bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increases in the Cation Exchange Capacity of Variable Charge Soils Following Superphosphate Applications
Authors: Gillman G. P. , Fox R. L. 
Published: July 2010

AbstractThe cation exchange capacity (CEC) of soils from field plots which were fertilized with concentrated superphosphate for 8 years has been measured. The superphosphate was added in amounts equivalent to those needed to raise solution P to 0.001 to 1.6 µg/ml in the adsorption isotherm. Three variable charge soils from Hawaii, a Hydrandept, a Gibbsihumox, and a Eutrostox were examined, using a new method for estimating the CEC of variable charge soils. This method takes account of pH and ionic strength conditions in the field. Agronomically significant increases in CEC of the surface horizons with increasing superphosphate application were obtained. As a result, the leaching of applied nutrients, Ca, Mg, and K, was retarded, and greater quantities of these cations were present in the 0–50 cm profile than in the plots receiving no P, despite the fact that more cations were removed from the P treated plots by crops grown in succession.
Sorption of Copper, Zinc, and Cadmium by Some Acid Soils
Authors: Kuo S. , Baker A. S. 
Published: July 2010

AbstractThe sorption of Cu, Zn, and Cd as a function of pH was examined for three acid soils. Sorption occurred at pH levels markedly below the zero point of charge (ZPC). Copper sorption increased with increasing pH, and Cu was preferentially sorbed over Zn and Cd. The presence of Cu interfered with the sorption of Zn and Cd. The sorption at higher pH levels varied with the source of hydroxide used. Sodium hydroxide had a greater ability than calcium hydroxide to disperse organic matter and to reduce the ability of the soils to retain metals. Reduction of heavy metal sorption at high pH levels was attributed to the formation of metal‐organic complexes. The metal sorptive capability of Chehalis (Cumulic Ultic Haploxerolls) soil was greater than that of Puyallup (Fluventic Haploxerolls) and Sultan (Aquic Xerofluvents) soils, perhaps due to its higher organic matter and Fe contents and its higher cation exchange capacity (CEC). Further investigation revealed that the CEC played a more important role than soil organic matter content in the sorption of the metals. The solubility of Al and Mn in the soil solution may also help to regulate sorption of heavy metals by acid soils.
Effects of pH and Neutral Electrolyte Concentration on Free Radicals in Humic Substances
Authors: Ghosh Kunal , Schnitzer M. 
Published: July 2010

AbstractElectron spin resonance (ESR) investigations on humic substances were carried out at different pH's and at different neutral salt concentrations, two of the main factors controlling chemical and biological reactions in soils. With increase in neutral electrolyte concentration, free radical concentrations of humic materials decreased. With both fulvic acid (FA) and humic acid (HA), spin contents increased after raising the pH from the near neutral to the alkaline range, because of the stabilization of semiquinone radicals. With FA, a minimum spin concentration region was observed from pH 5.0 to 6.5. Potentiometric titrations revealed that activities of both electron donor and electron acceptor groups in humic molecules were at a minimum around that pH range. Between pH 5.0 and 6.5, a range into which many agricultural soils fall, humic materials appear to be chemically least reactive, which may explain, at least in part, their stability in soils.
Carbon and Nitrogen Movement from Surface‐Applied Wheat (Triticum aestivum) Straw
Authors: Cochran V. L. , Elliott L. F. , Papendick R. I. 
Published: July 2010

AbstractThe N immobilization potential of surface‐applied wheat (Triticum aestivum L.) straw as compared with incorporated straw was evaluated in the laboratory with soil columns. The columns were leached weekly and C and N content of the leachate determined. Leachate C/N ratios for straw alone exceeded 20:1 on several occasions and reached a maximum of 56, indicating a potential for N immobilization. Less than 5% of the total C in the straw was recovered in the leachates, providing an immobilization potential of <5 kg N ha−1. Leachate C/N ratios from 1‐, 2‐, and 4‐cm deep soil columns with surface‐applied wheat straw and no fertilizer N ranged up to 55:1, 30:1, and 22:1, respectively, while the highest leachate C/N ratio from the 4‐cm mixed straw treatment was 30:1. A significant percentage of mineralized N was immobilized in the top 1 and 2 cm of soil by surface residues. Much less N was immobilized in the 4‐cm soil columns. Thus, placement of fertilizer N several centimeters below the soil surface would alleviate possible N immobilization from organic C leached from surface crop residues.The amount of applied N recovered in the leachate during 9 weeks of incubation ranged from 60 to 70% for all soil column treatments with or without surface straw. There was no significant differences between treatments. In contrast, the recovery of applied N from the mixed straw treatment was only 36%, indicating a much greater potential for N immobilization with mixed than with surface straw. The quantity of the fertilizer N added probably masked the immobilization potential of the surface residues. Fertilizer N stimulated early release of C from the straw alone treatment, but after 9 weeks of incubation the overall C loss from both fertilized and unfertilized straw was about 30%.
Comparison of Nitrogen and Sulfur Mineralization in Soils
Authors: Tabatabai M. A. , Al‐Khafaji A. A. 
Published: July 2010

AbstractThe relationship between N and S mineralization has not been well understood. In this study, field‐moist soil‐grass beads mixtures were packed in glass columns and leached with 100 ml of 0.01M KCl and incubated at 20 or 35°C. The leaching procedure was repeated every 2 weeks for a total of 26 weeks. The leachates were analyzed for mineral N and S. Expressed as percentages of soil organic N, the total amounts of N mineralized at 20°C ranged from 1.8 to 6.7 (avg = 3.8%) and, at 35°C, ranged from 8.3 to 26.8 (avg = 16.6%). Expressed as percentages of soil organic S, the total amounts of S mineralized at 20 and 35°C ranged from 3.5 to 13.3 (avg = 7.8%) and from 8.9 to 34.9 (avg = 22.8%), respectively. Results indicate that organic S is depleted faster than organic N.The cumulative amounts of N and S mineralized in each of the 12 soils studied were linear with time of incubation. The rates (µg/g soil/week) of N and S mineralized at 20°C ranged from 1.7 to 4.2 (avg = 2.9) and from 0.5 to 1.2 (avg = 0.8), respectively. At 35°C, the rates of N and S mineralized ranged from 7.7 to 17.0 (avg = 12.5) and from 1.6 to 3.5 (avg = 2.5). The ratios of N/S mineralized during 26 weeks of incubation at 20 and 35°C ranged from 2.4 to 4.4 (avg = 3.5) and from 3.4 to 6.1 (avg = 5.0). At 35°C, the ratios of N/S mineralized were significantly correlated with soil pH. Rates of S mineralization, however, were significantly, but negatively, correlated with soil pH.The average Q10 of N mineralization of the soils was 3.0, and that of S mineralization was 1.9. The amounts of N and S mineralized during 26 weeks of inclubation were significantly correlated at 20°C (r = 0.95***) and at 35°C (r = 0.79**).
Effects of Temperature and Iron(III) Concentration on the Hydrolytic Formation of Iron(III) Oxyhydroxides and Oxides
Authors: Wang Ming K. , Hsu Pa Ho 
Published: July 2010

AbstractFe(ClO4)3 solutions, of concentration ranging from 0.01M to 0.1M, were hydrolyzed at different temperatures and periodically analyzed up to 14 months. The reaction products were very different in their appearance and stability. For a given iron(III) concentration, the sample appearance changed as the temperature of preparation changed. Beginning as true solutions at lower temperatures, the samples progressively appear as coarse precipitates, turbid suspensions and clear sols as the temperature of preparation increases. For a given temperature of preparation, the products showed the same sequence of changes with decreasing Fe(III) concentration. The products are largely goethite, with an occasional presence of lepidocrocite when prepared at 37°C or below, but are hematite and/or goethite when prepared at 55°C or above. The results suggest that the differences in appearance and stability merely reflect the distribution of particle size but not the mineralogical composition. The degree of supersaturation is suggested as the key factor governing the initial number of nuclei relative to the concentration of monomeric Fe(III) ions, which, in turn, governs the appearance and stability of hydrolyzed Fe(III) solutions. A change in temperature results in changes in the reaction rate as well as the equilibrium constant and, thus, the degree of supersaturation.
Mineralogical Characteristics and Transformations of a Vertical Rock‐Saprolite‐Soil Sequence in the North Carolina Piedmont: I. Profile Morphology, Chemical Composition, and Mineralogy
Authors: Calvert C. S. , Buol S. W. , Weed S. B. 
Published: July 2010

AbstractA lithologically continuous vertical rock‐saprolite‐soil sequence was studied in order to determine its mineralogical characteristics and transformations. The soil was a Typic Hapludult from the North Carolina Piedmont formed on granitic gneiss. The profile was sampled in 19 horizons, from the surface to slightly altered rock, on the basis of morphology and depth. Though weathering intensity was generally antipathetic with depth, this was not always the case, especially in the deep saprolite where two horizontal weathering fronts moved in opposite directions from a single fracture plane. The soil material differed morphologically from the saprolite by having soil structure and clay skins.Elemental analysis of the samples revealed a release of Ca and Na from the altering rock, and a subsequent decrease in abrasion pH, presumably due to rapid plagioclase alteration. Aluminum seemed to precipitate initially as an Al‐rich clay mineral in the altering rock. However, this clay was rapidly resilicated coincident with a decrease in abrasion pH. The most rapid changes occurred in the deepest saprolite horizons.
Solute Transport in Aggregated Porous Media: Theoretical and Experimental Evaluation
Authors: Rao P. S. C. , Rolston D. E. , Jessup R. E. , Davidson J. M. 
Published: July 2010

AbstractBreakthrough curves (BTC's) for 36Cl‐ and 3H2O displacement through water‐saturated columns of aggregated and nonaggregated porous media were measured at pore‐water velocities varying over an order of magnitude (2 to 96 cm/hour). These BTC's were used to verify two conceptual solute transport models in which the pore‐water was partitioned into inter‐ and intra‐aggregate regions. In both models, convective‐dispersive solute transport was assumed to be limited to the inter‐aggregate pore‐water region, while the intra‐aggregate pore‐water was assumed to behave as a diffusion sink/source for solute. The rate of solute transfer between the two pore‐water regions was described either by Fick's second law of diffusion written in spherical coordinates (Model I) or was assumed proportional to the concentraion difference between the two regions (Model II). Values of all input parameters in each model were measured in independent experiments rather than by curvefitting to the measured BTC's. Agreement between calculated and measured BTC's at all velocities was good for both models. The value of the mass transfer rate coefficient in Model II was found to vary with aggregate radius, time, and pore‐water velocity. This result was predicted based on theory and experimental results presented in an earlier paper. Conditions under which solute diffusion in aggregates leads to tailing or asymmetry in measured BTC's (during saturated water flow) were identified from a sensitivity analysis using Model I. For certain aggregate radii and pore‐water velocities, the diffusion sink/source effects of the aggregates could be incorporated into the dispersion coefficient, and this lumped‐parameter approach was used to successfully describe the measured BTC's.
A Combined Salt Transport‐Chemical Equilibrium Model for Calcareous and Gypsiferous Soils
Authors: Robbins C. W. , Wagenet R. J. , Jurinak J. J. 
Published: July 2010

AbstractChemical precipitation‐dissolution and cation exchange subroutines were interfaced with an existing water movement‐salt transport model. Three model options available for testing the prediction of salt transport and storage were (i) individual ion transport without soil interaction, (ii) precipitation and dissolution of lime and gypsum during transport, and (iii) cation exchange in addition to the precipitation‐dissolution reactions. The transport model also predicts relative crop growth and water uptake as affected by soil moisture and salinity. The chemical subroutine used by the second and third options calculated ionic activities, corrected for ionic strength and ion pair formation, and was used to calculate lime and gypsum precipitation and dissolution. Cation activities were also used to calculate Ca, Mg, Na, and K exchange equilibria by a method that allows for addition of any number of exchangeable cations. Values predicted by the three options for EC, SAR and Ca, Mg, Na, K, Cl, SO4, and HCO3 concentrations were compared to experimental data obtained from a lysimeter study and were only satisfactorily predicted when both chemical precipitations and cation exchange were considered for a gypsiferous and a nongypsiferous soil irrigated with a high, medium, and low CaSO4 water at two leaching fractions.
Nitrogen Mineralization as Affected by Soil Moisture, Temperature, and Depth
Authors: Cassman K. G. , Munns D. N. 
Published: July 2010

AbstractVariation in the rate of N mineralization in a Yolo soil profile was studied using in vitro incubation methods. Negligible amounts of NH4‐N were recovered from leachates, indicating that the rate of N mineralization was the primary factor controlling N availability. During a 13‐week incubation at 25°C, 42% of the total estimated N mineralized was derived from the surface soil (0 – 18 cm), whereas 58% was contributed from the 18‐ to 108‐cm depths. Cumulative N mineralization in the 0‐ to 18‐cm and 18‐ to 36‐cm depth samples followed first‐order kinetics and was linear with respect to the square root of the incubation time. The mineralization rate constant differed more than twofold between the 0‐ to 18‐ and the 18‐ to 36‐cm depth samples. At lower depths (36 – 72 and 72 – 108 cm) the relationship between cumulative N mineralization and the square root of time was curvilinear.Interactive effects of soil temperature and moisture were also examined in an experiment with four incubation temperatures (15, 20, 25, and 30°C) in factorial combination with six soil moisture levels (0.1, 0.3, 0.7, 2, 4, and 10 bars). There was a significant moisture × temperature interaction; N mineralization increased above that expected from additive effects at 30°. Multiple regression was used to generate an equation that predicted net N mineralization as a function of soil temperature and moisture.The apparent effect of soil water content on N mineralization depended on experimental procdure. When soil water content was varied by adding water to air‐dry soil without complete equilibration, N mineralization declined linearly with water content. In contrast, there was a sharp decline between 0.3‐ and 2‐bar treatments and a more gradual decline at higher matric suctions when soil was equilibrated by pressure‐membrane desorption before incubation. These results indicate that both quantity and distribution of soil water affect in vitro estimates of N mineralization.
Biodegradation and Stabilization after 2 Years of Specific Crop, Lignin, and Polysaccharide Carbons in Soils
Authors: Martin J. P. , Haider K. , Kassim G. 
Published: July 2010

AbstractThe purpose of this study was to follow the biodegradation and stabilization in two soils of specific carbons of model and cornstalk lignins, lignin monomer alcohols, wheat straw, and the polysaccharide fraction of wheat straw over a 2‐year incubation period using 14C‐labeled substrates. Incubations were carried out in a closed, constantly aerated system and the 14CO2 released determined at specific intervals. After incubation the amounts of residual 14C in various soil humus fractions, in the biomass, and that solubilized by acid hydrolysis were determined. During the 2‐year period, about 40% of the ring and two‐side chain carbons of coniferyl and coumaryl alcohol units in model and cornstalk lignins had evolved as CO2. Losses of CH2OH and three‐side chain and of OCH3 carbons varied from 52 to 69%. The degradation rate was most rapid during the first 3 to 6 months of incubation. total C losses from whole wheat straw and cornstalks for comparison at 2 years were about 72% and for the polysaccharide portion of the wheat straw, 83%. During the first 6 months about 47% of the two‐side chain and ring carbons and 61 to 66% of the other carbons of free coniferyl alcohols had evolved as CO2. During the next 18 months these values had increased only about 11%. A major portion of the residual lignin carbons was recovered in the HA fractions, relatively small quantities were lost upon 6M HCl hydrolysis, and < 1% was estimated to be in the biomass. Most of the residual wheat straw C and especially the polysaccharide carbon was solubilized upon 6M HCl hydrolysis, 3 to 8% was still present in biomass, and 50% remained in the NaOH extracted soil. The results indicate that the major portions of the lignin carbons are incorporated into the more resistant or aromatic portions of the soil humus. The polysaccharide carbons, on the other hand, are metabolized and utilized for energy and synthesis of cell polymers, primarily proteins and polysaccharides, some of which are stabilized in the humus but are still susceptible to acid hydrolysis. Loss as CO2 and distribution of the residual carbons of free lignin alcohols in HA and losses upon 6M HCl hydrolysis were intermediate between the lignin and polysaccharide carbons.
Reflectance Technique for Predicting Soil Organic Matter
Authors: Krishnan P. , Alexander John D. , Butler B. J. , Hummel John W. 
Published: July 2010

AbstractThe objective of this research was to study the spectral reflectance of the selected soils in the infrared and visible wavelength regions and to identify optimal wavelengths for predicting the soil's organic matter content. Samples representative of soils of different texture and predicted organic matter content were collected from different areas in Illinois. Measurements of the spectral reflectance of soil samples in the infrared and visible wavelengths regions were recorded with a multipurpose computerized spectrophotometer with a Cary Model 14 monochromator attachment operated in a single beam mode. A stepwise multiple linear regression program was used to analyze the reflectance data and to determine the optimum wavelengths for predicting the organic matter content of the soil. An iterative procedure was used to identify the wavelengths that correlated best with organic matter content. No absorption peak due to soil organic matter was found in the infrared and visible regions of the spectrum scanned. The optimal wavelengths for predicting percent organic matter content are 0.6236 and 0.5644 µm and the model is of the form:Organic matter content = K × d log(r‐10.6236)/dλ0.6234 / d log(r‐10.5844)/dλ0.5844
Soil Shrinkage Relationships of Texas Vertisols: II. Large Cores
Authors: Yule D. F. , Ritchie J. T. 
Published: July 2010

AbstractAlthough soil shrinkage in the field has been related to water content changes, this relationship has not been correlated with small core measurements or defined in terms of structural and shrinkage water loss phases. Since field measurements are limited by the accuracy of the water content determination, undisturbed cores (73 cm diam and 140 cm long) from the eight Vertisols studied previously were studied to accurately measure water loss (by weighing). Sorghum plants were established, and a single drying cycle was studied. Vertical shrinkage was measured at the surface and at the 15‐, 35‐, 55‐, 95‐, and 115‐cm depths, and the water content profile was measured with neutron moisture and gamma density probes. These data were interpreted in terms of the shrinkage pattern found in the cores and with the use of small core data obtained by Yule and Ritchie. (1980).Although the water loss data were confounded by large soil evaporation from shrinkage cracks at the side of the cores, the evidence suggested that the shrinkage response was a combination of structural and shrinkage water loss phases. Consequently, the shrinkage curve for the soil surface asymptotically approached the theoretical equidimensional, normal curve. Shrinkage curves with profile depth tended to parallel the soil surface curve. The water content profiles obtained were not precise, but shrinkage parameters calculated for various depth increments resembled the small core data obtained previously. The results showed that small core data could be used to predict field shrinkage responses if field soil water content profiles are known.
Recovery of Nitrogen by Rice from Blue‐Green Algae Added in a Flooded Soil
Authors: Wilson J. T. , Eskew D. L. , Habte M. 
Published: July 2010

AbstractUptake of N from a blue‐green alga (Aulosira 68) by rice (Oryza sativa L.) was studied in a greenhouse pot experiment. When a suspension of the alga was buried 5–7 cm deep, 52% of the N added was recovered in the grain and straw of the first rice crop, and an additional 5% was recovered by a ratoon crop and by a subsequent transplanted crop. Additions of NH4Cl equivalent to 100 kg N/ha did not affect the recovery of algal N. Surface placement of the alga reduced recovery by the first crop to 37% of the added N.
Nitrogen Transformations in Sewage Sludge—Amended Soils as Affected by Soil Environmental Factors
Authors: Terry R. E. , Nelson D. W. , Sommers L. E. 
Published: July 2010

AbstractThe objectives of this study were to determine the effects of soil pH, soil moisture tension, sludge application rate, incubation temperature, and nitrification inhibitor on N transformations in soils amended with an 15N‐labeled sewage sludge. Less than 0.1% of added sludge‐N was lost from any of the samples due to NH3 volatilization. Nitrification rates were faster in sludge‐amended soils as compared to nonamended acidic soils treated with NH4+‐N. Adding calcareous sewage sludge to acid soils produced a more favorable pH for nitrification. Nitrification was faster in sludge‐amended soil having an initial pH of 7.5 than in samples at pH 6.0 or 5.3. Nitrite‐N accumulated to levels of 100 µg/g in sludge‐treated soils with high pH values (∼ 7.5). Nitrification proceeded at a faster rate in sludge‐amended soils adjusted to −0.25 and −0.5 bar moisture tension than in soils at −1 bar. Nitrification rates were not greatly affected by sludge application rate, although more time was required for complete nitrification of greater quantities of NH4+‐N. Nitrapyrin inhibited nitrification for 112 days, after which nitrifying ability recovered. Temperature was the only factor evaluated which markedly affected mineralization of sludge‐organic N and immobilization of added inorganic‐N. The rates of both mineralization and immobilization increased as temperatures increased. At the end of 168 days of incubation at 21°C, 40% of added sludge‐organic N was mineralized in silt loam soils, but up to 26% of added NH4+‐N was immobilized. There were only small net changes in inorganic‐N concentrations in sludge‐amended soils after 168 days of incubation.