bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal Pattern of Oxygen Concentration in a Hydromorphic Soil
Authors: Sierra J. , Renault P.
Published: July 2010

Oxygen deficiency negatively affects crop yield and has a major impact on soil biological activity. This work was performed to ascertain the factors affecting the O2 concentration in a soil profile, and to analyze the hypothesis used in O2 transport models. Oxygen concentration was measured using platinum microelectrodes. Soil porosity, water content, temperature, groundwater depth, and microbial respiration were analyzed as the driving variables affecting O2 concentration. Soil respiration was well described by a Michaelis kinetics; the maximal rate of respiration for the 0‐ to 0.1‐m layer (2.5 × 10‐5 mol m‐3 s‐1) was five times higher than for the 0.3‐ to 0.5‐m layer. This implies that the simplification of vertical homogeneity and zero‐order kinetics for O2 consumption are invalid to estimate O2 transport. In the topsoil, the amplitude of the changes in O2 concentration after rainfall decreased in the order autumn > winter > summer. At 0.2 m for rainfall of ≈40 mm, the O2 concentration decreased 0.09 m3 m‐3 within 3 d after rainfall in autumn, and 0.05 m3 m‐3 within 6 d in winter. The fluctuations observed in O2 concentration after rainfall indicated that the steady‐state approximation used in models is too restrictive to describe O2 transport in soil. In the subsoil, O2 concentration varied slightly due to low O2 consumption (≈10‐7 mol m‐3 s‐1). Oxygen concentration in the topsoil was negatively associated with the water‐filled pore space, except for measurements taken immediately after rainfall >30 mm d‐1, which indicated the presence of entrapped air. This suggests that the hypothesis of instantaneous equilibrium between water content and soil O2 concentration is a reasonable simplification except for the 12‐ to 24‐h following high‐intensity rainfall.
Irrigation of Peppermint for Optimal Yield
Authors: Mitchell A. R. , Yang C. L.
Published: July 2010

Little field research has documented the water use of peppermint (Mentha piperita L.), an important irrigated crop of the Pacific Northwest grown for oil and tea leaves. Our objective was to determine a peppermint yield—water use function and to develop a crop coefficient (Kc) to relate crop evapotranspiration (ET) to potential ET. Trials were conducted from 1992 to 1994 at Madras, OR on a Madras loam mesic Aridic Argixeroll (fine‐loamy, mixed, mesic Xerollic Duriargid). A line‐source sprinkler irrigation system was used to impose five irrigation treatments ranging from 30 to 120% of the ET required for maximum yield. Evapotranspiration was measured by monitoring the water balance components of irrigation, precipitation, drainage, and soil water storage. Peppermint yield was sensitive to irrigation, with both deficit and excess irrigation lowering oil yields compared with the optimum treatment, which was 324, 388, 364, and 487 mm season‐1 for the four trials. Peppermint ET‐yield functions exhibited a greater transpiration component (89%) than other crops due to its thick canopy that reduces soil evaporation. The highest yielding irrigation treatment kept the soil water pressure between −18 and −50 kPa in the top 0.3 m. The Kc followed the general three‐lines model with an initial value of 0.3 that increased to 0.85 at mid‐season and declined to 0.5 at harvest. Thermal units were used to normalize the inflection points for the Kc curve for 2 yr of the trial (1993 and 1994). Late winter tillage in 1992 delayed peppermint growth and shifted the Kc curve.
Development and Evaluation of ENVIRO‐GRO, an Integrated Water, Salinity, and Nitrogen Model
Authors: Pang X. P. , Letey J.
Published: July 2010

Development of a multicomponent model for crop yield and potential groundwater degradation applicable for irrigated agriculture is important. The ENVIRO‐GRO model was developed to simulate (i) water, salt, and N movement through soil with a growing plant; (ii) plant response to matric potential, salinity, and N stresses; (iii) drainage and salt and N leaching; and (iv) cumulatively relative transpiration and relative N uptake, and consequent crop relative yield. This model does not account for denitrification. The utility of the model was illustrated by simulating the effects of irrigation amount, irrigation salinity, and N application on yield and N leaching. The results demonstrated the effects of complex interactions and feedback mechanisms in the plant‐soil‐water‐salinity‐N system. Factors leading to reduced plant growth caused lower transpiration, which created more leaching of salts and N. The simulated interactions are consistent with observed behaviors. Evaluation was done by comparing simulated results with published results of an experiment that had N application rates of 0, 90, 180, and 360 kg N ha‐1 and water application rates of 21, 63, and 105 cm. Agreement between simulated and observed corn (Zea mays L.) relative yield and total N uptake was generally good. The difference between mean observed and predicted values was <0.06 for corn relative yield and 1.34 kg N ha‐1 for total N uptake. Linear regression analyses revealed excellent agreement results for the 63‐cm irrigation and a tendency for the model to overpredict results for the 21‐cm irrigation and underpredict results for the 105‐cm treatment.
Three Decades of Observed Soil Acidification in the Calhoun Experimental Forest: Has Acid Rain Made a Difference?
Authors: Markewitz Daniel , Richter Daniel D. , Allen H. Lee , Urrego J. Byron
Published: July 2010

Three decades of repeated soil sampling from eight permanent plots at the Calhoun Experimental Forest in South Carolina allowed us to estimate the rate of soil acidification, the chemical changes in the soil exchange complex, and the natural and anthropogenic sources of acidity contributing to these processes. During the first 34 yr of loblolly pine (Pinus taeda L.) forest growth, soil pH, (pH in 0.01 M CaCl2) decreased by 1 unit in the upper 0‐ to 15‐cm of soils and by 0.4 and 0.3 units in the 15‐ to 35‐ and 35‐ to 60‐cm layers, respectively. Throughout the 0‐ to 60‐cm horizon, base cation depletion averaged 1.57 kmolc ha‐1 yr‐1 and effective and total acidity increased by 1.26 and 3.28 kmolc ha‐1 yr‐1, respectively. A forest H+ budget estimated for these decades indicated that 38% of soil acidification was due to acid deposition, while 62% of soil acidification was attributed to the internal functioning of the ecosystem. Soil samples archived during the three‐decade experiment also document decreases in soil‐adsorbed SO2‐4, presumably in response to decreasing atmospheric inputs in recent years.
Formation and Stability of Hydroxy Aluminum‐Iron‐Montmorillonite Complexes: Influence of Ferrous Iron
Authors: Violante A. , Krishnamurti G. S. R. , Huang P. M.
Published: July 2010

Synthetic hydroxy Al‐Fe gels were prepared at pH 6.0 by mixing different amounts of Fe(ClO4)2 to a solution of Al(ClO4)3 (5 mol Al kg‐1 clay) to result in an initial Fe(II)/Al molar ratio (R) of 0, 0.1, 0.3, 0.5, 1.0, and ∞, both in the absence and presence of Na‐saturated montmorillonite. The suspensions were aged up to 100 d at 25°C or 30 d at 70°C. Gibbsite was formed in all the samples (R = 0–1.0) after 30 d of aging at 25°C or 1 d at 70°C, except in the sample formed at R = 1.0, where gibbsite was detected only after >2 mo of aging at 25°C or after aging for 6 d at 70°C. At R = ∞, lepidocrocite, goethite, and ferrihydrite were the Fe oxides/oxyhydroxides formed in the absence of montmorillonite. No crystalline Fe oxides were observed in the presence of montmorillonite. After aging, the degree of interlayering in the montmorillonite was observed to be always greater in the samples where Al and Fe were coprecipitated than in the samples formed at R = 0 or ∞. After prolonged aging up to 100 d at 25°C or 30 d at 70°C, the interlayering was stabilized in the samples formed at R = 0.1 to 1.0, with d‐spacings ranging from 1.48 to 1.85 nm or from 1.55 to 1.74 nm, respectively. All the samples aged for 100 d at 25°C or 30 d at 70°C were treated using acid ammonium oxalate. The oxalate‐extractable Fe/Al molar ratios of the acid ammonium oxalate extractable mixed hydroxy Al‐Fe complexes were much higher than the initial solution Fe/Al molar ratios. The stabilized short‐range ordered materials present in the interlayers of montmorillonite in the samples that formed at R values ranging from 0.1 to 1.0 were apparently Al‐substituted Fe oxides.
Turnover of Detrital Organic Carbon in a Nutrient‐Impacted Everglades Marsh
Authors: DeBusk W. F. , Reddy K. R.
Published: July 2010

Phosphorus loading to the Everglades from nearby agricultural areas has become a major concern, and is considered to be a significant factor in the encroachment of cattail (Typha domingensis Pers.) and other rapidly growing vegetation into endemic sawgrass (Cladium jamaicense Crantz) marsh. The objectives of this research were to evaluate the variability in turnover of organic C in plant and soil detrital pools along a P enrichment gradient in an Everglades marsh and to identify substrate characteristics and environmental factors controlling C turnover. Potential rates of C mineralization in plant litter and peat were determined by measuring aerobic and anaerobic microbial respiration under controlled conditions in laboratory incubations. Potential C mineralization decreased with depth and, consequently, substrate age, in the plant‐soil profile. Within individual detrital pools [standing dead plant material, soil litter layer, surface peat (0–10 cm depth) and subsurface peat (10–30 cm depth)], potential C mineralization decreased down gradient from the source of nutrient loading to WCA‐2A. Overall, 91% of the variability in aerobic C mineralization in peat and plant litter was accounted for by substrate P concentration and lignocellulose composition. Anaerobic C mineralization rates were consistently about one‐third of aerobic rates. Results indicated that organic C turnover in detrital pools in WCA‐2A is significantly affected by accelerated P loading, but is also controlled by O2 availability and substrate C quality.
Scaling Water Retention Curves for Soils with Lognormal Pore‐Size Distribution
Authors: Kosugi K. , Hopmans J. W.
Published: July 2010

The scaling theory approach has been widely used as an effective method to describe the variation of soil hydraulic properties. In conventional scaling, reference retention curves and scaling factors are determined from minimization of residuals. Most previous studies have shown that scaling factors are lognormally distributed. In this study, we derived physically based scaling factors, assuming that soils are characterized by a lognormal pore‐size distribution function. The theory was tested for three sets of retention data. Two data sets included samples of a sandy loam soil, and one set included samples of a loamy sand soil. Individual soil water retention data were fitted to the retention model proposed by Kosugi (1996). The parameters of the model are the mean and variance of the log‐transformed poreradius distribution. Scaling factors and parameters of the reference curve were computed directly from the parameters of individual soil water retention functions. Assuming that (i) the soil pore radius of a study area is lognormally distributed and (ii) soil samples are obtained from random sampling of effective soil pore volume from the study area, we have proposed a theoretical interpretation of the lognormal scaling factor distribution. Scaling results for all three data sets compared well with those obtained using the conventionals caling method.
The Significance of Hysteresis in Modeling Solute Transport in Unsaturated Porous Media
Authors: Mitchell Robert J. , Mayer Alex S.
Published: July 2010

Previous investigations disagree as to the appropriateness of neglecting hysteresis with regard to predicting solute transport under transient conditions, primarily because of the unique porous media and conditions used in these studies. In the present study, the significance of hysteresis in predicting solute transport in the near‐surface region is investigated using one‐dimensional, homogeneous numerical experiments with a fully hysteretic flow and transport model. The experiments involve introduction of a solute pulse, followed by intermittent cycles of infiltration, redistribution, and evaporation. Comparisons are made between transient hysteretic simulations and simulations ignoring hysteresis. Hysteretic and nonhysteretic simulations conducted with porous media that have large differences between wetting and draining characteristic curves exhibited the greatest variation in solute migration behavior. Larger differences between maximum and minimum water contents also produced greater impacts when hysteresis was considered. However, the results indicate that the magnitude of the deviations between hysteretic and nonhysteretic simulations is not a simple function of each independent parameter, but rather depends on the combined values of many or all of the hydraulic parameters. As the solute travels further into the vadose zone, the effects of hysteresis are reduced. In general, hysteresis had a minor effect on solute transport in the systems considered in this work.
Stratigraphic Approach to Alteration in Mineral Soils: The Heavy Metal Example
Authors: Kleber Arno , Mailänder Reiner , Zech Wolfgang
Published: July 2010

Quantifying post‐depositional alteration of mineral soil material is complicated by the fact that many soils consist of layered parent materials with varying indigenous composition. Part of our study site in the Steigerwald Mountains of northern Bavaria was cultivated during the Middle Ages and later reforested. Soil erosion removed the upper materials, exposing a deposit to contamination from the surface, whereas nearby, the deposit remained protected by overlying layers. We compared heavy metal concentrations within that deposit across this boundary of varying protection. No significant results were obtained for Cd; however, the concentrations of Pb and Cu increase by about 100% or more where the protecting cover thins. The Pb and Cu values provide a measure of the gross post‐depositional alteration of that deposit. We expect this procedure can help quantify various pedogenic alterations by comparison with essentially the same, unaltered parent material.
Origin and Acceptance of the Term Pedology
Authors: Simonson Roy W.
Published: July 2010

After F.A. Fallou (1794–1877) introduced the term pedology in Saxony in 1862, it was dormant for some decades. Acceptance and general use of the term began in Russia following development of a new approach to the study of soils by Dokuchaiev and his students in the late 1870s and early 1880s. Soil scientists elsewhere in the world did not pick up the term, however, before the 20th century. Widespread use followed the First International Congress of Soil Science, held in the USA in 1927. The Congress and associated activities gave the term a big boost, not only in the USA. In 1929, the American Soil Survey Association, precursor of the Soil Science Society of America, adopted a resolution urging that pedology be accepted as the proper name for scientific investigations of soils. Teaching of the Dokuchaiev factors of soil formation, which began soon afterward, promoted progressively wider acceptance of the term, especially in the USA. These trends culminated in adoption of pedology as the name for a division of the Soil Science Society of America in 1994. During the same period, acceptance of the term was underway in all parts of the world.
Soil Shrinkage Characteristic Curve in Clay Soils: Measurement and Prediction
Authors: Crescimanno Giuseppina , Provenzano Giuseppe
Published: July 2010

Laboratory determination of soil hydraulic characteristics (HC) is performed on cylindrical confined soil cores, while resin‐coated small natural aggregates are prevalent for determining the Soil Shrinkage Characteristic Curve (SSCC). Because of the different geometry and volume of clods and cores, incorporation of shrinkage in HC of clay soils could be affected by the use of SSCC determined on natural aggregates or on confined cores. The objectives of this study were (i) to investigate differences between the SSCC obtained on resin‐coated natural aggregates (volume V = 20–30 cm3) and on cylindrical confined cores having a volume (650 cm3) close to that of cores used for HC laboratory determination, (ii) to test the performance of different models proposed for analytical interpretation of the SSCC, and (iii) to derive regression equations predicting the SSCC from routinely measured soil physical properties. Using twenty‐one Sicilian soils of variable shrink‐swell behavior, we found significantly larger specific volume (n), indicating less shrinkage, in the cylindrical confined cores. The investigation also proved the good fitting of a two‐line model to the measured SSCC and the possibility to predict the basic shrinkage line from the clay content. These results suggest that incorporation of shrinkage in HC of clay soils should be based on the SSCC measured or predicted on cores with geometry and dimensions as those used for routine laboratory measurement of HC.
The Colding Equation for Soil Drainage: Its Origin, Evolution, and Use
Authors: van der Ploeg R. R. , Marquardt Maria , Kirkham M. B.
Published: July 2010

The derivation of the ellipse equation by the Danish engineer Colding in 1872 marked the beginning of a new epoch in the field of soil drainage. Little is known about the circumstances that led to the derivation of this equation or about the evolution of the Colding equation in later years. Therefore, we decided to survey the early European literature on these subjects. The survey revealed that Colding's derivation was based mainly on research published by the French engineer Delacroix in 1859 and by the Danish engineer Hannemann in 1870. Although Colding used soil water flow concepts as developed earlier by Darcy and Dupuit, it is possible he was not familiar with the work of these French engineers. After Colding's equation had been widely used for drainage design purposes in Denmark, his equation appeared in the German literature around the turn of the century. From Germany, the Colding equation spread to other European countries and to the USA. In the 1930s and the 1940s, the Colding equation was modified by Hooghoudt in the Netherlands and by Aronovici and Donnan in the USA. The Hooghoudt equation is used today as a drainage design standard in various parts of the world.
A Capacitance Sensor with Planar Sensitivity for Monitoring Soil Water Content
Authors: Ruth B.
Published: July 2010

A pair of isolated parallel wires in a frame were used as a capacitance sensor for soil water content determination. Due to the high dielectric constant of water, rising water content of th esoil between the wires increases the capacitance. As the frame and the wires have a horizontal position in the soil, no preferential vertical water flow is induced by the sensor. The total wire diameter of 1.1 mm and the separation of 2.5 mm leave enough space for undisturbed natural water flow. The sensitive volume has a thickness given by the wire separation of 2.5 mm and the open frame area of 5 by 5 cm. Measurements in two soil types (loamy sand and loamy silt) showed a rise of the capacitance from 15 to 65 pF when the water content increases from 0 to 0.45. A theoretical consideration exhibits the relationship between the measured dielectric constant εM and the volumetric water content θ given by εM = A(θ + Z)/(θ + N) with three parameters A, Z, and N depending only on the sensor geometry and dielectric constants. The corresponding fit function determined the parameters and approximated the calibration curve with a root mean square (RMS) deviation of 0.024, indicating the accuracy of the method. No significant difference in the εM‐θ relationship could be obtained between the two soils. Measurements with eight sensors at depths between 1 and 15 cm yield the time‐dependent water content profile with a resolution of 1 cm during the watering and drying of the soil.
Technical Note: Rapid Measurement of Soil Sorptivity
Authors: Smith Roger E.
Published: July 2010

A simple and fast method is described for measuring surface soil sorptivity, S. Rather than measure the progress of infiltration flux for a long initial period, the cumulative infiltration is measured in the early stage in which the gravity effect is negligible. The theory behind the method is sound and simple, and measurements may be taken in only a few minutes using a small single ring. It is applicable to find S for both ponded and flux surface boundary conditions.
Atomic Force Microscopy and Surface Characteristics of Iron Oxides Formed in Citrate Solutions
Authors: Liu C. , Huang P. M.
Published: July 2010

Surface geometry of minerals greatly influences the physical, chemical, and biological processes occurring on the surface. However, a quantitative or even a qualitative description of the surface geometry of minerals has proven to be extremely difficult. In our study, the fine‐scale morphology (1 by 1 µm scale) and surface geometry described by mean surface roughness and surface fractal dimension of Fe oxides formed at various concentrations of citrate, which is common in terrestrial and aquatic environments, were investigated by atomic force microscopy (AFM). Specific surface area and Point of Zero Salt Effect (PZSE) of the Fe oxides, as well as P adsorption, were also studied. Citrate present during the formation of Fe oxides significantly altered the fine‐scale morphology, surface geometry, and other surface characteristics of the products. The mean surface roughness and surface fractal dimension determined by AFM measured the degree of the disorder of surface structure of Fe oxides. The modification of the surface characteristics of the Fe oxides by coprecipitated citrate through fundamental structural changes and the blocking of P‐adsorption sites by citrate affected the P adsorption. Due to the hindrance of the crystallization process, P adsorption per unit weight of the Fe oxides formed at 10‐3 M citrate was very significantly enhanced. The fine‐scale morphology, surface geometry, and related surface characteristics of Fe oxides formed under the influence of organic acids merit close attention as we advance our understanding of their surface chemistry pertaining to dynamics and transformations of nutrients and pollutants in terrestrial and aquatic environments.
Amino Sugars in Native Grassland Soils along a Climosequence in North America
Authors: Amelung W. , Zhang X. , Flach K. W. , Zech W.
Published: July 2010

Characterizing amino sugars is important for further understanding soil organic matter (SOM) dynamics in terrestrial ecosystems. This study was designed to evaluate the impact of climate on amino sugars in 18 surface soil (0–10 cm) samples along a climosequence of native grasslands from central Saskatchewan, Canada, to Southern Texas, USA. Mean annual temperature (MAT) ranged from 0.9 to 23.4°C and mean annual precipitation (MAP) from 300 to 1308 mm. In all samples, the contents of soil organic C, glucosamine, mannosamine, galactosamine, and muramic acid were determined. Both the ratios of glucosamine to galactosamine and of glucosamine to muramic acid were related to the moisture regime. With increasing MAP, increasing proportions of amino sugars were glucosamine. This glucosamine is possibly derived from the chitin of fungi. The proportion of bacterial‐derived amino sugars, such as muramic acid, declined as MAP increased. The relationship between amino sugar concentrations (mg kg‐1 soil organic C) and MAT followed a parabolic regression model; the maximum of the amino sugar concentration occurring at the mesic temperature regime. On the basis of hierarchical cluster analysis the sites could be divided into two groups, which coincided with the Northern‐central and Southern grasslands. We hypothesize that in the Northern‐central grasslands frost limits amino sugar production whereas in the Southern grasslands higher winter temperatures >0°C favor amino sugar decomposition.
Chloride Versus Sulfate Salinity Effects on Alfalfa Shoot Growth and Ionic Balance
Authors: Soltanpour P. N. , Ippolito J. A. , Rodriguez J. B. , Self J. , Gillaume M. , Al‐Wardy M. M. , Mathews D.
Published: July 2010

Information on Cl vs. SO4 salinity effects on alfalfa (Medicago sativa L) dry matter yield (DM) and cation‐anion balance is limited. Consequently, we compared Cl and SO4 salinity effects on shoot DM and ionic balance for Archer and Ladak varieties of alfalfa. A modified, flowing Hoagland solution, buffered with CaCO3, was the control: electrical conductivity (EC) = 0.7 dS m‐1. Chloride or SO4 salts of K, Ca and Mg were added to the control to get iso‐EC solutions (2–11 dS m‐1). Shoot cations (Ca, Mg, K, and Na) and their sum (C), anions (Cl, SO4, NO3 and H2PO4) and their sum (A), and DM were measured. Organic anions (C‐A) were calculated in mmolc kg‐1. The calculated hydroponic osmotic potentials (π) were from 1.4 to 1.7 times lower in Cl than in iso‐conductive SO4 solutions. As EC increased, DM decreased equally for both varieties in iso‐conductive Cl and SO4 solutions. Solution π decreased, shoot H2PO4 declined below its critical level of 65 mmolc kg‐1, shoot C stayed constant, shoot A increased; and therefore, shoot C‐A decreased. The shoot C‐A was lower in SO4 solutions. In Cl solutions shoot Cl exceeded the toxic level of 282 mmolc kg‐1. The DM was correlated positively with π, shoot H2PO4, and C‐A, and negatively with shoot Cl and SO4. We conclude that (i) iso‐conductive Cl or SO4 salinity depress DM equally, but isoosmotic SO4 is more depressive; (ii) the yield declines are probably due to any one or a combination of low water potential, toxic shoot Cl and possibly SO4, and deficiencies of shoot P and organic anions; (iii) neutral organic solutes were probably responsible for osmotic adjustment, since total ionic charges (2C) stayed constant; and (iv) P deficiency occurred despite high solution P, due to Cl or SO4 competition in saline environments.
Barometric Process Separation: New Method for Quantifying Nitrification, Denitrification, and Nitrous Oxide Sources in Soils
Authors: Ingwersen J. , Butterbach‐Bahl K. , Gasche R. , Richter O. , Papen H.
Published: July 2010

A method (Barometric Process Separation, BaPS) was developed for the quantification of gross nitrification rates and denitrification rates in oxic soil using intact soil cores incubated in an isothermal gas tight system. Gross nitrification rates and denitrification rates are derived from measurements of changes (i) in air pressure within the closed system, which are primarily the result of the activities of nitrification (pressure decrease), denitrification (pressure increase), and respiration (pressure neutral), and (ii) of O2 and CO2 concentrations in the system. Besides these biological processes, the contribution of physicochemical dissolution of produced CO2 in soil water to the pressure changes observed is to be considered. The method allows collection of additional information about the contribution of nitrification and denitrification to N2O emission from soil, provided simultaneous measurements of N2O emission are performed. Furthermore, BaPS can be used to quantify the percentage of N2O lost from nitrification. The advantage of BaPS is that disturbance of the soil system is minimized compared with other methods such as the use of gaseous inhibitors (e.g., acetylene) or application of 15N compounds to the soil. We present the theoretical considerations of BaPS, results for nitrification rates, denitrification rates, and identification of soil N2O sources in a well‐aerated coniferous forest soil using BaPS. The suitability of BaPS as a method for determination of gross nitrification is demonstrated by validation experiments using the 15N‐pool dilution technique.
Structural Charge and Cesium Retention in a Chronosequence of Tephritic Soils
Authors: Chorover Jon , DiChiaro Marnie J. , Chadwick Oliver A.
Published: July 2010

Mineral transformation during the course of soil development is probably coupled to time‐dependent trends in surface‐charge and selective adsorption behavior, but the relationships are not well documented. The density of permanent (structural) charge is subject to change as a result of accretion or depletion of 2:1 layer‐type silicates. The objectives of this study were to measure changes in (i) Cs+ selectivity and (ii) structural charge as affected by pedogenic mineral transformations in an age sequence of Hawaiian soils. The Cs+ → Li+ exchange experiments were conducted on soils collected from six sites [basaltic parent material deposited 0.3, 20, 150, 400, 1400 and 4100 thousands of years (ky) ago]. Identical exchange experiments were performed with kaolinite, montmorillonite, and illite for comparison. Selectivity for Cs+ on soils and clays increased with adsorbed mole fraction of Cs+. Cesium‐accessible structural charge of the surface soils increased initially with soil age from 20 mmolc kg‐1 at the 0.3 ky site to 113 mmolc kg‐1 at the 400‐ky site. Increased weathering beyond 400 ky reduced structural charge to 21 mmolc kg‐1 for the oldest site. Parallel results were observed for subsurface soils with maximum structural charge of 138 mmolc kg‐1 measured for the 400 ky site. The magnitude of Cs retention in the soils is correlated with the presence of 2:1 layer‐type silicates detected by x‐ray diffraction (XRD) after removal of poorly crystalline constituents. The results indicate a modest accumulation of secondary 2:1 layer‐type silicates (with larger accumulations of poorly crystalline clays), followed by their subsequent decline, during the course of soil weathering.
Soil Organic Matter Changes in Intensively Cropped Dryland Systems
Authors: Bowman R. A. , Vigil M. F. , Nielsen D. C. , Anderson R. L.
Published: July 2010

Continuous cropping or decreasing the frequency of summer fallow (F) in cereal‐based dryland rotations may have benefits other than greater water utilization and erosion control. We hypothesized that rotations with no fallow or minimum fallow frequency can produce more biomass and cover than the traditional winter wheat (Triticum aestivum L.)‐summer fallow systems (W‐F), and ultimately, greater amounts of soil organic matter (SOM). To this end, we evaluated changes in various pools of SOM at the 0‐ to 5‐ and 0‐ to 15‐cm depths on a Weld loam (fine, smectitic, mesic aridic Paleustolls) that were caused by (i) decreasing fallow or increasing cropping intensities, (ii) specific rotations of the same length but with different crop sequencing, and (iii) accumulated residue and roots from reduced‐ or notillage from 1993 to 1997. Total soil organic carbon (SOC) and N for the 0‐ to 5‐cm depth increased by =20% with continuous cropping rotations compared with W‐F rotations. Particulate organic matter‐carbon (POM‐C) doubled, while POM‐N, and soluble organic C (OC) increased by one third for the same comparison. At the 0‐ to 15‐cm depth, SOC, POM‐C, and POM‐N did not differ among systems with fallow, nor among systems with cropping intensities greater than W‐F. Thus, significant differences always existed between W‐F and continuous cropping. Generally, fallow had a negative influence on SOC accumulation, and continuous cropping a positive influence on surface SOM. Changes in SOC did not correlate with yields in the five‐year comparison of this ongoing study.
Structure Repair of a Compacted Vertisol with Wet‐Dry Cycles and Crops
Authors: Pillai U. P. , McGarry D.
Published: July 2010

We hypothesized that the four rotation crops: wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.) Merr.], lablab [Lablab purpureus (L.) Sweet] and mung bean [Vigna radiata (L.) R. Wilczek] differ in their ability to repair soil structure. The study was conducted on a Typic Haplustert, Queensland, Australia, locally termed a Black Earth and considered a prime cropping soil. Large (0.5‐m depth by 0.3‐m diam.) soil cores, collected from compacted wheel furrows in an irrigated cotton (Gossypium hirsutum L.) field, were subjected to three, six, or nine wet‐dry cycles that simulated local flood irrigation practices. After each cycle, soil profiles were sampled for clod bulk density, image analysis of soil structure, and evapotranspiration. Generally, all crops improved soil structure over the initial field condition but lablab and mung bean gave improvements to greater depths and more rapidly than wheat and sorghum. Mung bean and lablab caused up to a threefold increase in clod porosity in the 0.1‐ to 0.4‐m soil layer after only three wet‐dry cycles, whereas sorghum required nine wet‐dry cycles to increase clod porosity in only the 0.2‐ to 0.3‐m layer, and wheat gave no improvement even after nine wet‐dry cycles. Image analysis of soil structure showed that lablab and mung bean rapidly (by three wet‐dry cycles) produced smaller peds with more interconnected pore space than wheat and sorghum. By nine wet‐dry cycles, sorghum achieved deep cracking of the soil but the material between the cracks remained large and dense. Evapotranspiration was double under lablab and mung bean compared with wheat and sorghum. Our results indicate greater cycles of wetting and drying under lablab and mung bean than wheat and sorghum that have led to rapid repair of soil compaction.
Heavy Metal Release from Soils in Batch pHstat Experiments
Authors: Schwarz Andreas , Wilcke Wolfgang , Zech Wolfgang , Stýk Jan
Published: July 2010

In Slovakia H+ input into soils is increasing because alkaline dust emissions have been reduced since 1990. Our objectives were to examine (i) the metal release in H+ buffer reactions of Slovak soils and (ii) the impact of the proton buffering on heavy metal partitioning. We used 10 soils (pH 7.4–3.6) in a batch pHstat experiment. Released ions were adsorbed to an ion‐exchange resin, while pH was kept constant. After reaction times of 10 min, 30 min, 1, 2, 4, 24, 48, and 96 h, soil and ion‐exchange resin were separated and ions were extracted from the resin. After 0, 4, and 96 h, we determined metal concentrations in seven fractions. On average, the total release after 96 h (in percentage of the total concentration) decreased in the order: Cd (74) > Pb (59) > Cu (29) > Zn (22) > Ni (17) > Cr (3.1), while the initial release rate into solution decreased in the order: Cd > Zn > Ni > Cu > Pb > Cr. After 48 h, only the Cr release rate was lower than that of Cd. Particularly in less acid soils, Pb, Cu, Zn, and Cd released by the dissolution of oxides were adsorbed onto the soil matrix, explaining the slower decrease of the Pb and Cu release rates. The percentages of weakly bound heavy metals decreased more markedly during the titration than those of metals bound to Fe oxides. Increased H+ inputs into Slovak soils will cause enhanced metal release into soil solution.
Predicting Solute Transport in Soils Second‐Order Two‐Site Models
Authors: Selim H.M. , Ma Liwang , Zhu Hongxia
Published: July 2010

Failure of numerous efforts to describe the movement of reactive solutes in soils is often due to inaccurate identification of solute–soil interactions or to the lack of independently derived model parameters. The main objective of this work was to test the applicability of chemical vs. physical nonequilibrium approaches in describing the transport of solutes in soils. The models evaluated are based on second‐order two‐site approaches (SOTS) with and without consideration of physical nonequilibrium in soils. The capability of these approaches for predicting the transport of metolachlor [2‐Chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] in Sharkey clay (very‐fine, smectitic, thermic Chromic Epiaquerts) soil columns of different aggregate sizes (<2, 2–4, and 4–6 mm) was examined. Moreover, two sets of model parameters were independently derived from the kinetic retention experiments. The first set was based on kinetic adsorption isotherms, and the second set utilized both adsorption and desorption kinetic retention (batch) results. Judging from data on the total root mean square error, parameters based on adsorption and desorption batch results provided breakthrough curve (BTC) predictions that are improved over those of parameters from adsorption kinetics only. The coupled physical and chemical nonequilibrium model (SOTS plus mobile–immobile [MIM]: SOTS–MIM) considerably improved BTC predictions for the 2‐ to 4‐ and 4‐ to 6‐mm soil aggregate sizes. We conclude that the modified SOTS and SOTS–MIM methods provided an improved description of metolachlor transport in the Sharkey soil. Based on total root mean square errors, the modified SOTS–MIM with parameters derived from adsorption and desorption kinetic retention experiments provided best overall BTC predictions.
Measurement of Hydraulic Properties During Constant Flux Infiltration Field Average
Authors: Si B. , Kachanoski R. G. , Zhang F. , Parkin G. W. , Elrick D. E.
Published: July 2010

Accurate measurement of in situ soil hydraulic properties is important for developing, testing, and applying water and solute transport theory. A method of measuring hydraulic conductivity (K), soil matric pressure head (ψ), and water content (θ) relationships is presented. The procedure uses a series of multipurpose time domain reflectometry (TDR) probes that measure both θ and ψ. The TDR probes are installed vertically and measure the rate of change of local soil water storage (q) along the probe during constant rate water application. The values of q are equal to local soil water flux, and assuming unit gradient, are set equal to K at the steady state θ and ψ measured at long times. The measured values of K, θ, and ψ from different water application rates are combined to obtain average K(θ) and θ(ψ) functions. To test the procedure, multipurpose TDR probes were installed vertically in a sandy soil every 0.15 m in a 7.5‐m‐long transect for a total of 50 probes per depth. This was repeated in parallel transects 0.1 m apart for four depths (0.2 m, 0.4 m, 0.6 m, 0.8 m) and a total of 200 probes. Six different water application rates were applied with subsequent drainage. Average K(θ) and θ(ψ) functions were obtained and used in an analytical solution for constant rate infiltration. Transient water storage changes were accurately predicted for all application rates.
A Computer Program for Soil Textural Classification
Authors: Gerakis Argyrios , Baer Brian
Published: July 2010

Manual classification of soils into textural classes with the USDA textural triangle is tedious. This computer program can perform the same task easier and faster. The algorithm is based on the fact that each point in the textural triangle represents a unique combination of sand and clay content. For a given textural class, all combinations of sand and clay content are bound by a polygon. Finding the textural class is equivalent to finding the polygon where a particular combination of sand and clay is located. Both a World Wide Web interactive version and a Windows 95 console program are available. On a 133 MHz Pentium microcomputer, the Windows version can classify 1000 soil samples in about a second.
Effect of Temperature and Water on Gaseous Emissions from Soils Treated with Animal Slurry
Authors: Maag Michael , Vinther Finn P.
Published: July 2010

Microbial respiration and denitrification are greatly affected by abiotic factors, but they are difficult to assess in natural environments. Under controlled conditions the interactions between temperature and soil water content on microbial respiration, N2O production, and denitrification in soil amended with animal slurries were studied. The effects of the abiotic factors on the biological processes were monitored for 8 wk in repacked soil cores amended with pig or cattle slurry. The soil cores were incubated at 43, 57, and 72% water‐filled pore space (WFPS) and at 10, 15, and 20°C with or without addition of 10% acetylene. The amount of N2O lost at 72% WFPS corresponded to 8 to 22% of the slurry's NH+4 content, but to only 0.01 to 0.9% at 43 to 57% WFPS. Denitrification losses at 72% WFPS accounted for 17 to 58% of the slurry's NH+4 content, but for only 0.01 to 1.2% at 43 to 57% WFPS. The amount of available C accounted for by denitrification was 8 to 16% of total respiration at 72% WFPS, but only 0.03 to 0.4% at 43 to 57% WFPS. Both N2O production and denitrification peaked earlier in the cattle‐slurry treated soil than in the pig‐slurry treated soil, whereas the total N loss was greatest from the latter. Neither amendments nor soil water contents seemed to affect the Q10‐values for the CO2 production, resulting in values between 1.6 and 2.6. At 72% WFPS, N2O production and denitrification had Q10‐values ranging between 3.3 and 5.4. High temperatures enhanced both aerobic respiration and denitrification, and aerobic respiration further enhanced denitrification by consuming oxygen, resulting in strong sensitivity of denitrification to temperature.
Phosphorus‐ and Nitrogen‐Based Manure and Compost Applications Corn Production and Soil Phosphorus
Authors: Eghball Bahman , Power James F.
Published: July 2010

Manure or compost application based on N needs of corn (Zea mays L.) may result in soil accumulation of P, other ions, and salt because the manure or compost N/P ratio is usually smaller than the corn N/P uptake ratio. This study was conducted from 1992 to 1996 to evaluate effects of P‐ and N‐based manure and compost application on corn yield, N and P uptake, soil P level, and weed biomass. Composted and noncomposted beef cattle (Bos taurus) feedlot manures were applied to supply N or P needs of corn for either a 1‐ or 2‐yr period. Phosphorus‐based manure or compost treatments also received additional fertilizer N as needed. Fertilized and unfertilized checks were also included. Manure or compost application increased corn grain yield in all 4 yr as compared with the unfertilized check. Annual or biennial manure or compost application resulted in corn grain yields similar to those of the fertilizer treatment. Phosphorus‐based manure or compost application resulted in similar grain yields to those for N‐based treatments but had significantly less soil available P level after 4 yr of application. Biennial manure or compost application resulted in corn yield similar to that for annual application but increased available P in the soil. Estimated N availability was 40% for manure and 15% for compost in the first year and was 18% for manure and 8% for compost in the second year after application. Weed biomass was more influenced by nutrient availability than any weed seed introduced by manure or compost application. When application rate is based on correct N or P availability, manure and compost can produce corn grain yields that are equal to or greater than that for fertilizer application. Annual P‐based manure or compost application is the most effective method of using these resources when soil P buildup is a concern.
Plant‐Available Potassium Assessment with a Modified Sodium Tetraphenylboron Method
Authors: Cox A. E. , Joern B. C. , Brouder S. M. , Gao D.
Published: July 2010

The conventional 1 M NH4OAc‐exchangeable potassium (K+) soil test is inadequate in soils where nonexchangeable K+ contributes significantly to crop nutrition. Studies were conducted (i) to compare the abilities of the 1 M NH4OAc method with a modified NaBPh4 method to estimate critical soil K+ levels, (ii) to estimate the contribution of nonexchangeable K+ to plant‐available K+, (iii) to compare the abilities of the 1 M NH4OAc method and the modified NaBPh4 method to estimate plant dry matter yield and plant‐available K+, and (iv) to compare the abilities of both methods to measure soil K+ balance. Winter wheat (Triticum aestivum L. ‘Abe’) was grown in eleven Midwestern soils in a greenhouse using consecutive 28‐d defoliation and regrowth cycles. Soils also were incubated for 6 mo with five K+ rates (0–809 mg K+ kg−1). Ammonium acetate‐ and NaBPh4‐extractable K+ (5‐min extraction period) were determined in soil samples taken after every three defoliation cycles and after incubation. Critical soil K+ levels could not be determined by either method alone but could be predicted by including cation‐exchange capacity (CEC) and illitic K+ content in regression models. Nonexchangeable K+ represented a significant portion of plant‐available K+ Plant‐available K+ and dry matter (DM) yield were well related to NH4OAc‐extractable K+ only in soils with low nonexchangeable K contribution (r2 = 0.889 and 0.915, respectively), but they were well related to NaBPh4‐extractable K+ in all soils (r2 = 0.984 and 0.874, respectively). Slopes for NH4OAc‐extractable K+ vs. soil K+ balance varied widely among soils (0.16–0.68) depending on NH4OAc‐extractable K+, illitic K+, and clay content, but for NaBPh4‐extractable K+ slopes were near unity. These studies suggest that the modified NaBPh4 method may be a superior K+ soil test compared to the NH4OAc method. Illite content and CEC data may help in developing better soil K+ management guidelines.
Nitrogen Fertilization Effects on Soil Carbon and Nitrogen in a Dryland Cropping System
Authors: Halvorson Ardell D. , Reule Curtis A. , Follett Ronald F.
Published: July 2010

No‐till (NT) increases the potential to crop more frequently in the Great Plains than with the conventional‐till (CT) crop–fallow farming system. More frequent cropping requires N input to maintain economical yields. We evaluated the effects of N fertilization on crop residue production and its subsequent effects on soil organic C (SOC) and total soil N (TSN) in a dryland NT annual cropping system. Six N rates (0, 22, 45, 67, 90, and 134 kg N ha−1) were applied to the same plots from 1984 through 1994, except 1988 when rates were reduced 50%, on a Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). Spring barley (Hordeum vulgare L.), corn (Zea mays L.), winter wheat (Triticum aestivum L.), and oat (Avena sativa L.)–pea (Lathyrus tingitanus L.) hay were grown in rotation. Crop residue production varied with crop and year. Estimated average annual aboveground residue returned to the soil (excluding hay years) was 2925, 3845, 4354, 4365, 4371, and 4615 kg ha−1, while estimated annual contributions to belowground (root) residue C were 1060, 1397, 1729, 1992, 1952, and 2031 kg C ha−1 for the above N rates, respectively. The increased amount of crop residue returned to the soil with increasing N rate resulted in increased SOC and TSN levels in the 0‐ to 7.5‐cm soil depth after 11 crops. The fraction of applied N fertilizer in the crop residue decreased with increasing N rate. Soil bulk density (Db) in the 0‐ to 7.5‐cm soil depth decreased as SOC increased. The increase in SOC with N fertilization contributes to improved soil quality and productivity, and increased efficiency of C sequestration into the soil. Carbon sequestration can be enhanced by increasing crop residue production through adequate N fertility.