bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidative Coupling of Phenols and Anilines by Peroxidase: Structure‐Activity Relationships
Authors: Berry Duane F. , Boyd Stephen A. 
Published: July 2010

AbstractWe 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

AbstractMathematical 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

AbstractParent 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

AbstractThis 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

AbstractUptake 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

AbstractA 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

AbstractTillage 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

AbstractThere 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.
The Prediction of Partial Anaerobiosis in Saturated Soil: A Transient Moving Boundary Problem
Authors: McConnaughey P. K. , Bouldin D. R. 
Published: July 2010

AbstractPast 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

AbstractMulched 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

AbstractAn 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

AbstractA 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

AbstractAlthough 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

AbstractA 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

AbstractExtraction 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

AbstractSelected 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.