bluuebunny/crossref_metadata_2025_split huggingface dataset:
Water Flow Through Layered Anisotropic Bedded Soil with Subsurface Drains
Authors: Rogers J. S. , Selim H. M. 
Published: July 2010

AbstractResults for steady‐state water flow in layered bedded soils with subsurface drains are presented. The soil was assumed to consist of one or more layers bounded below by an impervious barrier and above by a soil surface of uniform slope. Each soil layer was considered water‐saturated and uniformly isotropic or anisotropic within the layer. Anisotropy was defined such that ζ ≠ κ where ζ and κ are the horizontal and vertical hydraulic conductivities, respectively. The finite element method was used in the numerical solution for steady and saturated flow. Although the numerical techniques presented can handle any number of layers, results are only presented for one‐ and two‐layered profiles. The effect of the degree of anisotropy (R) and equivalent hydraulic conductivity (K) for individual layers (where R = [ζ/κ]1/2 and K = [ζ κ]1/2) on drain outflow, water seepage along the soil surface, and the relative flow within each layer was investigated. The presence of subsurface drains increased the total flow into the bedded soil surface and decreased (often eliminated) water seepage outflow along the sloping soil surface. The influence of the depth of subsurface drains below the ground surface was dependent upon both K and R of the soil layers. In general, higher K and higher R in the layer containing the subsurface drain resulted in higher drain flows.
Glass Microelectrode Techniques for In Situ pH Measurements
Authors: Conkling B. L. , Blanchar R. W. 
Published: July 2010

AbstractGlass pH‐sensitive microelectrodes with lengths < 0.1 mm and diameters < 0.05 mm have many potential uses for in situ soil pH measurements. Physically stable glass microelectrodes which responded rapidly to pH were constructed and their response to soil chemical and physical influences measured. The pH of nine inorganic salts and organic acid solutions measured with the glass microelectrode were compared to those measured with a glass macroelectrode. A slope of 0.92, an intercept of 0.35, and regression coefficient of 0.99 indicated good agreement. Soil suspension pH measured with glass micro‐ and macroelectrodes was compared for eight soils. A slope of 1.26, an intercept of −1.19, and regression coefficient of 0.96 indicated a slight variation. These differences were partly attributed to unavoidable electrode placement problems. In general pH measured with macro‐ and microelectrodes compared very well. The influence of soil water pressure gradients in the range of −10 to −1500 kPa near the pH and reference electrodes on microelectrode pH measurements was studied. No significant differences in pH values due to moisture gradients were observed when the reference electrode was placed in soil at water pressures greater than −33 kPa. Standard deviations in pH where the glass microelectrode was placed in soil with water pressures from −10 to −1500 kPa varied from 0.07 to 0.17 indicating that moisture gradients have little influence on measured pH. Results indicate that glass pH microelectrodes are suitable for use in soil systems.
Carbon and Nitrogen Mineralization Kinetics in Soil Previously Amended with Sewage Sludge
Authors: Boyle Michael , Paul E. A. 
Published: July 2010

AbstractMicrobial mineralization rates of organic carbon (C) and nitrogen (N) were determined on the same sludge‐amended and nonamended soil samples. The purpose of this integrated approach was to high‐light the long‐term dynamics of N release with C stabilization in sludge‐affected soil. Three application rates of digested municipal sludge, check, 45 Mg ha−1 and 180 Mg ha−1, were incorporated into field plots annually for 8 years, with no addition during the subsequent 3 years. Barley was grown on the site each spring of the 11 years. In an 87‐week laboratory incubation experiment conducted on soil samples collected 3 years after the last sludge addition, N and C mineralization rates (kn, kc) increased with sludge application rate. Soil nitrogen mineralization potentials (No) increased with sludge application, unlike carbon mineralization potentials (Co) which did not correlate with sludge application. The C/N ratio of the mineralized organic matter decreased with sludge application rate. Three years after field incorporation of sludge, decomposition of the organic fraction can be described as a set of two first‐order rate reactions. One fraction is characterized by a large stable element (high No, Co and low kn, kc); the second fraction consists of a smaller labile portion which is characterized by low No, Co and high kn, kc values. The microbial biomass decreased to less than half of its original amount after 20 weeks of incubation in all soil treatments.
Determination of Plant‐available Phosphorus by the Iron Hydroxide‐impregnated Filter Paper (Pi) Soil Test
Authors: Menon R. G. , Hammond L. L. , Sissingh H. A. 
Published: July 2010

AbstractThe use of iron hydroxide‐impregnated filter paper (Pi) strips as a collector for phosphorus (P) in soil suspension offers a new approach to soil testing for plant‐available P. To correlate the Pi test with crop response, four soils ranging in pH from 4.5 to 8.2 were incubated with three rates of P either as triple superphosphate (TSP) or central Florida phosphate rock (CFPR), and P was measured in these soils by the Pi, Bray 1, Bray 2, double acid, Olsen, water, and resin extraction methods. Two successive crops of maize (Zea mays L.) were grown on these soils in greenhouse pots, and the dry matter yield and P uptake by maize were correlated with the soil test values. The Pi gave highly significant correlation with crop response in all four soils. Across all soils, P source, rates of application and crops, Pi gave the best correlation (0.870) with P uptake and dry matter yield. The next best correlation with dry matter yield was that of Olsen extractable P. The Pi test showed potential as a tool for prediction of P fertilizer requirements in soils.
Soil Acidification From Ammonium‐Nitrogen Fertilization in Moldboard Plow and Stubble‐Mulch Wheat‐Fallow Tillage
Authors: Rasmussen Paul E. , Rohde C. R. 
Published: July 2010

AbstractContinued use of ammonium‐based (NH4‐N) fertilizer can lower soil pH to levels deleterious to crop growth. The depth and intensity of acidification is affected by rate and type of N fertilizer, and differs with tillage systems. Change in soil pH in relation to applied N was determined for one conventional (moldboard plow) and two stubble‐mulch (offset disk, subsurface sweep) tillage treatments in a winter wheat (Triticum aestivum L.)‐fallow rotation receiving cumulative N application of 493, 728, 986, 1221, 1714, and 2207 kg N ha−1 over 44 yr. Nitrogen was applied as (NH4)2SO4 from 1940 to 1961 and as NH4NO3 from 1962 to 1983. The soil was a Walla Walla silt loam (Typic Haploxeroll) containing 200 g clay and 11 g organic C kg−1 in the upper 30 cm. Soil pH (1:2 soil/0.01 M CaCl2) decreased linearly with increasing N application in both conventional and stubble‐mulch tillage. Acidifying effects were concentrated in the top 7 cm of stubble‐mulched soil but distributed to 22 cm or below with moldboard plowing. The rate of pH decline in the top 22 cm of soil was greater for moldboard plow than for disk or sweep tillage, 0.38 vs. 0.21 and 0.28 units, respectively, per Mg of applied N ha−1. Linear regression analysis predicted that 2.7, 4.8, and 3.5 Mg N ha−1 would acidify the 0‐ to 22‐cm soil depth to a pH deleterious to wheat growth with moldboard plow, offset disk, and sweep tillage, respectively. However, the more rapid decrease in pH in the 0‐ to 7‐cm zone with disk or sweep tillage may sooner predispose stubble‐mulch systems to negative effects of acid conditions within the seed zone. Nitrogen applied as NH4NO3 produced more acidity per unit of N than did (NH4)2SO4, but NH4NO3 was applied at much higher rates at a later date so unbiased comparison is difficult.
Modeling Soil and Plant Phosphorus Dynamics in Calcareous and Highly Weathered Soils
Authors: Sharpley A. N. , Singh U. , Uehara G. , Kimble J. 
Published: July 2010

AbstractLabile and organic phosphorus (P) and sorbed P are required as the minimum data set to run a soil‐plant P cycling model recently developed for continental U.S. soils. Labile and organic P and P sorption index were related to physical and chemical properties of 23 calcareous (>50 g kg−1 CaCO3 content) and 32 highly weathered soils (>30% Al saturation), to allow estimation of these P forms from readily available soil data. The P sorption or fertilizer availability index was estimated as the fraction of fertilizer P remaining as labile (resin extractable) P following incubation of soil and fertilizer. Labile P was linearly related (R2 = 0.71–0.90) to soil test P measured by Olsen (calcarous soils) and by Bray, Colwell, Mehlich III, and Truog methods (highly weathered soils). Organic P was also linearly related to organic C (R2 = 0.87) and total N (R2 = 0.89) content of all soils. Fertilizer P availability index decreased with increased incubation time from 30 to 180 d, with the decrease related to CaCO3 and extractable Fe and Al contents of calcareous and highly weathered soils, respectively. At the present time, the model uses a 180‐d incubation value of fertilizer P availability index, which can be estimated from CaCO3 and clay contents of the calcareous and highly weathered soils, respectively. Using these relationships, accurate simulations were obtained of P transformations during 60‐yr cultivation of calcareous Houston Black clay and yield of maize (Zea mays L.) on two highly weathered Hawaiian soils receiving varying amounts of fertilizer P.
Compaction and Root Modifications of Soil Aeration
Authors: Asady G. H. , Smucker A. J. M. 
Published: July 2010

AbstractSoil compaction and the incipient aeration and mechanical impedance stresses are known to reduce root growth and function. Little is known, however, regarding the influence of root accumulations adjacent to a compacted area upon the aeration status of the soil profile below the root mass. This study was designed to measure plant root and soil aeration interactions with soil compaction. A clay soil was compacted to bulk densities in 1.1, 1.4 and 1.7 Mg m−3 in soil columns planted to dry edible bean (Phaseolus vulgaris L.). Mechanical resistances of these soil compaction treatments were 0.43, 2.14, and 5.50 MPa, respectively. Oxygen diffusion rates (ODR) were below the critical level for the 1.7 Mg m−3 treatment at all plant growth stages measured. As root accumulations increased at the 0.10‐ to 0.25‐m depths, ODR dropped below critical values for all bulk densities. Lower O2 concentrations above the soil surface decreased ODR both earlier and at shallower depths. Root plugging of 5% or more of the aeration pores significantly reduced the diffusion of O2 into and CO2 out of the soil regions below and adjacent to areas with the greatest accumulation of roots.
A Method to Determine Soil‐Entrapped Denitrification Products in Submerged Soils
Authors: Katyal J. C. , Holt L. S. , Gadalla A. M. 
Published: July 2010

AbstractTo measure the contribution of soil‐entrapped gases to denitrification in submerged soils, a soil‐filled cylindrical bag (7 cm in height by 5‐cm diam) made from stiff polyester cloth net was positioned in the center of potted Crowley silt loam soil. Denitrification of 15N‐labeled KNO3 (14.85 atom % excess, applied at 100 kg N ha−1) was complete in 16 d after fertilization; 71% of the KNO3 was denitrified, mainly as N2 gas, with 41% trapped in the soil and 30% present in the headspace. Although no significant change in denitrification occurred during the subsequent 8 d, 15N recovery from soil‐entrapped gases declined (from 41.2 to 28.4%), whereas that from gases present in headspace increased (from 29.6 to 43.9%). Regardless of time of sampling, around 90% of the 15N was recovered. These results demonstrate that in situ placement of soil‐filled polyester cloth net bags before fertilization is a practical approach for sampling submerged soils to assess the contribution of soil‐entrapped gases to denitrification loss.
Use of Oxygen Flux Density to Estimate Critical Air‐filled Porosity of a Vertisol
Authors: Hodgson A. S. , MacLeod D. A. 
Published: July 2010

AbstractWaterlogging studies of Vertisols require an accurate estimate of critical aeration levels. Gaseous O2 exchange was characterized in the top 0.3 m of a furrow‐irrigated Typic Pellustert by measuring quasi‐steady state diffusion through intact soil cores sampled in the field over a range of soil‐water content. Cores were taken at 0.1‐m depth increments from below the cropped ridges at major crack sites, a quarter of the distance between major cracks, and midway between major cracks in order to sample the nonrandom heterogeneity caused by vertical cracks running across the ridges. The relationship between oxygen flux density (F) and air‐filled porosity (ε) above the 0.2‐m depth at the three positions was described by a two‐stage linear model and fitted by optimization. Values of F and ε for soil below 0.2 m were restricted largely to the first (horizontal) stage of the model. For all other combinations of depths and positions, the model fitted the data with high precision (r2 > 0.84). The F of major crack sites was not increased relative to soil at other sites having the same ε. In wet soil, crack sites were sealed by the soil swelling and hence diffusion was inhibited. In dry soil, small cracks, fissures, and pores between the major cracks allowed similar rates of diffusion to that in the major cracks at the same ε. The minimum ε at which gaseous diffusion first occurred (ε0) was 0.145 ± 0.006 m3 m−3. This exceeds the previously accepted limit of ε = 0.1 m3 m−3, and may reflect a high proportion of occluded pores in this finetextured soil. The study evaluated an improved method of quantifying the aeration status of this soil and shifted the emphasis from oxygen content to oxygen flux as a more pertinent parameter of soil aeration in cropping situations. The technique is simple, rapid, and appropriate for routine sampling.
Effect of Aluminum Treatments on Permeability and Cation Status of a Smectitic Clay
Authors: Wada Koji , Beppu Yoshihisa 
Published: July 2010

AbstractAluminum sulfate or Al2(SO4)3 and CaCO3 mixtures were added to a smectitic clay in which Al3+, Al(OH)2+, Al(OH)+2, and Al(OH)3 formed when wetted with water. The treatment increased the permeability of the soil leached with distilled water. The permeability increased in the order of Al(OH)3 < Al(OH)+2, Al(OH)2+ < Al3+ and with the amount of Al, but its relative increase decreased with increasing addition of Al. The treatment with a relatively small amount of Al3+ (e.g., 5 cmol Al kg−1) was recommended to this soil having cation exchange capacity of 29 cmol kg−1 for its efficiency in increasing the permeability and permissible decrease of exchangeable Ca, Mg, and K. The acidity and exchangeable cation status as well as cation exchange capacity should, however, be considered in the choice of the treatment for a soil. There was a correlation between the permeability and the amount of Al retained by the soil. The contribution of exchangeable Al (monomeric Al3+) to the permeability was much higher than that of nonexchangeable Al (polymeric hydroxy‐Al cations) when evaluated in terms of molar quantities, indicating the importance of electric charge on an Al atom and the location of these Al cations on the bonding between clay particles.
Phosphate Fractions in Calcareous Vertisols and Inceptisols of Spain
Authors: Solis P. , Torrent J. 
Published: July 2010

AbstractCalcareous Vertisols and associated Inceptisols are abundant around the River Guadalquivir Valley, southern Spain. They support a profitable rainfed agriculture; little is known, however, about their phosphate status and fertility. For this reason the phosphate fractions in the Ap horizons of 24 of such soils were studied. The calcium carbonate equivalent of the samples ranged between 46 and 628 g kg−1 and the citrate‐dithionite‐bicarbonate (CBD)‐extractable Fe (Fe4) between 1.1 and 11.6 g kg−1 soil. Total P ranged from 331 to 1051 mg P kg−1 soil; organic P represented usually <10% of total P. Of the inorganic P, the HCl‐P (Ca phosphates) fraction was the most abundant (39–77% of total P). The fraction extracted specifically by NaOH (nonoccluded Fe‐ and Al‐bound P) was present in very small amounts. The citrate‐bicarbonate (CB)‐extractable P (P sorbed on active surfaces) ranged from 13.1 to 66.1 mg P kg−1 soil and had values similar to the resin‐extractable (labile) P. The CDB‐P (P occluded in the Fe oxides) was correlated with Fed (r = 0.92) and ranged from 7.8 to 52.0 mg P kg−1 soil. The changes in labile P associated with cropping with wheat (Triticum aestivum L.) or incubation with added P could be accounted for by changes in the CB‐P fraction. The CDB‐P and HCl‐P fractions also changed, albeit less markedly; absolute changes were similar for both fractions but relative changes were much higher for the CDB‐P. This suggests that Fe oxides (mainly as goethite) are very active in releasing and fixing P, and that occluded P is relatively mobile. The values of the Olsen and Colwell tests were correlated with labile P. The fraction of labile P extracted by these tests was negatively correlated with Fe4. Consequently labile P can be predicted, in practice, from P tests and Fed values.
Ecology of Fast‐Growing and Slow‐Growing Mesquite‐Nodulating Rhizobia in Chihuahuan and Sonoron Desert Ecosystems
Authors: Jenkins Michael B. , Virginia Ross A. , Jarrell Wesley M. 
Published: July 2010

AbstractProsopis glandulosa (mesquite) is effectively nodulated by both fast‐growing (FG) and slow‐growing (SG) rhizobia. The distribution of indigenous, free‐living, FG and SG rhizobia, and their morphological and symbiotic characteristic associated with the rooting systems of mesquite were investigated. The three warm desert ecosystems studied were an arroyo, a sand dune, and a playa in the Chihuahuan Desert of New Mexico, and a sand dune and playa in the Sonoran Desert of southern California. The FG rhizobia dominated the free‐living rhizobial population from 0‐ to 8‐m depth, at the New Mexico playa. In contrast to the New Mexico playa, the surface 1 m of soil under mesquite at the California playa was dominated by SG rhizobia, otherwise FG rhizobia dominated to 9‐m depth. Slow‐growing rhizobia dominated the lowest depths of the mesquite rooting system in both playas. Slow‐growing rhizobia dominated the entire rooting zone of both sand dune ecosystems. Fast‐growing rhizobia dominated the upper 2 m and SG rhizobia dominated below 2 m in the mesquite rooting zone at the New Mexico arroyo. Regression analysis indicated that the distribution of FG and SG rhizobia was related to the concentration of total soil salts (electrical conductivity) (r2 = 0.20). Chi‐square analysis of the distribution of colony morphologies indicated distinct rhizobial populations in each ecosystem. The FG rhizobial population at the New Mexico playa was highly effective and had a high frequency of Hup+ phenotypes. The FG rhizobia isolated from the arroyo were, in contrast, less effective and had a low frequency of Hup+ phenotypes. The SG rhizobial population at the arroyo was highly effective and had a high frequency of Hup+ phenotypes. The SG rhizobial population at the New Mexico dune system was, in contrast, mainly ineffective and had a low frequency of Hup+ phenotypes. The relationship between the variable distribution of FG and SG rhizobia and environmental factors associated with the ecosystems is discussed.
Influence of Electrolyte Concentration on Quaternary Cation Exchange by Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison 
Published: July 2010

AbstractA study of Na‐K‐Ca‐Mg exchange on specimen illite in a perchlorate background of varying ionic strength is reported. Sodium‐saturated Silver Hill illite was reacted at pH 7 with perchlorate solutions of differing Na/Ca or Na/Mg ratio and total electrolyte concentration (9.2, 5, 3.6, 2 and 1 molc m−3). All soluble and exchangeable cations were measured directly. No effect of the total electrolyte concentration on the total adsorbed charge was observed. The exchange isotherms and Vanselow selectivity coefficients based on the composition data showed that Silver Hill illite exhibited more or less equal affinity for Ca and Mg. Both bivalent cations were slightly preferred to Na in the three more concentrated electrolyte backgrounds, but at concentrations of 2 and 1 molc m−3, a slight preference for Na over Ca and Mg was observed. Exchangeable K, which represented 6 to 18% of the total adsorbed charge, decreased with the content of exchangeable Ca or Mg and, at a given bivalent charge fraction, was dependent on the total perchlorate concentration. The clay exhibited a very high preference for K over the three other cations which increased as the content of exchangeable K decreased.
Influence of Electrolyte Concentration and Exchangeable Cations on the Flocculation of Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison 
Published: July 2010

AbstractThe light transmission and optical density of suspensions of Silver Hill illite were investigated at pH 7 in mixed Na‐K‐Ca‐Mg perchlorate solutions of variable composition, with total charge concentrations varying between 1 and 10 molc m−3. The quantitative relationship between percentage light transmission (T), a measure of flocculation, and bivalent exchangeable cation charge fraction (Eblv) was found to be independent of whether the bivalent cation was Ca2+ or Mg2+. As the total perchlorate concentration was decreased, the graph of T vs. Eblv changed gradually from an upward‐inclined line with nonzero y‐intercept, to a sigmoid curve with zero y‐intercept, to a “step function” with a definite threshold value of the bivalent charge fraction above which flocculation occurred. For total perchlorate concentrations below 5 molc m−3, a sharp rise in suspension optical density, a measure of dispersion, was observed as the charge fraction of exchangeable Na was increased from 0.05 to 0.20. For perchlorate concentrations above 5 molc m−3, only a gradual increase in turbidity with exchangeable Na charge fraction was found. These results indicate that the relation between flocculation/dispersion and exchangeable cations for illite depends sensitively on the total electrolyte concentration, but not on the type of bivalent exchangeable cation.
Accelerated Rates of Selenium Volatilization From California Soils
Authors: Karlson U. , Frankenberger W. T. 
Published: July 2010

AbstractVolatilization of alkylselenides from soils spiked with labeled Se was monitored in a continuous flow system by using activated carbon traps and counting the recovered 75Se. Surface soils from a known Se‐problem area in California were used throughout this study. Inoculation with fungal isolates from these soils, including Acremonium falciforme, Penicillium citrinum, and Ulocladium tuberculatum enhanced Se evolution in nonsterile and autoclaved soils. The fraction of added Se volatilized per unit time was dependent upon Se level, soil series, Se species, and C amendment. Without C amendment, volatilization rates were up to an order of magnitude higher with Se(IV) as the Se source, when compared to Se(VI). Carbon addition in the form of pectin accelerated Se evolution 2‐ to 130‐fold, which was more pronounced with Se(VI) and with the less active soils. Hence with C amendment, Se(VI) was volatilized almost as rapidly as Se(IV) by all soils. With three pectin amendments over a period of 118 d, total Se volatilization ranged from 11.3 to 51.4% of the added Se. A minimum Se threshold for alkylselenide production was not found, applying Se additions as low as 10 µg kg−1 soil.