bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaching of a Soluble Chemical under Field Crop Conditions
Authors: Smith S. J. , Ahuja L. R. , Ross J. D.
Published: July 2010

The leaching pattern of surface‐applied bromide is examined in an active rootzone of a sorghum‐sudangrass [Sorghum sudanense (Piper) Stapf] crop in Southern Plains field plots. Data were collected for eight soils, comprising five soil orders, over three growing seasons. The position of the leaching front (solute center of mass) was better predicted generally by Burns' equation, which assumes chromatographic‐type, sequential mixing of solute with soil water, than by Levin's equation, which assumes the leaching front moves with the velocity of water flowing above field capacity. With both equations effective rainfall was used, by correction for the soil water deficit caused by evapotranspiration above the leaching front. The leaching pattern in the soil profile was described quite well by a simplified version of the convective‐dispersive solute transport equation, which assumed constant average values for the dispersion coefficient, D, a plant uptake factor, β, and flow velocity, V̄. Plant uptake of solute was assumed to be proportional to its concentration in soil water during passage through the root zone, with an effective average value of the proportionality constant applicable on a seasonal basis. The average value of D among soils was fairly uniform, 1.36 ± 0.56 cm2 d−1. Therefore, in practice a single value of D will probably suffice for many soils and conditions. Necessary inputs for obtaining V̄ can be obtained from plant growth and water balance components of CREAMS, or other appropriate models. In the case of β, some additional information is needed regarding its relationship to specific growth factors.
Effects of Fertilization on Soil Solution pH and Manganese Concentration
Authors: Petrie S. E. , Jackson T. L.
Published: July 2010

The effects of fertilizers on the soil solution pH and Mn concentration were studied in a laboratory experiment. A Tulana silt loam variant (medial, nonacid, mesic, Mollic Andequepts) with 18% organic matter was placed in incubation trays. Simulated fertilizer bands were made in the soil and marked with washed white silica sand. Nitrogen (N) was applied at 0 or 22 kg/ha as (NH4)2SO4, NH4Cl, or urea. Phosphorus (P) was applied at 0 or 19 kg/ha as Ca(H2PO4)2 and manganese (Mn) was applied at 0 or 5.6 kg/ha as MnSO4. All fertilizer rates were based on 0.25‐m row spacing. An unaltered portion of the soil solution was removed by centrifugation. The soil solution pH and Mn concentrations were measured in samples collected in the fertilizer band and 0.025 m from the band at 7, 14, and 28 d after fertilization. At 7 d after fertilization the soil solution pH in the fertilizer band was lowered from 8.12 to 7.30 by (NH4)2SO4 and from 7.75 to 7.21 by NH4Cl. In contrast, urea fertilization increased the soil solution pH from 7.75 to 8.01. Application of Ca(H2PO4)2 with N fertilizers lowered the soil solution pH regardless of N source. The soil solution pH tended to remain depressed at 14 and 28 d after fertilization when (NH4)2SO4 plus Ca(H2PO4)2 or NH4Cl plus Ca(H2PO4)2 were applied but increased when urea plus Ca(H2PO4)2 were applied. The pH changes at 0.025 m from the fertilizer band were approximately one half those occurring in the fertilizer band. The soil solution Mn concentration in the fertilizer band increased from 7.3 × 10−7 mol/L in the band receiving no fertilizer to 3.28 × 10−6, 5.82 × 10−6, and 2.18 × 10−6 mol/L in the (NH4)2SO4, NH4Cl, and urea bands, respectively, at 7 d after fertilization. At 28 days after fertilization the Mn levels were 4.55 × 10−6, 4.19 × 10−6, and 5.5 × 10−7 mol/L in the (NH4)2SO4, NH4Cl, and urea bands, respectively. When Mn was included with N fertilizer the soil solution Mn concentration increased from 7.3 × 10−7 to 4 × 10−4, 3 × 10−4, and 4.8 × 10−4 mol/L in the (NH4)2SO4, NH4Cl, and urea bands, respectively, at 7 d after fertilization. The Mn concentration in the (NH4)2SO4, NH4Cl, and urea bands fell to 2.8 × 10−4, 2.2 × 10−4, and 9 × 10−5 mol/L, respectively, at 28 d after fertilization.
Soil Test Phosphorus and Solubility Relationships in Calcareous Soils
Authors: Havlin J. L. , Westfall D. G.
Published: July 2010

Irrigated alfalfa (Medicago sativa L.) was established in 1976 on two Colorado Soils [Keith clay loam (Aridic Argiustolls) and Ravola loam (Typic Torrifluvents)] to determine the residual value of fertilizer P. Triple superphosphate was applied annually at rates of 25 and 50 kg P ha−1, with 75 kg P ha−1 applied triennially and at seeding. Phosphorus solubility (in 0.01M CaCl2) and NaHCO3 ex tractable P were measured initially and in the third and sixth years of the study. The resulting calcium hydroxide (Ca(OH)2) and monocalcium phosphate (Ca(H2PO4)2) potentials were related to known solubility products for distinct mineral phases. Phosphorus solubility in the 0‐ to 7.5‐cm depth increased in all fertilized treatments after three years in both soils. No further increases in P solubility, NaHCO3‐P, or P uptake were observed over the next 3 yr. According to solubility diagrams residues of octacalcium phosphate (OCP) were apparently accumulating in the surface 7.5‐cm layer at NaHCO3‐P levels >32 mg kg−1. Below this extractable P level β‐tricalcium phosphate (TCP) apparently controlled P solubility.
Six Years of Phosphorus and Potassium Fertilization of Irrigated Alfalfa on Calcareous Soils
Authors: Havlin J. L. , Westfall D. G. , Golus H. M.
Published: July 2010

Long‐term irrigated alfalfa (Medicago sativa L.) field experiments at two locations in Colorado [Keith clay loam (Aridic Argiustolls) and Ravola loam (Typic Torrifluvents)] were established to (i) determine the magnitude and frequency of P and K fertilization required to maintain initial soil tests, and (ii) evaluate the residual value of soil and fertilizer P and K. Ten P and K treatments (3 annual, 1 triennial, and 1 initial application) were used. Alfalfa yield, P and K uptake, NaHCO3‐extractable P, and NH4C2H3O2‐exchangeable K were measured over 6 production years. Soil test P declined in both soils to levels where significant yield responses to fertilizer P were expected, but none were observed. Organic P mineralization and/or an extensive mycorrhizal association were suggested as contributing factors to P availability. Generally, application of 50 kg P ha−1 maintained initial NaHCO3‐P at both locations, while soil P declined below the initial level for all other P rates. Phosphorus uptake was significantly increased by P fertilization on the Keith soil, due to lower NaHCO3‐P level, but not on the Ravola soil. Soil test K remained at high levels in both soils and no yield responses to fertilizer K were observed. Application of 380 and 5 kg K ha−1 were calculated to maintain initial NH4C2H3O2‐K in the Keith and Ravola soils, respectively. The low maintenance requirement of the Ravola soil was due apparently to a high nonexchangeable K release rate which buffered exchangeable K near 100 mg kg−1. Potassium uptake was significantly increased by K fertilization in the Ravola soil, due to a lower exchangeable K level, but not in the Keith soil. The results indicate very large P and K reserves exist in both soils and unless improved forage quality influences the economic benefit from P and K fertilizer application, fertilization of these soils would not be recommended.
Effect of Fertilizer Phosphorus Placement on the Availability of Phosphorus
Authors: Sleight D. M. , Sander D. H. , Peterson G. A.
Published: July 2010

Greenhouse studies were conducted with oats (Avena sativa L.) to determine why band applications of fertilizer P are often more effective than broadcast applications of equal rates. Phosphorus fertilizer solutions tagged with 32P were applied to the soil with different spacing distances between solution application points. All the P fertilizer was applied at approximately equal distance from oat seeds (48 mm), while application points were spaced 0, 16, 32, and 48 mm from one another. Investigations were conducted using two soils, a Uly silt loam subsoil (fine‐silty, mixed, mesic Typic Haplustolls) with soil pH 8.4, a calcium carbonate equivalent of 4.2%, and 1.2 mg kg−1 NaHCO3‐extractable P; and a Thurman loamy fine sand (sandy, mixed, mesic Udorthentic Haplustills) with soil pH 5.9 and 11 mg kg−1 Bray and Kurtz no. 1‐extractable P. On the high pH calcareous silt loam soil, yield and P uptake were greatest when application points were spaced far apart. However, on the acid loamy fine sand, no relationship was found between the spacing of the application points and P uptake. It was concluded that on the loamy fine sand, movement of P from a single spot increased the probability that root‐fertilizer contact would occur, whereas no such movement occurred in the silt loam. The amount of P uptake by oats was nearly proportional to the volume of soil containing the applied P fertilizer. Apparently, the early beneficial effects of banding are obtained mainly from placing all of the fertilizer where contact by active roots is likely, rather than from any increase in availability that may be obtained from decreased soil‐fertilizer contact associated with banding. If this is the case, then soils in which P is relatively immobile, most efficient use of P fertilizer will be made by the young plants if the fertilizer is mixed thoroughly with the soil near the seed into which a high concentration of roots will grow.
Soil Loss Reductions from Conservation Tillage Practices
Authors: Cogo N. P. , Moldenhauer W. C. , Foster G. R.
Published: July 2010

Soil loss reductions by residue cover (mulch) under field conditions were verified by deriving a mulch factor for no‐till, chisel plowing plus disking, and spring sweep tillage using anchored and unanchord corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] residues on a 4.5% slope 10.5 m long on Russell silt loam soil. A mulch factor was also derived for sweep tillage using anchored wheat residue on a 6.5% slope Martinsville loam soil, for simulated slope lengths of 35, 60, 85, 110, and 135 m. Both soils are Typic Hapludalfs. The studies were conducted using simulated rainfall and field plots. A crop residue mulch was relatively more effective than roughness alone in reducing soil loss on smoother soil surfaces and on the longer slopes. Corn residue was more effective in reducing erosion than soybean residue, and residues partially incorporated into the soil were more effective in reducing soil loss than residues loose on the surface. The findings showed that the b‐value in the mulch factor (Fm)‐% residue cover (M) equation Fm = e‐bM varied appreciably depending on roughness, and type and incorporation of the residue.
Shallow‐Layer Soil Water Potential Changes Due to Waterdrop Impact
Authors: Cruse R. M. , Francis P. B.
Published: July 2010

Soil shear strength is inversely related to soil water matric potential (ψm), which changes in the soil during a rainstorm. An understanding of surface soil ψm changes due to rainfall may give an insight in soil erosion dynamics. Changes in soil water matric potential (ψm) under 1‐ and 3‐mm simulated soil surface seals were monitored following single waterdrop impacts on the soil surface. Selected ψm's were applied to the base of the seals with a hanging water column during the tests. After waterdrop impact, changes in ψm were detected within 2 to 3 s under 1‐mm surface seals and within 6 to 10 s under 3‐mm surface seals. The time required for ψm to equilibrate with the preimpact ψm (that ψm applied continuously with the hanging water column) ranged from 160 to 280 s. Equilibration time decreased slightly with increasing preimpact ψm's and was significantly affected by the type of soil material used to make the seal, the applied ψm, and the thickness of the seal. Increases in ψm under the 1‐mm surface seal due to waterdrop impact ranged from 0.3 to 0.5 kPa depending on ψm applied via the hanging water column. Smaller ψm changes were observed under the 3‐mm surface seal.
Oxidative Coupling of Phenols and Anilines by Peroxidase: Structure‐Activity Relationships
Authors: Berry Duane F. , Boyd Stephen A.
Published: July 2010

We investigated the relationship between molecular structure and reactivity for the peroxidase mediated coupling of substituted anilines and phenols. We undertook this study to gain a better understanding of the oxidative coupling processes operative in soil involving peroxidase enzymes. The relative reaction rates of the various substituted aniline and phenol compounds (electron donors) were determined by measuring electron donor disappearance using high pressure liquid chromatography. The effects of structure on reactivity were treated quantitatively by use of the Hammett equation. We found a good correlation between electron donor rate constants and their respective Hammett substituent σ+ constants which indicated the formation of a positively charged transition state as the rate controlling step. The ρ values obtained from these correlations were negative, demonstrating that reactivity was increased by the presence of electron‐donating substituents on the aromatic ring which act to stabilize the positively charged transition state. These results suggested that the reaction rates depended on electron density at the reaction center (−NH2 or ‐OH) in a predictable manner.
Phosphorus and Potassium Uptake of Field‐Grown Soybean Cultivars Predicted by a Simulation Model
Authors: Silberbush M. , Barber S. A.
Published: July 2010

Mathematical models for calculating nutrient uptake by plants grown in soil have been successfully verified in pot experiments. However, few attempts have been made to verify the models for predicting nutrient uptake under field conditions. The Cushman mathematical model was tested for prediction of P and K uptake by soybeans (Glycine max L. Merr.) grown in the field; five cultivars were grown each year for 3 years. Experimental site varied with year. The soils used were Raub silt loam (fine silty, mixed, mesic Aquic Argiudolls) and Chalmers silt loam (fine silty, mixed, mesic Typic Haplaquolls). Observed P and K uptake was obtained from plant analysis. Root system size was obtained by taking soil core samples, washing the soil from the roots, and measuring root length and mean root radius. Root kinetic parameters for P and K influx were measured in solution culture experiments conducted in a controlled climate chamber. Soil nutrient supply parameters were measured in the laboratory on surface and subsoil samples. The model accurately predicted K uptake by the different cultivars grown in both soils and P uptake from the high‐P (52 µM in the soil solution) Chalmers soil. Prediction of P uptake from the low‐P (7.8 µM in the soil solution) Raub soil was 30 to 35% of the observed P uptake, even though predicted uptake by root hairs was included in the calculation. The difference may have been partly due to acidification of the rhizosphere soil by root exudate, which increased P concentration in soil solution and consequently increased P uptake.
Mineralogy of Soils Developed in Periglacial Deposits of Southwestern Canada
Authors: Lim C. H. , Jackson M. L.
Published: July 2010

Parent materials of glacio‐lacustrine soils, Holocene loess, glacial rock flour, and slate samples from Alberta, Saskatchewan, and Red River plain were characterized mineralogically by X‐ray diffraction (XRD) and chemical techniques. The texture became finer and the fine clay/coarse clay ratios higher (0.5 to 3.6) in progressing from the overthrust mountains, to nearby loess, then to glacio‐lacustrine materials. The clay mineral distribution illustrated lithological, geomorphological, and weathering relationships. The XRD peak broadening indicated weathering to irregularly interstratified phyllosilicate minerals in Holocene loessial materials originating from fresh rock flour carried by the Athabasca River flowing out of the mountains near Jasper. The smectite content increase (4 to 34%) and the mica content decreased (52 to 20%) from near the overthrust mountains to the glacio‐lacustrine plains overlying nonmarine and marine sediments. Mica, smectite, and chlorite (8–20%) constituted the predominant minerals in the clay fractions. Smectite was the most abundant (20–34%) mineral in the clay of the glacio‐lacustrine materials, particularly in the <0.2‐µm fractions (60–85%). This was attributed mainly to glacial movement of weathered ash‐falls of Cretaceous sedimentary provenance. Some vermiculite (5–10%), kaolinite (3–11%), fine or poorly crystalline materials (4–14%), quartz (4–10%), and feldspars (1–2%) were also present. Chlorite, detrital mica, and sodic feldspar in both the clay and silt fractions indicated significant contributions for metamorphic and diagenetic source rocks to all samples, including the most distant “macro‐composite” glacio‐lacustrine samples.
Boundary Conditions for Displacement Experiments through Short Laboratory Soil Columns
Authors: van Genuchten M. Th. , Parker J. C.
Published: July 2010

This paper presents a discussion of the physical and mathematical significance of various boundary conditions applicable to one‐dimensional solute transport through relatively short laboratory soil columns. Based on mass balance considerations, it is shown that a first‐type or concentration‐type condition at the inlet boundary incorrectly predicts the volume‐averaged or resident concentration inside both semi‐infinite and finite systems. A third‐type or flux‐type inlet boundary condition preserves mass in semi‐infinite systems, but underpredicts effluent concentrations from finite columns unless a local transformation is used to convert volume‐averaged concentrations into flux‐averaged concentrations. This transformation leads to an expression for the effluent concentration that is identical to the solution for the semi‐infinite system using a concentration‐type boundary condition. For column Peclet numbers greater than about five, the resulting analytical expression for the effluent curve is shown to be nearly identical to the analytical solution for a finite system based on a flux‐type inlet boundary condition and a zero‐concentration gradient at the exit boundary. Both solutions correctly preserve mass in the system; other solutions of the convective‐dispersive transport equation are shown to be inappropriate for analyzing column effluent data.
Fate of Nitrogen‐15 Applied to Spring Wheat Grown for Three Consecutive Years in a Semiarid Region
Authors: Feigenbaum Sala , Seligman N.G. , Benjamin R. W.
Published: July 2010

Uptake and recovery of fertilizer N applied to spring wheat was monitored over a 3‐yr period in a semiarid region. Tagged fertilizer with enrichment from 8.9 to 28.5 atom % 15N was applied as KNO3 at rates equivalent to 180 kg N ha−1 as a single application or split equally over 3 yr. The wheat was grown in 1.25‐ × 1.25‐m open plots and in 0.3‐m diam microplots enclosed by hard plastic tubes that were inserted 0.6 m into the ground. The 15N enrichments in plant and soil were determined by emission spectrometry. In open plots fertilizer N recovery in plant and soil was 976 g kg−1 in the first year and 697 to 721 g kg−1 in subsequent years. In the tubes, equivalent recoveries were 755 to 841 g kg−1 and 377 to 560 g kg−1. The greater loss in the tubes is attributed to denitrification that could have occurred under excess waterlogging caused by the rim of the tubes that protruded about 0.05 m above the soil surface. In a dry year, 338 to 558 g kg−1 of the applied fertilizer N was found as mineral N in the soil and, especially in the open plots, was utilized in the second growing season, after which only negligible amounts remained in the mineral N fraction. At the end of the third year, 69 to 84 g kg−1 of the applied fertilizer N was found in the soil as organic N. At the end of 3 yr, recovery of fertilizer N was lower when determined directly with 15N than when determined by difference between treatments and control. The additional N could result from the controversial “priming effect” of fertilizer N application on release of soil N, although the evidence is not conclusive. It is concluded that when fertilizer N is applied in a dry season, a large amount of residual mineral N in soil remains at the end of the growing period. This N can be utilized in subsequent years and should be taken into account when determining fertilizer requirements. In a wet years, losses can be significant and residual fertilizer N in the soil is negligible.
A Proposed Land Suitability Classification for Potato: II. Experimental
Authors: Manrique L. A. , Uehara G.
Published: July 2010

A land suitability classification developed for potato (Solanum tuberosum L.) was tested by using soil survey and Soil Taxonomy data of 62 soils from Hawaii, California, Brazil, New Zealand, and Malaysia. The testing procedure also included potato field experiments with irrigation and fertilizer application in three of the 62 soils (Kohala, Ustic Humitropepts; Wahiawa, Tropeptic Eutrustoxs; Kukaiau, Hydric Dystrandepts). Land suitability assessments were obtained at zero, low, and high levels of agricultural inputs. At zero or low input, 87 to 94% of the soils were classified as unsuitable for potato production. Nutrient availability, soil acidity, and water availability were the main constraining factors. At high input, most constraints were removed and 99% of the soils became suitable for potato production. Potato yield response to irrigation and fertilizer application for the Wahiawa, Kohala, and Kukaiau soils were consistent with the land suitability assessment. The results indicate that reliable land suitability assessments for potatoes can be obtained by using this Soil Taxonomy‐based land suitability classification.
Tillage and Residue Effects on Wheat, Sorghum, and Sunflower Grown in Rotation
Authors: Unger Paul W.
Published: July 2010

Tillage methods affect soil surface conditions and amounts of crop residue retained on the soil surface, which, in turn, affect water infiltration and subsequent evaporation. The objectives of this study were to determine the effect of tillage methods and wheat residue levels on soil water storage and use, and on crop growth and yields. The study, conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls), involved an irrigated winter wheat (Triticum aestivum L.)‐dryland grain sorghum [Sorghum bicolor (L.) Moench]‐dryland sunflower (Helianthus annuus L.) cropping system. A 330‐d fallow period occurred between wheat harvest and sorghum planting and a 210‐ to 270‐d fallow period (overwinter) occurred between sorghum harvest and sunflower planting. Wheat was planted 30 to 60 d after sunflower harvest. After wheat harvest, residues were partially removed from one‐half of the plots; residues on the other half were not removed. Then, moldboard‐, disk‐, rotary‐, sweep‐, and no‐tillage treatments were applied. Soil water content increases during fallow after wheat averaged 89, 109, 85, 114, and 141 mm for the respective tillage treatments, and averaged 97 and 118 mm for the low and high residue treatments. Precipitation averaged 316 mm during fallow. The differences in stored water significantly affected sorghum growth; grain and forage yields; and seed test weight, weight/seed, and protein. Sorghum grain yields averaged 2.56, 2.37, 2.19, 2.77, and 3.34 Mg/ha with the respective tillage treatments. The tillage treatments had no residual effect on subsequent sunflower and wheat yields. However, including sunflower in the rotation apparently allowed extraction of water from deeper in the profile than that extracted by sorghum, thus increasing the utilization of water resources for crop production. In addition, the earlier harvest date for sunflower allowed wheat to be planted at a more optimum time than that which is possible when wheat is planted after grain sorghum harvest.
Phosphorus Losses as Affected by Tillage and Manure Application
Authors: Mueller D. H. , Wendt R. C. , Daniel T. C.
Published: July 2010

There is a lack of data on conservation tillage under field conditions characteristic of a dairy operation. Thus, simulated rainfall was used to compare total P (TP), algal‐available P (AAP), and dissolved molybdate‐reactive P (DMRP) losses from the conventional, chisel, and no‐till systems for corn both with and without surface‐applied manure prior to tillage. Rainfall was applied at several times during the growing season of 1978 and 1979. A portion of the previous year's residue was removed in 1978 and all the residue was left in 1979. Concentrations and losses of TP and AAP among unmanured tillage treatments were similar to trends observed for sediment concentrations and losses. In 1978, the chisel and no‐till systems were ineffective in reducing TP and AAP losses relative to the conventional system. In contrast in 1979, lower TP and AAP losses occurred from unmanured chisel and no‐till sites relative to unmanured conventional sites. In both years of the experiment, surface spread manure increased DMRP concentrations where the manure was not completely incorporated by tillage. In contrast, little difference was observed in DMRP concentrations among unmanured treatments. Manure also increased AAP concentrations for no‐till but had only a slight effect and no effect for the chisel and conventional systems, respectively. AAP concentrations from manured sites followed the order no‐till > conventional = chisel. Differences in runoff volumes among treatments influenced P losses. Runoff losses were relatively high for no‐till, particularly after planting, and losses of DMRP and AAP were very high where manure was surface applied. Often, runoff was reduced for the chisel system relative to other tillage systems, and consequently these reductions increased the effectiveness of this system in reducing P losses.
Flux‐Controlled Constant Potential Absorption Using a Programmable Pump
Authors: Bond W. J.
Published: July 2010

The construction and operation of a pump that provides the appropriate flux boundary condition to simulate constant potential horizontal absorption is described. It is demonstrated experimentally that this flux boundary condition is equivalent to the constant potential boundary condition and that its application overcomes the problem of poor reproducibility in experiments.
The Prediction of Partial Anaerobiosis in Saturated Soil: A Transient Moving Boundary Problem
Authors: McConnaughey P. K. , Bouldin D. R.
Published: July 2010

Past models of partial anaerobiosis in saturated aggregates or thin layers of sediment have assumed steady‐state conditions. In this paper, the transient case in one dimension is described. A numerical boundary‐tracking technique was derived to solve the transient case, and a “quasi‐steady‐state” approximate solution was presented. The numerical method yielded accurate results for two test problems, and was shown to converge as the computational mesh was refined. A dimensionless transient problem was solved and the transient numerical solution and a “quasi‐steady‐state” approximation yielded similar results for aerobic/anaerobic boundary velocities < 7 × 10−3 m d−1. This boundary velocity is much greater than those noted in the literature. The results demonstrate that the quasi‐steady‐state approximation is an acceptable description of aerobic/anaerobic boundary movement and oxygen consumption rates under most soil conditions.
Infiltration Rate of Slot Mulches: Measurement and Numerical Simulation
Authors: Redinger G. J. , Campbell G. S. , Saxton K. E. , Papendick R. I.
Published: July 2010

Mulched soil slots may be used to increase infiltration and reduce runoff and erosion on land where infiltration is restricted by soil freezing or low soil permeability. To establish optimum slot dimensions and spacing, the effect of slot width, slot depth, and saturated hydraulic conductivity on infiltration must be determined. A numerical solution to the soil water flow equation in two dimensions was used to simulate slot mulch infiltration. The Kirchhoff integral transform was used to reduce the nonlinearity of the coefficients, and the finite difference equations were solved using a Newton‐Raphson procedure. Simulations were in reasonable agreement with field measurements. A sensitivity analysis was used to show the effect of simulated changes in saturated conductivity, slot dimensions, and slope on water infiltration into the slots. The effect of slope on infiltration was negligible. A function was derived which predicts steady infiltration rate, given values for saturated conductivity, slot depth, and slot width.
A Predictor‐Corrector Method for Measurement of Hydraulic Conductivity and Membrane Conductance
Authors: Mualem Y. , Klute A.
Published: July 2010

An experimental procedure is developed for the measurement of the hydraulic conductivity of unsaturated soil on wetting and drying processes taking into account the hysteresis phenomenon. The proposed method expedites the measurement of the hydraulic properties, minimizes experimental errors, and avoids ambiguity due to hysteresis. The dependence of the membrane conductance in a flow cell on the soil water content was also investigated. The membrane conductance decreases by several orders of magnitude as the soil dries, and increases following a wetting process. A power function seems to represent quite well the relationship between the membrane relative conductance and the soil relative hydraulic conductivity.
Arsenite Sorption and Desorption in Soils
Authors: Elkhatib E. A. , Bennett O. L. , Wright R. J.
Published: July 2010

A linear form of the Freundlich isotherm was used to describe arsenite [As(III)] sorption by the A and B horizons of five West Virginia soils. Arsenite sorption conformed to the Freundlich isotherm over the entire concentration range for all the soils. Simple correlation coefficients and multiple regression equations were used to relate soil properties to parameters of the Freundlich equation. Iron oxide percentage and pH were the soil properties most closely related to parameters of As(III) sorption. The rate of As(III) sorption by the A and B horizons of an Upshur soil was rapid initially and decreased with time. A modified form of the Freundlich equation was used to explain the As(III) sorption rate data. Arsenite sorption was not reversible; only a small amount of the sorbed As(III) was released after five desorption steps. The modified Freundlich equation was also used to describe As(III) desorption rate. Simple and multiple regression calculations indicated that iron oxides and pH were correlated with the rate of As(III) desorption by the investigated soils.
Field Evaluations of Zinc Sources Band Applied in Ammonium Polyphosphate Suspension
Authors: Hergert G. W. , Rehm G. W. , Wiese R. A.
Published: July 2010

Although the importance of the addition of Zn to a fertilizer program for corn (Zea mays L.) production has been recognized for some time, the question of effectiveness of source and rate has not been completely resolved. This is especially true for situations where Zn is applied in fluid fertilizers. The objective of this study was to evaluate the effect of five Zn sources [ZnEDTA, Zn‐NH3 complex, ZnO, ZnSO4, and Zn(NO)3)2] applied at five rates (0, 0.11, 0.33, 1.12, and 3.36 kg Zn ha−1) on the growth and yield of irrigated corn on sandy soils. The experiments were conducted at four locations during a 2‐yr period. All Zn sources were suspended in ammonium polyphosphate and applied to the side of and below the seed at planting. Whole corn plants were collected at two growth stages and analyzed for Zn. Significant differences among Zn sources for Zn uptake were shown. ZnEDTA performed poorly at two sites due to early season leaching; however, it was the superior source at a calcareous site. The Zn‐NH3 complex was the superior source at one of the sites. The 0.1M HCl and DTPA soil tests correlated well with early Zn uptake for the noncalcareous sites. The critical DTPA soil test level for grain response at these locations was near 0.4 mg kg−1. Grain yields were increased by Zn fertilization at only two locations and there were no differences among Zn sources or significant Zn rate by source interactions. Regression equations for the responsive sites showed that between 1 and 2 kg Zn ha−1 was required to attain maximum yield. Although Zn uptake indicated differences in performance of Zn sources, the differences were not reflected in grain yield.
Soil Temperature in a Row Crop with Incomplete Surface Cover
Authors: Horton R. , Aguirre‐Luna O. , Wierenga P. J.
Published: July 2010

A method is presented to predict soil temperature distribution between rows of crops that partially shade the soil surface. The method combines a model for predicting time and location of soil surface shading with a model for two‐dimensional soil heat transfer. The track of shadow model is general, and requires only plant shape parameters, field location coordinates, row spacing, and row direction to predict soil surface shading as a function of time. The soil heat transfer model is an explicit finite difference approximation of the transient conduction equation, allowing for time and space dependence of soil thermal properties. The surface boundary temperatures are computed by partitioning the surface net radiation into the sensible air, latent, and ground heat flux components. Standard meteorological inputs required to compute the energy partitioning are global radiation, air temperature and humidity, and windspeed. Observed and computed temperature distributions show agreement for a 1‐d simulation. To predict surface energy partitioning and soil temperature accurately for longer periods of time, the method must be expanded to account for water transport.
Extraction by Barium Salts of Heavy Metals from Two Chilean Soils
Authors: Ahumada I. A. , Schalscha E. B. , Pratt P. F. , Mattigod S. V.
Published: July 2010

Extraction of Cd, Cu, Ni, and Zn by BaCl2 and Ba(ClO4)2 solutions from El Recuerdo (Vertisol) and Puerto Octay (Andept) soils was used to measure the amounts of metals remaining extractable during a 60‐d storage period under air‐dry and wet conditions. The El Recuerdo soil with an original pH of 7.3 sorbed about twice the amounts of metals sorbed by the Puerto Octay soil with an original pH of 5.5. The percent of the sorbed metal that remained extractable was in the order of Cd > Ni > Zn > Cu for El Recuerdo but Ni > Cd > Zn > Cu for the Puerto Octay soils. The decrease in pH associated with metal sorption was greatest for Cu which also showed the maximum fixation against extraction with Ba. The amounts of metals remaining extractable generally decreased with time, indicating that fixation reactions were essentially complete in 15 d in most cases and continued beyond the 15‐d period in a few cases. The BaCl2 solution desorbed more Cd than Ba(ClO4)2, but this effect of anion was not shown for the other metals, which agrees with the fact that the stability constants for soluble Cl complexes for Cd are greater than for the other metals. Only small and inconsistent differences were found for storage in air‐dry as compared to wet conditions.
Principal Component Analysis of Prairie Pothole Soils in North Dakota
Authors: Richardson J. L. , Bigler R. J.
Published: July 2010

Selected soil properties in several semipermanent wetlands were compared using a vegetation‐zone model. Principal component analysis was employed for variable analysis. Relative distribution of soil properties does not appear to be strongly related to water levels and would not change if large but infrequent variations in water level occurred. Salinity (electrical conductivity) was the most important soil variable among the wetlands studied, and salinity differences among wetlands are probably due to discharge from higher wetlands and water sources. Differences in organic carbon distribution as determined by principal component analysis were also significant. In general the soil surface is continually enriched with organic matter but the organic matter decreases with depth and presumably with time. Also, the organic matter influences CaCO3 precipitation and dissolution. Sedimentation processes are important in producing texture differences among these soils; the pond interiors are fine textured and the edges are coarse textured. The edges also become coarser textured near the surface as the ponds fill with sediment.
Hydraulic Properties of Some Soils with Paralithic Contacts
Authors: Paetzold R. F. , Mausbach M. J.
Published: July 2010

Several soils containing paralithic contacts over sedimentary materials were studied. Hydraulic and related soil physical properties were determined in an effort to explain root restriction associated with paralithic contacts. These properties were evaluated for their usefulness as criteria in confirming the presence and location of paralithic contacts. Bulk density ranged from 1.21 to 1.78 Mg m−3 in C horizons and from 1.17 to 2.05 in Cr horizons. No statistical difference was found between C and Cr horizon bulk densities. Paired determinations showed no statistical difference in bulk density between the horizon immediately above and the horizon immediately below a paralithic contact. Similar results were obtained for total porosity and air‐filled porosity at 33 kPa water content except that there was a statistical difference in air‐filled porosity at 33‐kPa water content between C and Cr horizons in fine‐textured soils. Although Cr horizons retained more water at both 33 and 1500 kPa than C horizons, the water retention difference was the same for both C and Cr horizons. Hydraulic conductivity values were similar for all horizons within a particular soil. No abrupt or unusual change, in any soil property measured, was observed at a paralithic contact. High bulk density and poor water supplying ability were eliminated as aids useful in identifying and locating paralithic contacts in the materials studied.
An Evaluation of Potassium Hydroxide Extractable Aluminum in Andepts (Andisols)
Authors: Kimble J. M. , Holzhey C. S. , Holmgren G. G. S.
Published: July 2010

Potassium hydroxide‐extractable Al is proposed as the basis of a field or laboratory criterion for the classification of Andepts (Andisols). Twelve pedons from volcanic‐derived parent material were studied, and in all of the pedons that met the existing criteria for an exchange complex dominated by amorphous material, KOH‐extractable Al was > 20g kg−1 (2%). Since this extraction is quick and easy and can be run in the field, it will allow soil scientists to distinguish andic materials from others in the field.
Field Identification of Spodic Horizons with Potassium Hydroxide Extractable Aluminum and Humic Acid Color
Authors: Holmgren G. G. S. , Yeck R. D.
Published: July 2010

Fifty‐nine previously classified soils were analyzed for humic acid color and KOH aluminum. These variables were used to develop alternate criteria for the spodic horizon by comparing data with the existing classifications. The resulting criteria are as follows: Humic acid color greater than or equal to 10 L platinum color units per gram or, maximum B horizon KOH‐extractable Al > 7 g kg−1 (0.7%), with a ratio of maximum Al in the B horizon to minimum Al in the E horizon of 2 or more. This latter requirement is necessary to distinguish Spododols from Andepts if the KOH aluminum criterion is used. Soils with discrepant classifications by laboratory data, field morphology, and by these alternate criteria were examined to bring out the reasons for the differences. A second set of soils was then examined in terms of the proposed criteria. Of this second set, 88% were classified by the proposed criteria in agreement with either the laboratory or the field estimate of the classification. The principal disagreements in both sets of soils could be explained as a consequence of the questionable exclusion from Spodosols of soils with low pyrophosphate (Fe + Al)/dithionite (Fe + Al) ratios and by the effect of high or low clay contents on the pyrophosphate (Fe + Al)/clay ratio requirement. In some cases, the classification more closely corresponds to the field morphology than does classification by the existing laboratory criteria. A principal advantage is that the procedures can be performed under field conditions.
Effects of Soybeans on Soil Properties Related to Soil Erodibility
Authors: Bathke G. R. , Blake G. R.
Published: July 2010

Research was conducted from 1980 to 1982 to examine the relationship between soybean (Glycine max L.) cropping and enhanced soil erodibility. Soil samples from the 1‐to10‐cm layer were taken from contiguous fields, cropped to soybeans and corn (Zea mays L.) the previous season, across Southern Minnesota in the spring of 1980 (1980 field survey) and the spring of 1982 (1982 field survey) and analyzed for their aggregation tendencies. In the 1980 field survey, aggregate size, stability, and carbon content were lower following soybeans than corn. The 1982 field survey indicated a reduced cloddiness in soybean fields when compared with corn fields by using a rapid field sieving test. Percent by weight of clods > 19 mm was less, and percent by weight of clods < 10 mm was greater following soybeans than corn. Field plots were established to study the soil‐protecting effect which has been attributed to a soybean canopy. A soybean canopy was not effective in maintaining aggregate size or stability during the growing season over that of a bare soil. Leaving soybean residue on the soil surface during winter resulted in larger, more stable aggregates than plots with no cover or residues. A second set of field plots was designed to investigate the effects of a soybean or corn crop and combinations of surface residue conditions on soil properties. Aggregates were of equal size but significantly less stable after soybeans compared with corn when sampled in the fall. In the spring the aggregates were less stable at one location and of equal stability at two locations, but were smaller in size due to soybean cropping at all locations. Replacing soybean with corn residue during winter generally had no consistent significant effect on soil aggregation. This leads to the conclusion that there is an effect of the growing crops themselves, or of their root remains, or both on soil aggregates, but not attributable to above‐ground residue differences between crops.
Tillage Effects on Surface Soil Physical Conditions and Sorghum Emergence
Authors: Unger Paul W.
Published: July 2010

Tillage and soil crusts, among other factors, influence seedling emergence. Crust strength (CS) is related to crust water content (WC), which is influenced by tillage. Tillage also influences surface soil physical conditions that may be related to CS. This study tested the hypothesis that different tillage methods result in different CS at similar times after rainfall or irrigation and determined which tillage‐mediated soil factors were responsible for CS differences of Pullman silty clay loam (fine, mixed, thermic Torrertic Paleustolls). Tillage treatments during fallow from winter wheat (Triticum aestivum L.) harvest to grain sorghum [Sorghum bicolor (L.) Moench] planting were moldboard (MT), disk (DT), rotary (RT), sweep (ST) and no‐tillage (NT). Initial tillage usually caused the greatest differences in surface conditions. Subsequent tillage and weathering eliminated most differences by sorghum planting time. Moldboard tillage, which covered most residues, usually had the greatest effect and NT, which maintained surface residues, usually had the least effect on surface conditions. Conditions evaluated were organic matter content, dry aggregate size, modulus of rupture of briquettes, crushing resistance of briquette fragments, random roughness, surface residues, and crust strength and water content. Sprinkler irrigations after sorghum planting did not result in crusts that impeded seedling emergence, but more intense rain may have caused problems. Because surface conditions generally improved with time after initial tillage, results of this study suggest that major tillage, where used, should be performed well before planting to minimize plant establishment problems. Adverse surface conditions can be minimized by using a conservation tillage system, such as NT.
Effects of Clearfelling and Site Preparation on Nitrogen Mineralization in a Southern Pine Stand
Authors: Burger J. A. , Pritchett W. L.
Published: July 2010

A clearcut forest site (45‐year‐old natural stand of Pinus elliottii Engelm. and Pinus palustris Mill.) was subjected to different intensities of site preparation to determine management impacts on N availability. Using a laboratory aerobic soil incubation technique, N mineralization potentials (N mineralizable over time) (No) were determined to be 25.0, 23.3, and 17.7 µg/g for soils from an uncut control area; a burned and chopped area; and a bladed, disced, and bedded area, respectively. The No of soil from the intensively treated area was significantly lower than the others when measured in the laboratory; however, simulations of field conditions indicated that more N may be mineralized in soils from intensively treated sites due to more favorable soil moisture and temperature conditions. Mineralization rates for these three areas, however, were not significantly different, and C/N ratios (28 and 26 for the chopped and bladed sites, respectively) for the clearcut and prepared areas did not suggest a difference in N availability. Ratios of organic matter/soluble carbon (OM/Ca) increased from 79 to 136 with treatment intensity and suggest that the N associated with the organic matter remaining on the most intensively treated site may be more resistant to decomposition. Nitrogen availability is a function of substrate quality and microenvironmental conditions. Harvesting and site treatment affected both of these. Laboratory determinations of No appear to be a better index of nitrogen availability than C/N, Cs, or total N, but do not adequately account for differences in mineralization due to treatment‐induced changes in the soil environment.
Extraction of Aluminum from Aluminum‐Organic Matter in Relation to Titratable Acidity
Authors: Hargrove W. L. , Thomas G. W.
Published: July 2010

This study was conducted to further characterize aluminum (Al)‐organic matter complexes and their role in soil acidity. The objective was to determine the extractability of Al from organic matter and to relate it to titratable acidity. Two samples of muck were treated with Al3+ in such a way as to achieve a range in Al saturation. The titratable acidity [determined conductimetrically with Ca(OH)2] of selected samples was compared to the Al extracted with 1 M KCl, 0.5 M CuCl2, 2 M HCl, 1 M NH4OOCCH3 (pH 4.8), 0.5 M CaCl2, and 0.33 M LaCl3. Results show that NH4OOCCH3 (pH 4.8) is a very poor extractant of Al associated with organic matter. For unbuffered salts, the effectiveness of the extractant generally decreased as the valence of the replacing cation decreased (i.e. La3+ > Ca2+ > K+). Copper is an exception to this rule as a result of its ionic structure and its tendency to form “inner sphere” complexes with organic matter, displacing a disproportionate fraction of the Al. Lanthanum extracts an amount of Al which seems well related to the titratable acidity and, thus, to the lime requirement. On the other hand, K+ extracts far too little Al, while Cu2+ extracts all of the Al present. The use of LaCl3 to predict lime requirement on field soils (especially where organic matter is increasing such as for no‐tillage, etc.) looks promising but needs widespread evaluation.