bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Microbial and Biochemical Changes Associated with Reduced Tillage
Authors: Doran John W.
Published: July 2010

The physical, chemical, and biological soil environment for reduced or no‐till farming differs greatly from that for conventional tillage. Evaluation of the soil microbial and biochemical environment greatly aids predictions of N availability to crop plants and in optimizing management practices for reduced and no‐till soils.

Surface soils from long‐term no‐till and conventional tillage plots at seven U.S. locations were characterized for microbial and biochemical components. The counts of aerobic micro‐organisms, facultative anaerobes, and denitrifiers in the surface (0–7.5 cm) of no‐till soils were 1.14 to 1.58, 1.57, and 7.31 times higher, respectively, than in the surface of plowed soil. Phosphatase and dehydrogenase enzyme activities and contents of water and organic C and N in the surface of no‐till soil were also significantly higher than those for conventional tillage. However, at the 7.5‐ to 15‐cm and 15‐ to 30‐cm depths these trends were reversed and microbial populations, enzyme activities, and water and organic C and N contents were the same or higher for conventional tillage than for no‐till. The trends in microbial populations with both tillage treatments were closely paralleled by soil enzyme activities and were also regulated by soil pH and levels of organic C and N. The surface 0‐ to 7.5‐cm of no‐till soil contained more potentially mineralizable N—20 to 101 kg/ha—than did that of plowed soils. This increased labile N reserve is apparently related to the higher microbial biomass present under no‐till soils.

Maximum aerobic microbial activity with conventional tillage extends to a greater depth than with no‐till. Microbial populations under no‐till decrease rapidly below the 7.5‐cm depth. At the 7.5‐ to 15‐cm depth counts of aerobic microor‐ganisms and nitrifiers were 1.32 to 1.82 times higher on the conventionally tilled soils. However, counts for facultative anaerobes and denitrifiers were 1.23 to 1.77 times higher for no‐till soil. Also, the proportion of the total aerobic population represented by facultative anaerobes and denitrifiers for no‐till was twice that for conventional tillage. Consequently the potential rate of mineralization and nitrification is higher with conventional tillage while that for denitrification is higher with no‐till.

Microbial population counts and the relative abundance of various microbial types suggests that the bochemical environment of no‐till soils is less oxidative than that under conventional tillage. Changes in tillage and fertilizer management practices required for no‐till soils should reflect the increased potential for immobilization of surface applied N and the lower levels of plant available NO3‐ as compared with those under conventional tillage.
Sulfur‐coated Urea and Urea Compared as Nitrogen Sources for Irrigated Corn
Authors: Sander D. H. , Moline W. J.
Published: July 2010

Sulfur‐coated urea (SCU) was compared to urea (U) to determine their value as N fertilizers for irrigated corn (Zea mays L.) production. Two soils were studied from 1970 through 1972, Cass sandy loam (Fluventic Haplustoll) and Holder silty clay loam (Udic Arguistoll). Comparisons were made with different rates of the two fertilizers and the results interpretated in terms of yields, N uptake, and residual NO3‐‐N in the root zone.

Results of the study indicated little difference between the performance of the two N fertilizers in terms of grain, forage yields, or in N uptake although N from SCU tended to be less available than from U. After 3 years of application, more NO3‐‐N was found in the root zone with SCU than U. This was especially apparent on the fine‐textured Holder soil and to a lesser extent on the sandy Cass soil. While the increased NO3‐‐N found after 3 years in the root zone did not affect fertilizer N need, data does suggest that SCU has potential for increased N efficiency by reducing leaching under moderate leaching situations.

The data emphasizes the need for more accurate N recommendations that will access NO3‐‐N in the root zone, N mineralization potential of the soil, and N in the irrigation water. It was possible to grow 92 to 94% of maximum corn yields without losses of N to the groundwater.
Evaluation of EDTA‐extractable Phosphorus as a Soil Test Procedure
Authors: Onken Arthur B. , Matheson Richard , Williams E. Jay
Published: July 2010

Diagnostic techniques involving complex systems such as soils and plants are rarely infallable. Thus, a constant research effort is underway to improve decision making by adding information to presently used methods and/or developing new techniques.

Predicting crop response to applied P requires a suitable extractant and a model that satisfactorily describes the yield response. A number of extractants and yield response models have been proposed and evaluated over the last 50 years. The objectives of the research reported here were to (i) develop a satisfactory procedure for extraction of P using one of these extractants (EDTA), (ii) evaluate this procedure using current mathematical and statistical models, and (iii) compare this procedure (by use of the models) with current procedures in order to determine if decision‐making could be improved.

Soil samples of four soil series from 23 location‐years of irrigated fertilizer response trials with grain sorghum (Sorghum bicolor L. Moench) were extracted with ammonium acetate, sodium bicarbonate, and EDTA. Extraction time for EDTA was established utilizing soils from two locations of known P response. The extraction procedures were evaluated by the following models: linear, quadratic, logarithmic, Mitscherlich, and the Cate‐Nelson analysis of variance method.

For the soils used, an extraction time for EDTA of 1.0 hour was established as a reasonable compromise between ability to distinguish with a high degree of certainty between soils on a P needs basis and an extraction time suitable for a routine analysis procedure. The Cate‐Nelson ANOVM (Analysis Variance Method) for partitioning soils for expected P response was found to be superior to the other models tested for all three extractants. For five of six models tested, the EDTA‐extraction procedure resulted in better predictability of P fertilizer needs than either the ammonium acetate or sodium bicarbonate extraction procedures. The combination of the EDTA‐extraction procedure and the Cate‐Nelson three‐class model resulted in the highest R2 value (0.71) of all combinations of models and extractants evaluated.
Effects of Banded and Residual Fertilizer Phosphorus on Dryland Spring Wheat Yield in the Northern Plains
Authors: Alessi J. , Power J. F.
Published: July 2010

Although phosphate fertilizers are commonly applied either by surface broadcasting or banding with the seed to dryland spring wheat (Triticum aestivum L.), data are limited on the residual effects of previous fertilization on plant growth and grain yield. This is especially true in regions where there are drought periods during the growing season. Therefore, the residual effects of P fertilization on spring wheat grown on Parshall fine sandy loam (Pachic haploboroll) were determined in a field study at Mandan, North Dakota. Fertilizer rates of 0, 20, 40, 80, and 160 kg P/ha were broadcast in 1968 to establish several levels of residual P in the soil. In 1969 subplots were established on each of the broadcast P plots, to which P was banded with the seed at the rate of 15 kg/ha either (i) repeated to the same subplot each year for 6 years, (ii) on a new subplot (previously unfertilized) each year, or (iii) not at all.

After 6 years of cropping, the residual effects of 160 kg P/ha broadcast in 1968 resulted in an average increase in grain yields of about 10% (200 kg ha−1 year−1. Banding of P with the seed resulted in an additional 10% increase in grain yields, with about half this increase due to current‐year banding and about half due to residual effects of banding in previous years. Residual effects of banding and broadcast treatments were additive, with little interaction. Average plant P concentrations (1969–1974) were significantly increased by both the P initially applied and by the banded‐P treatments at all growth stages. NaHCO3‐soluble P levels in the 0‐ to 15‐cm soil depth decreased with time for all broadcast P treatments, but repeated banding of P on the same plot each year increased NaHCO3‐soluble P levels during the 6 years of study. An exception was the 160‐kg P/ha broadcast‐P treatments where NaHCO3‐soluble P level was still decreasing. The addition of banded P decreased percent fertilizer P recovery in grain, especially when P was repeatedly banded each year on the same site. Since yield increases resulted from banding P with the seed even when soil test levels were high, it was concluded that banding P may be beneficial for spring wheat in the cool springs of the northern Great Plains no matter what soil test level is present.
Minesoil Genesis and Morphology in a Spoil Chronosequence in Montana
Authors: Schafer W. M. , Nielsen G. A. , Nettleton W. D.
Published: July 2010

Minesoils from 1 to 50 years old in southeastern Montana were compared to adjacent natural soils. Due to their maninfluenced origin, minesoils had several unique morphological properties which made them difficult to classify. Weakly consolidated rock fragments, common in minesoils, acted in part like soil in supplying water and in part like rock in preventing root penetration. Low chroma mottles were common in minesoils without the influence of a high water table. Organic C content from 0–10 cm soil depth reached levels found in natural soils within 30 years, but will not reach equilibrium at 20–50 cm for 400 years or more. Litter accumulation was common under pioneer vegetation on minesoils resulting in wide C/N ratios; reduction in available N; successional stagnation; and reduced plant community production. Soluble salts were leached downward in minesoils in tens of years, but thousands of years will probably be required for carbonate removal to occur in the upper 50 cm. Soil structure developed more quickly near the soil surface (10–50 years) than below 10 cm (50–200 years), and was attained sooner in clayey than in sandy minesoils. Many characteristics of minesoils are expected to always be different from natural soils. Well‐designed minesoils can be highly productive, however, in a few cases perhaps exceeding the potential of natural soils.
Wheat Straw Composition and Placement Effects on Decomposition in Dryland Agriculture of the Pacific Northwest
Authors: Douglas C. L. , Allmaras R. R. , Rasmussen P. E. , Ramig R. E. , Roager N. C.
Published: July 2010

Field‐measured characteristics of cereal residue decomposition under semiarid dryland agriculture are needed for systematic management of residue in reduced tillage systems. Straw placement, loading rate, and nutrients are all important characteristics. Straw composition and placement, at a moderate loading rate, were evaluated for their effects on decomposition. Wheat straw with three different N and S contents was contained in fiberglass cloth bags which were placed above, on, and below the soil surface to simulate, respectively, standing stubble, straw matted on the surface, and straw plowed under. Weight loss and changes in N and S content were measured during a 26‐month period in a winter wheat (Triticum aestivum L.)‐pea (Pisum sativum L.) rotation. After 26 months exposure residue losses were 25, 31, and 85% for placements above, on, and in the soil, respectively. Above‐surface and on‐surface straw showed a nearly constant decomposition rate with little response to weather variables; decomposition rate of buried straws responded to both soil moisture and temperature. Mineralization or immobilization of N and S were sensitive to placement and initial nutrient content of the straws. Net N mineralization in buried straw varied from 17 to 2 kg N/ha as straw composition varied from 0.78 to 0.20% N. When placed above or on the surface net N mineralizations ranged from 6 to −4 kg N/ha as straw varied from 0.78 to 0.20% N. Net S mineralization paralleled N mineralization, however, magnitudes were smaller. First‐order rate constants for weight loss successfully characterized the placement and straw composition effects.
Effects of Fire on Soil Nutrients in Clearcut and Whole‐tree Harvest Sites in Central Michigan
Authors: Adams Paul W. , Boyle James R.
Published: July 2010

Surface‐mineral soil samples from adjacent northern red oak (Quercus rubra L.)‐bigtooth aspen (Populus grandidentata Michx.) sites harvested by contrasting methods were evaluated for available Ca, Mg, K, P, and total N before and after a wildfire. Abundant slash from clearcutting contributed to significant and persistent increases in Ca, Mg, K, and N following fire. Sample data grouped by variations in estimated surface burn intensity revealed no significant differences, indicating that slash windrows did not appreciably localize nutrient increases. Minimal residues from whole‐tree harvest released smaller quantities of Ca, Mg, and K, and total N exhibited no significant change. Significant increases in soil Ca, Mg, K, and P at both sites occurred within a month after burning. Five months after the fire, soil Ca, Mg, K, and P at both sites generally decreased, in some cases to prefire levels. Cation leaching losses from the surface soils, monitored by porous cup lysimeters at the 1‐m depth, increased within 2 months after the fire, but losses appeared to stabilize within 5 months. Leaching losses of Ca were significantly greater in the clear cut site. Although short‐term soil nutrient changes following fire were generally positive, the long‐term effects on site quality remain in question due to the probable net loss of organic matter and nutrients through volatilization and accelerated leaching.
Dissolution of Biogenic Opal as a Function of its Physical and Chemical Properties
Authors: Bartoli F. , Wilding L. P.
Published: July 2010

Several factors examined herein which control opal dissolution are: specific surface area, Al content, hydration state, age, and rate of organic matter biodegradation of the encasing vegetative tissues. These factors are covariable with opal of different origin. Recent (6 months old) opal phytoliths of deciduous origin are most hydrated (11%), have lower A1 content (2%) and highest dissolution (9 mg Si/liter, cold water; 50 mg Si/liter, hot water; and 3 mg Si/liter under natural environments). In contrast, opal of coniferous origin is older (30 months), more rigid, has higher Al content (3 to 4%), is encased within litter that is more slowly biodegradable and yields lower dissolution (2 to 3 mg Si/liter, cold water; 20 mg Si/liter, hot water; and 0.5 mg Si/liter under natural environments). Gramineous phytoliths associated with understory forest vegetation generally are intermediate in the above properties and dissolution. Biogenic opal has solubilities that approximate geologic opal‐A. It is relatively stable and not sufficiently labile under most soil environments to support observed soluble Si levels.
Comparison of One‐step Outflow Laboratory Method to an in situ Method for Measuring Hydraulic Conductivity
Authors: Jaynes D. B. , Tyler E. J.
Published: July 2010

The unsaturated hydraulic conductivity, K, of three soil horizons; the C horizon of a Plainfield sand (Typic Udipsamment), the C horizon of a Ringwood silt loam (Typic Argiudoll), and the B2t horizon of a Plano silt loam (Typic Argiudoll) was measured using a variation of the one‐step porous membrane outflow method. The method was adapted for measuring K using small (7.65 cm high by 7.65 cm in diam) undisturbed soil cores at soil water pressure potentials > −100 mbars. Comparison of these K values with values previously measured in situ for the same horizons with the crust test agreed within an order of magnitude or less. The discrepancy was probably due to hysteresis in the θ‐ψ relation.

The one‐step outflow method yields satisfactory results near saturation but cannot be used to measure saturated K values. Compared to other methods, the one‐step outflow procedure requires less time to measure K for many types of soils and facilititates the running of many samples simultaneously.
Linearized Moisture Flow with Root Extraction for Three Dimensional, Steady Conditions
Authors: Warrick A. W. , Lomen D. O. , Amoozegar‐Fard A.
Published: July 2010

A mathematical model is presented to simulate plant water uptake assuming steady‐state conditions and an unsaturated hydraulic conductivity as an exponential function of pressure head. By choosing the conductivity to be of this form, the moisture flow equation is linear, allowing analytical solutions to be developed in a closed form. Geometries considered possess radial symmetry and are appropriate to describe trickle irrigation. These include matrix potentials for points, discs, and cylinders which can be taken either as sources or sinks. These provide the basic building blocks to simulate varied steady‐state withdrawal patterns. The solution for the cylinder is newly derived; the other solutions were already available. Nonsymmetric cases can result from superpositions. Examples include pressure head distributions for four sink‐source combinations.
Irrigation Water Requirement for Dissolution of Gypsum in Sodic Soil
Authors: Hira G. S. , Singh N. T.
Published: July 2010

Laboratory studies were conducted to determine the effect of exchangeable sodium content of the soil and the particle size of gypsum on the irrigation water needs for dissolving gypsum mixed in sodic soils. Gypsum dissolution increased with an increase in the exchangeable Na content of the soil. About 4 cm of water was sufficient to dissolve all the agricultural grade gypsum of <0.26‐mm size. The amount of water required to dissolve the added gypsum and to reclaim a sodic soil did not increase with the amount of gypsum added, provided it equalled the gypsum requirement.

The effect of particle size of gypsum on its dissolution and the applicability of the equal‐reduction hypothesis were examined. The dissolution of gypsum was approximately predicted by a dissolution equation based on particle surface area if the initial particle sizes were neither very coarse (<0.5 mm) nor very fine (>0.1 mm). The water required for complete dissolution of gypsum computed from a dissolution equation, increased from 2.8 cm to 15.9 cm as gypsum particle size increased from < 0.1 mm to 0.5–2.0 mm.
Flocculation Value and Gel Structure of Sodium/Calcium Montmorillonite and Illite Suspensions
Authors: Oster J. D. , Shainberg I. , Wood J. D.
Published: July 2010

The flocculation value, the minimum salt concentration which causes flocculation within 24 hours, was determined for mixtures of Na‐ and Ca‐montmorillonite (API‐25) and Fithian illite (API‐35). The equivalent fraction of exchangeable Na+, ENa, varied from 0 to 1. We prepared Na/Ca clay suspensions by adding the appropriate amounts of homoionic dry clays to a series of Na/Ca chloride solutions (0.2 to 80 molc m−8; 0.2 to 80 meq liter−1) with appropriate sodium adsorption ratio and shaking the mixture for 1 hour. The flocculation value of Ca‐montmorillonite (0.25 molo m−3) increased rapidly with small amounts of exchangeable Na+: the flocculation value for an ENa of 0, 0.2, 0.4, and 1 was 0.25, 6, 9, and 12 molc m−3, respectively. The flocculation values for Ca‐ and Na‐illite were 0.25 and 55 molo m−3, respectively, and increased linearly with ENa. Van der Waals attraction forces are mainly responsible for flocculation of Ca‐montmorillonite and illite systems. Edge‐to‐face attraction is dominant in flocculating Na‐montmorillonite. The large effect of small amounts of exchangeable Na+ in montmorillonite suspensions results from demixing of exchangeable ions whereby Na+ is the predominant cation on the external surfaces when ENa < 0.20.
Heterovalent, Ternary Cation Exchange Equilibria: NH4+‐Ba2+‐La3+ Exchange on Montmorillonite
Authors: Elprince A. M. , Vanselow A. P. , Sposito Garrison
Published: July 2010

Data were obtained at 25°C on the composition of the aqueous solution and exchanger phases in NH4‐Ba‐La, La‐Ba, La‐NH4, and Ba‐NH4 aqueous systems comprising the chloride salts of the three cations and a montmorillonite clay from Nevada. The data for the three binary cation exchange systems were incorporated into a thermodynamic model which was used to predict the composition of the aqueous solution phase of the ternary NH4‐Ba‐La system as a function of exchanger phase composition. The model employed, known as the subregular model, involved a MacLaurin expansion of the exchanger phase rational activity coefficients to third order in the mole fractions of the exchanger components. The constant coefficients in the MacLaurin expansion could be determined solely with experimental data on the infinite‐dilution, rational activity coefficients of exchanger components in binary exchange systems. Thus no data on ternary exchange systems were required to apply the model. The model calculations were in reasonably good agreement with experiment, suggesting that further efforts to predict ternary exchange behavior from binary exchange data are warranted.
Potential Errors in the First‐order Model for Estimating Soil Nitrogen Mineralization Potentials
Authors: Smith J. L. , Schnabel R. R. , McNeal B. L. , Campbell G. S.
Published: July 2010

Nitrogen mineralization incubations were conducted using an aerobic leaching procedure. Two agricultural soils and one forest soil were incubated under aerobic conditions, including periodic leaching of mineral N using either 100 ml of 0.01M CaCl2, 30 ml of 0.01M CaCl2, or 30 ml of 0.05M CaCl2. Mineral and organic N were determined for each leachate. Significant amounts of organic N were leached with the mineral N. Leaching with 30 ml of 0.05M CaCl2 removed significantly less mineral N, but the 100 ml 0.01M of CaCl2 and 30 ml of 0.01M CaCl2 treatments were not significantly different. Although not statistically significant, 30 ml of 0.01M CaCl2 consistently leached less organic N than did the other two treatments. Amounts of organic N leached ranged from 13 to 163% of total mineralized N.

The mineralization reactions were assumed to follow first‐order kinetics. A comparison was made between root mean square (RMS) deviations of experimental data from a nonlinear least squares (NLLS) equation and the more traditional least squares fit of a straight line to log‐transformed data. The NLLS equation gave a more precise fit to the data and hence more accurate estimates of both the N mineralization potential (N0) and the mineralization rate constant (k) for each soil.
Critical Soil Manganese Deficiency Levels for Four Extractants for Soybeans Grown in Sandy Soil
Authors: Shuman L. M. , Boswell F. C. , Ohki K. , Parker M. B. , Wilson D. O.
Published: July 2010

Soil extractants for Mn are often assigned critical deficiency levels based on indirect experimental evidence. This research was undertaken to calibrate four soil Mn extractants for critical deficiency levels using soybeans [Glycine max (L.) Merr. cv. ‘Ransom’]. Two adjacent field experiments were conducted on Olustee‐Leefield sand (Ultic Haplaquod‐Arenic Plinthaquic Paleudult) with soil pH, microelement, and Mn rate variables. Leaf samples taken at the R‐2 growth stage were analyzed for Mn and soil samples were analyzed for pH and extractable Mn by four separate procedures. Critical deficiency levels were determined using the Cate‐Nelson procedure as well as by comparing tissue Mn critical levels with soil Mn levels using a regression method. The latter method was unsatisfactory for determining critical levels except for two extractants for 1 year. Critical deficiency levels based on the Cate‐Nelson method averaged over the 3‐year experiment period were Double Acid—2.6 ppm, DTPA — 0.22 ppm, Mehlich (NH4Cl‐NH4F) — 1.8 ppm, and AB‐DTPA (NH4HCO3‐DTPA) — 0.4 ppm. Leaf Mn vs. extractable soil Mn correlation coefficients were best for the two DTPA‐based extractants, but all four coefficients were similar when soil pH was included in multiple regression equations.
Calcium Carbonate in a Calcareous Soil from the Jordan Valley, Israel: Its Origin as Revealed by the Stable Carbon Isotope Method
Authors: Magaritz Mordeckai , Amiel Abraham J.
Published: July 2010

The development of calcareous soil in semiarid zones is accomplished by dissolution and reprecipitation of calcium carbonate (CaCO3) minerals. The proportion of carbonate in the soil of the Jordan Valley that is pedogenic in origin was determined using the stable C isotope method. Forty to sixty percent of the carbonate remaining in soil horizons A and B undergo dissolution and reprecipitation processes. These changes were detected by the decrease in the 13C/12C ratio from the parent material average (−2.5‰) to the B horizon value (−7.4‰). A scale is proposed to determine the percentages of pedogenic carbonate in soil.
Iron Coatings on Rice Roots: Morphology and Models of Development
Authors: Chen C. C. , Dixon J. B. , Turner F. T.
Published: July 2010

Scanning electron microscopy and X‐ray microanalysis were employed to characterize the morphological properties of iron coatings on rice roots at different growth stages. This information is needed for further understanding of the influence of Fe coatings on rice plant development. Rice root coatings are visible about 1 week after flooding as a brownish discoloration which thickens with age of the root. No coating was found on younger parts of major roots near their tips or on young secondary roots which are critical regions of nutrient uptake. Roots of ‘Brazos’ cultivar rice (Oryza sativa L.) plants grown in Beaumont clay soil had a relatively thin coating of FeOOH mixed with soil particles before panicle differentiation. As a rice plant approached maturity and the outermost cell wall of the root decomposed, a mixture of FeOOH and soil particles began to fill the rectangular spaces that had once been occupied by epidermal cells. Casts in open cell cavities are porous and rough on the exterior side of the root. There were many shapes of casts and they generally matched the varied shapes of the outer layer of epidermal cells of rice roots. Roots of Brazos cultivar rice grown to maturity in Katy fine sandy loam soil have completely developed polyhedral casts. Precipitation of relatively pure FeOOH on cell walls formed hollow casts with the shapes of the original cells. The models presented describe hypothetical steps in the formation of the two types of casts observed by the oxidation of Fe2+ by O2 and precipitating of iron on the walls of closed and open cell cavities.
Gas Chromatographic System for Precise, Rapid Analysis of Nitrous Oxide
Authors: Mosier A. R. , Mack L.
Published: July 2010

A gas chromatographic (GC) system for the sensitive, rapid, and precise analysis of nitrous oxide (N2O) was developed. The system employs a two‐part GC column that can be separated and the first section back‐flushed to remove contaminants while sample analysis continues. Nitrous oxide was detected by an electron capture detector. The GC system was suitable for analyzing small volumes of gas samples for ambient levels of N2O at the rate of 10 samples per hour with a precision of about 1 ppb.
Soil Consistence: Effect of Particle Size
Authors: Ibanga Iniobong J. , Bidwell Orville W. , Powers William L. , Feyerherm Arlin M. , Williams Wayne W.
Published: July 2010

Briquets composed of sand (0.05–2.00 mm) silt (0.002–0.05 mm), and clay (<0.002 mm) mixtures were hardest when dominantly clay and/or sand and softest or least hard when dominantly silt. Where soils had equal amounts of clay, those with highest amounts of sand, with one exception, were the hardest. Low surface area of sand requires much less clay “mortar” to cement the fewer sand grains per given volume than do the more numerous, smaller silt particles.
Absorption of Water by Soil: Some Effects of a Saturated Zone
Authors: Smiles D. E. , Perroux K. M. , Zegelin S. J.
Published: July 2010

Absorption by soil of water supplied at constant pressure and at constant rate is described. Particular attention is paid to the process when the surface water potential is greater than that at which the soil saturates.

Analyses, which directly integrate Darcy's law for both saturated and unsaturated regions using the flux‐potential relation (related to the flux‐concentration relation of Philip through the appropriate moisture characteristic), predict behavior in accord with experimental data. Analyses which treat the unsaturated region as a problem of diffusion‐of‐θ are “correct” only if the soil water diffusivity, measured using the method of R. Bruce and A. Klute, is interpreted with care.

To avoid erroneous prediction it is imperative that the measurement of diffusivity be preceded by an independent measurement of the moisture characteristic. This latter relation is a necessary specification of the soil water system. It should always be presented in a test of flow theory, and it identifies the suction at which the soil saturates and hence the suction at which Bruce and Klute type experiments should be performed.
Changes in the Humic Acid Fraction of Soil Resulting from Sludge Application
Authors: Boyd Stephen A. , Sommers Lee E. , Nelson Darrell W.
Published: July 2010

Humic acids (HA) extracted from sludge, soil, and sludge‐amended soil were characterized by elemental and functional group analyses and visible and infrared spectroscopy. Humic acid extracted from a Chalmers soil appeared to be similar to an average HA (Schnitzer, 1978). Humic acid extracted from Chicago sludge, as compared to the average HA and Chalmers HA, had a lower C/H ratio, increased N content, decreased total acidity and carboxyl content, and a lower absorptivity. With respect to the average HA and Chalmers HA, the sludge HA appeared to be a more aliphatic, N‐enriched polymer with decreased amounts of carboxyls and phenolic hydroxyls. Proteinaceous materials associated with the sludge HA appeared to be the major source of N enrichment. In general, HA's extracted from the sludge‐amended soil had increased N contents, lower C/H ratios, lower values of total acidity and phenolic hydroxyl, somewhat lower values of CO2H groups, and lower absorptivities as compared to HA from soil not receiving sludge amendment. Sludge organic matter was apparently recovered in HA extracted from soil 2 and 14 months after sludge application. The association of sludge‐borne proteinaceous and aliphatic materials with the sludge and sludge‐amended soil HA fractions was indicated by increased amide and C‐H stretch infrared absorptions as well as by the increased N contents and decreased C/H ratios. The observation of proteinaceous materials associated with HA extracted from sludge‐amended soil as long as 14 months after application suggested these proteinaceous materials were resistant to decomposition, possibly as a result of their incorporation into the HA structure. Fatty acids may be associated with HA's extracted from sludge and sludge‐amended soil through esterification to phenolic hydroxyls.
Effects of Titration Rate, pH, and Drying Process on Cation Exchange Capacity Reduction and Aggregate Size Distribution of Montmorillonite Hydroxy‐Aluminum Complexes
Authors: Keren R.
Published: July 2010

The effects of rate of titration of montmorillonite + AICI3 with NaOH, and of drying on CEC reduction, C‐axis spacing, and aggregate size distribution of montmorillonite hydroxy‐Al complexes at the pH range of 5–10, were studied. The CEC reduction was found to be influenced by the titration rate. While the CEC of the montmorillonite was 0.92 meq/g, the CEC of the clay hydroxy‐Al complexes was 0.27, 0.31, 0.39, and 0.45 at titration rates of 0.025, 0.1, 0.4, and 0.8 meq NaOH/min, respectively. The mean aggregate size and the C‐axis spacing of the clay hydroxy‐Al complexes decreased as the pH of the suspensions increased. The CEC of the montmorillonite hydroxy‐Al complexes after drying was higher than the nondried systems at a pH above 7.5, whereas no difference was observed at the lower pH range (pH 5–6). The CEC and the C‐axis spacing for both the dried and nondried systems were highly correlated.
Determination of Soil Solution Electrical Conductivity from Bulk Soil Electrical Conductivity Measurements by the Four‐Electrode Method
Authors: Nadler A. , Frenkel H.
Published: July 2010

Soil electrical conductivity (ECa) by the four electrode method was studied in the laboratory as a function of soil water electrical conductivity (ECw) and water content in six soil types. A linear relationship between ECa and ECw was valid only at salinities > 4 mmho/cm. At very low salinity levels the contribution of the surface conductance was not constant and had a higher contribution than ECw to measured ECa. A method for calculating the partial contribution of surface conductance to ECa as a function of ECw and clay content is applied including a correction for dependence on the soil water content.
A Comparison of Cross‐Contamination in Distillation Units Used in Total Nitrogen and Nitrogen‐15 Analyses
Authors: Reeder J. D. , O'Deen W. A. , Porter L. K. , Lober R. W.
Published: July 2010

A laboratory study was conducted to investigate 15N cross‐contamination errors between distilled standards [1 mg N as (NH4)2SO4] with various 15N excess contents (0, 3, or 10% excess 15N). Several stills differing in rate of distillation and construction were tested. We also compared the effectiveness of the ethanol (ETOH) cleansing technique with the (NH4)2SO4 cleansing technique in reducing cross‐contamination errors. The ETOH wash was less effective than the (NH4)2SO4 wash in reducing cross‐contamination errors for samples with normal abundance 15N but was equally effective in reducing cross‐contamination errors for samples with high‐enrichment 15N. The (NH4)2SO4 wash sometimes significantly diluted high‐enrichment 15N samples.

Ammonia seemed to be absorbed and sporadically released from the nonglass components of the partial‐glass still. Replacing the rubber and teflon components with glass and decreasing the glass surface area of the distillation unit decreased cross‐contamination errors and increased the percent recovery of atom % 15N from the distillation unit.
Predicting Slash Pine Response to Nitrogen and Phosphorus Fertilization
Authors: Kushla J. D. , Fisher R. F.
Published: July 2010

The Cooperative Research in Forest Fertilization (CRIFF) soil groups based on soil drainage class and depth to and nature of the B horizon, were as good as or better than Soil Conservation Service soil series or Coile soil units at predicting slash pine (Pinus elliottii var. elliottii Engelm.) response to N and P fertilization. Some CRIFF soil groups demonstrate much greater uniformity of response than others. Within these soil groups, soil properties and foliar analyses were used to better predict fertilizer response. The properties valuable for predicting response varied from soil group to soil group, but those most consistently valuable were measures of available soil water, extractable soil P, the amount of silt plus clay in the surface soil, and foliar N and P. A model with from two to four significant variables was developed for each CRIFF soil group. The coefficients of determination (R2) for these models ranged from 0.52 to 0.99.
Mineralizable Soil Nitrogen as an Index of Nitrogen Availability to Forest Trees
Authors: Powers Robert F.
Published: July 2010

Soil N mineralized during 14‐day anaerobic incubation at 30°C is evaluated as an index of forest soil fertility and site productivity. Mineralizable soil N determined under standard conditions correlates significantly with N mineralized anaerobically for 6 months in the field, with site index and yield potential of Pinus ponderosa L. growing on volcanic, metavolcanic, and metasedimentary soils, and with foliar concentrations of N. Soils testing less than 12 ppm of mineralizable N are judged clearly deficient, but stands of pine and fir on soils testing as high as 16 ppm of N still may respond well to fertilization. Absolute variability in mineralizable soil N decreases with soil depth and increases with the magnitude of the soil test mean, but relative variability is constant. Comparing ammonium produced during laboratory incubation with that mineralized over 6 months in the field shows that field soil temperature has a strong bearing on the interpretation of the laboratory test.
A Method for Obtaining Soil‐Free, Soil‐Solution Grown Plant Root Systems
Authors: Cappy J. J. , Brown D. A.
Published: July 2010

A method has been developed by which soybean plants are grown deriving all nutrients from the soil solution without direct root‐soil contact. This soil‐packet plant culturing system consists of approximately 125 soil packets arranged in a plexiglas growth box to provide maximum packet surface area for root proliferation. Each soil packet consists of 35 g of soil enclosed in an envelope constructed from semipermeable filtration membrane material. The membrane allows the passage of water and ions between the soil and root but does not allow direct root‐soil contact. Thus, an intact soil‐free root system develops. Soybean plants grown using the soil‐packet system were larger than those grown in an equivalent amount of soil in a pot. Root systems of packet‐grown plants required less time and effort for removal and suffered less damage than did root systems of pot‐grown soybeans.
Effects of Wetting and Drying, and of Exchangeable Cations, on Boron Adsorption and Release by Montmorillonite
Authors: Keren R. , Gast R. G.
Published: July 2010

The effect of drying and rewetting sequences on boron adsorption and desorption by Na‐ and Ca‐montmorillonite suspensions was determined with (i) nondried suspensions, (ii) suspensions dried prior to boron addition, and (iii) suspensions dried once or twice after boron adsorption. Boron adsorption in the nondried suspensions was completely reversible for both the Na‐ and Ca‐systems. There was little effect of exchangeable cation species (Na+ vs. Ca2+) on boron adsorption in the pH values of 7.0 and 7.2. There was a significant exchangeable cation effect, however, at higher pH's, with the Ca‐system adsorbing the greatest amount of boron. Boron adsorption on clays dried prior to boron addition was essentially the same for the nondried systems, indicating that the drying and rewetting sequence does not have any effect on the adsorption sites of the clay. The amount of boron adsorbed increased with drying and wetting after boron addition for both the Na‐ and Ca‐systems, with the greatest increase occurring after the first drying‐wetting cycle for both systems. Drying and rewetting of the clay suspensions after boron addition not only increased the amount of boron adsorbed, but significantly reduced the reversibility of the adsorption process as well. The relative amount of reversibility of adsorbed boron is a complex function of the drying and rewetting cycles, pH, and type of exchangeable cations.
The Kinetics of Phosphorus Desorption from Soil
Authors: Sharpley A. N. , Ahuja L. R. , Yamamoto M. , Menzel R. G.
Published: July 2010

The kinetics of P desorption for several soils was investigated at different water/soil ratios, during a short period of time, so that the results could be related to P release from agricultural soil to rainfall and runoff water. For all soils the logarithm of P release (Pd) was linearly related to the logarithm of contact time (t) at any given water/soil ratio (W) and P amendment and to logarithm of W at any given contact time and P amendment. The amount of P released was also directly proportional to the amount of desorbable P (Po) in the soil initially. The following simplified empirical model was developed to describe the desorption of soil P,

Pd = KPotαWβ,

where K, α, and β are constants. The simplified model gave a reasonably good description of P desorption from five southwestern soils and provided similar values of the constants K, α, and β, for each soil, over a range of experimental conditions. Consequently, we suggest that average values of the constants for each soil can be used in the model to describe P release for general applications.
Characterization of Diverse Rhizobium trifolii Isolates
Authors: Hagedorn C. , Caldwell B. A.
Published: July 2010

Forty cultures of Rhizobium trifolii isolated from diverse soils in western Oregon were characterized on the basis of host‐plant specificity and serological and cultural reactions. There was large variation in effectiveness when the rhizobia were examined on 12 cultivars of subclover (Trifolium subterraneum L.), although most of the strains demonstrated fair to average effectiveness on the majority of the subclover cultivars. The rhizobia were of generally poor effectiveness with other Trifolium species. Antibiotic resistant mutants were selected for two of the strains, and these were tested on the subclover cultivars as a mixed inoculum. Six cultivars were preferentially nodulated by one of the two strains, and individual plants that contained one of the strains in the majority of its nodules were identified. Thirty‐four of the isolates could be categorized into six serological groups based on whole‐cell agglutination reactions, whereas three cultures demonstrated very specific antibody reactions and could be identified on this basis. All 40 strains grew in acid broth at pH 4.5, but only 12 out of 40 grew at pH 3.0. At neutral pH, the mean generation time was 1½ to 3 hours, although there were a few that grew faster. At pH 4.5 the generation times were increased for most of the cultures but usually by only 1 or 2 hours. The serological groupings and growth characteristics were not found to be related to the effectiveness categories of the strains in any apparent way. The possibilities for selecting clover lines that are preferentially nodulated by a specific Rhizobium strain and identifying isolates that have research potential based on effectiveness patterns among different host‐plant cultivars are described.
Land Forming Effects on Dryland Sorghum Production in the Southern Great Plains
Authors: Jones O. R.
Published: July 2010

The effectiveness of selected low‐cost, water‐conserving land forming systems in preventing runoff and increasing dryland grain sorghum [Sorghum bicolor (L.) Moench] yields on Pullman clay loam was evaluated for 4 years (1975–1978) at Bushland, Tex. Systems investigated were mini‐bench terraces (5 m wide), conservation mini‐bench terraces (9 m wide with a ratio of watershed to level bench area of 1:1), and three configurations of contour furrows. Runoff was measured from conventional graded furrows (0.25% grade) that were used for the check treatment. Total runoff for the 4 years was 258 mm, about 15% of total precipitation. All systems that retained runoff on the field produced significantly greater yields and had greater water‐use efficiencies than the graded furrow system. Grain yield and water‐use efficiency were significantly greater with mini‐bench terraces than with any other treatment. Mean annual grain yield on mini‐bench terraces was 2,380 kg/ha, compared to 1,210 kg/ha on conventional graded furrows. Minibenches, conservation mini‐benches, and large contour furrows controlled erosion and retained all precipitation from a storm of 75‐year expected frequency. In that storm, conventional furrows overtopped and failed to retain runoff.
A Method for Measuring the Vertical and Horizontal Ksat of Clay Soils with Macropores
Authors: Bouma J. , Dekker L. W.
Published: July 2010

A field method is presented for measuring the vertical and horizontal Ksat of a cube of soil (25 × 25 × 25 cm) which is carved out in situ and covered with gypsum. A vertical Ksat is measured by infiltrating water into the exposed upper surface and by collecting it below the exposed lower surface of the cube. The cube is then turned. The two open surfaces are covered with gypsum, which is removed from the other two vertical sidewalls. These turn into surfaces for percolation after again turning the cube. A vertical Ksat is now measured which represents the horizontal Ksat of the cube in its original position in the soil. The method is inexpensive and simple, creates the required large sample in clay soils, does not involve compaction of soil, can be used above the water table, and defines Ksat in terms of direction.
Spatial Variability of Steady‐State Infiltration Rates as a Stochastic Process
Authors: Sisson J. B. , Wierenga P. J.
Published: July 2010

Steady‐state infiltration rates were measured in a field plot with infiltrometers of 5‐, 25‐, and 127‐cm inside diameter. Measurements were made with the three ringsizes along five parallel transects, spaced 125 cm apart. The infiltrometers were placed adjacent to each other along each transect (i.e., one hundred twenty‐five 5‐cm rings, twenty‐five 25‐cm rings, and five 127‐cm rings per transect). Infiltration rates were found to be lognormally distributed for all ringsizes and autocorrelated for the 5‐cm ringsize. The 5‐cm data showed that a large fraction of the water infiltrated through a small fraction of the plot area. Autocorrelation functions were determined and power spectrums computed. A first‐order autoregressive process was found to describe the 5‐cm data, and variances of samples composited along a transect agreed with sample variances. The variances for the 25‐ and 127‐cm infiltrometers were compared with sample variances, assuming a simple two‐dimensional autocovariance function. Agreement was found for the 127‐cm rings, but not for the 25‐cm rings.
Distribution and Plant Availability of Soil Zinc Fractions
Authors: Iyengar S. S. , Martens D. C. , Miller W. P.
Published: July 2010

This laboratory and greenhouse investigation was under‐taken to study the distribution and plant availability of zinc in different soil fractions. Total Zn (TZn) in 19 soils, which varied widely in chemical and physical properties, was fractionated into water‐soluble plus exchangeable (CA‐Zn), specifically adsorbed (AC‐Zn), organically bound (PYRO‐Zn), Mn‐oxide bound (HAH‐Zn), Al‐ and Fe‐oxide bound (AMOX‐Zn), and residual (RES‐Zn) forms. There was a wide variation in the magnitude of these fractions among soils. Most of the TZn, on an average, was present in the AMOX‐Zn (∼25%) and RES‐Zn (∼70%) fractions. The CA‐Zn, AC‐Zn, PYRO‐Zn, and HAH‐Zn fractions averaged 0.4, 3.3, 2.5, and 2.0% of the TZn, respectively. The CA‐Zn in the 19 soils increased with a decrease in soil pH, whereas the AC‐Zn increased with an increase in soil pH. The PYRO‐Zn in the soils varied directly with organic C and soil pH, HAH‐Zn increased with an increase in both soil pH and free Mn, AMOX‐Zn correlated more closely with free Al than with free Fe, and RES‐Zn varied positively with soil clay. A seven‐variable regression model, which included the six Zn fractions and soil pH, accounted for 94% of the variability in Zn uptake by corn plants (Zea mays L.) from these soils. This model separated soils that supplied inadequate amounts of Zn from those that supplied adequate amounts.