bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apparatus for Studying Pesticide Degradation in the Vadose Zone
Authors: Isensee Allan R. 
Published: July 2010

AbstractAn apparatus was constructed to study pesticide degradation in situ under vadose‐zone conditions. The apparatus consists of a 15‐cm (i.d.) casing and an enclosed vadose exposure chamber wherein pesticide‐treated soil cores, placed in the chamber, can be equilibrated with the surrounding vadose zone at selected depths. Monitored for 100 d, O2 concentrations at 0.5‐, 1.0‐, and 2.0‐m depths were nearly identical to O2 concentrations in control samplers, indicating that the apparatus was in equilibrium with the soil atmosphere and is appropriately isolated from the surface atmosphere. Both radiolabeled and unlabeled pesticides can be studied in the apparatus because the chamber is self‐sealing in the event of unexpected flooding.
Soil Water Diffusivity as Explicitly Dependent on Both Time and Water Content
Authors: Guerrini Ivan A. , Swartzendruber D. 
Published: July 2010

AbstractReliable experimental data do not always conform with customary soil‐water flow theory for truly rigid porous media. The purpose of this study was to derive a mathematical description capable of accommodating such data. A new mathematical solution was obtained for the absorption of water by an unsaturated horizontal column of soil termed semirigid, but which does not swell in the ordinary sense of a change in bulk density. Nonetheless, the semirigid soil does undergo microlevel rearrangement of its particles, envisaged as introducing an auxiliary dependence on time t into the diffusivity D in addition to the usual dependence on the volumetric water content, θ that is, D = D(θ,t). With product‐form separation of variables introduced at two stages of the solution process, there emerges the new variable λ equal to distance x divided by a new time function [Q(t)]1/2. Subject to modest constraint, Q(t) may be selected to best describe the particular soil in question. Choosing [Q(t)]1/2 = tn with exponent n as a positive constant, thus yielding λ = xt‐n instead of the classical Boltzmann form xt−1/2, the new solution was tested experimentally on a set of published data not conforming to customary flow theory for rigid media. The new solution provided a greatly improved description of these data, with exponent n = 0.46362 instead of 1/2 as for rigid media. The diffusivity function is D(θ,t) = 2nE(θ)t2n‐1, where E(θ) is a diffusivity‐like function of θ alone.
Competitive Sorption of Cobalt, Copper, and Nickel Ions by a Calcium‐Saturated Soil
Authors: Harter R. D. 
Published: July 2010

AbstractSolution ionic composition strongly affects ion sorption onto solid surfaces. This study evaluated the effect of competing ions on heavymetal sorption by soil. Investigations were conducted on Ca‐saturated soil in 0.5 mmol L−1 CaCl2 solution. Sorption of Ni2+, Co2+, and Cu2+ in binary metal‐Ca and ternary Ni‐Co‐Ca or Ni‐Cu‐Ca systems were evaluated. Sorption occurred in the order Cu > Ni ≈ Co, with the soil exhibiting selectivity to Cu2+, but not to Ni2+ or Co2+. Nickel sorption was equivalent to Ca2+ release, but neither Co2+ nor Cu2+ sorption was accompanied by an equivalent Ca2+ release. In the ternary systems, neither Co2+ nor 0.016 mmol L−1 Cu2+ caused a significant decrease in Ni2+ sorption. At 0.079 mmol L−1, Cu2+ did cause an observable decrease in Ni2+ sorption. Copper sorption was not affected by Ni2+, but Co2+ sorption decreased in direct proportion to Ni2+ sorption. Apparently, Ni2+ was retained by an exchange mechanism, but Co2+ and Cu2+ sorption was more complex. Nickel competed with Co2+ for sorption sites to a greater extent than did Co2+ for Ni2+ sites. Copper was selectively sorbed from the Ca2+ solution, while Co2+ and Ni2+ were able to compete with Ca2+ only in very dilute solutions. Maintaining a near‐neutral soil pH may not always be the best strategy for minimizing heavy‐metal mobility. Some ions appear unable to compete with Ca2+ for sorption sites at ionic strengths representative of near‐neutral pH. Thus, while absolute solubility may be controlled, mobility in solution may be enhanced by increased ionic strength as the soil pH approaches neutrality.
Measuring Adsorption Isotherms Using Continuous, Unsaturated Flow through Intact Soil Cores
Authors: Qualls Robert , Haines Bruce L. 
Published: July 2010

AbstractConventional batch adsorption‐isotherm experiments are conducted under conditions that are generally not representative of field conditions. Our objective was to develop and illustrate a technique that uses continuous, unsaturated flow through intact soil cores and gives information analogous to standard batch absorption experiments. Soil cores were placed on filter funnels and continuous flow was induced by controlled vacuum. Solution, 10 times the weight of the soil, was applied and recycled until apparent equilibrium concentrations were observed. While the total solution‐to‐soil ratio was 10:1, the amount in contact with soil at any instant was small. The procedure was replicated on separate cores with different initial solute concentrations to give different final equilibrium concentrations as a function of solute adsorbed per gram of soil. The technique was illustrated by observing adsorption of forest floor dissolved organic C to cores of AB horizon soil, and was compared with conventional batch adsorption data. Isotherms using both methods were linear but the slope of the batch isotherm was somewhat less. This flowthrough technique provides a way to obtain adsorption‐isotherm data under more realistic conditions.
Iron‐Manganese Relationships in White Lupine Grown on a Calciaquoll
Authors: Moraghan J. T. 
Published: July 2010

AbstractThe Fe chelate of ethylenediamine‐di‐O‐hydroxphenylacetic acid (EDDHA) applied to calcareous soils strongly suppresses Mn accumulation in many plants with Strategy I Fe‐stress responses. However, white lupine (Lupinus albus L. cv. Kiev), a legume with proteoid roots, does not show this typical suppression. This study was conducted to determine under greenhouse conditions the influence of NaH2PO4‐P (0, 60, and 120 mg kg−1) and FeEDDHA‐Fe (0, 1, 2, 4, and 8 mg kg−1) rates on Mn accumulation by both inoculated (Bradyrhizobium lupini) and NH4NO3‐N (80 mg kg−1) treated white lupine grown on a Wheatville loam (coarse‐silty over clayey, frigid Aeric Calciaquoll). Application of 60 and 120 mg P kg−1 decreased shoot Mn concentrations six‐ and 17‐fold, respectively, presumably due to suppression of proteoid roots. Inoculated plants generally had at least twice the shoot Mn concentration of their N‐treated counterparts. FeEDDHA had little effect on suppressing shoot Mn concentration except in plants treated with 120 mg P kg−1. Symptoms atypical of P deficiency, apparently due to Mn toxicity, developed in plants grown without added P. In contrast, N‐treated plants grown with 120 mg P kg−1 and 8 mg Fe kg−1 developed an abnormality resembling Mn deficiency. Ammonium nitrate and added P, but not high shoot Mn concentration, intensified Fe‐deficiency chlorosis in leaflets. Complex interactions involving the source of N and availability of Fe, P, and Mn affected the growth of white lupine on the Wheatville soil.
Lime Effects on Phosphorus Availability in a Calcareous Soil
Authors: Westermann D. T. 
Published: July 2010

AbstractCrop yields are sometimes reduced on irrigated calcareous soils with elevated lime concentrations. This study was conducted to determine the influence of lime on P availability. The effects of acid‐equivalent lime concentrations and P fertilization rates on NaHCO3‐soluble P, anion resin‐extractable P, P‐adsorption isotherms in 0.01 M CaCl2, and P uptake by sudangrass [Sorghum bicolor (L.) Moench] and potato (Solanum tuberosum L.) were investigated in the greenhouse on soil samples from the Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid). Plant P uptake was increased by P fertilization and decreased by increasing lime concentration. Phosphorus uptake was curvilinearly related to solution P (extracted by 0.01 M CaCl2). Solution P concentrations increased linearly as the resin‐extractable P/equilibrium buffer capacity (EBC) ratio increased, where EBC is the slope of the P‐adsorption isotherm at the indigenous equilibrium P concentration. The EBC increased as the lime concentration increased. Phosphorus applications increased solution P and resinextractable P and decreased EBC within a given lime concentration. These data indicate that the soil‐test P concentration or P fertilization rate should increase as the lime concentration increases to provide the same degree of P availability and plant P uptake in this calcareous soil.
Phosphorus, Nitrogen, and Carbon Fractions in Litter and Soil of Southern Pine Plantations
Authors: Polglase P. J. , Jokela E. J. , Comerford N. B. 
Published: July 2010

AbstractThe long‐term productivity of intensively managed loblolly (Pinus taeda L.) and slash pine (P. elliottii Engelm. var. elliottii) plantations will be determined largely by the effect of silvicultural practices on subsequent release of N and P from litter and soil. This study characterized labile P, N, and organic‐C fractions in the Oi, Oe1, and Oe2 horizons of needle litter and the A horizon of soil from plots receiving weed control, fertilizer treatments, or both. Because fertilizer had been placed in localized bands around the base of each tree, samples could be collected away from these areas and analyzed without interference from residual fertilizer. Samples were analyzed for inorganic P (Pi), organic P (Po), organic N (No), sugars, and phenols in a sequential‐extraction procedure of cold, then hot, trichloroacetic acid (TCA). Inorganic P was about 40% of total P in Oi horizon needles of reference (untreated) plots, and about 75% of total P in fertilized plots. In loblolly pine, addition of fertilizer caused the concentration of P in Oi horizon needles to about double, this increase being accounted for by accumulation of Pi. Total P decreased between the Oi and Oe1 horizons of litter, indicating a large net release of P during the early stages of decomposition. This depletion in total P was wholly accounted for by depletion of Pi. Only about 20% of the total N in Oi horizon needles was labile (soluble in TCA), and N fractions were unaffected by cultural treatments. Total N concentration increased during decomposition, mostly through progressive accumulation of the residual (insoluble) N fraction.
Crop Rotation and Residue Management Effects on Soil Carbon and Microbial Dynamics
Authors: Collins H. P. , Rasmussen P. E. , Douglas C. L. 
Published: July 2010

AbstractUnderstanding microbial dynamics is important in the development of new management strategies to reverse declining organic‐matter content and fertility of agricultural soils. To determine the effects of crop rotation, crop residue management, and N fertilization, we measured changes in microbial biomass C and N and populations of several soil microbial groups in long‐term (58‐yr) plots under different winter wheat (Triticum aestivum L.) crop rotations. Wheat‐fallow treatments included: wheat straw incorporated (5 Mg ha−1), no N fertilization; wheat straw incorporated, 90 kg N ha−1; wheat straw fall burned, no N fertilization; and wheat straw incorporated, 11 Mg barnyard manure ha−1. Annual‐crop treatments were: continuous wheat, straw incorporated, 90 kg N ha−1; wheat‐pea (Pisum sativum L.) rotation (25 yr), wheat and pea straw incorporated, 90 kg N ha−1 applied to wheat; and continuous grass pasture. Total soil and microbial biomass C and N contents were significantly greater in annual‐crop than wheat‐fallow rotations, except when manure was applied. Microbial biomass C in annual‐crop and wheat‐fallow rotations averaged 50 and 25%, respectively, of that in grass pasture. Residue management significantly influenced the level of microbial biomass C; for example, burning residues reduced microbial biomass to 57% of that in plots receiving barnyard manure. Microbial C represented 4.3, 2.8, and 2.2% and microbial N 5.3, 4.9, and 3.3% of total soil C and N under grass pasture, annual cropping, and wheat‐fallow, respectively. Both microbial counts and microbial biomass were higher in early spring than other seasons. Annual cropping significantly reduced declines in soil organic matter and soil microbial biomass.
Determination of Bioavailable Phosphorus in Soil
Authors: Thien S. J. , Myers R. 
Published: July 2010

AbstractAvailable soil P (AP) is usually based on inorganic P (Pi) soil‐test levels, a practice that ignores the potential contribution of organic P (Po) mineralization. Our objective was to develop a P‐availability index that included both Pi and Po dymanics. Fourteen Kansas soils, ranging in bicarbonate‐extractable Pi from 1.5 to 21.5 mg P kg−1, were used. One set of soils was untreated and another enriched with C + N source to raise microbial activities and create a biological sink for P. The treated soil was designated as bioactive. After 7 d of incubation, we measured the quantity of NaHCO3‐extractable Pi, total P (Pt), and inorganic plus microbial P (Pi+m) in both soils and used these data to describe the size of the labile Po, microbial P (Pm), immobilized Pi (Pimmob), potentially mineralizable Po (Pmin), total bioavailable P, and bioavailable Po pools. Bioactive soils always had less Pi than untreated soils after incubation, probably, because of microbial immobilization. Labile Po in the bioactive soils averaged 2.4 times greater than in untreated soils. Labile Po after incubation averaged 2.8 times greater than the Pi level prior to incubation in bioactive soils and remained essentially the same in untreated soils. Clearly, microbial activity enhanced Po availability, an increase in AP that would not be apparent in soil tests where chemical extractions measure only Pi. We combined the Pi, Po, and Pm pools to create a bioavailable‐P index. This index differed from the typical soil‐test P index (preincubation Pi) more for the bioactive soil (r2 = 0.50) than for the untreated soil (r2 = 0.74). These data suggest this extraction scheme can enhance understanding of the P‐supplying power and P nutritional dynamics of certain soils.
Imhoff Cone Determination of Sediment in Irrigation Runoff
Authors: Sojka R. E. , Carter D. L. , Brown M. J. 
Published: July 2010

AbstractThere is a need to rapidly quantify erosion from irrigated farmland. The prevailing method consists of collecting runoff samples, then filtering, drying, and weighing them to determine sediment concentration. Labor cost and slow data availability prompted development of a faster, less expensive technique. Sediment settling volume in a graduated vessel was expected to correlate well with total mass of suspended sediment. Eight soils varying in texture, mineralogy, and organic‐matter content were sampled, fragmented, and air dried. A series of 1‐L suspensions was prepared with sediment concentrations from 1 to 30 g L−1. Samples were either hand shaken for 30 s or mechanically blended for 60 s. Suspensions were decanted into graduated Imhoff cones and allowed to settle for 0.5 h (1800 s). The series was repeated three times for each soil. Settling volume was regressed against sediment concentration (total sediment, g L−1). Field calibrations for two soils were developed from furrow runoff samples. Laboratory regressions had a mean r2 of 0.99. Field regressions of two soils had r2 of 0.94 or higher. Cone design did not permit accurate volume estimates of the first 1 mL, causing slopes and intercepts to very among field regressions for sediment concentrations < 1.0 g L−1. These samples, however, represent negligible erosion, and therefore have little value. Slope and intercept of field regressions corresponded closely to 30‐s‐shaken laboratory regressions but different statistically at P ≤0.05. The technique provided a rapid, inexpensive, and accurate suspended‐sediment determination in the field for concentrations >1.0 g L−1. Several settling‐volume predictions based on textural components and organic‐matter content had r2 >0.60. Laboratory 30‐s hand‐shaken calibrations may be adequate for diagnostic purposes, but individual field calibrations should be performed for research purposes.
Rapid Weathering of a Trioctahedral Mica by the Roots of Ryegrass
Authors: Hinsinger Philippe , Jaillard Benoit , Dufey Joseph E. 
Published: July 2010

AbstractThe weathering of a trioctahedral mica (phlogopite, 2–100‐µm particle size) was investigated in the rhizosphere of ‘Turilo’ Italian ryegrass (Lolium multiflorum Lam.). A special culture vessel made it possible to simulate a one‐dimensional macroscopic rhizosphere by developing a root mat on a polyamide net. This root mat was laid down on a mica‐agar substrate that was cut into slices 0.5 mm thick (parallel to the root mat) after 1, 2, 3, and 4 d of contact. The phlogopite mica was the sole source of both K and Mg for the plants. Whereas there was no significant release of Mg as a consequence of the roots' activity, K was released and concomitantly the mica lattice expanded after 3 d of continuous exposure to the root mat, in response to K uptake by plants. After 4 d, the vermiculitization of the phlogopite was detectable up to 1.5 mm from the root surface (i.e., the root mat) by x‐ray diffractometry. Such rapid mineralogical changes induced by roots support the view that primary minerals such as trioctahedral micas might contribute significantly to the supply of K to the plants, at least around the most active parts of the roots.
Sequential Reduction and Oxidation of Inorganic Nitrogen, Manganese, and Iron in Flooded Soil
Authors: Patrick W. H. , Jugsujinda A. 
Published: July 2010

AbstractWhen a soil is flooded, the curtailment of O2 diffusion into the soil causes the microorganisms decomposing organic matter to switch from O2 to alternate electron acceptors. Three alternates utilized by facultative microorganisms when O2 becomes depleted are NO‐3, Mn4+ compounds, and Fe3+ compounds. We studied the sequence of reduction of these three redox systems under controlled redox potential conditions. The redox potential of soil suspensions was changed stepwise in 50‐mV increments from oxidized to reduced conditions and from reduced to oxidized conditions and maintained at each new potential for 15 d, at which time NO‐3, NH+4, Mn2+, and Fe2+ concentrations in the soil solution were analyzed. The results of this study showed that the oxidation and reduction of the three electron acceptors were sequential, with no overlap in the oxidation or reduction of the NO‐3 and Mn systems and little overlap in oxidation and reduction of the Mn and Fe systems. In the oxidized‐to‐reduced experiment, the critical redox potential at which all of the NO‐3was reduced and Mn2+ first appeared in the soil solution was approximately 200 mV. The critical redox potential at which Fe2+ appeared was 100 mV. For all three redox systems, the critical redox potentials for the oxidized‐to‐reduced transition were approximately 50 mV lower than for the reduced‐to‐oxidized transition.
Formation of Calcium and Magnesium Molybdate Complexes in Dilute Aqueous Solutions
Authors: Essington M. E. 
Published: July 2010

AbstractIn order to increase our understanding of the chemistry of Mo in soil, waste‐affected soil, and waste‐disposal environments, it is imperative to understand the processes controlling the aqueous and solid‐phase distribution of Mo. Recent research shows the importance of alkaline earth metal ion pairs with molybdate in aqueous solutions. However, ion association constants for these species have not been rigorously determined. The objectives of this study were to measure conditional ion association constants (log cQ) for the formation of Ca and Mg molybdate ion pairs. Potentiometric titrations were performed at pH 7 and 25 °C in NaNO3 ionic media. The logcQ values were converted to the zero‐ionic‐strength molar reference state (log Q) using the Davies equation. The mean log Q and standard free energy of formation (ΔGof) values for the formation of CaMoO04 are 2.57 ± 0.08 and −1405.19 ± 1.60 kJ mol−1, respectively. The mean log Q and ΔGof values for the formation of MgMoO04 are 3.03 ± 0.13 and −1309.08 ± 2.06 kJ mol−1, respectively.
Statistical Evaluation of Arsenic Adsorption Data Using Linear‐Plateau Regression Analysis
Authors: McGeehan S. L. , Naylor D. V. , Shafii B. 
Published: July 2010

AbstractFew studies have utilized a statistical approach for comparisons of adsorption data. Our objective was to evaluate the suitability of linear‐plateau regression analysis to identify the As adsorption plateau and facilitate statistical comparison of As‐adsorption rates and maxima. Three northern Idaho soils exhibiting a range in As‐adsorption capacity were tested. Batch techniques with ion chromatographic determination of arsenite and arsenate were used. The linear‐plateau regression model provided a good fit for the adsorption‐rate data. The time required to attain an adsorption plateau ranged from 2 to 8 h, depending on soil characteristics and As species. The model allowed statistical identification of the As‐adsorption plateau and subsequent comparison of As‐adsorption rates and maxima through use of analysis of covariance and least significant difference procedures.
Evaporation from Ridge‐Tilled Soil Covered with Herbicide‐Killed Winter Wheat
Authors: Heilman J. L. , McInnes K. J. , Gesch R. W. , Lascano R. J. 
Published: July 2010

AbstractCotton (Gossypium hirsutum L.) in the High Plains of Texas is frequently planted in ridge‐tilled soil covered with standing winter wheat (Triticum aestivum L.) residue created by killing the wheat in the spring with a herbicide. A study was conducted on an Olton sandy clay loam (fine, mixed, thermic Aridic Paleustoll) to determine how the winter wheat residue affects the surface energy halance and water vapor conductance of ridge‐furrow tilled soil. Surface energy‐balance measurements were obtained with the Bowen ratio method and evaporation from the residue was estimated gravimetrically. Flux measurements were combined with measurements of vapor density at the surface and at an elevation of 1 m to calculate a conductance for water vapor transport. Although the residue was tall (0.25 m) and relatively dense (76% ground cover), evaporation from the soil beneath the residue after irrigation was high, accounting for >60% of net irradiance (Rn). Evaporation from the residue itself was negligible. The combination of standing residue and ridge‐tilled soil created high spatial variability in the energy balance, and in surface vapor density and wind speed, suggesting high spatial variability in evaporation and soil drying. The residue decreased evaporation from wet soil, and wind enhanced vapor transport through the residue. Conductances calculated for bare, ridged soil were 1.2 to 2.7 times higher than values obtained in the presence of residue, with differences between bare and residue‐covered soil increasing with wind speed. Water vapor conductance increased linearly with wind speed measured at 1.0 m, but values were lower than those reported in the literature for other residue systems.