach to conservation planning to 

achieve some degree of sustainability. 

The same general principles that Hugh Hammond Bennett 

set forth in 1947 are still applicable in the development of 

effective conservation management systems on cropland. 

The principles are summarized as follows: 

• Consideration and focus on the producer’s goals. As a 

part of this goal setting process, an evaluation is made 

of the producer’s farm and livestock facilities, machinery, and economic situation. The product of this 

principle results in the establishment of three action 

statements that further define the goal. The statements 

are 

– the quality of life that the producer wants derived 

from the agro-ecosystem; 

– the forms of production and management tools 

required to deliver the quality of life; and, 

– a description as to what the farm’s landscape or 

the desired future condition is to look like (Savory 

1988). 

Also, the description includes the producer’s expectation of the farm’s production ability to be sustained. 

• Evaluation of the needs and capability of each cropland acre. 

• Incorporate the producer’s willingness to implement 

and adapt new technology and practices. 

• Consideration of the landscapes relationship and 

function to the entire farm and watershed. 

• Continued presence of the conservationists with the 

producer. In any holistic approach to management of 

the agro-ecosystem there is a requisite for monitoring 

and assessment of the function of the system. 

In addition, there will be assessment indicators and events 

that will demand re-planning. In many cases the specific 

management tools will need to be altered, or in some cases 

a current tool is abandoned and a different one implemented. 

507.10 Cropland conservation management

systems —humid east

507.11 Typical cropland resource concerns

One or more of the resource problems listed are a concern 

on cropland in the humid east of the United States. 

• Erosion from water or wind, or both 

• Soil condition 

• Soil compaction 

• Available water (too much, too little) 

• Pests (weeds, insects, diseases) 

• Soil/plant nutrient management 

• Quality of runoff or ground water, or both 

• Pesticide management, selection, drift, leaching, 

runoff, and resistance 

• Economics 

• Compliance with USDA programs and other Federal, 

State, and locals laws 

507.12 Purposes, effects, and impacts of the

major cropland conservation management systems

Practices/treatments used to address the resource concerns 

about cropland situations often have complimentary effects 

on the resource concerns. For example, by selecting a rotation of different crops (conservation crop rotation practice) 

to meet soil erosion, soil condition, and producer needs; the 

practice also has complimentary effects on reducing weed, 

disease, and insect pressures (pest management practice). 

Likewise, a practice/treatment selected to treat one concern 

may have an adverse effect on another resource concern. 

For example, the use of the no-till practice may be effective 

to reduce erosion, improve soil condition, and reduce nutrient and pesticide runoff; but no-till may have an adverse effect on the production system if a proper crop rotation and 

nutrient and pest management are not implemented at the 

same time. Therefore, as a cropland management system is 

planned, it is critical to understand all the effects of the 

practices/treatments being considered on the total production system. 
507–2 (190-V-NAM, 3rd Ed., October 2002) 

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Part 507

Table 507-1 has examples of some of the major purposes 

and expected effects of the most commonly used practices/ 

treatments on cropland. The purposes identified are expressed in the National Practice Standards as well as additional purposes/effects for local consideration. 

Conservation management systems for cropland include a 

combination of practices/treatments necessary to address 

existing and anticipated soil, water, air, plant, animal, and 

human resource concerns, and treat all the concerns to a 

minimum acceptable level. Cropland involves the growing 

of annual or a mixture of annual and perennial crops. To 

produce crops requires the continued management of soil, 

water, air, plants, and their associated components to meet 

the objectives of the producer and to maintain a sustainable 

production base. 

A large number of potential practices/treatments can be 

used on cropland. However, there are few major practices/ 

treatments that form the foundation (or core) of most cropland conservation management systems. The major practices/treatments that form the core of cropland management 

systems involve those that relate to the 

• selection and rotation of crops, 

• tillage or planting system (crop establishment), 

• residue management, 

• fertility management, and 

• pest management. 

Other major practices/treatments include irrigation management, surface and subsurface water management, contouring, buffer strips, and filter strips. 

To successfully produce crops in an economical and sustainable manner requires an accurate assessment of the resources’ (soil, water, air, plants, animals, human) capabilities and limitations. The core practices of crop rotation, timing and type of tillage, how the residue is managed, nutrient 

management, and pest management are almost always involved to address the capabilities and limitations (resource 

concerns) of any cropland management system. 

Other common practices/treatments used in cropland management systems include 

• cover crops, 

• cross wind strips, 

• waste utilization, 

• subsoiling, 

• terraces, 

• subsurface drainage, 

• surface drainage, 

• grassed waterways, and 

• water and sediment control basins (control concentrated flow/gully erosion). 

Cropland management systems must address the following: 

• Crop(s) to be grown within the resource capabilities 

and limitations. 

• Producer’s needs and concerns. 

• Crop(s) establishment. 

• Residue management. 

• Nutrient management. 

• Pest management. 

• Soil water management. 

• Sustainability of the management system. 

The first step in developing a cropland management system 

is to fully assess the resource capabilities and limitations (a 

resource assessment) and determine the producer’s capabilities, limitations, and objectives. This will establish the 

baseline to begin to build an effective conservation management system for cropland. One must also keep in mind that 

although different cropland systems may have the same 

practices planned, the treatment within those practices may 

be different to meet different purposes. In addition, cropland systems with the same combination of practices but 

planned for different purposes may have different effects on 

the resources and concerns. 

507.13 Economics of the major agronomic

practices/treatments

To assess the economics of the agronomic practices is often 

difficult. The traditional method used to assess the economics of various agronomic practices is to compare different 

methods to achieve a given treatment or purpose. For example, a seedbed must be prepared for planting. One 

method would be to use mulch-till and compare that cost to 

using no-till. It is critical that the costs involved in agronomic practices/treatments be carefully analyzed. For example, in the mulch-till vs. no-till scenario mentioned previously, if the producer owns both mulch-till tools and no-till 

tools, one can only evaluate operation and maintenance 

costs of the equipment because the costs of the equipment 

are already incurred regardless of the system used. 

Most agronomic type practices/treatments do not require a 

direct outlay of cash. Many of the practices and treatments 

are often more of a change in management techniques 

rather than a formal installation. 
(190-V-NAM, 3rd Ed., October 2002) 507–3 

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Manual 

Cropland Conservation

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Part 507

Table 507-1 Example of major purposes and expected effects of commonly used conservation practices/treatments on cropland 

 Practice/treatments Purposes and effects 

 and National Practice 

 Standard code 

Conservation crop rotation Reduce sheet, rill, and wind erosion 

Code 328 Produce needed feed for livestock 

Produce needed residue for soil organic matter 

Manage soil nutrient levels 

Improve soil condition, tilth, health 

Manage or break pest cycles, or both 

Improve wildlife food and cover 

Residue management Reduce sheet, rill, and wind erosion 

Code 329 series Improve air quality (reduced dust and soil particlate in the air) 

 No-till and strip-till (A) Improve soil condition, tilth, health 

 Mulch till (B) Improve soil available water content 

 Ridge-till (C) Reduce nutrient and pesticide runoff 

Reduce sedimentation 

Reduce trips across the field (compaction potential) 

Reduce time demands for seedbed preparation 

Reduce cost of equipment and field operations 

Improve wildlife cover 

Residue management, Reduce sheet, rill, and wind erosion 

Code 344 Provide residue for livestock grazing 

 Seasonal Provide food and cover for wildlife 

Manage available soil water 

Reduce runoff during selected times of the year 

Contour farming Reduce sheet and rill erosion 

Code 330 Reduce power requirements 

Improve soil available water content 

Reduce surface runoff 

Reduce nutrient and pesticide runoff 

Safety during field operations 

Contour buffer strips Reduce sheet, rill, and wind erosion 

Code 332 Improve soil condition, tilth, health 

Contour stripcropping Improve soil available water content 

Code 585 Reduce surface runoff 

Field stripcropping Reduce nutrient and pesticide runoff 

Code 586 Reduce sedimentation 

Reduce power requirements 
507–4 (190-V-NAM, 3rd Ed., October 2002) 

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Manual 

Cropland Conservation

Management Systems

Part 507

To select the most cost-effective cropland management system, first develop two or more alternative management systems that adequately treat the resources and meet the 

producer’s objectives. Then evaluate each system, comparing the total costs to implement each system to the expected 

impacts and returns of that system. 

507.20 Resource concerns and effects-dryland regions of the Great Plains and

western United States

In discussing major cropland management practices within 

the Great Plains and western regions of the United States, a 

distinction must be made between the term’s dryland and 

rain fed. Rain-fed agricultural systems can be used to describe agricultural systems that exclude irrigation as a water 

source and generally fall into two categories. The first category of rain-fed agricultural systems are those that emphasize maximum crop yields, significant production inputs, 

and disposal of excess water, while the second category of 

rain-fed agricultural systems characterize the dryland systems (Stewart 1988; Stewart and Burnett 1987). 

Several investigators have proposed various definitions of 

dryland or dry farming (Duley and Coyle 1955; Hargreaves 

1957; Higbee 1958). Common to all definitions, these “dryland” systems are those which describe production techniques under limited precipitation and usually severe resource concern constraints. The resource constraints include 

soil erosion by both wind and water; periods of water stress 

of significant duration; and limited production inputs. Another distinction is that the dryland systems focus on crop 

yield sustainability and water conservation/water harvesting 

techniques. To further define dryland Oram (1980) has suggested six criteria to be used in describing dryland regions 

and systems: 

1. Occurrence of very high intensity rainstorms. 

2. Potential evapotranspiration exceeds the precipitation 

for a minimum of 7 months during the year. 

3. Decreased reliability and increased precipitation 

variability as annual precipitation decreases. 

4. Low total annual precipitation accompanied with at 

least one pronounced dry season. 

5. Large annual precipitation variations from year-toyear. 

6. Large monthly variations in precipitation. 

Table 507-1 Example of major purposes and expected effects of commonly used conservation practices/treatments on cropland— 

Continued 

 Practice/treatments Purposes and effects 

 and National Practice 

 Standard code 

Nutrient management Provide the necessary nutriends for plan growth 

Code 590 Manage soil fertility at desitable and economic levels 

Reduce nutrient leaching and runoff 

Pest management Manage weeds, insects, and diseases within established threshold levels 

Code 595 Reduce Pesticide runoff and leaching 

Reduce pest tolerance and resistance to cultural, biological, and chemical treatments 

Filter strips Reduce offsite sedimentation 

Code 393 Reduce nutrient and pesticide runoff 

Biologically treat runoff 

Improve infiltration and treatment of runoff 

Provide food and cover for wildlife 
(190-V-NAM, 3rd Ed., October 2002) 507–5 

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Agronomy 

Manual 

Cropland Conservation

Management Systems

Part 507

Common to all of the regions is the non-beneficial use of 

soil water through evaporation and the practice of summer 

fallow. There are, however, a number of general distinctions other than crop adaptability that can be made between 

the regions. The distribution and types (snow versus rainfall) of precipitation differ greatly. Snow management can 

be used effectively to increase soil water storage in the 

northern regions. Detailed descriptions of these regions are 

in Cannell and Dregne (1983). 

507.23 Principles and guidelines of dryland

conservation Management systems

(a) Basic principles

In natural ecosystems the successional process advances until something limits it. Moreover, as succession continues, 

the complexity, diversity, and stability increases (Savory 

1988). The result of a complex, diverse, and stable ecosystem is increased productivity. Secondly, everything that occurs within an ecosystem can be described in terms of the 

effectiveness, or lack of effectiveness in the water cycle, nutrient cycle, succession itself, and the flow of carbon (energy) through the ecosystem. 

The same concepts can certainly be applied to dryland 

agroecosystems. The successional process in a natural system is analogous to the sequence of crops in rotation. Like 

natural systems, the successional process of dryland systems can advance until something limits it. In most cases, 

this limiting factor is climate. The holistic approach, 

though, teaches us that there may be additional limitations. 

The most common of these include economics and market 

forces. 

507.21 Defining and describing dryland regions

A number of attempts have been made to quantitatively describe and categorize dryland regions. The older accepted 

approaches generally included some form of the 

Thornthwaite precipitation effectiveness index (P-E) are 

presented and reviewed elsewhere (Brengle 1982). 

Stewart (1988) reviews two methods hereby referred to as 

the FAO method and the UNESCO (United Nations Educational, Scientific and Cultural Organization) method. Based 

on the length of growing season the FAO method delineates 

dryland climatic regions as dry, arid, and semiarid. The 

UNESCO method delineates four dryland zones (hyperarid, 

arid, semiarid, subhumid) based on an index, called the climatic aridity index. Both methods use daily values of precipitation (P) and potential evapotranspiration (ETp). Since 

daily values are evaluated, an appropriate energy balance 

method for estimating ETp for short time steps should be 

used. This would include the Penman method or one of its 

several variations based on local conditions and available 

data. 

FAO Method. The length of the growing period in the 

FAO method is the number of days that have a mean daily 

temperature greater than 44 degrees Fahrenheit (6.5 °C) 

during the year when P is greater than 50 percent of ETp 

(0.5 ETp), plus the number of days required to use about 4 

inches (10 cm) of stored soil profile water. Regions classified as dry are those where P never exceeds 0.5 ETp; arid 

where the length of the growing period is between 1 and 74 

days; and, semiarid where the growing period is between 75 

and 119 days. 

UNESCO Method. The UNESCO method uses the climatic aridity index. The climatic aridity index (CAI) is the 

ratio of the precipitation (P) to the potential evapotranspiration (ETp) (CAI=P/ETp). The four climatic zones are delineated in table 507-2. 

507.22 Regional resource settings of dryland

cropping areas of the United States

In the United States and Canada, six distinct dryland-farming regions can be identified. The six regions are the Southern Great Plains, Central Great Plains, Northern Great 

Plains, Canadian Prairies, Pacific Northwest, and the Pacific Southwest (fig. 507-1). Also shown are the five specific areas of dryland production. 

Table 507-2 Climatic zone delineation 

 Zone CAI 

Hyperarid CAI < 0.03 

Arid O.03 <CAI < 0.20 

Semiarid 0.20 < CAI < 0.50 

Subhumid 0.5 0< CAI < 0.75 
507–6 (190-V-NAM, 3rd Ed., October 2002) 

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Part 507

The underlying principles directed at the development of a 

sustainable dryland cropping system include three elements. 

These elements are: 

• rotation intensity, 

• rotation diversity, and 

• management. 

First, any given crop rotation must have a crop succession 

of sufficient intensity to assure maximum use of effective 

precipitation. 

Secondly, the crop rotation must have sufficient diversity, 

which is central to the whole-system management philosophy. Agroecosystem diversity is more than the interaction 

and manifestation of physical and biochemical processes. It 

includes all of the concepts related to not only the promotion of effective nutrient cycling and expansion of disease 

and weed control strategies. Diversity also considers human 

and economic factors, in that the crop rotation must have 

sufficient diversity for distributing workloads and economic 

risks. Gleissman (1998) outlines six specific benefits and 

characteristics of diverse agroeco-systems. The following 

can be identified and applied to the dryland areas: 

• Greater stability and diminished external input requirements. Stability not only includes the lack of 

fluctuating crop yields; but also includes the ability to 

spread out workload and fixed costs; and the reduction in weather and price risks. 

• Greater harvestable biomass production potential. 

• Larger soil carbon pool resulting from increased total 

biomass. 

• Diminished need for external nutrient inputs resulting 

from efficient nutrient cycling. 

• Reduced risk of economic crop loss resulting from 

greater species diversity. 

• Increased opportunity to break insect and disease 

cycles; and potential for effective application biological control strategies. 

Thirdly, the crop rotation that has sufficient intensity and 

diversity must be managed properly. The proper management levels include using tillage and planting methods that 

reduce soil disturbance and renewing dependence on cultural practices that will reduce reliance on costly technology. 

(b) Intensity

The intensity of crop rotations in the dryland areas of the 

United States can be based on the water use patterns of the 

various crops (Beck and Doerr 1992; Beck 1997). The 

higher the water use the greater the intensity. Crops can be 

divided into high water use crops and low water use crops. 

High water use crops are those full-season summer-grown 

crops such as corn, sunflower, soybean, and cotton. Low 

water use crops are those classified as short-season and 

cool-season crops. Examples include small grains, flax, millet, and lentils. 

The application of the method gives arbitrary increasing 

values with increasing crop water use; respectively. That is, 

• fallow (no crop water use) has a zero (0) value; 

• low water use crops has a value of one (1); and 

• high water use crops has a value of two (2). 

The intensity is equal to the sum of all of the crop water-use 

values, divided by the number of crops and fallow in the rotation. For example, a winter wheat-fallow rotation has an 

intensity of only 0.50 (0+1=1 divided by 2); and a spring 

wheat-winter wheat-corn-sunflower rotation has an intensity 

of 1.50 (1+1+2+2=6 divided by 4). 

(c) Diversity

Ecologists have developed several measures of diversity. 

The most widely used procedures are the Shannon, 

Simpson, and Margalef diversity indices (Gleissman, 1998). 

The Natural Resources Conservation Service, formerly Soil 

Conservation Service, has made several attempts at describing the influence of crops and tillage on productivity and 

sustainability (Soil Conservation Service 1976; King 1977). 

A much simplified and holistic approach to describing diversity has been proposed by Beck (1996). The diversity index accounts for the different crop types and their intervals 

within the rotation. The crop types considered are as follows: 

• Cool-season grasses (winter wheat, spring barley) 

• Warm-season grasses (corn, millet, sorghum) 

• Cool-season broadleaf (flax, lentils, canola) 

• Warm-season broadleaf (soybean, cotton, dry bean, 

sunflower) 

In addition, the index accounts for ecological considerations such as those relating to weed and disease pressures, 

as well as workload distribution and the conflicts between 

operational interferences. These include planting interference of one crop with the harvest of another crop in the rotation. Diversity values generally range from –0.50 (winter 

wheat-fallow) to nearly 4.0 for highly diverse rotations such 

as spring wheat-winter wheat-soybean-corn. 
(190-V-NAM, 3rd Ed., October 2002) 507–7 

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Figure 507–1 Major dryland regions and production areas of the United States and Canada. (Cannel and Dregne 1988) 

Alberta

Washington

Saskatchewan Manitoba

Montana North Dakota

South Dakota

Nebraska

Kansas

Oklahoma

Texas

New Mexico

Colorado

Wyoming

Idaho

Nevada California

Oregon

Arizona

Utah
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Both the intensity and diversity indices, as defined, offer 

tools that can be used to evaluate rotations. The utility of 

these tools is particularly useful during the initial planning 

phases. 

507.24 Factors in planning dryland cropping systems

The following factors need to be considered in planning 

dryland-cropping systems: 

• Historic precipitation patterns and rainfall probabilities. 

• Crop marketability and potential profitability. 

• Insect cycles and potential disease organisms. 

• Crop water use patterns. 

• Snow management. 

• Weed control options and evaluation of ability to 

rotate herbicide types. 

• Optimum row widths. 

• Potential phytotoxicity. 

• Equipment needs. 

507.25 Major cropping systems and technologies for the dryland regions of

the United States

As previously mentioned, the resource constraints of the 

dryland regions of the United States are three-fold: 

• soil erosion by both wind and water; 

• periods of water stress of significant duration; and, 

• limited production inputs. 

Probably the most important factor affecting the constraint 

associated with limited production inputs is soil fertility. 

The inability to make precise fertilizer recommendations 

under diverse and variable precipitation patterns comprises 

efforts in obtaining maximum economic returns. 

The focus of dryland systems is on crop yield sustainability 

and water conservation/water harvesting techniques. Thus, 

the sequence of crops and the characteristics of each crop 

control every other aspect of the cropping system. 

Briefly, table 507-3 identifies the major crops, crop rotations, and management technologies. 
(190-V-NAM, 3rd Ed., October 2002) 507–9 

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Table 507–3 Major cropping systems and water and soil conservation management technologies for U.S. dryland agricultural regions 

U.S. dryland - - - - - - - - - - - - Cropping systems - - - - - - - - - - - - Water and soil conservation management technologies 

agricultural Crops Crop rotations 

regions 

Southern Winter Wheat (WW) con’t OC • No-tillage • Bench terraces 

 Great Plains Grain Sorghum (SO) con’t WW • Weed Control • Mulch-tillage 

Cotton (OC) WW-fallow • Summer fallow • Alternate irrigation/dryland 

Sunflower (SF) WW-SO/SD-fallow • Vertical mulching • Variable rate planting 

Forage Sorghum (SD) WW-OC-fallow • Terrace • Delayed planting dates 

Alfalfa (AL) con’t SO/SD • Contouring • Nutrient management 

Guar (GU) WW(3)-OC(3)-fallow • Furrow diking • Pest management 

OC-SF • Furrow blocking 

 Central Winter Wheat (WW) WW-fallow • No-tillage • Snow management 

 Great Plains Grain Sorghum (SO) WW-SO/SD-fallow • Mulch-tillage –tall wheatgrass barriers 

Sunflower (SF) WW-CG-fallow • Terrace –annual crop barriers 

Forage Sorghum (SD) WW-SF-fallow • Contouring • Nutrient management 

Grain Corn (CG) con’t SO/SD • Weed control • Stripcropping 

Millet (MO) WW-MO-fallow • Summer fallow • Pest management 

Dry bean (BD) SF/SG-BD 

con’t BD 

 Northern Barley (BA) WW/WS-fallow • No-tillage • Snow management 

 Great Plains Winter Wheat (WW) BA-fallow • Mulch-tillage –tall wheatgrass barriers 

Spring Wheat (WS) WW/WS-BA-fallow • Summer fallow –annual crop barriers 

Oats (OT) WS-WW-fallow • Weed control –field shelterbelts/ 

tree windbreaks 

Flax (FL) WW-BA-SB –bench terraces w/ 

grassed dikes 

Safflower (SA) WS-SF/SA/SB • Nutrient management 

Sunflower (SF) WS-OT-SF/SA/FL-BA • Stripcropping 

Grain Corn (CG) WS-WW-CG-SB/SF • Pest management 

Soybean (SB) BA-WW-CG-SB/SF 

Alfalfa (AL) WW-CG-MO-fallow 

Millet (MO) WW-SF-fallow 

CG-SB 

WS-FL/SF/SA-fallow 

BA-CG 

 Pacific Spring Lentil (LDs) WW-LDs/PF • Slot mulching • Nutrient management 

 Northwest Winter Lentil (LDw) WW-LDw • No-tillage • Stripcropping 

Spring Barley (BAs) BAs-fallow • Mulch tillage • Pest management 

Rapeseed (RB) BAs-PF • Summer fallow 

Green Pea (PG) RB-fallow • Weed control 

Austrian Winter Pea (AW) PG-RB • Terrace 

Winter Wheat (WW) AW-WW-BAs • Contouring 

Spring Wheat (WS) WW-AW-BAs/WS 

Spring Pea (PF) WS-fallow 

WW-fallow 

 Pacific Winter Wheat (WW) WW-fallow • Water harvesting • Terrace 

 Southwest Pasture (PT) WW-PT-fallow • Summer fallow • Snow melt control w/ flyash 

Spring Barley (BAs) BAs-fallow • No-tillage • Weed control 

BAs-BAs-fallow • Mulch tillage • Pest management 

• Nutrient management 
507–10 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Cropland Conservation

Management Systems

Part 507

Subpart 507B References

Bauer, A., and A.L. Black. 1981. Soil carbon, nitrogen, and 

bulk density comparisons in two cropland tillage systems after 25 years and in virgin grassland. Soil 

Science Society of America J. 45:1166-1170. 

Beck, D.L., and R. Doerr. 1992. No-till guidelines for the 

arid and semi-arid prairies. Agricultural Exp. Sta. 

Publ. B712. South Dakota State University. 

Brookings, SD. 

Beck, D.L. 1996. Increasing the Efficient Utilization of 

Precipitation on the Great Plains and Prairies of 

North America. Dakota Lakes Research Farm. 

Pierre, SD. 

Beck, D.L. 1997. Crop diversity aids time and equipment 

needs. Proceedings, Vol. 9. Colorado Conservation 

Tillage Association. Sterling, CO. 

Brengle, K.G. 1982. Principles and Practices of Dryland 

Farming. Colorado Associated University Press. 

Boulder, CO. 

Cannell, G.H., and H.E. Dregne. 1983. Chapter 1— 

Regional Setting. In H.E. Dregne and W.O. Willis 

(eds.) Dryland Agriculture. Agronomy Monograph 

23. American Society of Agronomy. Madison, WI. 

pp. 3-17. 

Duley, F.L., and J.J. Coyle. 1955. Farming where rainfall is 

8-20 inches a year. In Yearbook of Agriculture, 

Washington, DC. 

Gleissman, S.R. 1998. Agroecology-Ecological Processes 

in Sustainable Agriculture. Ann Harbor Press. 

Chelsea, MI. 

Haas, H.J., C.E. Evans, and E.F. Miles. 1957. Carbon and 

nitrogen changes in Great Plains soils as influenced 

by cropping and soil treatments. U.S. Department of 

Agriculture, Tech. Bull. 1164. Washington, DC. 

Hargreaves, M.W.M. 1957. Dry Farming in the Northern 

Great Plains, 1900-1925. Harvard Univ Press. Cambridge, MA. 

Higbee, E. 1958. American Agriculture: Geography, Resources, Conservation. John Wiley and Sons, Inc. 

New York, NY. 

King, A.D. 1977. Soil conditioning indices for irrigated 

crops in Colorado. Technical Note No. 52. Soil 

Conservation Service. Denver, CO. 

Oram, P. 1980. What are the world resources and constraints for dryland agriculture? In Proceedings of the 

International Congress for Dryland Farming. Dept. 

Agriculture. Adelaide, South Australia. 

Reicosky, D.C., W.D. Kemper, G.W. Langdale, C.L. Douglas, Jr., and P.E. Rasmussen. 1995. Soil organic 

matter changes resulting from tillage and biomass 

production. J. Soil and Water Conserv. 20:253-261. 

Savory, A. 1988. HolisticResource Management. Island 

Press, Washington, DC. 

Stewart, B.A. 1988. Chapter 14—Dryland Farming: The 

North American Experience. In Unger, P.W., W.R. 

Jordan, T.V. Sneed, and R.W. Jensen (eds.) Challenges in Dryland Agriculture-A Global Perspective. 

International Conference on Dryland Farming. Texas 

Agricultural Experiment Station. College Station, TX. 

 Stewart, B.A. and E. Burnett. 1987. Water conservation 

technology in rainfed and dryland agriculture. In Jordan, W.R. (ed.) Water and Water Policy in World 

Food Supplies. Texas A&M Univ. College Station, 

TX. 

U.S. Department of Agriculture, Soil Conservation Service. 

1976. Soil conditioning indices for major irrigated 

and non-irrigated crops grown in the United States. 

Technical Note No. 27. West National Technical 

Center. Portland, Oregon. 
(190-V-NAM, 3rd Ed., October 2002) 508–i 

Soils

Contents:

Part 508

Subpart 508A Agronomic responsibilities in soil surveys 508–1

Subpart 508B Agronomic soil interpretations 508–1

Subpart 508C Soil management 508–2

508.30 Soil conditioning index for cropland management systems—background .....508–2 

508.31 The benchmark condition ...............................................................................508–3 

508.32 Basis for the organic matter (OM) component ............................................... 508–4 

508.33 Basis for the field operations (FO) component ............................................... 508–7 

508.34 Basis for the erosion (ER) component ............................................................508–8 

508.35 Subfactor values and their relationship ........................................................... 508–8 

508.36 Calculating the Soil Conditioning Index ........................................................ 508–9 

508.37 Calibration of the Soil Conditioning Index to other research sites ............... 508–11 

Subpart 508D References 508–11 

(190-V-NAM, 3rd Ed., October 2002) 508–1 

Part 508 Soils 

Subpart 508A Agronomic responsibilities in soil surveys

(Reserved) 

Subpart 508B Agronomic soil

interpretations

(Reserved) 

Technical guidance for developing Ecological Site Descriptions and Forage Suitability Groups are in the National 

Range and Pasture Handbook. 
508–2 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Subpart 508C Soil management

508.30 Soil conditioning index for cropland

management systems—background

(a) Regional versions of the Soil Conditioning

Index

In 1964, Wayne Austin published Conservation Agronomy 

Technical Note No. 27, Soil Conditioning Rating Indices 

for Major Irrigated and Non-Irrigated Crops Grown in the 

Western United States, through the then SCS West National 

Technical Center (WNTC), Portland, Oregon. This Technical Note was revised by J.W. Turelle in 1967, and again reprinted by F.L. Brooks in 1974. 

A.D. King and others prepared a shorter version in 1986 

through the South National Technical Center (SNTC), Fort 

Worth, Texas. 

(b) A National Version

This version of the rating procedure adapts the concept for 

use nationwide, by introducing the effects of climate on organic matter decomposition at various geographic locations. 

The latest version of the Soil Conditioning Index is available as an Excel spreadsheet at 

ftp://ftp.nssc.nrcs.usda.gov/pub/agronomySCIfiles/

The important components of the Index (SCI) include 

• the amount of organic material returned to the soil, 

• the effects of the tillage and planting system on 

organic matter decomposition, and 

• the effect of predicted erosion associated with the 

management system. 

Rating values for these variables were determined subjectively, and are described below. 

(c) The concept

For much of its history, NRCS worked primarily on the 

problem of soil erosion on agricultural and other lands. Predictive/evaluation tools such as the Universal Soil Loss 

Equation (USLE) and the Wind Erosion Equation (WEQ) 

enhanced conservation planning for erosion control. 

New concepts of planning developed in the 1990's broadened the planning approach to consider five resources— 

soil, water, air, plant, and animal—and multiple resource 

concerns associated with each resource. 

One area of concern is degradation of soil quality through 

processes that are influenced by management. One such 

concern is organic matter decline under cultivation. The 

Soil Conditioning Index is a tool to predict the consequences of management actions on the state of soil organic 

matter. 

Precedents for this predictive tool are in WNTC Technical 

Note No. 27 (1964) and the SNTC version developed in 

1986, discussed in 508.30 (a). 

This version of the Index predicts organic matter change 

qualitatively, not quantitatively. It predicts one of three outcomes — organic matter decline, organic matter increase, 

or organic matter equilibrium. 

The procedure depends on the assumption that the amount 

of biomass that must be returned, to maintain equilibrium, 

is directly proportional to rate of decay. In moist climates, 

decomposition is more rapid than in dry climates, thus more 

biomass is needed. The same is true comparing warm to 

cool climates. Maintenance amounts of crop residue at locations throughout the United States were calculated based on 

this assumption. 

The Index considers organic material (biomass) produced 

and returned to the soil, the influence of climate on organic 

matter decay, the influence of tillage, and the influence of 

erosion. 

Decomposition functions of Revised Universal Soil Loss 

Equation (RUSLE) were used to estimate relative rates of 

plant residue decomposition at different locations. Climate 

at each location is expressed as average monthly precipitation and average monthly temperature. 

(d) Components of the Soil Conditioning Index

A combination of effects causes degradation of soil condition. Wind and water erosion remove fine soil particles, organic matter, and plant nutrients, thus reducing productivity 

and the ability of the soil to hold water. Excessive tillage 

accelerates erosion and organic matter decay, and causes 

compaction. Crop rotations which produce low amounts of 

residue, and/or which involve extensive residue removal, 

result in inadequate amounts of organic material returned to 

the soil. 
(190-V-NAM, 3rd Ed., October 2002) 508–3 

National 

Agronomy 

Manual 

Part 508 Soils

The formula for the Soil Conditioning Index is: 

SCI = OM + FO + ER 

where: 

SCI is the Soil Conditioning Index: Soil Conditioning 

Index estimates the combined effect of three variables 

on trends in soil organic matter. Soil organic matter 

trends are assumed to be an indicator of improvement or 

degradation of soil condition. 

OM is organic material: This component accounts for 

the effect of organic material returned to the soil. 

Organic material from plant or animal sources may be 

either grown and retained on the site or imported to 

the site. 

FO is field operations: This component accounts for the 

effect of field operations that stimulate organic matter 

breakdown. Tillage, planting, fertilizer application, 

spraying and harvesting crush and shatter plant 

residues and aerate or compact the soil. These effects 

increase the rate of residue decomposition and affect 

the placement of organic material in the soil profile. 

ER is erosion: This component accounts for the effect of 

removal or sorting, or both, of surface soil material by 

the sheet, rill, or wind erosion processes that are 

predicted by water and wind erosion models. It does 

NOT account for the effect of concentrated flow 

erosion such as ephemeral or classic gullies. Erosion 

contributes to loss of organic matter and decline in 

long-term productivity. 

(e) Using the Soil Conditioning Index to evaluate

conservation practices and systems

The Soil Conditioning Index tool predicts the effect of management systems on soil organic matter. Soil organic matter 

level is a primary indictor of soil condition. It affects such 

soil characteristics and processes as cation exchange, aggregate stability, water holding capacity, and soil biological activity. Soil condition is the degree to which a soil maintains 

the ability to accept, store and release water, nutrients, and 

energy, to promote and sustain root growth, to sustain soil 

biological and chemical processes, and to resist erosion, 

compaction, and other management impacts. 

(i) The Index evaluates the effect of farming practices on 

soil organic matter. The Index expresses whether the 

cropping sequence, soil disturbing operations, and other 

management inputs tend to increase or decrease soil 

organic matter under a given climatic regime. 

(ii) Similar to the way in which water and wind erosion 

models are used to assess the effects of management 

systems on water and wind erosion, the Soil Conditioning Index is a tool to estimate the effect of the same 

management systems on the physical condition of the 

soil resource. Like erosion models, it has broader application than any single practice, but can be used to evaluate how changes in single practices influence the effect 

of the management system on the soil resource. 

(iii) Because erosion (the present or a planned system) is 

one of the variables considered, erosion estimates using 

RUSLE or WEQ, or both, are part of the Soil Conditioning Index procedure. 

When the crop rotation is managed as part of a system to 

maintain or improve soil condition, criteria for design of the 

rotation should include the use of high-residue crops in 

cropping sequences. The rotation should be supplemented 

as needed by additional sources of organic matter such as 

cover crops, green manure crops, or animal manure. 

Management of plant residue to maintain or improve soil 

condition includes limitations on residue removal by any 

means including grazing. 

Management of field operations to maintain or improve soil 

condition involves limiting the number of tillage operations 

and the degree of soil disturbance by each operation. 

Any combination of practices that help stabilize the site by 

controlling erosion within specified limits conserves soil organic matter. These systems may include any of the practices discussed above, as well as supporting practices such 

as terraces, stripcropping, or windbreaks. 

508.31 The benchmark condition

This kind of predictive tool requires a point of reference or 

benchmark. A situation was selected where the impact on 

organic matter of various management systems and production levels could be determined from the research. The selected location was the experiment station at Renner, Texas, 

from 1948 to 1959. 

The benchmark condition is a specific combination of organic material produced by the crop rotation, tillage and 

planting operations, and associated erosion that resulted in 

maintaining soil organic matter at a steady state during 12 

years of research (Laws, 1961). The same three variables 
508–4 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

are the basis for determining maintenance amounts of crop 

residues and calculating the Soil Conditioning Index at any 

location when compared to the benchmark condition as a 

point of reference. 

The time and location define the climate during the period 

of the research. Published papers tell us about the crops 

grown, production levels, tillage and residue management, 

and associated organic matter trends. Reasonable assumptions can also be made about amounts of erosion under the 

research conditions. Research results at Renner are described throughout this section, and are summarized in table 

508.5. 

508.32 Basis for the organic matter (OM)

component

(a) Background

This subfactor is based on the amount of organic material 

returned to the soil (residue, roots, cover crops, green manure crops, animal waste) for organic matter maintenance or 

restoration. The maintenance amount is the assumed 

amount, expressed as Residue Equivalent Value (see 

508.32(c)), that must be returned to the soil annually to 

maintain soil organic matter at a constant level (neither increasing nor decreasing). 

Table 508.1 shows the maintenance amounts, for locations 

throughout the United States, that apply when tillage and 

erosion are similar to conditions during the Blacklands 

Farming Systems Studies at Renner, Texas, 1948–59. The 

Organic Material Subfactor (OM) = 0 when these conditions apply [see 508.35(a)(1)(i)]. The maintenance amount 

varies by climate, based on precipitation and temperature 

that govern biomass production and rates of decay. These 

are the maintenance amounts used to calculate the Soil Conditioning Index. 

(b) The organic material budget

(1) Amount returned to the soil

(i) Amount produced on the site—Crop sequence and 

management affect organic matter maintenance. The 

kind of crops grown, their yields, removal of products 

from the field, and management of remaining residues, 

all affect the amount of organic material returned to the 

system, and soil organic matter levels. 

(ii) Amount added or lost—Accounting for additions of 

organic material such as manure or mulch. 

Residue removed at harvest or during the non-crop 

season include harvest for silage, grazing of crop aftermath, removal for bedding, burning, and similar practices. These losses are accounted for when estimating 

residue returned. 

Physical losses not accounted for are those caused by 

shattering, materials blown from the field by wind or 

carried off the field by runoff water. 

(iii) Root mass—Calculations of residue produced 

include estimated root mass to a depth of 4 inches. These 

estimates are based on the ratio of maximum root mass 

in the top 4 inches to above ground residue produced at 

harvest, taken from the RUSLE data base (see table 

508.6 — RUSLE crop parameter data). 

(2) Climatic effects on decomposition of organic

material

(i) Climate, particularly temperature and precipitation, 

affects plant growth, biological activity, and organic 

matter decomposition. 

(ii) An inverse relationship exist between mean annual 

temperature and the level of organic matter in regions of 

comparative rainfall. Higher temperatures stimulate microbial decomposition more than they stimulate plant growth. 

The decay processes that break down organic matter are 

more rapid in warmer climates and go on for a longer 

period during the year. 

(iii) Organic matter levels also vary with precipitation. 

Both plant growth and rates of organic matter decay are 

higher where rainfall is high. Relatively little organic 

matter is found in arid soils where vegetation is sparse, 

because the raw materials are lacking. 

(c) Determining the maintenance amount at

Renner, Texas

(1) Maintenance amounts of crop residues are based

on results of the Blacklands Farming Systems

studies at the Renner research station, 1948-59.

(i) Residue production and trends in soil organic 

matter—Table 508.5 summarizes the crop rotations used 

in the Renner experiments, the amount of above ground 

crop residues produced, and the effect on soil organic 

matter content. System 8 (wheat-cotton-sorghum, not 

fertilized) and System 9 (wheat-cotton-sorghum, fertilized, manure added) are the basis for the conclusions in 

this paper. 
(190-V-NAM, 3rd Ed., October 2002) 508–5 

National 

Agronomy 

Manual 

Part 508 Soils

System 8 produced an average of 3,865 pounds of 

aboveground crop residue per year, and percent organic 

matter declined 0.14 percent during the 12-year experiment (1948 to 1959). 

Wheat 5,114 lb/ac/yr x 4 yr = 20,456 lb/ac 

Cotton 3,015 lb/ac/yr x 4 yr = 12,060 lb/ac 

Grain sorghum 3,466 lb/ac/yr x 4 yr = 13,864 lb/ac 

Total crop residue = 46,380 lb/ac 

Average crop residue = (46,380 lb/ac)/12 yr 

 = 3,865 lb/ac/yr 

System 9 produced an average of 4,189 pounds of 

aboveground crop residue per year. In addition, each 

plot received four applications of manure, totaling 20 

tons per acre. Assuming open lot manure at 50 percent 

moisture content, dry matter applied = 10 tons per acre. 

Percent organic matter increased 0.64 percent during the 

12 year experiment. 

Wheat 5,318 lb/ac/yr x 4 yr = 21,272 lb/ac 

Cotton 3,237 lb/ac/yr x 4 yr = 12,948 lb/ac 

Grain sorghum 4,013 lb/ac/yr x 4 yr = 16,052 lb/ac 

Manure 5,000 lb dry matter/ac/yr x 4 yr 

= 20,000 lb/ac 

Total crop residue + manure = 70,272 lb/ac 

Average crop residue + manure 

= (70,272 lb/ac)/12 yr = 5,856 lb/ac/yr 

(2) Estimating the maintenance amount

(i) The maintenance amount at Renner was estimated by 

analysis of System 8 and System 9. (See table 508.5.) 

(ii) Percent organic matter (OM) increased 0.78 percent 

with 1991 pounds additional aboveground residue. 

Interpolating, OM loss/gain = 0 (steady state) when 

aboveground biomass = 4,222 lb. 

[(.14/.78) x 1991] + 3,865 = 4,222 lb 

(iii) Factoring the amount of residue supplied by each 

crop and manure equally gives the following: 

Wheat [(.14/.78) x 204] + 5,114 = 5,151 lb/ac/yr x 4 

 yr = 20,604 lb/ac 

Cotton [(.14/.78) x 222] + 3,015 = 3,055 lb/ac/yr x 4 

yr = 12,220 lb/ac 

Grain Sorghum [(.14/.78) x 547] + 3,466 

= 3,564 lb/ac/yr x 4 yr = 14,256 lb/ac 

Manure [(.14/.78) x 5,000] + 0 = 897 lb/ac/yr x 4 yr 

= 3,588 lb/ac 

Total crop residue + manure = 50,668 lb/ac 

Average crop residue + manure = (50,668 lb/ac)/12 

yr = 4,222 lb/ac/yr 

(iv) Adjustment for root mass. The values calculated 

above are increased to account for root mass in the upper 

4 inches, using root mass adjustments from table 508.6. 

Wheat 5,151 lb/ac x 1.259 = 6,485 lb/ac 

Cotton 3,055 lb/ac x 1.118 = 3,415 lb/ac 

Grain sorghum 3,564 x 1.291 = 4,601 lb/ac 

Manure 897 x 1.0 = 897 lb/ac 

Total above and below ground residue + manure = 

15,398 lb/ac 

Average all residue + manure = (15,398 lb/ac)/ 

3 yr = 5,133 lb/ac/yr 

(v) 5,133 pounds per acre per year is the calculated 

amount of above and below ground residue, including 

manure, at which organic matter content of the Renner 

plots stabilized. See 508.32(d)(3) for conversion to 

Residue Equivalent Value (REV). 

(d) Residue equivalent values

To deal with variability in the rate of decomposition between various classes of crop residues, Residue Equivalent 

Values (REV) were developed to convert all crop residues 

to a common standard. Crop Group C, which includes corn, 

grain sorghum, and sunflower is used as the standard because these crops are commonly grown throughout much of 

the United States, and because the RUSLE decomposition 

coefficient (0.016) is intermediate in value among eight major crop groups. The Residue Equivalent Value of any plant 

material is its mass expressed as the equivalent mass of 

Crop Group C residue, based on relative annual decomposition rates. The following conversion factors for eight crop 

groups at Renner, Texas are calculated from their relative 

decomposition rates at Renner. 
508–6 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Crop groups and crops Conversion

 to REV

A Small grains, except NW wheat 1.27 

and range region: 

Oats 

Barley 

Flax 

Manure, surface application, 

straw or newspaper bedding 

Millet 

Rye 

Wheat, spring 

Wheat, winter 

B Cotton; burley tobacco; peanuts: 1.01 

Cotton 

Peanuts 

Sugarcane 

Tobacco 

C Corn; grain sorghum; sunflower: 1.00 

Canola 

Corn 

Safflower 

Sorghum 

Sudan 

Sunflower 

Tomato plantain 

D Small grains, except NW wheat 0.97 

and range region; canola; grasses: 

CRP grassland 

PNW barley 

PNW winter wheat 

Bromegrass 

Manure, swine, beef and dairy, 

open lots and buildings, no bedding 

Orchardgrass 

Ryegrass cover 

Tall fescue 

Winter cover 

Crop groups and crops Conversion

to REV

E Legumes: 0.96 

Alfalfa 

Broccoli 

Cabbage 

Red clover 

F Soybeans; sugar beets: 0.94 

Beans, field 

Cauliflower 

Soybean 

Strawberry 

Sugarbeets 

G Vegetables and specialty crops: 0.93 

Asparagus 

Beans, green-snap 

Beans, lima 

Carrot 

Cucumber 

Lentils 

Manure, swine, beef and dairy, 

 settling basin 

Muskmelon 

Native cover, PR 

Peas 

Peppers 

Potato, sweet 

Potato, white 

Pumpkin 

Radish 

Squash, summer 

Tomato, fresh market 

Tomato, processing 

Watermelon 

H Manure, surface application, 0.93 

poultry litter: 
(190-V-NAM, 3rd Ed., October 2002) 508–7 

National 

Agronomy 

Manual 

Part 508 Soils

Examples of finding Residue Equivalent Values: 

3,200 lb soybean residue x 0.94 

= 3,008 lb Residue Equivalent Value (REV) 

4,000 lb wheat residue x 1.27 = 5,080 lb REV 

Applying these conversion factors to the maintenance 

amounts of aboveground residue at Renner (calculated 

above) gives the following: 

Wheat 6,485 lb x 1.27 = 8,236 lb REV 

Cotton 3,415 lb x 1.01 = 3,449 lb REV 

G Sorg 4,601 lb x 1.00 = 4,601 lb REV 

Manure 897 lb x 0.97 = 870 lb REV 

Total residue + manure expressed as REV 

= 17,156 lb/ac 

Average residue + manure expressed as REV (17,156 

lb/ac)/3 yr = 5,719 lb/ac/yr 

The maintenance amount of above and below ground residue at Renner has a calculated Residue Equivalent Value of 

5,719 lb/ac/yr when tillage and erosion are similar to conditions during the research. Maintenance amounts and REV 

conversion factors at other locations in the United States are 

shown in table 508.1. 

Continuously updated versions of the tables of 

data for the worksheets are located at: 

ftp://ftp.nssc.nrcs.usda.gov/pub/agronomy/SCIfiles/

(e) Determining the maintenance amount at other

locations

The maintenance amount of crop residues determined 

above is applicable at Renner under the field conditions that 

existed at the research plots during the years of the research. At other locations, this amount is adjusted to account for differences in climate (monthly average precipitation and temperature). The adjusted amount is applicable 

when soil disturbance by tillage and the amount of erosion 

are similar to those conditions during the research at 

Renner. 

When the effects of tillage and other field operations are 

more severe than the system used on the Renner plots, the 

amount of crop residue needed for maintenance of organic 

matter is correspondingly greater. When these effects are 

less severe, the maintenance amount is correspondingly 

less. In the same way, the amount needed for maintenance 

is greater when predicted erosion exceeds the estimated 

erosion on the Renner plots (4 tons/ac/yr), and is less when 

predicted erosion is less than 4 tons per acre per year. 

The following procedure was used to establish maintenance 

amounts and subfactor values: 

• As discussed, the maintenance amount at Renner, 

Texas, was determined to be 5,719 lbs of above and 

belowground residue (Residue Equivalent Value). 

• Using the C factor routines of RUSLE, the annual 

decay rate of Crop Group C (corn, grain sorghum, 

sunflower) residue at Renner, Texas (30.95 inches 

average annual precipitation and 65.1 degrees mean 

annual temperature) was calculated. 

• Annual decay rates of Crop Group C residue at other 

locations were then calculated in the same manner. 

Assuming that the average annual amount of residue 

needing to be returned is directly proportional to 

annual rates of decay: 

– The maintenance amount at any location = 

[(decay at the location)/(decay at Renner, 

TX)] x 5719, and 

– The subfactor value (OM) at the location = 

[residue returned (REV) - maintenance 

amount (REV)] x [1.0/maintenance amount 

(REV)]. 

508.33 Basis for the field operations (FO)

component

(a) Background

Tillage increases the rate of decay as well as the hazard of 

organic matter loss caused by erosion. The frequency, 

depth, and aggressiveness of each tillage operation determine the magnitude of the effects on aeration, lifting, shattering or compaction. Clean tillage systems consisting of 

one deep primary and two or more secondary operations result in the most soil disturbance. Noninversion tillage (mixing or undercutting), involving fewer tillage trips and retaining more residues on the surface, results in slower decay 

rates as well as less loss to erosion. No-till systems result in 

the least soil disturbance. 

(b) The Soil Disturbance Rating (SDR)

Each soil disturbing field operation was evaluated for its 

impact on Inversion, Mixing, Lifting, Shattering, Aeration, and Compaction. Each of these six impacts was subjectively assigned a value of 0 through 5, with 0 being no 

impact and 5 being severe impact. See table 508.2. The Soil 

Disturbance Rating (SDR) for each field operation is the 

sum of the six impact values. 
508–8 (190-V-NAM, 3rd Ed., October 2002) 

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Manual 

Part 508 Soils

(c) The Soil Disturbance Rating at Renner

The Soil Disturbance Rating (SDR), cumulative and average annual, at the Renner, Texas research plots is calculated 

as follows: 

Soil disturbance operations Rating (SDR)*

Year 1: Grain sorghum 

Chop cotton stalks 3 

Tandem disk (finishing) 18 

Tandem disk (finishing) 18 

Planter, runner shoe 1 

Row crop cultivate (multiple sweeps) 19 

Row crop cultivate (single sweep) 16 

Harvest 5 

Year 2: Winter wheat 

Shred sorghum residue 3 

Buzzard wing sweeps 21 

Tandem disk (finishing) 18 

Tandem disk (finishing) 18 

Drill wheat, hoe opener 17 

Harvest 5 

Year 3: Cotton 

Tandem disk (primary tillage) 26 

Tandem disk (finishing) 18 

Tandem disk (finishing) 18 

Planter, runner shoe 1 

Row crop cultivate (multiple sweeps) 19 

Row crop cultivate (multiple sweeps) 19 

Row crop cultivate (multiple sweeps) 19 

Row crop cultivate (single sweeps) 16 

Harvest 5 

Cumulative Soil Disturbance Rating (SDR) 303 

Average Annual SDR = 303/3 = 101 

*Soil Disturbance Rating (SDR) values are in table 508.2 

508.34 Basis for the erosion (ER) component

(a) Estimated erosion at Renner

Actual erosion, 1948 to 1959, on the Renner research plots 

is unknown. Erosion levels at about 4 tons per acre per year 

are assumed to have occurred, based on the following 

RUSLE calculation: 

Rainfall factor R = 290. 

Soil: Houston black clay, soil erodibility factor K 

= 0.32 adjusted to 0.29; soil loss tolerance T 

= 5 tons/ac/yr 

Estimated slope: 1% x 300 ft, slope factor LS = 0.17. 

Crop rotations and field operations as described above, 

estimated cropping-management factor C = 0.286. 

Straight-row farming, support practice factor P 

= 1.0. 

Estimated erosion = 290 x 0.29 x 0.17 x 0.286 x 1.0 

= 4.0 tons/ac/yr 

508.35 Subfactor values and their relationship

(a) Subfactor values

Each subfactor has a value of 0 (zero) for conditions at assumed equilibrium (soil organic matter maintained, neither 

increasing nor decreasing). A subfactor will have a negative 

value when its effects tend to decrease soil organic matter, 

compared to the benchmark condition at Renner; it will 

have a positive value when its effects tend to increase soil 

organic matter compared to the benchmark condition. The 

range of values is described below. 

(b) Organic Material (OM) subfactor

This subfactor value equals 0 (equilibrium) at Renner when 

above and below ground biomass (grown on the site or applied) = approximately 5,719 pounds of Residue Equivalent 

Value (REV). At other locations this maintenance amount is 

adjusted for climate (precipitation and temperature). 

At any given location, the subfactor value = 0 when the 

amount of residue produced or applied to the site is equal to 

the adjusted maintenance amount for that location. The 

subfactor value = -1.0 when no biomass is grown on or applied to the site. All other positive and negative values are 

proportionate to this relationship. 
(190-V-NAM, 3rd Ed., October 2002) 508–9 

National 

Agronomy 

Manual 

Part 508 Soils

Organic Material (OM) subfactor values are calculated as 

follows: 

[Residue returned (REV) 

 – maintenance amount (REV)] 

x (1.0/maintenance amount) 

Field Operations (FO) subfactor :

Field operations (tillage and planting systems) are assigned 

positive or negative values based on the number, type, and 

severity of tillage operations compared with the system 

used at Renner. 

The subfactor value = 0 for the system used on the Renner 

research plots (SDR =101). 

The subfactor value = +1.0 (plus 100%) when no soil disturbance occurs (SDR = 0). All other positive and negative 

values are proportionate to this relationship. 

Field Operations (FO) subfactor values are in table 508.3. 

Erosion (ER) subfactor :

The subfactor value = 0 when predicted erosion is 4 tons 

per acre per year, and = +1.0 (plus 100%) when predicted 

soil loss = 0. Estimated erosion in excess of 4 tons per acre 

per year, is assigned negative values. 

The organic matter enrichment of eroded sediment decreases as erosion increases and rills become more dominant, because organic matter is greatest at the surface. 

Therefore the appropriate erosion subfactor relationship is 

curvilinear. 

Erosion (ER) subfactor values are in table 508.4. 

Relative weighting of subfactor values

The Soil Conditioning Index is the sum of the three 

subfactor values, weighted for their relative importance. 

The weighting factors are: 

Organic material 40% 

Field Operations 40% 

Erosion 20% 

508.36 Calculating the Soil Conditioning Index

(a) To determine the maintenance amount of crop

residue at your location

Table 508.1 gives the maintenance amount of crop residue 

at selected locations in pounds per acre per year, expressed 

as Residue Equivalent Value (REV), when the subfactor 

values for Field Operations (FO) and Erosion (ER) = 0 

(Reference Condition). 

(b) To evaluate the present cropping-management

system

Determine the Organic Material subfactor:

Determine the total amount of residue produced on the site 

by the crop rotation (crop yield x pounds per unit of yield x 

residue to yield ratio). Adjust for root mass. Residue production parameters for various crops as used in RUSLE are 

in table 508.6. Adjust for any residue removed from or 

added to the site. 

Convert residue amounts for each crop to Residue Equivalent Value (REV). REV conversion factors for seven crop 

groups are given for selected locations in table 508.1. 

Divide total REV for the crop rotation by number of years 

in the rotation to determine average annual REV. 

Calculate the Organic Material (OM) subfactor value. 

[Residue Returned (REV) – Maintenance Amount 

(REV)]x[1.0/Maintenance Amount (REV)] 

Determine the Field Operations subfactor:

List all field operations (tillage, planting, fertilizing, cultivating, etc.). Find the Soil Disturbance Rating (SDR) for 

each operation in table 508.2. Total the Soil Disturbance 

Rating values and divide the cumulative total by the number 

of years in the rotation to determine average annual Soil 

Disturbance Rating. 

Find the corresponding field operations (FO) subfactor 

value in table 508.3. 

Determine the Erosion subfactor:

Determine predicted average annual erosion using RUSLE 

or WEQ, or both, if applicable. 

Find the corresponding Erosion (ER) subfactor value in 

table 508.4. 
508–10 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Calculate the Soil Conditioning Index (SCI):

SCI = (OM x 0.4) + (FO x 0.4) + (ER x 0.2) 

If the SCI value is negative, soil organic matter is predicted 

to be decreasing, and corrective measures should be 

planned. If the SCI value is zero or positive, soil organic 

matter is predicted to be stable or increasing. 

(c) To evaluate one or more alternative systems:

To formulate alternatives, plan changes in the croppingmanagement system that will address negative subfactor 

values. For example: 

• If the Organic Material (OM) subfactor is negative, 

plan for additional high residue crops in the rotation, 

and/or limit residue removal. 

• If the Field Operations (FO) subfactor is negative, 

plan changes in the tillage/planting system to reduce 

the number and/or severity of field operations. 

• If the Erosion (ER) subfactor is negative, consider 

supporting practices such as terracing, strip cropping, 

etc., as well as changes in the crop rotation or field 

operations. 

Describe the alternative system (rotation and field operations) and follow the same procedure as (b) To evaluate the 

present cropping-management system above. 

(d) Example problem

Site information

Location: Lincoln, NE 

Soil: Sharpsburg silty clay loam 

Soil loss tolerance T = 5 tons/ac/yr 

Slope: 6% x 200 ft 

Supporting conservation practices: None 

Maintenance amount (table 508.1): 

5455 lb/ac/ yr, REV 

Crop rotation: 

Year 1 - Corn, 125 bu/ac 

Year 2 - Drilled soybeans, 35 bu/ac 

Residue management: 

All residues returned, 5399 lb/ac/yr, REV Organic Material subfactor OM 

[(RP - MA)/MA] = -0.01 

Present management system

Fall mulch tillage 

Year 1 

Chisel plow, straight points 

Tandem finishing disk 

Field cultivator, w/sweeps 

Plant corn, double disk opener 

Harvest 

Year 2 

Chisel plow, straight points 

Tandem finishing disk 

Field cultivator, w/ sweeps 

Drill soybeans, double disk opener 

Harvest 

Cumulative Soil Disturbance Rating SDR (table 

508.2) = 138 

Average annual SDR = 138/2 = 69 

Field Operations subfactor FO (table 508.3) = +0.31 

Predicted erosion = 10.5 tons/ac/yr 

Erosion subfactor ER (table 508.4) = –1.28 

Soil Conditioning Index SCI 

= OM x 0.4 + FO x 0.4 + ER x 0.2 

= (–0.01 x 0.4) + (0.31 x 0.4) + (-1.28 x 0.2) 

= –0.004 + 0.124 – 0.256 = (–)0.136 

The SCI value is negative. Soil organic matter is predicted 

to be decreasing, and corrective measures should be 

planned. Erosion is the major factor affecting organic matter loss. Some alternatives are: 

• change to a no-till system, which will reduce erosion 

and minimize soil disturbance, or 

• apply measures such as terracing and contour farming 

to reduce erosion. 

Alternative management system

No till 

Year 1 

Broadcast fertilizer 

Plant corn, >2-inch fluted coulters 

Harvest 

Year 2 

Drill soybeans, single disk opener 

Harvest 

Cumulative Soil Disturbance Rating SDR (table 508.2) = 

26 

Average Annual SDR = 26/2 = 13 

Field Operations Subfactor FO (table 508.3) = +0.87 

Predicted erosion = 3.2 t/ac/yr. Erosion Subfactor ER 

(table 508.4) = +0.25 

Soil Conditioning Index SCI 

= OM x 0.4 + FO x 0.4 + ER x 0.2 

= (–0.01 x 0.4) + (0.87 x 0.4) + (0.25 x 0.2) 

= -0.004 + 0.348 + 0.05 = +0.39 

The SCI value is positive. Soil organic matter is predicted to be increasing, and this alternative is suitable. 
(190-V-NAM, 3rd Ed., October 2002) 508–11 

National 

Agronomy 

Manual 

Part 508 Soils

508.37 Calibration of the Soil Conditioning

Index to other research sites

Research data from locations in the Corn Belt (Clarinda, 

Iowa) and the Northern Great Plains (Culbertson, Montana) 

was used to test the Soil Conditioning Index procedure under varying conditions of crops, tillage, and climate. The index agreed, within reasonable limits, with results of the research. 

At Clarinda, Iowa, under a continuous corn rotation that ran 

for 12 years, cornstalk residue grown on the plots were removed each fall after grain harvest. Chopped residue were 

then artificially applied in amounts of O, 1,785, 3,569, 

7,139, and 14,278 pounds per acre per year. A system of 

moldboard plowing and clean tillage was used. Erosion was 

estimated to average 5.6 tons/acre/year. Under these conditions, organic carbon decreased when 3,569 pounds per 

acre per year of residue was applied, and increased when 

7,139 pounds per acre per year was applied. By interpolation, organic carbon stabilized when about 5,156 pounds 

per acre per year was applied under the research conditions. 

When 5,156 pounds of above ground residue is returned 

(OM subfactor = +0.08), tillage includes fall moldboard 

plowing followed by two spring tillage operations (FO 

subfactor = +0.11), and erosion is 5.6 tons/acre/year (ER 

subfactor =-0.30), the Soil Conditioning Index = +0.01.) 

Research at Culbertson on a spring wheat—summer fallow 

system maintained organic matter at a constant level when 

only 316 pounds per acre per year of wheat residue was returned in alternate years. Slow decomposition because of 

the relatively cool dry climate, subsurface tillage, and low 

erosion rates helped offset the effect of low residue 

amounts. In this experiment, four residue levels were established in the spring following harvest by removing or adding wheat straw —0, 1,500, 3,000, and 6,000 pounds per 

acre. Tillage to control weeds during the summer fallow 

year usually consisted of five operations with a V-blade. A 

tandem disk operation was performed in the following 

spring just before planting. With 316 pounds of residue returned in alternate years (OM subfactor = -0.82), stubble 

mulch fallow (FO subfactor = +0.41), and erosion of 1 ton/ 

acre/ year (ER subfactor = +0.75), the Soil Conditioning Index = -0.02. 

Subpart 508D References

Acton, D.F. 1990. A Soil Quality Evaluation Program for 

Assessing Agricultural Sustainability in Canada — A 

draft proposal. 

Austin, Wayne W. 1960. Soil Productivity Index. U.S. 

Dept. Agric. Soil Conservation Service [Western 

States] Technical Note, Agronomy No. 13. 

Franzmeier, D.P., G.D. Lemme, and R.J. Miles. 1985. Organic carbon in soils of North Central United States. 

Soil Sci. Soc. Am. J. 49: 702-708. 

Fryrear, Donald W. 1981. Long-Term Effect of Erosion and 

Cropping on Soil Productivity. Geological Society of 

America, Special Paper 186. 

Karlen, D.L., D.C. Erbach, T.C. Kaspar, T.S. Colvin, E.C. 

Berry, and D.R. Timmons. 1990. Soil tilth: A review 

of past perceptions and future needs. Soil Sci. Soc. 

Am. J. 54: 153-161. 

King, A.D. and others. 1987. Soil Condition Indices for the 

Southeast. 

Klemme, A.E., and O.T. Coleman. 1939. Evaluating Annual Changes in Soil Productivity. Missouri 

Agricultural Experiment Station Bulletin 405. 

Klemme, A.E., and O.T. Coleman. 1949. Evaluating Annual Changes in Soil Productivity. Missouri 

Agricultural Experiment Station Bulletin 522. 

Laws, W. Derby. 1961. Farming Systems for Soil Improvement in the Blacklands. Texas Research Foundation 

Bulletin 10. 

Lucas, R.E., and M.L. Vitosh. 1978. Soil Organic Matter 

Dynamics. Michigan State University Research Report. 

Parton, W.J., D.S. Schimel, C.V. Cole, and D.S. Ojima. 

1987. Analysis of Factors Controlling Soil Organic 

Levels in Great Plains Grasslands. Soil Science Soc. 

Am. J. 51: 1173-1179. 

Salter, R.M., and T.C. Green. 1933. Factors affecting the 

accumulation and loss of nitrogen and organic carbon 

on cropped Soils. Jour. of the Am. Soc. of Agron. 25: 

622-630. 
508–12 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Soil Conservation Service, Temple, Texas. 1987. Soil Condition Rating Indices. Technical Note — Agronomy 

TX-8. 

Soil Conservation Service, West Technical Service Center, 

Portland, Oregon. 1974. Soil Conditioning Rating Indices for Major Irrigated and Non-Irrigated Crops 

Grown in the Western United States. Technical Note 

No. 27. 

Tiessen, J., J.W.B. Stewart, and J.R. Bettany, 1982. Cultivation effects on the amounts and concentration of 

carbon, nitrogen, and phosphorus in grassland soils. 

Agronomy Journal 74: 831-835. 
(190-V-NAM, 3rd Ed., October 2002) 508–13 

National 

Agronomy 

Manual 

Part 508 Soils

City Location State MaintenCode ance amt. Small Cotton, Corn, Forage Legumes, Soybeans, Vege- Poultry 

including Grains sugarcane, grain grasses, cabbage, field tables, litter 

roots except tobacco, sorghum, winter & Broc- beans, specialty 

Pacific and canola, cover, coli sugar crops & 

NW & Peanuts Safflower manure- beets, manuremanure & Sun- open lots cauli- settling 

with flower & Pacific flower, basin 

bedding NW Small & strawmaterials Grains berries 

Reference Crop Crop Crop Crop Crop Crop Crop Crop 

Condition Group A Group B Group C Group D Group E Group F Group G Group H 

1001 BIRMINGHAM AL 5943 1.19 1.01 1.00 0.98 0.98 0.97 0.97 0.96 

1002 MOBILE AL 6053 1.14 1.01 1.00 0.99 0.99 0.98 0.98 0.98 

1003 MONTGOMERY AL 5960 1.18 1.01 1.00 0.98 0.98 0.97 0.97 0.97 

2150 BIG DELTA AK 3652 1.64 1.04 1.00 0.90 0.73 0.79 0.94 0.64 

2151 BIG DELTA IRR AK 4024 1.59 1.04 1.00 0.91 0.80 0.81 0.73 0.68 

2340 FAIRBANKS WSO AK 3047 1.71 1.05 1.00 0.89 0.62 0.75 0.76 0.57 

2341 FAIRBANKS IRR AK 4194 1.57 1.04 1.00 0.92 0.83 0.82 0.68 0.70 

2430 HOMER WSO AK 3605 1.65 1.04 1.00 0.90 0.72 0.78 0.77 0.63 

2490 KENAI AK 3501 1.66 1.04 1.00 0.90 0.70 0.78 0.72 0.62 

50680 RAWLINS WY 3056 1.71 1.05 1.00 0.89 0.86 0.78 0.72 0.57 

50720 ROCK SPRINGS WY 2996 1.72 1.05 1.00 0.89 0.86 0.75 0.69 0.56 

51001 WASHINGTON DC 5774 1.25 1.01 1.00 0.97 0.97 0.75 0.68 0.94 

80000 GUAM PB 6132 1.08 1.00 1.00 1.00 1.00 0.95 0.94 0.99 

80040 KOROR PB 6145 1.06 1.00 1.00 1.00 1.00 0.99 0.99 1.00 

80080 MAJURO PB 6143 1.06 1.00 1.00 1.00 1.08 1.00 1.00 1.00 

80100 PAGO PAGO PB 6142 1.06 1.00 1.00 1.00 1.00 1.00 1.00 1.00 

80120 POHNPEI PB 6143 1.06 1.00 1.00 1.00 1.08 1.00 1.00 1.00 

80130 KOSRAE PB 6144 1.06 1.00 1.00 1.00 1.08 1.00 1.00 1.00 

80140 CHUUK PB 6144 1.06 1.00 1.00 1.00 1.08 1.00 1.00 1.00 

80180 YAP PB 6143 1.06 1.00 1.00 1.00 1.08 1.00 1.00 1.00 

81000 GUAM IRR. PB 6136 1.07 1.00 1.00 1.00 1.08 1.00 1.00 0.99 

This data is excerpted from this table in sciver11.xls. The latest version of the Soil Conditioning Index is located at: 

ftp://ftp.nssc.usda.gov/pub/agronomy/SCIfiles/

Table 508-1 Maintenanace amounts (residue equivalent pounds) and Residue Equivalent Value factors 
508–14 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Table 508-2 Soil Disturbance Ratings 

- - - - - - - Soil disturbing actions - - - - - - - - Soil 

Operation Field Operations Disturbance 

number Inver- Mixing Lifting Shat- Aera- Compac Rating 

sion tering tion tion 

1 Add mulch 0 0 0 0 0 5 5 

2 Aerator, field surface, ground driven 1 1 2 3 4 1 12 

3 Aerial seeding 0 0 0 0 0 0 0 

4 Bale straw or residue 0 0 0 0 0 3 3 

5 Bed shaper 1 1 1 1 1 2 7 

6 Bed shaper, 12 in 1 1 1 1 1 2 7 

7 Bedder, hipper, disk hiller 5 5 5 5 5 4 29 

8 Bedder, hipper, hiller 12 in high 5 5 5 5 5 4 29 

9 Bedder, hipper, hiller 15 in high 5 5 5 5 5 4 29 

10 Bedder, hipper, hiller 18 in high 5 5 5 5 5 4 29 

11 Begin growth 0 0 0 0 0 0 0 

12 Begin new growth 0 0 0 0 0 0 0 

13 Begin weed growth 0 0 0 0 0 0 0 

14 Bulldozer, clearing 5 5 5 5 5 5 30 

15 Burn residue 0 0 0 0 0 0 0 

169 Seedbed finisher 2 3 2 5 3 4 19 

170 Shredder, flail or rotary 0 0 0 0 0 3 3 

171 Shredder, rotary, regrow veg 0 0 0 0 0 3 3 

172 Shredder, rotary, remove residue 0 0 0 0 0 3 3 

173 Sprayer, kill crop 0 0 0 0 0 3 3 

174 Sprayer, post emergence 0 0 0 0 0 3 3 

175 Stalk puller 2 1 0 1 1 1 6 

176 Striptiller w/middlebuster on beds 4 4 3 4 4 4 23 

177 Subsoiler 1 2 2 4 5 1 15 

178 Subsoiler bedder (ripper/hipper) 5 5 5 5 5 4 29 

179 Subsoiler ripper, 24 to 40 in. deep 1 2 2 5 5 1 16 

180 Sweep plow 20-40 in wide 0 0 5 5 4 3 17 

This data is excerpted from this table in sciver11.xls. The latest version of the Soil Conditioning Index is located at: 

ftp://ftp.nssc.usda.gov/pub/agronomy/SCIfiles/
(190-V-NAM, 3rd Ed., October 2002) 508–15 

National 

Agronomy 

Manual 

Part 508 Soils

Average Field Average Field 

annual operations annual operations 

soil subfactor soil subfactor 

distri- value distri- value 

bution bution 

rating rating 

0 1.00 46 0.55 

1 0.99 47 0.54 

2 0.98 48 0.53 

3 0.97 49 0.52 

4 0.96 50 0.51 

5 0.95 51 0.50 

6 0.94 52 0.49 

7 0.93 53 0.48 

8 0.92 54 0.47 

9 0.91 55 0.46 

10 0.90 56 0.45 

11 0.89 57 0.44 

12 0.88 58 0.43 

13 0.87 59 0.42 

14 0.86 60 0.41 

15 0.85 61 0.40 

16 0.84 62 0.39 

17 0.83 63 0.38 

18 0.82 64 0.37 

19 0.81 65 0.36 

20 0.80 66 0.35 

21 0.79 67 0.34 

22 0.78 68 0.33 

23 0.77 69 0.32 

24 0.76 70 0.31 

25 0.75 71 0.30 

26 0.74 72 0.29 

27 0.73 73 0.28 

28 0.72 74 0.27 

29 0.71 75 0.26 

30 0.70 76 0.25 

31 0.69 77 0.24 

32 0.68 78 0.23 

33 0.67 79 0.22 

34 0.66 80 0.21 

35 0.65 81 0.20 

36 0.64 82 0.19 

37 0.63 83 0.18 

38 0.62 84 0.17 

39 0.61 85 0.16 

40 0.60 86 0.15 

41 0.59 87 0.14 

42 0.58 88 0.13 

43 0.57 89 0.12 

44 0.56 90 0.11 

45 0.55 91 0.10 

Average Field Average Field 

annual operations annual operations 

soil subfactor soil subfactor 

distri- value distri- value 

bution bution 

rating rating 

92 0.09 138 -0.37 

93 0.08 139 -0.38 

94 0.07 140 -0.39 

95 0.06 141 -0.40 

96 0.05 142 -0.41 

97 0.04 143 -0.42 

98 0.03 144 -0.43 

99 0.02 145 -0.44 

100 0.01 146 -0.45 

101 0.00 147 -0.46 

102 -0.01 148 -0.47 

103 -0.02 149 -0.48 

104 -0.03 150 -0.49 

105 -0.04 151 -0.50 

106 -0.05 152 -0.51 

107 -0.06 153 -0.52 

108 -0.07 154 -0.53 

109 -0.08 155 -0.54 

110 -0.09 156 -0.55 

111 -0.10 157 -0.55 

112 -0.11 158 -0.56 

113 -0.12 159 -0.57 

114 -0.13 160 -0.58 

115 -0.14 161 -0.59 

116 -0.15 162 -0.60 

117 -0.16 163 -0.61 

118 -0.17 164 -0.62 

119 -0.18 165 -0.63 

120 -0.19 166 -0.64 

121 -0.20 167 -0.65 

122 -0.21 168 -0.66 

123 -0.22 169 -0.67 

124 -0.23 170 -0.68 

125 -0.24 171 -0.69 

126 -0.25 172 -0.70 

127 -0.26 173 -0.71 

128 -0.27 174 -0.72 

129 -0.28 175 -0.73 

130 -0.29 176 -0.74 

131 -0.30 177 -0.75 

132 -0.31 178 -0.76 

133 -0.32 179 -0.77 

134 -0.33 180 -0.78 

135 -0.34 181 -0.79 

136 -0.35 182 -0.80 

137 -0.36 183 -0.81 

Average Field 

annual operations 

soil subfactor 

distri- value 

bution 

rating 

184 -0.82 

185 -0.83 

186 -0.84 

187 -0.85 

188 -0.86 

189 -0.87 

190 -0.88 

191 -0.89 

192 -0.90 

193 -0.91 

194 -0.92 

195 -0.93 

196 -0.94 

197 -0.95 

198 -0.96 

199 -0.97 

200 -0.98 

201 -0.99 

202 -1.00 

203 -1.01 

204 -1.02 

205 -1.03 

206 -1.04 

207 -1.05 

208 -1.06 

209 -1.07 

210 -1.08 

211 -1.09 

212 -1.10 

213 -1.11 

214 -1.12 

215 -1.13 

216 -1.14 

217 -1.15 

218 -1.16 

219 -1.17 

220 -1.18 

221 -1.19 

222 -1.20 

223 -1.21 

224 -1.22 

225 -1.23 

226 -1.24 

227 -1.25 

228 -1.26 

229 -1.27 

Table 508-3 Field operations subfactor 
508–16 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Table 508-3 Field operations subfactor—continued 

Average Field 

annual operations 

soil subfactor 

distri- value 

bution 

rating 

230 -1.28 

231 -1.29 

232 -1.30 

233 -1.31 

234 -1.32 

235 -1.33 

236 -1.34 

237 -1.35 

238 -1.36 

239 -1.37 

240 -1.38 

241 -1.39 

242 -1.40 

243 -1.41 

244 -1.42 

245 -1.43 

246 -1.44 

247 -1.45 

248 -1.46 

249 -1.47 

250 -1.48 

251 -1.49 

252 -1.50 

253 -1.51 

254 -1.52 

255 -1.53 

256 -1.54 

257 -1.55 

258 -1.55 

259 -1.56 

260 -1.57 

261 -1.58 

262 -1.59 

263 -1.60 

264 -1.61 

265 -1.62 

266 -1.63 

267 -1.64 

268 -1.65 

269 -1.66 

270 -1.67 

271 -1.68 

272 -1.69 

273 -1.70 

274 -1.71 

275 -1.72 

Average Field Average Field 

annual operations annual operations 

soil subfactor soil subfactor 

distri- value distri- value 

bution bution 

rating rating 

276 -1.73 322 -2.19 

277 -1.74 323 -2.20 

278 -1.75 324 -2.21 

279 -1.76 325 -2.22 

280 -1.77 326 -2.23 

281 -1.78 327 -2.24 

282 -1.79 328 -2.25 

283 -1.80 329 -2.26 

284 -1.81 330 -2.27 

285 -1.82 331 -2.28 

286 -1.83 332 -2.29 

287 -1.84 333 -2.30 

288 -1.85 334 -2.31 

289 -1.86 335 -2.32 

290 -1.87 336 -2.33 

291 -1.88 337 -2.34 

292 -1.89 338 -2.35 

293 -1.90 339 -2.36 

294 -1.91 340 -2.37 

295 -1.92 341 -2.38 

296 -1.93 342 -2.39 

297 -1.94 343 -2.40 

298 -1.95 344 -2.41 

299 -1.96 345 -2.42 

300 -1.97 346 -2.43 

301 -1.98 347 -2.44 

302 -1.99 348 -2.45 

303 -2.00 349 -2.46 

304 -2.01 350 -2.47 

305 -2.02 351 -2.48 

306 -2.03 352 -2.49 

307 -2.04 353 -2.50 

308 -2.05 354 -2.51 

309 -2.06 355 -2.52 

310 -2.07 356 -2.53 

311 -2.08 357 -2.54 

312 -2.09 358 -2.55 

313 -2.10 359 -2.55 

314 -2.11 360 -2.56 

315 -2.12 361 -2.57 

316 -2.13 362 -2.58 

317 -2.14 363 -2.59 

318 -2.15 364 -2.60 

319 -2.16 365 -2.61 

320 -2.17 366 -2.62 

321 -2.18 367 -2.63 

Average Field 

annual operations 

soil subfactor 

distri- value 

bution 

rating 

368 -2.64 

369 -2.65 

370 -2.66 

371 -2.67 

372 -2.68 

373 -2.69 

374 -2.70 

375 -2.71 

376 -2.72 

377 -2.73 

378 -2.74 

379 -2.75 

380 -2.76 

382 -2.78 

383 -2.79 

384 -2.80 

385 -2.81 

386 -2.82 

387 -2.83 

388 -2.84 

389 -2.85 

390 -2.86 

391 -2.87 

392 -2.88 

393 -2.89 

394 -2.90 

395 -2.91 

396 -2.92 

397 -2.93 

398 -2.94 

399 -2.95 

400 -2.96 

401 -2.97 

402 -2.98 

403 -2.99 

404 -3.00 
(190-V-NAM, 3rd Ed., October 2002) 508–17 

National 

Agronomy 

Manual 

Part 508 Soils

Rate of Erosion Rate of Erosion 

erosion value erosion value 

0.00 1.00 11.75 -1.48 

0.25 0.94 12.00 -1.52 

0.50 0.88 12.25 -1.56 

0.75 0.81 12.50 -1.60 

1.00 0.75 12.75 -1.64 

1.25 0.69 13.00 -1.68 

1.50 0.63 13.25 -1.72 

1.75 0.56 13.50 -1.76 

2.00 0.50 13.75 -1.80 

2.25 0.44 14.00 -1.84 

2.50 0.38 14.25 -1.88 

2.75 0.31 14.50 -1.92 

3.00 0.25 14.75 -1.96 

3.25 0.19 15.00 -2.00 

3.50 0.13 15.25 -2.03 

3.75 0.06 15.50 -2.06 

4.00 0.00 15.75 -2.09 

4.25 -0.05 16.00 -2.12 

4.50 -0.10 16.25 -2.15 

4.75 -0.15 16.50 -2.18 

5.00 -0.20 16.75 -2.21 

5.25 -0.25 17.00 -2.24 

5.50 -0.30 17.25 -2.27 

5.75 -0.35 17.50 -2.30 

6.00 -0.40 17.75 -2.33 

6.25 -0.45 18.00 -2.36 

6.50 -0.50 18.25 -2.39 

6.75 -0.55 18.50 -2.42 

7.00 -0.60 18.75 -2.45 

7.25 -0.65 19.00 -2.48 

7.50 -0.70 19.25 -2.51 

7.75 -0.75 19.50 -2.54 

8.00 -0.80 19.75 -2.57 

8.25 -0.85 20.00 -2.60 

8.50 -0.90 20.25 -2.63 

8.75 -0.95 20.50 -2.65 

9.00 -1.00 20.75 -2.68 

9.25 -1.05 21.00 -2.70 

9.50 -1.10 21.25 -2.73 

9.75 -1.15 21.50 -2.75 

10.00 -1.20 21.75 -2.78 

10.25 -1.24 22.00 -2.80 

10.50 -1.28 22.25 -2.83 

10.75 -1.32 22.50 -2.85 

11.00 -1.36 22.75 -2.88 

11.25 -1.40 23.00 -2.90 

11.50 -1.44 23.25 -2.93 

Table 508-4 Erosion subfactors 

Rate of Erosion Rate of Erosion 

erosion value erosion value 

23.50 -2.95 34.50 -3.77 

23.75 -2.98 34.75 -3.79 

24.00 -3.00 35.00 -3.80 

24.25 -3.03 35.25 -3.81 

24.50 -3.05 35.50 -3.82 

24.75 -3.08 35.75 -3.83 

25.00 -3.10 36.00 -3.84 

25.25 -3.12 36.25 -3.85 

25.50 -3.14 36.50 -3.86 

25.75 -3.16 36.75 -3.87 

26.00 -3.18 37.00 -3.88 

26.25 -3.20 37.25 -3.89 

26.50 -3.22 37.50 -3.90 

26.75 -3.24 37.75 -3.91 

27.00 -3.26 38.00 -3.92 

27.25 -3.28 38.25 -3.93 

27.50 -3.30 38.50 -3.94 

27.75 -3.32 38.75 -3.95 

28.00 -3.34 39.00 -3.96 

28.25 -3.36 39.25 -3.97 

28.50 -3.38 39.50 -3.98 

28.75 -3.40 39.75 -3.99 

29.00 -3.42 40.00 -4.00 

29.25 -3.44 

29.50 -3.46 

29.75 -3.48 

30.00 -3.50 

30.25 -3.52 

30.50 -3.53 

30.75 -3.55 

31.00 -3.56 

31.25 -3.58 

31.50 -3.59 

31.75 -3.61 

32.00 -3.62 

32.25 -3.64 

32.50 -3.65 

32.75 -3.67 

33.00 -3.68 

33.25 -3.70 

33.50 -3.71 

33.75 -3.73 

34.00 -3.74 

34.25 -3.76 
508–18 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

System Crop Crop - - - - Residue returned - - - - - - - - - - Organic matter - - - Total 

number grown grown By crop By system At start At 12 years residue 

(lb/acre) (lb/acre) (lb/acre) (percent) (percent) (ton/acre) 

8 Wheat 984 5,114 

Cotton 762 3,015 

Sorghum 2,410 3,466 3,865 3.34 3.2 23.2 

9 Wheat 1,128 5,318 

Cotton 870 3,237 

Sorghum 2,945 4,013 4,189 3.53 4.17* 44.9** 

*Increase or decrease is statistically significant at a probability of 5%. 

**Includes 5 tons of manure applied to row crops after 1954. 

Table 508-5 The effects of the farming systems on crop yields, residue production and maintenance of the soil organic matter (Texas 

A&M, Renner Research Station published research 
(190-V-NAM, 3rd Ed., October 2002) 508–19 

National 

Agronomy 

Manual 

Part 508 Soils

Crop Crop name Harvest Yield Pounds Residue: Above Surface Sub-surface Roots Root- Crop 

code Units per unit Yield Ground decomp. decomp. in top mass group 

number ratio residue coeff. coeff. 4 inches adjust- 

(lb) (lb) ment 

2 alf. brome /oat, harv tons 1 2000 1 2000 0.019 0.019 4300 3.15 E 

3 alf. brome, fall seed tons 1 2000 1 2000 0.019 0.019 2500 2.25 E 

4 alf. brome, spring seed tons 1 2000 1 2000 0.019 0.019 4300 3.15 E 

5 alf. brome, spring seed tons 1 2000 1 2000 0.019 0.019 4300 3.15 E 

6 alf. brome tons 1.8 2000 1.0286 3703 0.019 0.019 4900 2.3232 E 

7 alf. brome, winter graze tons 1.8 2000 1.0286 3703 0.019 0.019 4900 2.3232 E 

8 alf. brome, senes tons 1.8 2000 1.0286 3703 0.019 0.019 4900 2.3232 E 

9 alf. brome, senes winter graze tons 1.8 2000 1.0286 3703 0.019 0.019 4900 2.3232 E 

10 alf. fall seed senes tons 1 2000 1 2000 0.02 0.02 2500 2.25 E 

11 alf. spring seed senes tons 1.6 2000 1 3200 0.02 0.02 2500 1.7812 E 

12 alf. spring seed y2 regrowth tons 1.6 2000 1 3200 0.02 0.02 2500 1.7812 E 

13 alf. yr2 senes to yr3 tons 1 2000 1 2000 0.02 0.02 3000 2.5 E 

14 alf. yr2 senes winter graze tons 1 2000 1 2000 0.02 0.02 3000 2.5 E 

15 alf. yr3 senes to yr4 regrowth tons 1 2000 1 2000 0.02 0.02 3500 2.75 E 

Table 508-6 RUSLE crop parameter data 

This data is excerpted from this table in sciver11.xls. The latest version of the Soil Conditioning Index is located at: 

ftp://ftp.nssc.usda.gov/pub/agronomy/SCIfiles/

262 Wheat, spring 14in rows bu 35 60 1.3 2730 0.008 0.008 950 1.3479 A 

263 Wheat, spring 7 in, NWRR bu 60 60 1.353 4870.8 0.017 0.017 720 1.1478 D 

264 Wheat, spring 7in rows bu 30 60 1.3 2340 0.008 0.008 970 1.4145 A 

265 Wheat, spring, 10 in, NWRR bu 40 60 1.353 3247.2 0.017 0.017 520 1.1601 D 

266 Wheat, winter 14in rows bu 45 60 1.7 4590 0.008 0.008 1200 1.2614 A 

267 Wheat, winter 7in rows bu 40 60 1.7 4080 0.008 0.008 1080 1.2647 A 

268 Wheat, winter cover lbs 4000 1 1 4000 0.017 0.017 400 1.1 D 

269 Wheat, winter graze out South lbs 800 1 1 800 0.008 0.008 1000 2.25 A 

270 Wheat, winter graze, grain bu 30 60 1.7 3060 0.008 0.008 850 1.2777 A 

271 Wheat, winter grazed forage lbs 2000 1 0.2 400 0.017 0.017 660 2.65 D 

272 Wheat, winter low yield NWRR bu 30 60 1.75 3150 0.017 0.017 250 1.079365 D 

273 Wheat, winter late seed NWRR bu 30 60 1.75 3150 0.017 0.017 150 1.047619 D 

274 Wheat, winter S.E. bu 40 60 1.7 4080 0.008 0.008 1070 1.2622 A 

275 Wheat, winter silage tons 2 2000 0.056 224 0.017 0.017 1000 5.4642 D 

276 Wheat, winter, early seed, 10 in bu 50 60 1.434 4302 0.017 0.017 690 1.160391 D 

277 Wheat, winter, early seeding bu 60 60 1.434 5162.4 0.017 0.017 970 1.187897 D 

278 Wheat, winter, hay or silage tons 2 2000 0.056 224 0.017 0.017 940 5.196429 D 

279 Wheat, winter, late seeding bu 70 60 1.43 6006 0.017 0.017 1080 1.17982 D 

280 Barley, spring, AK bu 30 48 1.5 2160 0.008 0.008 830 1.3842 A 

281 Broccoli, AK lbs 9500 1 0.30526 2900 0.02 0.02 250 1.0862 E 

282 Bromegrass, seedng yr, AK tons 1.5 2000 1 3000 0.017 0.017 1700 1.5666 D 

283 Bromegrass, y2 senesc to yr3 AK tons 1 2000 1 2000 0.017 0.017 2500 2.25 D 

284 Bromegrass, yr3 senesc to yr4 AK tons 1 2000 1 2000 0.017 0.017 2500 2.25 D 

285 Cabbage, AK cwt 230 100 0.11 2530 0.02 0.02 240 1.0948 E 

286 Canola, spring, AK bu 25 50 2.4 3000 0.016 0.016 800 1.2666 C 

287 Cauliflower, AK lbs 10300 1 0.25 2575 0.02 0.02 290 1.1126 E 
508–20 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils
(190-V-NAM, 3rd Ed., October 2002) 508–21 

National 

Agronomy 

Manual 

Part 508 Soils
508–22 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 508 Soils

Conversions

Soil weight = 2,000,000 pounds per acre furrow slice 

(one acre to a depth of 6 2/3 in.) 

Soil organic matter (humus) = Soil organic carbon x 1.72 

Soil organic carbon = Soil organic matter x 0.58 

Weight of residue x 0.30 = Soil organic matter 

OM content of eroded sediment = Soil OM x 1.5 

Annual rate of soil organic matter (humus) decay: 

Loam or clay loam . . . . 2.5% of total soil reserve 

Sandy loam . . . . . . . . . . 3.5% of total soil reserve 

Loamy sand . . . . . . . . . . 4.5% of total soil reserve 
(190-V-NAM, 3rd Ed., October 2002) 509–i 

Data Management

Contents:

Part 509

Subpart 509A Introduction and responsibilities 509–1

509.00 Background ......................................................................................................509–1 

509.01 Responsibilities ................................................................................................509–1 

Subpart 509B Database management 509–2

509.10 Databases for erosion prediction tools ............................................................509–2 

509.11 Pesticide properties database ..........................................................................509–2 

509.12 Plant nutrient content database .......................................................................509–2 

190-V-NAM, 3rd Ed., October 2002) 509–1 

Part 509 Data Management

Subpart 509A Introduction and responsibilities

509.00 Background

NRCS’ s agronomic data exists in both electronic and hard 

copy formats, and is maintained at many different locations 

by a large number of people. There is no organized network 

among those who maintain the data to facilitate data sharing 

and to ensure against duplication of effort in data collection. Coordination is needed among all those in NRCS who 

collect, use, and manage data to share similar data sets that 

may apply in more than one state or region. This will reduce 

workloads and ensure data accuracy and integrity. 

A large portion of the agronomic data used by NRCS is 

contained in data files developed for the implementation of 

various tools at the State and field office level, such as erosion prediction, nutrient management and pest management 

tools. 

509.01 Responsibilities

The national agronomist is responsible for preparation of 

national policy and instructions pertaining to data management. 

The cooperating scientists for water and wind erosion are 

responsible for developing and maintaining data for the 

implementation and application of erosion prediction models. They work directly with the National database coordinator for RUSLE2 and WEPS in developing and maintaining the databases used in these models. They provide national coordination for the development of Climate Zones, 

Crop Management Zones, Crop Management Templates, 

and assist in assigning dates of operations used in developing Crop Management Templates for erosion prediction 

tools. 

The national nutrient management specialist isresponsible 

for developing and maintaining databases for assisting 

States with implementation and application of nutrient management tools. 

The national pest management specialist is responsible for 

developing and maintaining databases for assisting States 

with implementation and application of pest management 

tools. 

The national database coordinator for RUSLE2 and WEPS 

is responsible for maintaining the national Vegetation and 

Operation databases used in these erosion prediction models. He/she assists in the coordination of Climate Zones, 

Crop Management Zones, dates of operations used in developing Management Templates, Crop Management Templates, and associated guidelines used in the Templates, and 

works closely with other national specialists to minimize 

duplication of effort in the Agency’s data collection efforts. 

RUSLE/WEPS regional contactsserves as the liaisons with 

other agronomists and erosion specialists in the regions and 

with the cooperating scientists for wind and water erosion. 

They are responsible for maintaining consistency, both 

within regions and between regions, in data used erosion 

prediction tools. 

At the State level, the appropriate State specialist (agronomist, nutrient/pest management specialist or water quality 

specialist) is responsible for proper use of NRCS databases 

in field office applications. They are also responsible for 

identifying if different or additional types of data are 

needed at the field level. 
509–2 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Part 509 Data Management

Subpart 509B Database management

509.10 Databases for erosion prediction

tools

(a) Crop and field operations databases

(1) An initial set of plant and operation data records has 

been developed under the leadership of ARS. These data 

records serve as guides for developing additional plant data 

records. Additional data records will be added to include 

all plant types and field implements and operations needed 

by NRCS. A national set of databases for each model, 

known as the NRCS Crop Database and the NRCS Operation Database, will be maintained by the agency. These official NRCS databases are to be used in RUSLE2 and 

WEPS 1.0 by NRCS field offices. The data records needed 

for the operations used and crops grown in the local area 

will be downloaded from the official databases onto field 

office computers. 

(2) The national database coordinator will manage the official NRCS databases. The coordinator is responsible for 

adding, modifying, and revising all parameter values in the 

Crop and Operation Databases. Agronomists or designated 

erosion specialists, in coordination with the RUSLE/WEPS 

regional contacts, can submit additions or revisions to the 

NRCS Crop or Operation databases. If additional crop or 

operation records or revisions of existing records are 

needed, States will furnish any available data inputs to the 

database coordinator through their regional contact. The database coordinator will coordinate the development of the 

record and issue it for peer review and eventual posting to 

the official NRCS database. All agronomists or designated 

erosion specialists will be notified when new records have 

been posted. 

(b) Climate databases

(1) For RUSLE2, the average monthly temperature and precipitation from one designated climate station will be used 

to represent each Climatic Zone. Local climate data 

records will be developed using these temperature and precipitation values, but location-specific R factor and 10-year 

storm EI values will be used in that local climate record.

The national database coordinator will provide national coordination and assist the States in developing local climate 

records. Only official NRCS RUSLE2 Climate Databases 

are to be used by NRCS field offices. The data records 

needed for the local area will be downloaded from the official NRCS Climate Database onto field office computers. 

 (2) Either simulated climate data (using WINDGEN and 

CLIGEN weather generators imbedded in the model) or actual climate data (stored in the model) will be used in 

WEPS 1.0. 

(c) Soil databases

A soil data download from the National Soils Information 

System (NASIS) will be created and placed on the field office computer in a Microsoft Access database in conjunction with the Customer Service Toolkit. This database will 

contain soil data to be used in that field office as inputs for 

RUSLE2 and WEPS 1.0. The soil database downloaded to 

each field office will be the official NRCS Soil Database 

and will be updated only as supported by agency policy. 

509.11 Pesticide properties database

The pesticide properties database is used by the National 

Agricultural Pesticide risk Analysis (NAPRA) model and 

the Windows-Pesticide Screening Tool (WIN_PST). These 

environmental risk screening tools are used to predict the 

potential for pesticides to move with water and eroded soil/ 

organic matter and affect non-target organisms. 

The national pest management specialist will work with the 

Agricultural Research Service and representatives of companies that produce pesticides to keep this database current. 

509.12 Plant nutrient content database

The Plant Nutrient Content Database contains estimates of 

the nitrogen, phosphorus, and potassium content in plant 

biomass for many agricultural crops. This information is 

useful to nutrient management planners who need estimates 

of plant nutrient content to develop nutrient management 

plans. It becomes particularly valuable when nutrient are 

applied in quantities that are a function of the nutrient content of plant biomass. 

The national nutrient management specialist will work with 

the Agricultural Research Service and Land Grant Universities to update and expand this database. 
190-V-NAM, 3rd Ed., October 2002) Glossary–1 

A factor The computed longtime average annual soil loss carried by runoff from specific 

field slopes in specified cropping and management systems. It is expressed in the 

RUSLE model in tons/acre/year. 

Abrasion Breakdown of clods, crusts, and plant material by the impact of particles moved 

by wind in saltation. The impacting particles may also abrade. Abrasion causes 

soil aggregates to break down progressively as wind erosion continues. 

Accelerated erosion Erosion of soil resulting from disturbance of the natural landscape. It results 

largely from the consequences of human activity, such as tillage, grazing and removal of vegetative cover. 

Adsorption The process by which atoms, molecules, or ions are taken up from the soil solution or soil atmosphere and retained on the surfaces of solids by chemical or 

physical binding. 

Aggregate stability The ability of a soil aggregate to resist various destructive forces, such as tillage, 

abrasion by wind or flowing water, or raindrop force. 

Aggregation, soil The cementing or binding together of primary soil particles (sand, silt, and clay) 

into a secondary unit, which unit contributes to the soil structure. 

Agronomic rate The rate at which fertilizers, organic wastes or other amendments can be added 

to soils for optimum plant growth. 

Air-dry weight Weight of a substance after it has been allowed to dry to equilibrium with the atmosphere. 

Amendment A substance added to the soil to improve plant growth, such as lime. 

Allelopathy Production of a substance by one organism that inhibits one or more other organisms. 

Angle of deviation The angle between prevailing wind erosion direction and a line perpendicular to: 

(1) the long side of the field or strip, when determining unsheltered distance using a wind erosion direction factor, or (2) row direction when determining effect 

of wind direction on the ridge roughness factor. 

Available water The capacity of a soil to hold water in a form available to plants, usually exholding capacity pressed in inches of water per inch of soil depth. Commonly defined as the 

amount of water held in the soil between field capacity and wilting point. 

Avalanching The increase in rate of soil flow with distance downwind across an area being 

eroded by wind. 

Biomass The total mass of living organisms in a given volume or mass of soil, or in a particular environment. Compare Phytomass. 

Biochemical oxygen The amount of oxygen required by aerobic organisms to carry out oxidative medemand (BOD) tabolism in water containing organic matter, such as sewage. BOD is used as an 

indirect measure of the concentration of biologically degradable material present 

in organic wastes. Also known as Biological oxygen demand. 

Glossary
Glossary–2 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Glossary

Bioremediation The use of biological agents to reclaim soil and water polluted by substances 

hazardous to the environment or human health. 

Buffer strip A narrow strip of grass or other close-growing vegetation that, when placed 

along the contour on a slope, traps sediment that was produced on the hillslope 

above. 

Bulk density, soil The mass of dry soil per unit bulk volume, including both solids and pore space. 

The value is expressed as grams per cubic centimeter (g/cm3) or megagrams per 

cubic meter, (Mg/m3). 

C factor - Water erosion Cover and management factor in RUSLE. It combines the effects of prior land 

use, crop canopy, surface cover, surface roughness, and soil moisture to predict a 

soil loss ratio for a crop or other vegetation, cropping period, or season. 

C Factor – Wind erosion Climatic factor in WEQ. It is an index of climatic erosivity, specifically wind 

speed and surface soil moisture. The factor for any given location is based on 

long-term climatic data and is expressed as a percentage of the C factor for Garden City, KS, which has been assigned a value of 100. 

Calcareous soil Soil containing sufficient free calcium carbonate or magnesium carbonate to effervesce visibly when treated with cold 0.1 N hydrochloric acid. High content of 

lime (up to about 5 percent), particularly in the clay fraction, appreciably increases erodibility by wind. 

Calcium carbonate equivalent The content of carbonate in a liming material or calcareous soil calculated as if 

all of the carbonate is in the form of CaCO3. See also Lime, agricultural. 

Canopy The vertical projection downward of the aerial portion of plants, usually expressed as percent of ground so occupied. 

Carbon cycle The sequence of transformations whereby carbon dioxide is converted to organic 

forms by photosynthesis or chemosynthesis, recycled through the biosphere (with 

partial incorporation into sediments), and ultimately returned to its original state 

through respiration or combustion. 

Carbon-nitrogen ratio The ratio of the mass of organic carbon to the mass of organic nitrogen in soil, 

organic material, plants, or microbial cells. 

Cation exchange capacity (CEC) The sum of exchangeable bases plus total soil acidity at a specific pH values, 

usually 7.0 or 8.0. It is usually expressed in milliequivalents per 100 grams 

(meq/100 g) or centimoles per kilogram (cmol/kg). 

Classical gully erosion Erosion caused by the action of runoff water in concentrated flow channels. 

These flow channels are well-defined, permanent drainageways that cannot be 

crossed by ordinary farming operations. 

Climatic erosivity The relative influence of climate on field erodibility by wind in different regions, 

specifically the effects of average wind speed and effective soil surface moisture. 
190-V-NAM, 3rd Ed., October 2002) Glossary–3 

Clod A compact, coherent mass of soil greater than 2 millimeters in equivalent diameter, often created by tillage or other mechanical disturbance of the soil. 

Coarse fragments Rock or mineral particles greater than 2 millimeters in diameter. 

Compost Organic residues, or a mixture of organic residues and soil, that have been 

mixed, piled, and moistened, with or without addition of fertilizer and lime, and 

generally allowed to undergo thermophilic decomposition until the original organic materials have been substantially altered or decomposed. 

Contour farming The practice of using ridges and furrows left by tillage to redirect runoff from a 

path directly downslope to a path around the hillslope. 

Cover crop Close-growing crop that provides soil protection, seeding protection and soil improvement between periods of normal crop production, or between trees in orchards and vines in vineyards. When incorporated into the soil, cover crops may 

be referred to as Green manure crops. 

Critical wind erosion period Period of the year when the greatest amount of wind erosion can be expected to 

occur from a field under an identified management system. It is the period when 

the combination of vegetative cover, soil surface conditions, and expected erosive winds result in the greatest potential for wind erosion. 

Crop residue management Maintaining stubble, stalks, and other crop residue on the soil surface or partially 

incorporated into the surface layer to reduce erosion, conserve soil moisture, and 

improve soil tilth. 

Crop rotation A planned sequence of several different crops grown on the same land in successive years or seasons, done to replenish the soil, reduce insect, weed and disease 

populations, or to provide adequate feedstocks for livestock operations. 

Crop tolerance to wind erosion Ability of crop plants to tolerate wind blown soil particles when in the seedling 

stage or exposure of plant roots where soil is eroded away, or burial of plants by 

drifting soil, or desiccation and twisting of plants by the wind. 

Crust A thin surface layer, where aggregates are bound together and the surface is 

sealed. It is more compact and mechanically stable than the soil material immediately beneath it. Crust is characterized by its dense, platy structure that becomes less distinct with depth until it merges with the soil below. Crust is a transitory condition. 

Deposition The accumulation of eroded soil material on the land surface when the velocity 

or transport capacity of the transporting agent (wind or water) is reduced. 

Desert pavement A non-erodible soil surface devoid of erodible materials or consisting of gravel 

or stones left on the land surface. It occurs in desert regions as a result of the removal of fine materials by wind or water erosion. Desert pavement is virtually 

non-erodible. 
Glossary–4 (190-V-NAM, 3rd Ed., October 2002) 

National 

Agronomy 

Manual 

Glossary

Detachment The removal of transportable fragments of soil material from the soil mass by an 

eroding agent, usually falling raindrops, running water, wind, or windblown soil 

particles. Detachment is the process that makes soil particles or aggregates available for transport. 

Drought year Any year when precipitation is less than 80 percent of the long-term normal. 

Dry aggregate A compound or secondary air-dry soil particle that is not destroyed by dry sieving. 

Dryland farming Crop production without irrigation (rain-fed agriculture). 

Dust storm A strong turbulent wind carrying large amounts of soil particles in suspension. 

E tables Tables derived from computer solutions (WEROS) of the Wind Erosion Equation that display values of average annual wind erosion per acre (E) for various 

combinations of soil erodibility (I), ridge roughness (K), climate (C), unsheltered 

distance (L), and vegetative cover (V). 

Effective precipitation That portion of the total rainfall precipitation which becomes available for plant 

growth. 

Electrical conductivity (ECe) The electrical conductance of an extract from a soil saturated with distilled water. The preferred units are decisiemens per meter (dS/m) at 25° C, but it may 

also be expressed as siemens per meter (S/m) or millimhos per centimeter 

(mmhos/cm). See Saline soil. 

Ephemeral gully erosion Erosion that occurs from the action of runoff water which concentrates in shallow flow channels when rills converge. These flow channels are alternately filled 

with soil by tillage operations and re-formed in the same general location by subsequent runoff events. 

Erodibility The susceptibility of soil to erosion. For water erosion, soils with low erodibility 

include fine textured soils high in clay that are resistant to detachment, and 

coarse textured soils high in sand that have low runoff. Soils having a high silt 

content are highly susceptible to erosion. For wind erosion, soil erodibility is related to the percentage of nonerodible surface soil aggregates larger than 0.84 

millimeters in size. Soil erodibility is expressed by the K factor in RUSLE, and 

by the I factor in the WEQ. 

Erosive wind energy The capacity of winds above the threshold velocity to cause erosion. Erosive 

wind energy is a function of the cube of wind speed and the duration of erosive 

winds. 

Erosive wind energy distribution The distribution of erosive wind energy over time at any geographic location. 

Erosivity The energy (amount) and intensity of rainstorms that cause soil to erode. Erosivity includes the effects of raindrop impact on the soil and the amount and rate of 

runoff likely to be associated with the rainfall event. 
(190-V-NAM, 3rd Ed., October 2002) Glossary–5 

National 

Agronomy 

Manual 

Glossary

Evapotranspiration The combined loss of water from a given area, and during a specified period of 

time, by evaporation from the soil surface and by transpiration from plants. 

Eutrophication A process that increases the amount of nutrients, especially nitrogen and phosphorus, in an aquatic ecosystem. Eutrophication occurs naturally over geological 

time but may be accelerated by human activities, such as poor nutrient management, waste disposal or land drainage, leading to an increase in aquatic vegetation and a decrease in plant diversity. 

Fallow The practice of leaving land uncropped, either weed-free or with volunteer vegetation, during at least one period when a crop would normally be grown; done 

to control weeds or accumulate water or available plant nutrients. 

Fertility, soil The quality of a soil that enables it to provide nutrients in adequate amounts and 

in proper balance for the growth of specified plants or crops. 

Fertilizer Any organic or inorganic material of natural or synthetic origin (other than liming materials) that is added to a soil to supply one or more plant nutrients essential to the growth of plants. 

Fertilizer analysis The percent composition of a fertilizer as determined in a laboratory and expressed as total N, available phosphoric acid (P2O5) equivalent, and watersoluble potash (K2O) equivalent. 

Fibric organic soil materials The least decomposed of all the organic soil materials, containing very high 

amounts of fiber that are well preserved and readily identifiable as to botanical 

origin. Compare Hemic organic soil and Sapric organic soil. 

Field capacity (Field water capacity) The content of water, on a mass or volume basis, remaining in a soil two to three 

days after being saturated with water, and from which free drainage is negligible. 

Friable A term describing soils that when either wet or dry can be easily crumbled between the fingers. 

Geologic erosion The wearing away of the earth’s surface by the forces of water and wind. Sometimes referred to as natural erosion, it is responsible for the natural topographic 

cycles, as it wears away higher points of elevation and constructs valleys and alluvial plains. 

Green manure crop Any crop grown for soil improvement by being incorporated into the soil while 

green or soon after maturity. See Cover crop. 

Greenhouse effect The absorption of solar radiant energy by the earth’s surface and its release as 

heat into the atmosphere; longer infrared heat waves are absorbed by the air, 

principally by carbon dioxide and water vapor, thus, the atmosphere traps heat 

much as does the glass in a greenhouse. 

Ground water That portion of the water below the surface of the ground at a pressure equal to 

or greater than atmospheric. See also Water table. 
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Hard seed Seed that is dormant due to a seed coat impervious to either water or oxygen. 

Hemic organic soil materials An organic soil that is intermediate in degree of decomposition between the less 

decomposed fibric and the more decomposed sapric materials. 

Hydrologic cycle The fate of water from the time of precipitation until the water has been returned 

to the atmosphere by evaporation and is again ready to be precipitated. 

Hydroseeding Planting seed in a water mixture by pumping through a nozzle that sprays the 

mixture onto a seedbed. The water mixture may also contain fertilizer and 

mulches. 

Inoculate To treat, usually seeds, with microorganisms to create a favorable response. 

Most often refers to the treatment of legume seeds with Rhizobium or 

Bradyrhizobium bacteria to stimulate dinitrogen fixation. 

Isolated field A field where the rate of soil flow is zero at the windward edge of the field due 

to the presence of a stable border. An isolated field is not protected by barriers 

and is exposed to open wind velocities. The Wind Erosion Equation applies to 

conditions on an isolated field. 

Isoline A line on a map or chart along which there is a constant value of a variable such 

as wind velocity or climatic erosivity. 

K factor - Water Erosion Soil erodibility factor in RUSLE that quantifies the susceptibility of soil particles 

to detachment and movement by water. The K value is the soil-loss rate per erosion index unit for a specified soil as measured on a standard plot, which is defined as a 72.6-ft length of uniform 9 percent slope in continuous clean-tilled fallow. 

K Factor – Wind Erosion The soil roughness factor K, for WEQ. It is a measure of the effect of oriented 

roughness (ridges) and random roughness (cloddiness) on erosion. See Random

Roughness and Ridge Roughness. 

Knoll An abrupt change in topography characterized by windward slope change greater 

than 3 percent and windward slope less than 500 feet long. 

Knoll erodibility The increase in wind erosion potential resulting from the compression of wind 

flowlines and accompanying increased velocity over the crest of knolls. A knoll 

erodibility factor is used to adjust estimated erosion where these conditions occur. 

Land capability The suitability of land for use without permanent damage. Land capability, as ordinarily used in the USA, is an expression of the effect of physical land conditions, including climate, on the total suitability for use, without damage, for 

crops that require regular tillage, for grazing, for woodland, and for wildlife. 

Land capability involves consideration of the risks of land damage from erosion 

and other causes and the difficulties in land use owing to physical land characteristics, including climate. 
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Land capability class One of the eight classes of land in the land capability classification of NRCS; 

distinguished according to the risk of land damage or the difficulty of land use; 

they include: 

Land suitable for cultivation and other uses. 

Class I - Soils that have few limitations restricting their use. 

Class II - Soils that have some limitations, reducing the choice of plants or requiring moderate conservation practices. 

Class III - Soils that have severe limitations that reduce the choice of plants or 

require special conservation practices, or both. 

Class IV - Soils that have very severe limitations that restrict the choice of 

plants, require very careful management or both. 

Land generally not suitable for cultivation (without major treatment). 

Class V - Soils that have little or no erosion hazard, but that have other limitations, impractical to remove, that limit their use largely to pasture, range, 

woodland, or wildlife food and cover. 

Class VI - Soils that have severe limitations that make them generally un 

suited for cultivation and limit their use largely to pasture or range, woodland, 

or wildlife food and cover. 

Class VII - Soils that have very severe limitations that make them unsuited to 

cultivation and that restricts their use largely to grazing, woodland, or wild 

life. 

Class VIII - Soils and landforms that preclude their use for commercial plant 

production and restrict their use to recreation, wildlife, water supply, or aesthetic purposes. 

Leaching The removal of soluble materials from one zone in soil to another via water 

movement in the profile. 

Liebig’s law of the minimum A logical principle of crop production, summarized as: The level of crop production is constrained by the essential element that is most limiting.

Lime, agricultural A soil amendment containing calcium carbonate, magnesium carbonate and other 

materials, used to neutralize soil acidity and furnish calcium and magnesium for 

plant growth. Classification, including calcium carbonate equivalent and limits in 

lime particle size, is usually prescribed by law or regulation. 

Loess Soil material transported and deposited by wind, consisting predominantly of 

silt-sized particles. 

LS factor The RUSLE factor that accounts for the combined effects of length and steepness of slope on soil loss. The factor value represents the ratio of soil loss on a 

given slope length and steepness to soil loss from a slope that has a length of 

72.6-ft and a steepness of 9 percent, where all other conditions are the same. 

Management period A period of time during a cropping sequence when cover and management effects are approximately uniform or otherwise result in uniform rates of erosion 

during the period. 

Mineral soil A soil composed mainly of, and having its properties determined by, mineral 

matter, with less than 20% organic matter. Compare Organic soil. 
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Mineralization The conversion of an element from an organic form to an inorganic state as a result of microbial activity. 

Mulch Any material such as straw, sawdust, leaves, plastic film, loose soil, or similar 

material that is spread or formed upon the surface of the soil to protect the soil 

and/or plant roots from the effects of raindrops, soil crusting, freezing, evaporation, etc. 

Mulch tillage Managing the amount, orientation, and distribution of crop and other plant residue on the soil surface year-round, while growing crops where the entire field 

surface is tilled prior to planting. 

Nitrogen cycle The continuous process by which nitrogen circulates among the air, soil, water, 

plants, and animals of the earth. Nitrogen in the atmosphere is converted by bacteria into forms that green plants can absorb from the soil; animals eat these 

plants (or eat other animals that feed on the plants); the animals and plants die 

and decay; the nitrogenous substances in the decomposed organic matter return 

to the atmosphere and the soil. 

No-till/Strip till Managing the amount, orientation and distribution of crop and other plant residues on the soil surface year-round, while growing crops in narrow slots, or tilled 

or residue free strips in soil previously untilled by full-width inversion implement 

Northwestern Wheat and Areas of non-irrigated cropland in the Pacific Northwest and mountainous reRange Region (NWRR) gions of the west. It includes portions of eastern Washington, north central Oregon, northern and southeastern Idaho, western Montana, western Wyoming, 

northern Utah and northern California. Rainfall and erosion processes in this region are dominated by winter events. 

Organic farming A crop production system that reduces, avoids or largely excludes the use of synthetically-produced fertilizers, pesticides, growth regulators and livestock feed 

additives. 

Organic soil A soil that contains a high percentage (greater than 20 percent) of organic matter 

throughout the solum. Compare Mineral soil

Oven-dry weight The weight of a substance after it has been dried in an oven at 105 degrees C to 

equilibrium. 

P factor The support practice factor in RUSLE. It is a measure of the soil loss with a specific support practice to the corresponding loss with upslope and downslope tillage. On cultivated land, support practices considered in RUSLE include contouring, stripcropping, buffer strips, and terraces. These practices principally effect 

erosion by modifying the flow pattern, grade or direction of surface runoff and 

by reducing the amount and rate of runoff. 

Permanent wilting point The largest water content of a soil at which indicator plants, growing in that soil, 

(Wilting coefficient) wilt and fail to recover when placed in a humid chamber. Often estimated by the 

soil water content at –1.5 MPa (-15 bars) soil matric potential. 
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Permeability The ease with which water, air, or plant roots penetrate or pass through a soil horizon. 

Phytomass The total mass of plant material in a given system or environment. Compare Biomass. 

Precipitation-effectiveness An index of the effectiveness of precipitation, calculated from mean monthly 

(PE) index precipitation and mean monthly temperature at a specific geographical location. 

A modified P-E index is used to represent effective surface soil moisture in calculation of the WEQ climatic factor C. 

Preponderance A ratio which expresses how much of the erosive wind energy occurs parallel to 

the prevailing wind erosion direction, as compared to the amount of erosive wind 

energy occurring perpendicular to the prevailing direction. A preponderance of 

1.0 indicates that as much wind erosion force occurs perpendicular to the prevailing direction as occurs parallel to that direction. A higher preponderance indicates more of the force is parallel to the prevailing wind erosion direction. 

Prevailing wind direction The direction from which winds most commonly occur. This may not be the 

same as the prevailing wind erosion direction. 

Pure live seed Percentage of pure germinating seed: (pure seed percentage x germination percentage)/100. 

Prevailing wind erosion direction The direction of erosive winds where there is potential for the greatest amount of 

soil to be moved, relative to the erosive force of winds from other directions. 

R equivalent (Req) factor The factor used in place of the RUSLE R factor in the Northwestern Wheat and 

Range Region of the U.S. to measure the unique effects of melting snow, rain on 

snow, and/or rain on thawing soil. Much of this soil loss occurs by rilling when 

the surface part of the soil profile thaws and snowmelt or rain occurs on the still 

partially frozen soil. 

R factor The rainfall and runoff factor in RUSLE that accounts for the energy and intensity of rainstorms. It is a measure of total storm energy times the maximum 30- 

minute intensity. 

Random roughness The standard deviation of the soil surface elevations when changes because land 

slope or nonrandom (oriented) tillage marks are removed from consideration. 

Random roughness decreases water erosion by ponding water and sediment in 

small localized depressions, decreasing transport capacity and runoff detachment 

of overland flow. Random roughness decreases wind erosion by increasing the 

threshold wind speed at which erosion begins and by trapping soil being moved 

by the wind. 

Reference condition A standard wind tunnel condition for small grain equivalent determination where 

small grain stalks 10 inches long are lying flat on the soil surface in 10-inch rows 

which are perpendicular to the wind direction, with stalks oriented parallel to the 

wind direction. 
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Relative field erodibility An index of relative erodibility under field conditions. Wind tunnel erodibility is 

adjusted for the effect of unsheltered distance and of the resistance of soil textural classes to breakdown of surface crusts by abrasion and avalanching. Compared to the wind tunnel, erodibility of a field surface is greater because the 

longer unsheltered distance allows abrasion and avalanching to occur. 

Ridge roughness The degree of oriented roughness determined by the height and width of ridges 

formed by tillage and planting implements. Ridges provide sheltered zones that 

trap moving soil particles. 

Rill A small, intermittent water course with steep sides; usually only several centimeters deep. 

Rhizobia Bacteria able to live symbiotically in roots of leguminous plants, from which 

they receive energy and often utilize molecular nitrogen. Collective common 

name for the genus Rhizobium. See Inoculate. 

Runoff That portion of precipitation or irrigation on an area which does not infiltrate, 

but instead is discharged from the area. 

RUSLE (Revised Universal Soil An empirical model that predicts long-term average annual soil loss from rainfall 

Loss Equation) and runoff for a given set of climatic conditions, on a defined land slope, and under a specified cropping and tillage management system. Expressed as 

A=RKLSCP, where E is the average annual soil loss in tons/acre/year, R is the 

rainfall-runoff factor, K is the soil erodibility factor, L is slope length, S is slope 

steepness, C is the cover-management factor and P is the support practice factor. 

RUSLE is an update of the USLE, and is made available as a computer program 

to facilitate calculations. 

Saline seep Intermittent or continuous saline water discharge at or near the soil surface under 

dryland conditions that reduces or eliminates crop growth. It is differentiated 

from other saline soil conditions by recent and local origin, shallow water table, 

saturated root zone, and sensitivity to cropping systems and precipitation. 

Saline soil A nonsodic soil containing sufficient soluble salt to adversely affect the growth 

of most crop plants. The lower limit of saturation extract electrical conductivity 

of such soils is conventionally set at 4 dS m-1 (at 25° C). Actually, sensitive 

plants are affected at half this salinity and highly tolerant ones at about twice this 

salinity 

Saltation Soil movement in wind where particles skip or bounce along the soil surface in 

response to wind forces. Particles in the size range from 0.1 to 0.5 mm (0.004 to 

0.02 in) usually move in this manner. 

Salt-affected soil Soil that has been adversely modified for the growth of most crop plants by the 

presence of soluble salts, with or without high amounts of exchangeable sodium. 

Salt tolerance The ability of plants to resist the adverse, nonspecific effects of excessive 

soluble salts in the rooting medium. 
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Sapric organic soil materials The most highly decomposed of the organic materials, having the highest bulk 

density, least amount of plant fiber, and lowest water content at saturation. Compare Hemic organic soil and Fibric organic soil. 

Seasonally variable K factor The average annual soil erodibility K factor value that has been adjusted to reflect the temporal variability associated with freezing and thawing or wetting and 

drying cycles during the year. 

Sheet erosion A form of water erosion in which a very thin layer is removed from the soil surface by detachment and overland flow. 

Small grain equivalent (SGe) The wind erosion control equivalent of vegetative cover, compared to a small 

grain standard. The standard (reference condition) is defined as small grain 

stalks 10 inches long lying flat on the soil surface in 10-inch rows which are perpendicular to the wind direction, with stalks oriented parallel to the wind direction. The small grain equivalent value is a function of kind, amount, and orientation of growing plants or plant residues on the soil surface. 

Soil erodibility index (I) The potential soil loss, in tons per acre per year, from a wide, level, unsheltered, 

isolated field with a bare, smooth, loose, and non-crusted surface, under climatic 

conditions like those in the vicinity of Garden City, Kansas. 

Soil loss tolerance (T) T is expressed as the average annual soil erosion rate (tons/acre/year) that can 

occur in a field with little or no long-term degradation of the soil resource thus 

permitting crop productivity to be sustained for an indefinite period of time. 

Soil surface moisture Adsorbed water films surrounding surface soil particles that increase the soil resistance to erosion. In developing the climatic factor, soil surface moisture is assumed to be proportional to the Thornthwaite Precipitation-Effectiveness (P-E) 

Index. 

Sorting Separation of various size classes of soil particles or aggregates during wind erosion. Soils tend to become coarser in response to continued sorting by erosion. 

Sprigging Vegetative establishment of herbaceous species using stolons, rhizomes, or tillers 

with soil. Vegetative material may be broadcast and then lightly covered with 

soil, or planted using a sprigging implement. 

Stable border A stable border defines the upwind boundary of an isolated field. It is an area 

with sufficient protection to prevent saltation from starting, and capable of trapping and holding incoming saltation from eroding areas upwind, thus preventing 

saltating soil particles from entering areas downwind. 

Stripcropping The practice of growing two or more crops in alternating strips along contours to 

control erosion. 

Surface armor A layer of coarse fragments or other non-erodible particles resistant to abrasion 

that remain on the soil surface after the removal of fine particles by erosion. 
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Surface creep Soil movement by wind in which the coarser fractions are transported by rolling 

and sliding along the ground surface, primarily by the impact of particles in saltation rather than by direct force of the wind. Particles greater than 0.5 mm (0.02 

in) in size are usually moved in this manner. 

Suspension Soil movement in wind whereby the finer fractions are transported over long distances floating in the windstream. Suspension is usually initiated by the impact of 

saltating particles. Particles moving in this manner are usually less than 0.1 mm 

(0.004 in) in size. Many suspension-size particles are created by abrasion during 

erosion. 

Threshold velocity The minimum velocity at which wind will begin moving soil particles from a 

smooth, bare, non-crusted surface. The threshold velocity is usually considered 

to be 13 mph at 1 foot above the soil surface, or 18 mph at 30 feet height. 

Tillage Conventional Primary and secondary tillage operations normally performed in 

preparing a seedbed and/or cultivating for a given crop grown in a given geographical area, usually resulting in little or no crop residues remaining on the surface after completion of the tillage sequence. 

Inversion Reversal of vertical order of occurrence of layers of soil, or of the 

soil within a layer. 

Non-inversive Tillage that does not mix (or minimizes the mixing of) soil horizons or does not vertically mix soil within a horizon. 

Subsoiling Any treatment to non-inversively loosen soil below the Ap horizon 

with a minimum of vertical mixing of the soil. Any treatment to fracture and/or 

shatter soil with narrow tools below the depth of normal tillage without inversion 

and with a minimum mixing of the soil. This loosening is usually performed by 

lifting action or other displacement of soil dry enough so that shattering occurs. 

Tilth The physical condition of soil as related to its ease of tillage, fitness as a seedbed, and its impedance to seedling emergence and root penetration. 

Total Maximum Daily Load The maximum quantity of a particular water pollutant that can be discharged into 

(TMDL) a body of water without violating a water quality standard. 

Transport The movement of detached soil material across the land surface or through the 

air by wind or running water. Transport of soil particles in wind is by three 

modes: (l) saltation, (2) suspension, and (3) surface creep. 

Transport capacity The maximum amount of soil material that can be carried by wind or running 

water under given conditions. 

Trap strip A strip of grass or other erosion-resisting vegetation, planted between cultivated 

strips or fields and having sufficient width, height, and density to trap and store 

incoming saltation. Trap strips are usually not tall enough to create significant 

barrier effects. 

Unit plot A standard plot used to experimentally determine factor values in USLE and 

RUSLE. It is arbitrarily defined as being 72.6-feet long, with a uniform slope of 

9 percent, in continuous fallow, tilled up and down the slope. 
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Unsheltered distance The distance across an erodible field, measured along the prevailing wind erosion direction, beginning at a stable border on the upwind side and continuing 

downwind to a non-erodible or stable area, or to the downwind edge of the area 

being evaluated. 

Unsheltered field A field or portion of a field characterized by the absence of windbreaks or barriers and fully exposed to open wind velocity. 

USLE (Universal Soil An empirical model that predicts long-term average annual soil loss for a given 

Loss Equation) set of climatic conditions, on a defined land slope, and under a specified cropping and tillage management system. It has been replaced by RUSLE. 

Vegetative cover factor The effect of vegetative cover in the Wind Erosion Equation. It is expressed by 

relating the kind, amount and orientation of vegetative material present on the 

field to its equivalent in pounds per acre of small grain residue in reference condition Small Grain Equivalent (SGe). 

Vegetative wind barrier Narrow strips of annual or perennial vegetation planted at intervals across fields 

for wind erosion control, snow management, or protection of sensitive crops. 

Barriers have sufficient height and density to create a sheltered zone downwind. 

In the protected zone, wind velocities are reduced enough to prevent saltation 

from beginning. Vegetative barriers may also trap incoming saltation, but this is 

a secondary function. 

Water erosion The detachment, transport, and deposition of soil particles by rainfall and runoff. 

Water table The upper surface of ground water or that level in the ground where the water is 

at atmospheric pressure. 

Wide field Any field with sufficient width to allow the rate of soil flow to reach the maximum that an erosive wind can sustain. This distance is the same for any erosive 

wind. It varies only and inversely with erodibility of the field surface. That is, the 

more erodible the surface, the shorter the distance in which maximum flow is 

reached. 

Windbreak A planting of trees, shrubs, or other vegetation, usually perpendicular or nearly 

so to the principal wind direction, to protect soil, crops, homesteads, roads, etc., 

against the effects of winds, such as wind erosion and the drifting of soil and 

snow. 

Wind erodibility group A grouping of soils that have similar properties affecting their resistance to wind 

erosion. 

Wind erosion The detachment, transport, and deposition of soil by wind. 

Wind erosion direction factor A numerical factor used to calculate the equivalent unsheltered distance. The 

factor accounts for field shape (length/width ratio), field width, preponderance, 

and angle of deviation of the prevailing wind erosion direction from a line perpendicular to the long side of the field or strip. 
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 WEQ (Wind Erosion Equation) An equation used to estimate wind erosion and design wind erosion control systems. Expressed as E=¦(IKCLV) where E is the average annual soil loss expressed in tons per acre per year; I is the soil erodibility; K is the soil ridge 

roughness factor; C is the climatic factor; L is the equivalent unsheltered distance 

across the field along the prevailing wind erosion direction; and V is the equivalent vegetative cover. 

Wind stripcropping A method of farming whereby erosion-resistant crop strips are alternated with 

strips of erosion-susceptible crops or fallow. Erosion-resistant strips reduce or 

eliminate saltation and act as soil traps designed to reduce soil avalanching. 

Strips are perpendicular or nearly so to the direction of erosive winds. 

Wind tunnel A duct in which experimental situations are created and tested by exposure to air 

streams under controlled conditions. Both laboratory and portable field wind tunnels are used in wind erosion research. 

Windbreak A living barrier of trees or combination of trees and shrubs designed to reduce 

wind erosion, conserve energy or moisture, control snow deposition, or provide 

shelter for livestock or wildlife. When used to control wind erosion, windbreaks 

deflect wind forces and reduce wind velocity in the downwind sheltered zone below the threshold required for initiation of soil movement. 

Yield The amount of a specified substance produced (e.g., grain, straw, total dry matter) per unit area.