bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model for the Release of Urea by Granules of Sulfur‐Coated Urea Applied to Soil
Authors: Jarrell W. M. , Boersma L. 
Published: July 2010

AbstractThe release of urea N from granules of sulfur‐coated urea (SCU) in soil must be predictable so that efficient use can be made of the fertilizer's slow release characteristics. The objective of this study was to develop and experimentally evaluate a mathematical model which makes it possible to forecast the release of urea from SCU granules as a function of time.Equations were formulated to describe the rate at which soil microorganisms remove coatings from initially intact granules, the rate at which holes appear in the coatings as a consequence of this removal, the rate of diffusion of urea through these holes into the soil, and the effects of temperature and soil water content on each process. These equations were incorporated into a computer program which calculated the amount of urea released on consecutive days over periods as long as 120 days.The effects of temperature and soil water content on the growth and activity of microorganisms were formulated on the basis of literature data. Temperature corrections for the diffusion process were based on the temperature dependence of the solubility of urea and the diffusion coefficient.The model was validated by comparing predicted rates of release with experimental results. The predictions made by using the model conformed with experimental results. The model calculations responded accurately to changes in temperature, soil water content, and differences in coating thickness and coating composition. The use of the model clearly points to the need for a more precise assessment of the factors which affect the release of urea from SCU granules.
Surface Reactivity of Aluminum Hydroxides Precipitated in the Presence of Low Molecular Weight Organic Acids
Authors: Kee Kwong K. F. Ng , Huang P. M. 
Published: July 2010

AbstractThe surface reactivities of aluminum hydroxides precipitated in systems at the initial Al concentration of 1.1 × 10−3M and the OH/Al molar ratio of 3.0 in the individual presence of 0, 10−6, and 10−4M, respectively, of citric, L‐malic, DL‐aspartic, and p‐hydroxybenzoic acids were investigated. The organic acids enhanced the specific surface of the precipitation products of hydrolytic reactions of Al through structural distortion. The development of surface charge and active sites for the retention of phosphate and Ca were thus promoted. The enhancement of the surface reactivities of the precipitation products of Al by the organic acids followed the sequence of the stability constants of the complexes of Al with the organic acids, namely, citric acid > malic acid > aspartic acid > p‐hydroxybenzoic acid. At the concentration of 10−4M organic acids, deviation from the latter sequence occurred in the development of positive surface charge and in the retention of phosphate. Specific adsorption of anions, while favoring the retention of Ca, counteracted the promoting influence of high specific surface on the development of the net surface positive charge and on the retention of phosphate of the precipitation products of Al. Among the organic acids used, with the exception of p‐hydroxybenzoic acid, a concentration of 10−4M, in contrast to 10−6M, was sufficiently high to stabilize the high specific surface and phosphate retention capacity of the precipitation products of Al during aging.This information is of significance in understanding the role of low molecular weight organic acids in the formation of short‐range ordered aluminum hydroxides and their subsequent surface reactivities with respect to P and Ca.
Cupric Ion Complexation by Fulvic Acid Extracted from Sewage Sludge‐Soil Mixtures
Authors: Sposito Garrison , Holtzclaw Kenneth M. , LeVesque‐Madore C. S. 
Published: July 2010

AbstractThe complexes formed between Cu2+ and fulvic acid extracted from sewage sludge were investigated by potentiometric titration of K/H fulvate with Cu(ClO4)3 at pH 5 and 25°C, in an ionic medium of 0.1M KClO4. Formation functions, giving the number of moles of Cu2+ bound per mole of K/H fulvate, were calculated from the titration data and plotted against the molar concentration of Cu2+, with the concentration of K/H fulvate being a fixed parameter for each plot. These functions were analyzed by the Scatchard plot method and were interpreted as evidence of: (i) a relatively strong 1:1 complex (log cK = 3.9) that is formed between Cu2+ and the most acidic functional groups in fulvic acid and (ii) a weaker set of complexes (log eK = 2) that is formed between Cu2+ and the more weakly acidic functional groups acting as both unidentate and bidentate ligands.
Atmospheric Sulfur as Related to Fertility of Ultisols and Entisols in South Carolina
Authors: Jones U. S. , Hamilton M. G. , Pitner J. B. 
Published: July 2010

AbstractContributions of atmospheric sulfur (S) to soil fertility at 15 locations in South Carolina were estimated during the 5‐year period 1973–77 by measuring the S content of precipitation samples accumulated at 30‐day intervals and by measuring the S collected in lead peroxide samplers exposed to the air at the same time intervals. The S content of precipitation was compared with similar data collected at three locations in 1953–55. Concurrently with the 1973–77 study, long‐term uniform field experiments designed to measure response of seven crops to S added in the fertilizer were conducted at selected locations. The mean estimated annual amount of S added to the soil in precipitation for the period 1973–75 was 11.3 kg per ha. The corresponding addition in 1953–55 was 6.3 kg/ha. The mean estimated amount of S added to the soil from the air and precipitation increased from 11.2 kg/ha in 1973 to 19.8 kg/ha in 1977. Sulfur added in the fertilizer resulted in an increased yield (10% probability level) for one crop at one location.
Establishment of the Lower Boundary of the Sola of Weakly Developed Soils that Occur in Oklahoma
Authors: Dawud Awni Y. , Gray Fenton 
Published: July 2010

AbstractThe main objective was to investigate the possibility of selecting one or more soil properties to aid in locating the solum lower boundary. Five pedons of weakly developed soils in western Oklahoma were selected. Chemical and physical measurements were made on both major samples and subsamples from designated horizons. The zone of organic matter accumulation was assumed to be the boundary of the solum since the organic matter accumulation is a function of the biological weathering. Different properties were correlated with each other within the zone of organic matter accumulation in order to select the properties which show a change coincident with that zone. Color, structure, texture, depth of calcium carbonate leaching, and base saturation did not show a change that could be correlated with the zone of organic matter accumulation. Bulk density did show change coincident with organic matter accumulation in soils with weak clay accumulation, therefore; it is suggested here that bulk density be used as a criterion for locating the solum lower boundaries of weakly developed soils of western Oklahoma.
Soil and Water Losses from Corn‐Soybean Rotations
Authors: Laflen J. M. , Moldenhauer W. C. 
Published: July 2010

AbstractMany people have observed what they felt was greater soil erosion by wind and water following production of soybeans. This experiment was conducted to measure the actual erosion following soybean production compared to that following corn production. Using natural rainfall plots at Beaconfield, Iowa, soil and water losses were measured from soybeans in a corn‐soybean rotation and from corn in this same rotation and grown continuously over a 7‐year period. Soil losses were found to be greater following soybeans than following corn in either a corn‐soybean rotation or in continuous corn. This means more precautions must be taken to control erosion when soybeans are grown on sloping lands than when corn is grown.
Crown‐Depth Soil Temperatures and Winter Protection for Winter Wheat Survival
Authors: Aase J. K. , Siddoway F. H. 
Published: July 2010

AbstractWinterkill of winter wheat (Triticum aestivum L.) can be a serious problem in marginal winter wheat growing areas of the world. Plants that are well hardened or conditioned when entering the winter season may withstand crown‐depth temperatures of about −20°C; less hardened cultivars, about −16°C.Experiments were initiated on a Williams loam (fine‐loamy, mixed Typic Argiborolls) near Sidney, Montana, to establish snow depth and protection requirements, based on a −16°C limit criterion at crown depth (3 to 5 cm), for reasonable assurance of winter wheat survival.Soil temperatures were measured at 0‐, 3‐, 10‐, and 50‐cm depths on fallow soil under various snow depths. In addition, a deep furrow drill was used to seed winter wheat on summer fallow with soil temperatures measured at 0, 3, and 10 cm and in standing stubble with soil temperatures measured at 0‐, 5‐, 15‐, 30‐, 60‐, and 90‐cm depths. Providing no other confounding factors such as snowmelt and subsequent ice‐crust formation are present, about 7 cm of snow is probably sufficient to prevent winterkill even when air temperatures occasionally approach −40°C. The deep furrow drill formed furrows deep enough to trap about 6 to 7 cm of snow. Standing stubble provided additional protection and caught and held snow.
Clay Mineralogy of Soils in the Nigerian Tropical Savanna Regions
Authors: Ojanuga A. G. 
Published: July 2010

AbstractThe clay mineralogy of soils from the moist southern Guinea savanna and subhumid northern Guinea savanna has been studied. All the soils occur on basement complex. Kaolinite is the dominant clay mineral in all the well‐drained soils, a property shared with the well‐drained soils of the humid tropical forests. In poorly drained soils montmorillonite forms in significant amounts in addition to kaolinite. Quartz is another mineral that occurs in the clay fraction of all the soils. Kaolinization is the dominant clay forming process under good soil drainage. The kaolinization process seems to be directed or favored by (i) the lowering of the pH of the weathering environment due to the temperature‐induced dissociation of soil water, (ii) marked leaching rainfall, and (iii) mineralogical composition of the soil or parent material. Under poor drainage montmorillonization becomes a significant clay‐forming process in addition to kaolinization due to the adequate silica, alumina, and base potentials of the soil solution.
Charge Characteristics of Soils with Variable and Permanent Charge Minerals: I. Theory
Authors: Uehara G. , Gillman G. P. 
Published: July 2010

AbstractThe net surface charge density of soil colloids consisting of mixtures of variable and permanent charge minerals is treated as the sum of the two types of surface charge. The permanent charge is assumed to be constant in magnitude, and negative, zero, or positive in sign, and the variable charge is permitted to vary in magnitude and sign with pH and electrolyte concentration. Based on these assumptions, relations are developed which show that there are two zero points of charge. The zero point of charge of the mixture as a whole is designated ZPNC and the zero point of charge of the variable charge component is designated pH0. The ZPNC can be determined by ion adsorption measurements, and pH0 by potentiometric titration. In mixtures, ZPNC is lower than pH0 when permanent charge is negative and higher than pH0 when the permanent charge is positive. The magnitude of the permanent charge can be determined by measuring cation and anion retention at the pH corresponding to pH0. Specific surface of mixed systems can be estimated by measuring negative ion adsorption at pH values sufficiently different from pH0.
Charge Characteristics of Soils with Variable and Permanent Charge Minerals: II. Experimental
Authors: Gillman G. P. , Uehara G. 
Published: July 2010

AbstractPotentiometric titration and ion adsorption data were analyzed according to theory which treats soils as mixtures of permanent and variable charge minerals. Evidence of permanent positive charge was found in a Spodosol and two Oxisols. Surface areas calculated from negative ion adsorption below and above the zero point of charge indicates that permanent and variable charges occupy the same area. Laboratory procedure for characterizing samples with mixed charges are described.
Clay Illuviation and Lamella Formation in a Psammentic Haploxeralf in Southern California
Authors: Torrent J. , Nettleton W. D. , Borst G. 
Published: July 2010

AbstractThe lamellae of a Psammentic Haploxeralf in San Diego County, California, contain more fine clay and less coarse clay than the interlamellar horizons. In most of the lamellae, argillans constitute the plasma. All this indicates the importance of illuviation in their formation. Since the deepest lamellae are below the wetting front in today's climate, it is concluded that the deepest ones were the first to form. Also, in the middle part of the pedon the lamellae have been broken by the formation of a sand window, an eluvial feature. Since there is carbonate in the upper but not the lower part, it is concluded that the pedon began to form in a climate much like that of today's at Santa Cruz, California. Santa Cruz is some 800 km to the north, receives about 80 cm of precipitation, and has a mean annual temperature of 14°C.
Reactions Between Monocalcium Phosphate Monohydrate and a Chromic Luvisol: I. The Morphology of Reaction Products
Authors: Davey B. G. , Shayan A. 
Published: July 2010

AbstractSamples, in field structural condition, of the surface (BR1) and subsoil (BR3) of a Chromic Luvisol from Mason, County of Cumberland, New South Wales, Australia, were reacted with pellets of monocalcium phosphate monohydrate (MCPM). The reaction products were investigated using a scanning electron microscope and by qualitative electron probe microanalysis. The morphology of many of the reaction products, some of which were crystalline, and others which appeared to be amorphous, was defined. The dominant reaction products were found to be calcium phosphates which usually contained Fe, Al, Mn, Si, and occasionally K dissolved from the soil matrix by the solution leaving the fertilizer pellets.The dominant reaction products at the pellet sites were found to be dicalcium phosphate dihydrate (DCPD) and dicalcium phosphate anhydrous (DCPA), together with a small amount of MCPM in the case of the subsoil (BR3).
Reactions of Partially Acidulated Phosphate Rock with Soils from the Tropics
Authors: Mokwunye A. Uzo , Chien S. H. 
Published: July 2010

AbstractEqual amounts of water‐soluble P in the form of granulated partially‐acidulated phosphate rock (20% by H3PO4) and concentrated superphosphate (CSP) were added to two Nigerian savanna soils and an Oxisol from Colombia. The amount of water‐extractable P was higher in soils treated with partially‐acidulated phosphate rock. Addition of phosphate rock to CSP resulted in an increase in the water‐extractable P. The results suggest that the presence of phosphate rock in partially acidulated phosphate rock or in the mixture of CSP and phosphate rock slowed down the immobilization of watersoluble P by reacting with some of the acidity produced during monocalcium phosphate hydrolysis, thus reducing the amount of acid available to solubilize soil Al and Fe. Reaction of acid with phosphate rock could release additional P to the watersoluble pool. The relative effectiveness of partially acidulated phosphate rock was highest in the Oxisol which had the highest capacity to sorb P.
The Effect of Heating on Humic Acid Structure and Electronic Spin Resonance Signal
Authors: Eltantawy I. M. 
Published: July 2010

AbstractESR and IR spectra were recorded and weight loss measured on soil humic acid after subjecting the humic acid to heat over the temperature range 25° to 600°C. Heating to 200°C enhanced the ESR signal (g = 2.0024), indicating an increase in the free radical content. No changes were observed in the g value, suggesting that the thermally generated and the original free radicals had similar structures. IR spectra indicated that structural modifications during heating include partial dehydroxylation and/or decarboxylation, vaporization of low‐boiling volatiles, oxidation, and solid state transition. The maximum weight loss was 20% after heating to 200°C.Heating humic acid from 200 to 400°C caused great structural changes and a loss of weight of about 90%. These structural changes slightly increased the free radical content, the increase occurring within the temperature range 25 to 400°C. It was due to structural modification of the heated substance and not due to increase in the percentage of carbon in the humic acid char.Humic acid residue was burnt off at 600°C with a 95% loss of weight.
Microbial Changes Associated with Residue Management with Reduced Tillage
Authors: Doran J. W. 
Published: July 2010

AbstractThe effects of corn residue on soil microbiological populations for dryland corn (Zea mays L.) production in Nebraska were closely related to placement of residue and soil water and pH regimes. Populations of bacteria, actinomycetes, and fungi increased two‐ to sixfold as a result of mulching. The response of fungi populations to residue application was limited by competition from bacteria and actinomycetes as related to changes in soil water content and pH regimes. Counts of nitrifying and denitrifying organisms in the surface soil increased 2‐ to 20‐fold and 3‐ to 43‐fold, respectively, in plots receiving surface applications of corn stover. The physical, chemical, and biological characteristics of the between‐row area differed dramatically from those of the within‐row area with the tillplant system. The soil‐water content, microbial populations, soil pH, and soil nitrate content of the between‐row area were significantly higher than those within‐row. Many of these differences were associated with the distribution of residue, soil, and surface applications of lime. Under more uniform moisture and soil conditions in the greenhouse, surface application of corn stover resulted in two‐ to fivefold increases in microbial populations. The additional responses of microbial populations to residue in the field were related to increased soil water contents. In addition, residues influenced the microbial response to application of both lime and herbicides. The application of residue reduced the inhibitory effect of herbicides on nitrifier populations. The changes in microbial ecology associated with residue management should influence decisions for alternate residue‐management and fertilizer practices with reduced tillage.
Amidase Activity in Soils: II. Kinetic Parameters
Authors: Frankenberger W. T. , Tabatabai M. A. 
Published: July 2010

AbstractStudies to determine the kinetic parameters of the amidasecatalyzed reaction in soils showed that the Km values of formamide, acetamide, and propionamide for this enzyme are similar to those of the same enzyme isolated from microorganisms. Application of the three linear transformations of the Michaelis‐Menten equation indicated that the apparent Km constants of the three substrates (formamide, acetamide, and propionamide) varied among the soils studied, but the results obtained by the three plots were similar. By using the Lineweaver‐Burk plot, the Km values of formamide, acetamide, and propionamide in eight soils ranged from 6.7 to 17.9mM (avg. 12.3), 4.0 to 5.1mM (avg. 4.6), and 10.1 to 20.2mM (avg. 14.5), respectively. The Km value is the lowest and affinity constant is the highest at optimum pH of amidase activity. With the substrate used in parentheses, the Vmax values of the eight soils ranged from 138 to 438 µg NH4‐N released/g soil per 24 hours (formamide), from 13 to 43 µg NH4‐N released/g soil per 24 hours (acetamide), and from 35 to 105 µg NH4‐N released/g soil per 24 hours (propionamide). The activation energy values for the amidase activity, expressed in kJ/mol, ranged from 43.3 to 49.8 (avg. 46.9), from 43.2 to 55.5 (avg. 50.0), and from 22.6 to 29.8 (avg. 26.5) using formamide, acetamide, and propionamide as substrates, respectively. The average temperature coefficient (Q10) of the amidase‐catalyzed reaction in the eight soils studied for temperature ranging from 10 to 60°C was 1.70 for formamide, 1.73 for acetamide, and 1.42 for propionamide.
Extension of Laboratory‐measured Soil Spectra to Field Conditions
Authors: Stoner Eric R. , Baumgardner Marion F. , Weismiller Richard A. , Biehl Larry L. , Robinson Barrett F. 
Published: July 2010

AbstractSpectral responses of two glaciated soils, Chalmers silty clay loam and Fincastle silt loam, formed under prairie grass and forest vegetation, respectively, were measured both in the laboratory under controlled moisture equilibria, and in the field under various moisture and crop residue conditions. An Exotech Model 20C spectroradiometer was used to obtain spectral data in the laboratory under artificial illumination. Reflectance measurements ranged from 0.52‐to 2.32‐µm in 0.01µm increments. Asbestos tension tables were used to maintain a 0.10‐bar moisture equilibrium following saturation of crushed, sieved soil samples. The same spectroradiometer was used outdoors under solar illumination to obtain spectral response from dry and moistened field plots with and without corn residue cover, representing the two different soils. Results indicate that laboratory‐measured spectra of moist soil are directly proportional to the spectral response of that same field‐measured moist bare soil over the 0.52‐ to 1.75‐µm wavelength range. The magnitudes of difference in spectral response between identically treated Chalmers and Fincastle soils are greatest in the 0.6‐to 0.8‐µm transition region between the visible and near infrared, regardless of field condition or laboratory preparation studied.
Genesis of a Typic Durixeralf of Southern California
Authors: Torrent J. , Nettleton W. D. , Borst G. 
Published: July 2010

AbstractSoils with duripans are common on old marine terraces in San Diego and Orange Counties. The Chesterton series illustrates their complexity. It has a duripan, an argillic horizon which is gleyed in the lower part, and a thick surface horizon having Fe‐Mn nodules. Initial weathering under a warm subhumid climate produced moderate amounts of kaolinite and smectite clay to a depth of several meters. With the onset of a drier climate, a duripan formed protecting the lower part of the former profile from further weathering. Horizons above the duripan later weathered under a cooler, more humid climate to form mostly kaolinitic clays, thus creating a clear mineralogical discontinuity. Simultaneously or subsequently, a relatively intense illuvial process produced a B2t horizon above the duripan. The wet conditions implied by the Fe‐Mn nodules and the mottles are no longer very pronounced. The morphology of the nodules suggests that they are relict features.