(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 (sta nding or flat), and spatial distribution. Spatial distribution relates to plant population, row spacing, and row direction relati ve 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 vegetation502–96 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



### Crop

Flax, standing stubbleBenchmark 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 components502–98 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



## 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)502–99 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502



## Subpart 502G References

Alcorn, K. and M.W. Dodd. 1984. Windbreaks for conservation: an annotated bibliography. Pub. No. WB84-01, Calif. Dept. Cons., Div. Land Resource Protection.

Armbrust, D.V. 1972. Recovery and nutrient content of sandblasted soybean seedlings. Agron. Jour. 64:707-708.

Armbrust, D.V. 1977. A review of mulches to control wind erosion. Trans. Amer. Soc. Agr. Engin. 20(5):904-905, 910.

Armbrust, D.V. 1979. Wind- and sandblast-damage to tobacco plants at various growth stages. Tobacco Sci. XXIII:117-119, and Tobacco International 181(20):63-65.

Armbrust, D.V. 1982. Physiological responses to wind and sandblast damage by grain sorghum plants. Agron. Jour. 74:133-135.

Armbrust, D.V., W.S. Chepil, and F.H. Siddoway. 1964. Effects of ridges on erosion of soil by wind. Soil Sci. Soc. of America Proc. 28(4):557-560.

Armbrust, D.V., and L. Lyles. 1985. Equivalent wind erosion protection from selected growing crops. Agron. Jour. 77(5):703-707.

Armbrust, D.V., G.M. Paulsen, and R. Ellis, Jr. 1974. Physiological responses to wind- and sandblast-damaged winter wheat plants. Agron. Jour. 66:421-423.

Bagnold, R.A. 1941. The physics of blown sand and desert dunes. Landon, Chapman, and Hall, 265 pp.

Bondy, Earl, Leon Lyles, and W.A. Hayes. 1980. Computing soil erosion by periods using wind energy distribution. Jour. Soil and Water Conserv. 35(4):173-176.

Chepil, W.S. 1945. Dynamics of wind erosion: I. Nature of movement of soil by wind. Soil Science 60:305-320. Chepil, W.S. 1945. Dynamics of wind erosion: II. Initiation of soil movement. Soil Science 60:397-411.

Chepil, W.S. 1945. Dynamics of wind erosion: III. The transport capacity of the wind. Soil Science 60:475-480.

Chepil, W.S. 1945. Dynamics of wind erosion: IV. The translocating and abrasive action of the wind. Soil Science 61:167-177.

Chepil, W.S. 1946. Dynamics of wind erosion: V. Cumulative intensity of soil drifting across eroding fields. Soil Science 61(3):257-263.

Chepil, W.S. 1946. Dynamics of wind erosion: VI. Sorting of soil material by the wind. Soil Science 61(4):331-340.

Chepil, W.S. 1956. Permanent methods of wind erosion control. The Kansas Crop Improvement Association Certified Seed Directory, pp. 66-67.

Chepil, W.S. 1957. Erosion of soil by wind. 1957 Yearbook of Agriculture (USDA) pp. 308-314.

Chepil, W.S. 1957. Sedimentary characteristics of dust storms: II. Visibility and dust concentration. Amer. Jour. Sci. 255:104-114.

Chepil, W.S. 1957. Width of field strips to control wind erosion. Kans. Agr. Expt. Sta. Tech. Bul. 92.

Chepil, W.S. 1958. Soil conditions that influence wind erosion. USDA Tech. Bul. No. 1185.

Chepil, W.S. 1959. Estimations of wind erodibility of farm fields. USDA, ARS, Prod. Res. Rpt. No. 25.

Chepil, W.S. 1959. Stripcropping for wind erosion control. Soil Conservation Magazine 24:153-156.

Chepil, W.S. 1959. Wind erodibility of farm fields. Jour. Soil and Water Conserv. 14(5):214-219.

Chepil, W.S. 1960. Conversion of relative field erodibility to annual soil loss by wind. Soil Sci. Soc. of America Proc. 24(2):143-145.502–100 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Chepil, W.S. 1960. How to determine required width of field strips to control wind erosion. Jour. Soil and Water Conserv. 15:72-75.

Chepil, W.S. 1962. Stubble mulching to control erosion. Proceedings of the Great Plains Council Workshopon Stubble Mulch Farming, Lincoln, Nebraska, February 8-9, 1962.

Chepil, W.S. 1963. Climatic index of wind erosion conditions in the Great Plains. Soil Sci. Soc. Amer. Proc. 27(4):449-452.

Chepil, W.S. 1963. The physics of wind erosion and its control. Adv. in Agronomy 15:211-302

Chepil, W.S. 1964. In the Great Plains, prevailing wind erosion direction. Jour. of Soil and Water Conser. 19(2):67-70.

Chepil, W.S. 1964. Wind erodibility of knolly terrain. Jour. Soil and Water Conserv. 19(5):179-181.

Chepil, W.S., F.H. Siddoway, and D.V. Armbrust. 1962. Climatic Factor for estimating wind erodibility of farm fields. Jour. Soil and Water Conserv. 17(4):162- 165.

Chepil, W.S. and N.P. Woodruff. 1954. Estimations ofwind 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 erosion. Soil Sci. Soc. Amer. Proc. 27(1):86-89.

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. 27(5):1405-1410.

Cole, George W., L. Lyles, and L.J. Hagen. 1983. A simulation model of daily wind erosion soil loss. Trans. Amer. Soc. Agr. Engin. 26(6):1758-1765. Durar, A.A. 1991. Simulation of soil-water dynamics for wind erosion modeling. Ph.D. diss. Kansas State Univ., Manhattan, KS (Diss. Abstr. 91-28491).

Durar, A.A., J.L. Steiner, S.R. Evett, and E.L. Skidmore. 1995. Measured and Simulated Surface Soil Drying.

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. 30 th 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):622-625.502–101 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

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. Jour. Range Mgmt. 33(2):143-146.

Lyles, L. and R.K. Krauss. 1971. Threshold velocities and initial particle motion as influenced by air turbulence. Trans. Amer. Soc. Agr. Engin. 14(3):563-566.

Lyles, L. and N.P. Swanson. 1976. Advances in wind and water erosion control. Proc. of Conservation TillageWorkshop, 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. Jour. Soil and Water Conserv. 37(6):344-347.

Lyles, L., and N.P. Woodruff. 1960. Abrasive action of windblown soil on plant seedlings. Agron. Jour. 52:533-536.

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 Agricultural Lands, American Soc. of Agron., 964-973.

Niles, J.S. 1961. A universal equation for measuring wind erosion. Agricultural Research Service Special Report 22-69.

Precheur, R., J.K. Greig, and D.V. Armbrust. 1978. The effects of wind and wind-plus-sand on tomato plants ( Lycopersicon esculentum L.). Jour. Amer. Soc. Hort. Sci. 103(3):351-355.502–102 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

Renard, K.G., G.R. Foster, G.S. Weesies, D.K. McCool, and D.C. Yoder, coordinators. 1997. Predicting SoilErosion by Water: A Guide To Conservation Planning With the Revised Universal Soil Loss Equation(RUSLE). U.S. Department of Agriculture, Agriculture Handbook 703, 404 pp.

Siddoway, F.H., W.S. Chepil, and D.V. Armbrust. 1965. Effect of kind, amount, and placement of residue on 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.

Skidmore, E.L. 1966. Wind and sandblast injury to seedling green beans. Agron. Jour. 58:311-315.

Skidmore, E.L. 1976. A wind erosion equation: development, application, and limitations. In ERDASymposium 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, 11 th 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 predictingsoil 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.

Stallings, J.H. 1951. Mechanics of wind erosion, USDA, Soil Conservation Service; SCS-TP-108.

Stoeckeler, J.H. 1962. Shelterbelt influence on Great Plains field environment and crops: a guide for determiningdesign and orientation. USDA, Forest Service, Production Research Report No. 62.

Sweeney, Tim A. 1984. Wind erosion estimator for Colorado. USDA, Soil Conservation Service.

Thornthwaite, C.W. 1931. Climates of North America according to a new classification. Geog. Review 21:633-655.

van Eimern, J. 1961. Effects of windbreaks and shelterbelts.Report of Working Group of Commission for Agricultural Meteorology, World Meteorological Organization, Geneva, Switzerland.

Wagner, L.E., and Hagen, L.J. 1992. Relationship between shelter angle and surface roughness and cumulative sheltered storage depth. In J. Karacsony and G. Szalai(eds.) Proc. of the International Wind Erosion Workshop of CIGR Budapest, Hungary, v. Section I, 10 pp. (Conference Proceedings)

Williams, C.L. 1983. Procedure for adjusting the climaticfactor for applying the wind erosion equation on irrigated land. USDA, Soil Conservation Service.

Williams, J.R. and K.G. Renard. 1983. Assessments of soil erosion and crop productivity with process models (EPIC). Unpublished draft.

Woodruff, N.P. 1975. Wind erosion research—past, present, and future. Proc. of 30 th Annual Meeting of Soil Conserv. Soc. Amer., August 10-13, 1975, San Antonio, Texas, pp. 147-152.502–103 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Wind Erosion Part 502

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.

Woodruff, N.P., and F.H. Siddoway. 1965. A wind erosion equation. Soil Sci. Soc. Amer. Proc. 29(5):602-608.

Woodruff, N.P., and F.H. Siddoway. 1973. Wind erosion control. Proc. of the National Conservation Tillage Conference, Des Moines, Iowa, March 28-30, 1973, pp. 156-162.

Woodruff, N.P., and W.S. Chepil. 1956. Implements for wind erosion control. Agr. Engin. 37:751-754, 758.

Woodruff, N.P., L. Lyles, J.D. Dickerson, and D.V.Armbrust. 1974. Using cattle feedlot manure to control wind erosion. Jour. Soil and Water Conserv. 29(3):127-129.

Woodruff, N.P., L. Lyles, F.H. Siddoway, and D.W. Fryrear. 1972. How to control wind erosion. USDA, Agricultural Research Service, Agr. Inf. Bul. No. 354, 22 pp.

Woodruff, N.P., J.D. Dickerson, E.E. Banbury, A.B. Erhart, and M.C. Lundquist. 1976. Selected trees and shrubs evaluated for single-row windbreaks in the Central Great Plains. USDA, ARS-NC-37, 15 pp.

Zingg, A.W., and N.P. Woodruff. 1951. Calibration of a portable wind tunnel for the simple determination of roughness and drag on field surfaces. Agron. Jour. 43:191-193.503–i (190-V-NAM, 3rd Ed., October 2002) 

# 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 dev elopment)

................................................... 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(190-V-NAM, 3rd Ed., October 2002) 503–ii190-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 somerotations 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 potentialfor 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 workingwith 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 pestmanagement, 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 croppingsystem. 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 forcesduring 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 surfacecover 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 cropshelp 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 qualit y — 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) National Agronomy Manual Crop Production Part 503

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 cropresidue 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 onthe 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 practicesResidue 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 controlshould utilize undercutting implements that minimize residue burial.

Ridge-till — Managing the amount, orientation, and distribution of crop and other plant residues on the soil surfaceyear-round, while growing crops on preformed ridges alternated with furrows protected by crop residue. The soil is503–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Crop Production Part 503

left undisturbed from harvest to planting except for nutrient injection. Planting is done in a seedbed prepared on ridgeswith sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between ridges. Weed control isdone 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 surfaceyear-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 orsome other system that retains little if any residue, is an important part of a crop production system. Crop response tovarious 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 adry 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 lefton 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 inversiontillage 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 isexcessive, 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 disturbedto 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) National Agronomy Manual Crop Production Part 503

Fertilizer placement — Starter fertilizer (nitrogen and phosphorus) is generally recommended to help overcome the affects of lower soil temperatures at planting time. Iffertility levels (P, K, and pH) are at maintenance levels before switching to a conservation tillage system, fertilityshould 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 thesoil 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 andcrop 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. Achange 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 cropshas 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 potentialinsect pressure, but management addresses this.

Disease control — Residue on the soil surface offers the potential for increased disease problems. However, thereare 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 isreduced. 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 farmmore acres than conventional tillage producers without additional labor because of the increased efficiency.503–5 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Crop Production Part 503



## Subpart 503C Nutrient management

(Under development) 

## Subpart 503D Pest management

(Under development)503–6 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Crop Production Part 503



## Subpart 503E Crop residue

503.40 Benefits of managing crop residue

Crop residue management is paramount to improving soilhealth. 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 bemaximized. 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 componentof 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 apH near neutral (pH 7.0), plant nutrients are most available. In addition, organic matter increases soil aggregatestability 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 CO 2 in just 19 days after moldboard plowing wheat residue as was produced by the crop. Carbon is the key component ofsoil 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 directlyrelated 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. Undisturbedroot 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 Direction503–7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Crop Production Part 503

The locations in the field where the line is stretchedout 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 beknown rather than the percent cover. Figure 503-3 illustrates the relationship between residue weight and percentresidue 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 biomassneeds 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 residue503–8 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Crop Production Part 503



## 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 Date503–10 (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 2345190-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 504504–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 Water Management Part 504190-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 soilprofile. 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 soilfrom 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 seasonbecause 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 orwormholes, 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 textureSoil 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 2mm 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. Rockfragment 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 ofsand, 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 cyclesof 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 clay504–2 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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 asreducing 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, resistdispersion 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 fieldcapacity water content, expressed as grams per cubic centimeter (g/cc) or pounds per cubic foot (lb/ft 3 ). 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 matterSoil 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, soilbulk 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 ofsoil-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 hasdrained because of gravity. For coarse textured soil, drainage occurs soon after a rain event because of relativelylarge 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,504–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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 canretain 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 ina 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 hasdrained 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 plantmoisture stress during hot daytime periods and yet have adequate soil moisture. In the laboratory, permanent wiltingpoint 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) National Agronomy Manual Water Management Part 504

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 isextracted, 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. Ofthese, texture is the predominant factor in mineral soil. Because of the particle configuration in certain volcanic ashsoil, the soil can contain very high water content at field capacity levels. This provides a high available water capacityvalue. 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 SoilSurvey 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 1.8504–5 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504



### (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 fora 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 develop ment, oxygen content, water movement and availability.



### (h) Soil depthSoil 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 restrictdownward water movement. For example, coarse sand underlying medium or fine textured soil requires saturation at the textural interface before substantial amounts of waterwill 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 overhardpans 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 becauseof 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 toroot 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 beenrock, 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, andcarbon 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 thesoil 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) National Agronomy Manual Water Management Part 504

Cation exchange capacity (CEC) is the total amount of cations held in a soil in such a way that they can be removedby 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 lowCEC hold fewer cations and may require more frequent applications of fertilizers than soils with high CEC. See Soilsurvey 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, EC

e , as the basis:

Salinity EC

e 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 wateravailable 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 extractcorrected 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 butalso 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 adesirable 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 (EC e x10 3 ) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 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 capacity504–7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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 aminimum 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 atconverting 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 earlyseason maturity, avoiding environmental stresses that reduce yield potential.

Other management factors that limit maximum productivityare 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 (ET c ), sometimes called crop consumptive use, is the amount of water that plants use in transpiration and building cell tissue plus water evaporatedfrom 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 ET c 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) isprobably the most commonly used. Little long-term historical data outside of a few ARS and university research stations are available.

(b) Estimated crop evapotranspiration (ET c ) More than 20 methods have been developed to estimate the rate of crop ET based on local climate factors. The simplestmethods 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 earlierreference crop research, mainly in the West, used 2-yearold alfalfa (ET r ). With grass reference crop (ET o ) known,ET estimates for any crop at any stage of growth can be calculated by multiplying ET o by the appropriate crop growth stage coefficient (k c ), usually displayed as a curve or table. The resulting value is called crop evapotranspiration (ET c ).The following methods and equations used to estimate reference crop evapotranspiration (ET o ). ET o methods and504–8 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

equations are described in detail in the Engineering FieldHandbook, Part 623, Chapter 2, Irrigation Water Requirements (1990). The reference crop used is clipped grass. Crop coefficients are based on local or regional growthcharacteristics. 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, andFAO 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, atemperature-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. TheFAO 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 cancause 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 504-3.504–9 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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) National Agronomy Manual Water Management Part 504

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 W hen 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.504–11 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

Table 504-4 Depth to which roots of mature crops will extractavailable 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 environmentfor 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 9The 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 characteristicsand 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) National Agronomy Manual Water Management Part 504

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 availablesoil 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 developmentand may be the controlling factor for soil moisture availability.

Variations and inclusions are in most soil map units, thusuniformity 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, awater 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 farmequipment 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 exceptthrough 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 occurand 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 0to 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.504–13 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504



## 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 decreaseevaporation 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 canopycloses. 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 andnot 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, thetwo soil surfaces show little difference in cumulative evaporation. However, with larger more frequent rains, less evaporation occurs from soil protected by surface residuethan 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. Shallowincorporation 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 thetime 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 developmentand 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 ofthe 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) National Agronomy Manual Water Management Part 504

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 decreasedby 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 by1.6 inches. Increasing the snow catch on a field can also increase spring melt runoff depending on the early spring soilinfiltration 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 coverageto 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 oncrop 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 theUnited 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 increasedsubsequent grain sorghum the following year. Similar results of water storage under high residue conditions, shownin 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 andstored as soil water), and small grain yields. However, fallow efficiencies up to 40 percent were reported in the1970’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 themoisture 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 properlyassessed 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 loweryields 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.504–15 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

greater than conventionally tilled systems. The initial yieldreductions 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 tohigh residue systems and may need to be managed with limited till systems such as ridge-till or fall and spring strip-tillmethods. 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 intensityImproving the relative efficiency of water use in crop production systems has been a major goal in achieving moreproductive modern crop production systems. Reducing water losses in cropping systems by changes in tillage systems, residue management, crop selection and sequence hasachieved 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 waterfor 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 thegrowing 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 residueorientation, 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 increasedWUE 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 producersin 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 tomaximize 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 thenorthern Great Plains. Flexible cropping is defined as seeding a crop when stored soil water and rainfall probabilitiesare 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) havedeveloped soil water guidelines and precipitation probabilities for barley and spring wheat for f lexible 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 seasonalneeds 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 a t harvest growing season precipitation 

## ( ) + 

# ( )504–16 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

various locations includes yield water-use-production functions for winter wheat, spring wheat, barley, oats, millet, corn, sunflower, dry beans, canola, crambe, soybean, andsafflower given soil moisture and rainfall-probability information (Brown and Carlson 1990; Vigil et al. 1995; Nielson1995). 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 Average504–17 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504



## 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 surfacedownslope 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 othersaline 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 adventof 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 tomove 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 movesinto 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 saltsand 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 waterplus 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 areimportant 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 croppingsystem 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 increasesconsiderably 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 rechargearea must be determined to be successful. Most recharge areas are within 2,000 feet and many are within 100 to 600feet of the discharge area, depending on the geology involved.504–18 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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 arehigher 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 expanddownslope, 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 cropplants. 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 isone 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 selectedagricultural 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 rootzone 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)504–19 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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 itreaches 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 disposalis difficult because of physical or legal limitations. However, before any control measures are implemented anevaluation 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 rootzone. 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 oftenthe 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 effectivelydraw 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 storedsoil 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) havedeveloped 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 seasonalneed 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 GreatPlains 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 inthe rotation utilize residual subsoil moisture below the normal rooting depth of small grains while disrupting diseaseand 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 beseeded 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 theseep area can begin. Crop selection is important when initiating crop production on the discharge area. In the northernGreat 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) National Agronomy Manual Water Management Part 504

Another approach that can be used on discharge areas is to manage salt-tolerant grasses seeded on the area. If the watertable 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 isbelow 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 movementthrough 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 indepth 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 shouldbe 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 probabilitiesfor 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 relatedto stored soil water and growing season rainfall. Montana State University Agricultural Experiment Station Special Report 35, 22 p.504–21 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

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. Runoffand 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 inthe 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-yieldrelations 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 placementeffects 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. 42:486.504–22 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Water Management Part 504

Unger, P.W., and A. F. Wiese. 1979. Managing irrigatedwinter 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.506–i (190-V-NAM, 3rd Ed., October 2002) 

# 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 506–4506–1 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Plant Attributes Part 506 

# 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 accomplishedwith grasses enhanced by a legume component for some nitrogen generation. Landscaping with shrubs and trees blend structures into surrounding landforms. Species and cultivarselection 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 speciesand establishment techniques. Water as rainfall or snowmelt, spring ice flows in streams, surface runoff, or seepageareas 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 settingas 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 areascan 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 seedingof constructed structures. It may be desirable to select species from several successional stages to include in the revegetation plan. Using species that grow on surroundingareas will help blend the structure into the landscape. Caution is needed when doing this, because local species maynot 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) National Agronomy Manual Plant Attributes Part 506

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. Forexample, 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 anticipatedcondition. 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 plantsor 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 finalgrading is finished and site conditions warrant this approach.506–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Plant Attributes Part 506



### 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 seedor 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 plantingdates. Spring seedings may be adequate where normal rainfall is available. However, the effect of annual weeds and midsummer droughts should be considered. Fall seedings inmany 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 canhelp 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 theplant 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; howeverwider ratios are acceptable. High pH or saline soil may require gypsum (CaSO 4 .2H 2 O) 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 thesize 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 seedby 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 thebulldozer 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) National Agronomy Manual Plant Attributes Part 506

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 specialfeatures 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 structuresor other critical areas. Mulch cover will help maintain favorable moisture conditions, prevent soil erosion by wateror 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 alsogrow 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 dispers ing 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.506–5 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Plant Attributes Part 506

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 sometimesdictate which mulch material is used. Many latex compounds and commercial products will control erosion andhold seed in place under some moisture and temperature regimes.

Competition is a problem with warm-season grassplantings. 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 thespring 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. Thecost 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 anchormulch 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 espe cially critical on droughty soils and for spring seedings. 

### 506.04 Disturbed land

(a) Planning principles Vegetative treatment of disturbed land areas requires someplanning 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 usedto protect areas before establishing more permanent and desirable species, or temporary wind breaks (wind fence) maybe 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 causeneeds 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, useof 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) National Agronomy Manual Plant Attributes Part 506

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 solutionis 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 betolerant 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 savingthe 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 materialwith 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 tothe 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.506–7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Plant Attributes Part 506



## Subpart 506B Suitability for crop production systems

506.20 Suitability for crop production

Crop selection in a properly designed rotation is critical tomaximize rotational benefits. A properly designed crop rotation provides an excellent tool in breaking insect, weedand 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 croplandacres 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 whileplacing greater reliance on crop selection and variety or hybrid characteristics. Conservation tillage or no-till methodsrequire changes in machinery, fertility programs, and pesticide use. In addition, crop and seed selection must also be reevaluated. Selecting a more desirable variety or hybridshould 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: varietyor 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 surfaceresidue, the importance of desirable variety or hybrid characteristics varies among crops. Some important common characteristics to consider are high-quality seed, the rightmaturity 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 maturitymay 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 ofgreater 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 thathave 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 astronger 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 importantdepending 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 Plant Attributes Part 506



### (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 ofresidue 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 cropssuch 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 fromthe 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 standingstubble 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 sensitiveto 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 durableresidue 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 ofdecay 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 survivalof 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 canbe 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.506–9 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Plant Attributes Part 506



## Subpart 506C References

American Nursery and Landscape Association. American Standard for Nursery Stock. 1997.57pp.507–i (190-V-NAM, 3rd Ed., October 2002) 

# 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 conservationmanagement 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 madeof 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 casesa 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 themajor cropland conservation management systems

Practices/treatments used to address the resource concerns about cropland situations often have complimentary effectson 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 effectiveto 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 thepractices/treatments being considered on the total production system.507–2 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems 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, nutrientmanagement, 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 (aresource assessment) and determine the producer’s capabilities, limitations, and objectives. This will establish thebaseline 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 maybe 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 oftendifficult. The traditional method used to assess the economics of various agronomic practices is to compare differentmethods 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 tousing 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.507–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems 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 requirements507–4 (190-V-NAM, 3rd Ed., October 2002) National Agronomy 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 theproducer’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 watersource 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 drylandsystems (Stewart 1988; Stewart and Burnett 1987). Several investigators have proposed various definitions of dryland or dry farming (Duley and Coyle 1955; Hargreaves1957; 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 stressof 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 drylandOram (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 wildlife507–5 (190-V-NAM, 3rd Ed., October 2002) National 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 summerfallow. There are, however, a number of general distinctions other than crop adaptability that can be made betweenthe 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 principlesIn natural ecosystems the successional process advances until something limits it. Moreover, as succession continues, the complexity, diversity, and stability increases (Savory1988). 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 theeffectiveness, 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 drylandagroecosystems. The successional process in a natural system is analogous to the sequence of crops in rotation. Likenatural 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 asthe 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 4inches (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 theratio 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 GreatPlains, 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 < 0.75507–6 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems 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. Itincludes 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 tospread 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 diseasecycles; and potential for effective application biological control strategies.

Thirdly, the crop rotation that has sufficient intensity anddiversity must be managed properly. The proper management levels include using tillage and planting methods thatreduce 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 andcool-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-usevalues, 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 SoilConservation 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 intervalswithin 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 betweenoperational 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.507–7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems Part 507

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

Okla homa Te xas New Me xico Colorado Wyoming Idaho

Nevada California Oregon

Arizona Utah507–8 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems Part 507

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.507–9 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Cropland Conservation Management Systems Part 507

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 technolog ies 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 Bar ley (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 management507–10 (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, andbulk 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 NorthernGreat 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.508–i (190-V-NAM, 3rd Ed., October 2002) 

# 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 be nchmark con dition

............................................................................... 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 508–11508–1 (190-V-NAM, 3rd Ed., October 2002) 

# 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 Soils Part 508



## 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 NationalTechnical 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 foruse 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 theproblem 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. TheSoil 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 changequalitatively, 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. Climateat each location is expressed as average monthly precipitation and average monthly temperature.



### (d) Components of the Soil Conditioning IndexA 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.508–3 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 or ganic 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 systemsThe 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 suchsoil 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 managementsystems 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 thesoil 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 usingRUSLE 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 bycontrolling 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 onorganic 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 variables508–4 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 theresearch 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 materialreturned 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 tomaintain 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. TheOrganic 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. Theseare 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-cropseason 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 ofcomparative 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, notfertilized) and System 9 (wheat-cotton-sorghum, fertilized, manure added) are the basis for the conclusions in this paper.508–5 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

System 8 produced an average of 3,865 pounds of aboveground crop residue per year, and percent organicmatter 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 valuesTo 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 decompositioncoefficient (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 ofCrop 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 Soils Part 508

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:508–7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 of5,719 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 thatexisted 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 ofone 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) National Agronomy Manual Soils Part 508



### (c) The Soil Disturbance Rating at RennerThe 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 valuesEach 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 whenabove 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. Thesubfactor 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.508–9 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 xresidue 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 Soils Part 508



### 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 beplanned. 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 = +0.39The SCI value is positive. Soil organic matter is predicted to be increasing, and this alternative is suitable.508–11 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508



### 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 ranfor 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 wasestimated 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 when7,139 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 whenonly 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 residueamounts. 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 followingspring 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 MatterDynamics. 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 Soils Part 508

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: 831-835.508–13 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 factors508–14 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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/508–15 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 subfactor508–16 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 -3.00508–17 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 -3.76508–18 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

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 research508–19 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508

Crop Crop name Harvest Yield Pounds Residue: Above S urface 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 E508–20 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508508–21 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508508–22 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Soils Part 508



## 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 reserve509–i (190-V-NAM, 3rd Ed., October 2002) 

# Data Management

Contents: 

# Part 509

Subpart 509A Introduction and responsibilities 509–1 509.00 Background

...................................................................................................... 509–1 509.01 Respons ibilities ................................................................................................ 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 ....................................................................... 509–2190-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 sharingand 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 ofvarious 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 ofnational policy and instructions pertaining to data management.

The cooperating scientists for water and wind erosion are responsible for developing and maintaining data for theimplementation 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 is responsible for developing and maintaining databases for assistingStates 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 andOperation 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 contacts serves 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 Data Management Part 509



## 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 thedatabase 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 datarecords 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 recordsneeded for the local area will be downloaded from the official NRCS Climate Database onto field office computers.

(2) Either simulated climate data (using WINDGEN andCLIGEN 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 InformationSystem (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 theAgricultural 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 areapplied in quantities that are a function of the nutrient content of plant biomass.

The national nutrient management specialist will work withthe 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 resultslargely 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. 

# GlossaryGlossary –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/cm 3 ) or megagrams per cubic meter, (Mg/m 3 ).

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 onlong-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 oflime (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 CaCO 3 . 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 ClodA 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, andgenerally 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 whenthe 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 issealed. 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 gravelor 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 soilparticles. 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 (EC e ) 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 filledwith 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 siltcontent 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.Glossary –5 (190-V-NAM, 3rd Ed., October 2002) 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 geologicaltime 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.

FertilizerAny 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 (P 2 O 5 ) equivalent, and watersoluble potash (K 2 O) 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 topographiccycles, 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

.Glossary –6 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 particlesto 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 knollerodibility 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 erosionand other causes and the difficulties in land use owing to physical land characteristics, including climate.Glossary –7 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 plantproduction 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

.Glossary –8 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 soiland/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 tilledor 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.Glossary –9 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 of1.0 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 (R eq ) 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.Glossary –10 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

Relative field erodibility An index of relative erodibility under field conditions. Wind tunnel erodibility isadjusted 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.

RillA 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.Glossary –11 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

Sapric organic soil materials The most highly decomposed of the organic materials, having the highest bulkdensity, 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 grainstalks 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 areawith 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.Glossary –12 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

Surface creep Soil movement by wind in which the coarser fractions are transported by rollingand 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 inpreparing 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 A p 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.

TilthThe 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.Glossary –13 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 thefield 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.Glossary –14 (190-V-NAM, 3rd Ed., October 2002) National Agronomy Manual Glossary

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 distanceacross 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 airstreams 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, windbreaksdeflect wind forces and reduce wind velocity in the downwind sheltered zone below the threshold required for initiation of soil movement.

YieldThe amount of a specified substance produced (e.g., grain, straw, total dry matter) per unit area.