bluuebunny/crossref_metadata_2025 huggingface dataset:
Cesium‐137 Distribution in a California Pelloxerert: Evidence of Pedoturbation
Authors: Southard R. J. , Graham R. C.
Published: July 2010

The distribution of 137Cs activity in soils provides a means of assessing physical transport of soil particles. We measured the activity of 137Cs along cracks and within peds of a Chromic Pelloxerert on the flood plain of an ephemeral stream in the Central Valley of California to assess the role of pedoturbation in the formation of a Vertisol. The 137Cs activity is highest in the upper 10 cm of the soil and generally decreases with increasing depth, although 137Cs activity is also high locally along cracks and at the bottom of some cracks near the average depth of cracking (base of Bss horizon, 72‐cm depth). Laterally (along cracks vs. ped interiors), the 137Cs activity varies greatly and shows no consistent pattern. Micromorphological evidence of stress‐oriented clay in soil fabric and locally high 137Cs activity below 72 cm indicate incorporation of surface materials into deeper cracks during drier‐than‐average years. Organic carbon (OC) content decreases regularly with depth, whereas CaCO3 content is uniform throughout the upper 72 cm. The nonhomogeneous 137Cs distribution demonstrates that pedoturbation has occurred. The rate of homogenization of soil material in the upper 72 cm exceeds 25 yr and is slower than the rate of OC accumulation and humification, but faster than the rate of carbonate redistribution. We attribute relatively high 137Cs activity throughout the upper 20 to 30 cm of the soil to incorporation of surface material into minor cracks that open during the dry season. The incorporation of sloughed materials at the base of larger cracks, where evidence of shearing (slickensides) is most strongly developed, is only locally significant and is probably not the dominant mechanism of pedoturbation.
Partitioning Variability of Soil Properties Affecting Solute Movement with Soil Taxonomy
Authors: Seyfried M. S. , Hornsby A. G. , Rao P. V.
Published: July 2010

Soil taxonomy provides a classification framework for large amounts of data collected in conjunction with soil survey work. This framework may be very useful in parameterizing models of solute movement. An important criteria for usefulness is that the classification groupings reduce sample variability. We used nested analysis of variance to assess the effectiveness of the USDA soil taxonomy in describing sample variability. Soil characterization data from a total of 689 pedons sampled by horizon in Florida were analyzed. Eleven different soil physical and chemical properties important to the modeling of solute movement in soils were selected. Depth effects were incorporated by using surface horizon and depth‐weighted average values to depths of 50, 100, and 150 cm. We found that the USDA soil taxonomy very effectively partitioned variance, as evidenced by average R2 values of 0.80 for surface samples and 0.90 for depth‐weighted averages. Effectiveness improved with depth of consideration, reflecting the importance of subsoil characteristics in the USDA soil taxonomy. In general, the most effective taxonomic levels were the order, great group, and subgroup. This indicates that it is reasonable to lump or extrapolate data within the family or subgroup levels to obtain better estimates of soil property values in Florida. We believe that these results are probahly qualitatively applicable to other soil properties and locations, hut that quantitative extrapolation should not be done without further study.
Methods for Analyzing Constant‐Head Well Permeameter Data
Authors: Elrick D. E. , Reynolds W. D.
Published: July 2010

The constant‐head well permeameter has proven to be a useful and versatile instrument for determining the in situ hydraulic properties of soils in the unsaturated (vadose) zone. The flow measurements are obtained under conditions of saturated‐unsaturated, three‐dimensional flow in the unsaturated zone. As a consequence, the steady‐state flow rate out of the permeameter is determined by both the field‐saturated hydraulic conductivity (Kfs) and the matric flux potential (φm) of the unsaturated soil. Because both Kfs and φm contribute to the flow, calculation of these parameters from well permeameter data requires either the solution of two (or more) simultaneous equations, or reduction of the problem to one equation in one unknown if additional information is known or estimated. Use of the simultaneous‐equations approach in heterogeneous soils can result in a high percentage of invalid (i.e., negative) Kfs and φm values. Negative results can be avoided and good estimates obtained, however, by using an independent measurement or site estimate of the ratio α* = Kfs/φm.
Apparatus for Studying Pesticide Degradation in the Vadose Zone
Authors: Isensee Allan R.
Published: July 2010

An 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

Reliable 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

Solution 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

Conventional 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

The 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

Crop 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

The 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

Understanding 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

Available 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

There 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

The 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

When 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

In 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

Few 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

Cotton (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.
Semiempirical Model of Soil Water Hysteresis
Authors: Nimmo John R.
Published: July 2010

In order to represent hysteretic soil water retention curves accurately using as few measurements as possible, a new semiempirical model has been developed. It has two postulates related to physical characteristics of the medium, and two parameters, each with a definite physical interpretation, whose values are determined empirically for a given porous medium. One parameter represents the fraction of the pore space that is not subject to Haines jump hysteresis. Its associated postulate is that a single value of this parameter characterizes a given medium, or, equivalently, that the medium is self‐similar with respect to the division between hysteretic and nonhysteretic pore space. The second parameter is the effective body‐to‐neck size ratio of the medium's largest pore. The second postulate specifies a particular relation between the size distributions of pore bodies and of pore necks. Tests of the model show that it provides high‐quality optimized fits to measured water content vs. matric pressure wetting curves for a wide variety of media. The parameter values obtained through optimization correlate plausibly with such media properties as uniformity of particles, complexity of structure, and degree of compaction. A practical use of this model is to provide a complete simulated main wetting curve for a medium where only a main drying curve and two points on the wetting curve have been measured. With additional development, it may be possible to do without the two measured wetting points if parameters can be evaluated from other measurements or known properties of the medium.
Ion Transport in an Allophanic Andisol under the Influence of Variable Charge
Authors: Ishiguro M. , Song K.‐C. , Yuita K.
Published: July 2010

Because the density of variable charge in a soil is influenced by the solution concentration and the pH, exchanging ion transport in the soil is also affected by them. In this study, the effect of variable charge on exchanging ion transport in an allophanic Andisol (Typic Hydrudand) that has negative and positive variable charges was investigated experimentally. Miscible‐displacement experiments were conducted under saturated and unsaturated (−1.96 kPa of soil water pressure) conditions. The cases studied here involved ion exchange under a constant total concentration condition and a constant pH condition. A SrBr2 solution was applied to the soil column, which was initially saturated with a CaCl2 solution. The miscible‐displacement experiments were carried out at different total concentration (0.001–0.1 molc L−1) and pH (4.2–7.65). Bromine flowed out slowly at lower pH due to the large anion‐exchange capacity (AEC). Strontium discharged slowly at higher pH due to the large cation‐exchange capacity (CEC). The counterion penetrated slowly at a lower concentration because the amount of the counterion contained in a unit of solution volume was small. Observed breakthrough curves (BTCs) agreed with those expected from measured exchange isotherms. Based on the relationship between the Sr BTC and the Br BTC, no notable differences were observed between the BTCs under saturated conditions and those under unsaturated conditions. The influence of the solution concentration and the pH cannot be ignored when considering ion transport in an allophanic Andisol.
Analysis of Fluorobenzoate Tracers by Ion Chromatography
Authors: Pearson R. J. , Inskeep W. P. , Comfort S. D.
Published: July 2010

Pentafluorobenzoic acid (PFBA), 2,6‐difluorobenzoic acid (2,6‐DFBA), and orthotrifluoromethylbenzoic acid (o‐TFMBA) are three fluorobenzoates that have recently been used as tracers to monitor soil water and solute movement in soil systems. These fluorobenzoates are typically analyzed by high‐performance liquid chromatography (HPLC) with ultraviolet (UV) detection and have reported retention times ranging between 9 and 12.5 min. Ion chromatography (IC) analysis of these fluorobenzoates using conductivity detection is possible and faster than the currently used HPLC methodology. This study demonstrates the reliability of IC for fluorobenzoate tracer analysis. Mixed and single standard solutions (0.10–25 mg L−1) of PFBA, 2,6‐DFBA, o‐TFMBA and LiBr were prepared and analyzed using IC‐conductivity detection. High resolution among all four tracers was achieved by the methodology presented. However, we found that Cl‐ interferes with o‐TFMBA analysis even at low concentrations (1.0 mg Cl‐ L−1). Retention times of o‐TFMBA, 2,6‐DFBA, and PFBA by IC analysis ranged between 1.79 and 2.62 min with a linear detection response achieved across a 0.25 to 25 mg L−1 concentration range. These results indicate that IC analysis is an accurate and expedient means of determining both single and multiple fluorobenzoate and Br‐ concentrations in soil solutions and natural waters.
Release of Nitrogen from Ureaform Fractions as Influenced by Soil pH
Authors: Tlustos P. , Blackmer A. M.
Published: July 2010

Ureaforms are slow‐release N fertilizers that have potential for minimizing problems associated with leaching of NO‐3 from soils and accumulations of NO‐3 in vegetable crops. We studied the effects of soil pH on rates of release of N from various ureaform fractions. Three fractions (soluble in cold water, insoluble in hot water, and soluble in hot water but insoluble in cold water) were separated from a 15N‐labeled ureaform, and mineralization of N from these fractions and from labeled urea was studied in six soils having pH values ranging from 5.2 to 7.8. The results showed that rates of inorganic N (NH+4 and NO‐3) release were extremely pH dependent; they varied > 100‐fold for the cold‐water‐insoluble fractions. The cold‐water‐insoluble fractions were largely responsible for slow release of N in acid soils, but these fractions and much of the cold‐water‐soluble fractions were essentially inert in soils above neutrality. The results suggest that successful use of ureaform fertilizers would require modifications in rates of application or composition of the ureaform to adjust for differences in soil pH.
Stability of Synthetic Sand‐Clay Aggregates after Wetting and Drying Cycles
Authors: Singer M. J. , Southard R. J. , Warrington D. N. , Janitzky P.
Published: July 2010

We hypothesized that the lack of structure and low aggregate stability characteristic of many California Central Valley soils was due, in part, to infrequent wetting and drying cycles. We created synthetic aggregates by drying a slurry of 0.1‐ to 0.5‐mm‐diam. acid‐washed quartz sand and varying amounts of Ca‐saturated reference smectite, kaolinite, or illite at 40 °C. The resulting dry mixtures were crushed and sieved, and the 0.5‐ to 1.0‐ and 1.0‐ to 2.0‐mm‐diam. synthetic “aggregates” were subjected to up to 80 wetting and drying cycles. The wet aggregate stability (Yoder method) of 1.0‐ to 2.0‐mm‐diam. aggregates with 5% clay decreased, regardless of clay type, after 32 wetting and drying cycles. The smectite and illite 0.5‐ to 1‐mm‐diam. aggregate stability did not change significantly after 32 cycles. Following a decrease after eight cycles, wet stability for the 0.5‐ to 1‐mm 5% kaolinite aggregates increased to equal the zero‐cycle stability after 32 cycles. Increasing clay content to 25% increased the initial smectite wet aggregate stability, but decreased the kaolinite and illite wet aggregate stability for both aggregate size fractions. Scanning electron micrographs of the smectite‐sand aggregates showed that the sand grains became more tightly packed and clay became more uniformly distributed over the grains and formed grain bridges with increasing number of cycles. We attribute variation in response to wetting and drying cycles to different clay‐clay and clay‐sand interactions caused by inherent structural differences among the clays.
Simultaneous Use of Transmitted and Incident Ultraviolet Light in Describing Soil Microfabrics
Authors: Hartmann C. , Tessier D. , Wilding L. P.
Published: July 2010

A technique for studying thin sections using both transmitted and incident (reflected) ultraviolet (UV) light has been developed. These two light modes used simultaneously may clearly distinguish pore space, plasma (micromass), and skeleton grains (coarse fraction). For this purpose, either a simple binocular or a petrographic microscope can be used. This technique is complementary to classical methods described in the literature for thin‐section analysis and will, at least under conditions discussed here, help alleviate problems encountered in examining thin sections when the skeletal and plasma phases confound porosity identification and measurement.
Liquid Component of Evaporative Flow in Two Tilled Soils
Authors: Jalota S. K. , Prihar S. S.
Published: July 2010

Shallow tillage is generally considered to reduce evaporation by checking upward liquid flow within and across the tilled layer. To verify this contention, we partitioned the total water loss from tilled soil into loss from the tilled (5‐cm‐deep) layer per se and upward flow across the interface of the tilled layer and untilled soil. This was done to verify the occurrence and extent of liquid flow across the junction of tilled and untilled soil and within the tilled layer, and to facilitate modeling evaporation from tilled soil. The determinations were made in 10‐cm‐i.d., 95‐cm‐deep columns filled with silt loam and sandy loam soils. For 1 or 2 d after tillage, water loss from the tilled layer constituted a major portion of the total flux. However, it became negligible after 7 d in the sandy loam and 12 d in the silt loam while the flux across the interface increased. Liquid flux across the interface in 30 d of drying after tillage amounted to 72 and 42% of total loss under low and high atmospheric evaporativity, respectively, in the silt loam and 20 and 30%, respectively, in the sandy loam. The total liquid flux, taken as the difference between the experimentally determined total loss from the tilled soil and the vapor flux computed from the tilled layer by Hanks' (1958) equation, was identical in both time pattern and magnitude to that computed from the moisture profiles predicted numerically from the water‐content gradients, diffusivity D(θ), and hydraulic conductivity K(θ). Thus, the upward capillary flow was not completely cut off by tillage; it was only retarded because of the change in D(θ).
Soil‐Macropore and Layer Influences on Saturated Hydraulic Conductivity Measured with Borehole Permeameters
Authors: Wu L. , Swan J. B. , Nieber J. L. , Allmaras R. R.
Published: July 2010

The borehole permeameter technique can produce erratic saturated hydraulic conductivity (Ksat) in soils with macropores and abrupt layers because operating theory assumes homogeneous and isotropic conditions. Dye application during an infiltration test demonstrated water movement in macropores and erratic Ksat or matric flux potential (ϕm). To evaluate the effects of macropores, cracks, and layered soil on Ksat and ϕm, a finite element solution of the Richards equation was used to simulate infiltration from a borehole (0.03‐m radius and 0.50 m deep) with a constant head (H) of 0.05 or 0.10 m. Borehole infiltration (for 2 h) was simulated for a Rozetta silt loam (fine‐silty, mixed, mesic Typic Hapludalf) with four configurations: homogeneous, layered, a cylindrical macropore centered at the borehole base, and a crack intersecting the borehole wall. Simulated flow rates were increased by 29% (with H = 0.05 m) and 21% (with H = 0.10 m) when a cylindrical macropore (4 mm by 0.10 m) was located at the borehole base. Respective increases were 25% (H = 0.05 m) and 20% (H = 0.10 m) when a crack extending 0.1 m laterally intersected the borehole wall. Three methods were tested for calculating Ksat. The simultaneous‐equations approach (SEA) using either the Guelph or the Philip model for a homogeneously configured borehole estimated Ksat within a factor of 2 from input Ksat, but the Laplace analysis method overestimated input Ksat by a factor of 5 to 12. The fixed α value (α = Ksat/ϕm) method with either the Guelph or Philip model estimated Ksat close to input Ksat when a proper α value was chosen, but the proper α value differed by soil and model. A negative Ksat was computed using the SEA with the Guelph model when macropores intersected the base of a borehole; negative Ksat or ϕm were produced when cylindrical macropores laterally intersected the borehole wall, depending on the vertical locations of the macropores. Soil with layered hydraulic properties also produced unrealistic Ksat.
Evaluation of the Relationship between Compressibility and Shear Strength of Andisols
Authors: McNabb D. H. , Boersma L.
Published: July 2010

Andisols, and other soils with low bulk density, are often considered less susceptible to compaction than soils with higher bulk densities. This study was initiated to test the hypothesis that high soil strength reduces the compressibility of soils with low bulk density. The compressibility and shear strength of three Andisols were compared with that of a fine‐textured soil of crystalline mineralogy with a higher bulk density. Soil compressibility was measured in one‐dimensional consolidation tests and shear strength was measured in direct shear tests. Cores of undisturbed soil were collected from the 7‐ to 12‐cm depth of four forested soils in western Oregon. Cores were saturated prior to testing. Compression indexes were 0.231 for the coarse‐textured Andisol, 0.262 and 0.275 for two fine‐textured Andisols, and 0.320 for the fine‐textured soil of crystalline mineralogy, which was significantly higher than that of the Andisols. The angle of internal friction of the Andisols ranged from 33.0 to 33.7°, but was 28.9° for the fine‐textured soil of crystalline mineralogy. A nonlinear model was successfully adapted to describe the relationship between bulk density and normal stress using data of these sample sets. These samples had different initial and compressed bulk densities. We concluded that Andisols are less compressible than other denser soils because of a high shear strength. The question of the susceptibility to compaction of soils with low bulk density must be reconsidered.
Unsaturated Transport Processes in Undisturbed Heterogeneous Porous Media: II. Co‐Contaminants
Authors: Jardine P. M. , Jacobs G. K. , O'Dell J. D.
Published: July 2010

Department of Energy facilities involved in defense‐related activities have generated huge quantities of low‐level radioactive mixed waste during the past several decades. The waste is composed of organically complexed contaminants, also known as co‐contaminants, which are typically disposed in shallow land burial sites. The objective of this study was to provide an improved understanding of the geochemical processes controlling co‐contaminant transport in heterogeneous, unsaturated subsurface media. Large undisturbed columns were isolated from a proposed waste site consisting of fractured saprolitic shale, and the steady‐state unsaturated transport of Co(II)EDTA2−, Co(II)EDTA−, and SrEDTA2− was investigated at −10 cm pressure head. Subsurface Fe and Al sources effectively dissociated the SrEDTA2− co‐contaminant and Sr was transported as a reactive, uncomplexed species. The EDTA readily complexed with Fe and Al, resulting in significant solid‐phase modification of the porous media via chelate‐enhanced dissolution and redox alterations. Displacement of Co(II)EDTA2− through the subsurface media was characterized by a MnO2‐mediated oxidation of the co‐contaminant with subsequent formation of Co(III)EDTA−. The latter co‐contaminant was an extremely stable complex that was transported through the subsurface as a single, reactive entity and exhibited an overall retardation that was similar to the uncomplexed contaminant Co2+. Modeling results using equilibrium and nonequilibrium formulations of the convective‐dispersive equation suggested that a large portion of the transported Co(III)EDTA− was controlled by time‐dependent sorption reactions with the solid phase. Although the solid‐phase retention of Co(III)EDTA− and Co2+ were similar, the sorption kinetics of the former were more sluggish relative to Co2+ and contaminant transport was accelerated in the presence of EDTA.
Growing Corn Root Effects on Interrill Soil Erosion
Authors: Bui Elisabeth N. , Box James E.
Published: July 2010

The relationship between plant roots and interrill soil erosion is important in dynamic soil erosion predictions. Rainstorm simulations of similar intensity (63.5 mm h−1) were conducted in the summer of 1989 on 1 by 1 m field plots of Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult) to study the effect of different root length densities, Lv (cm cm−3), of corn (Zea mays L.), during vegetative, preanthesis, and anthesis plant developmental stages on interrill soil erosion. Sediment loss and runoff data were assigned to treatments, Lva, on the basis of Lv range to reduce rooting variability associated with plant developmental stage. To avoid confounding by canopy cover, corn plants were cut at the stem base and removed for the first four sets of simulations. A reference set of simulations was performed on a fallow plot containing no roots, Lva0. Runoff and detached sediment were collected in buckets from each plot during successive 5‐min intervals over a 1‐h period. Thirty cores, 5 cm in diam. and 5 cm deep, were taken from each 1‐m2 plot and roots were washed from the cores and measured. Means for runoff and detached sediment were generally not significantly different for the high Lv or Lva, and Lva0. When Lva was <1.5 cm cm−3, runoff and detached sediment were significantly lower during the first 30 min of simulated rainfall. High densities of live corn roots did not reduce interrill soil erosion from a moldboard‐plowed Cecil sandy loam.
Evaluating Nitrate Recovery by Ion‐Exchange Resin Bags
Authors: Wyland L. J. , Jackson L. E.
Published: July 2010

Ion‐exchange resin (IER) bags were tested as traps for leached soil NO−3‐N. In laboratory experiments, IER bags recovered 84.7% of the NO−3‐N from solutions containing 0.09 to 40.74 g NO−3‐N kg−1 resin, but recovery decreased at higher concentrations. In soil columns, NO−3‐N recovery was poor (36.2%) when NO−3‐N moved slowly through the soil profile after a rapid single pulse, but improved (87.1%) when higher flow was sustained. In the field, estimates of leached NO−3‐N using IER bags fell within the range of values estimated from soil cores and suction lysimeters. Advantages of IER bags are attributed to cumulative recovery of NO−3‐N during passive interception of gravitational water flow.
Plant Responses to Sulfate and Chloride Salinity: Growth and Ionic Relations
Authors: Curtin D. , Steppuhn H. , Selles F.
Published: July 2010

Growing salt‐tolerant crops is one of the more cost‐effective strategies for coping with soil salinity, which is a significant factor affecting crop production and agricultural sustainability on the Canadian prairies. This study was carried out to determine if salt tolerance data, generated by traditional Cl (NaCl/CaCl2) salinization procedures, are appropriate to the prairies, where SO4 salinity predominates. Barley (Hordeum vulgare L., cv. Bonanza) and kochia [Kochia scoparia (L.) Schrad.] seedlings were grown in sand culture and salinized with either Cl or SO4 salts. The latter system was designed to mimic the natural salinity of prairie soils. The results showed that plant responses to salinity depend on the kind of salts (sulfates or chlorides) contributing to salinity as well as on the total electrolyte concentration. Growth was significantly better (by an average of 17%) on the SO4 system. However, barley salinized with SO4 salts developed severe Ca deficiency at high salt concentrations (electrical conductivity [EC] 17.5–27.5 dS m−1) because of low solubility of Ca. Kochia, which is more efficient than barley in absorbing Ca, was not limited by Ca. Barley and kochia tended to have higher selectivity for nutrient cations (Ca, Mg, and K) over Na when the plants were grown on the Cl salt system. This may be an indication of a beneficial effect of the high Ca supply in the NaCl/CaCl2 salt system on membrane selectivity. Our results show that there are many possible interactions between salt concentration, salt type, and plant nutrition. The significance of these interactions for salt tolerance testing may vary from crop to crop and may depend on factors such as the nutrient concentration in the growing medium. From a practical standpoint, however, response functions generated by NaCl/CaCl2 salinization probably provide an acceptable measure of the tolerance of most crops to SO4 salinity.