bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study of the Effects of Noncapillary‐Sized Pores Upon Infiltration
Authors: Edwards W. M. , van der Ploeg R. R. , Ehlers W.
Published: July 2010

A numerical solution to the unsaturated soil moisture flow equation was used to model infiltration into a soil containing surface‐connected noncapillary holes. Input parameters used to demonstrate the model were those from an untilled silt loam soil whose infiltration characteristics are strongly influenced by worm holes, especially when rainfall rates are high. The two‐dimensional model allows for vertical infiltration from the soil surface and for lateral infiltration from a vertical hole after excess precipitation on the surface runs into the hole.

The model shows that the number of holes per unit soil area, as well as the diameter and depth of the holes, greatly influence infiltration and surface runoff. The assumption of noncapillary flow through continuous holes or cracks may be used to explain some of the observed deviations from capillary flow theory and the fast movement of surface‐applied agricultural chemicals through the soil profile.
Hydrodynamic Dispersion During Infiltration of Water into Soil
Authors: Elrick D. E. , Laryea K. B. , Groenevelt P. H.
Published: July 2010

The analysis of hydrodynamic dispersion during one‐dimensional sorption of water by soil (horizontal flow) is extended to include the gravitational effects present during one‐dimensional infiltration (vertical flow). A power series form for the solution is developed in a manner similar to that developed by Philip for water movement during infiltration. Similar to the sorption analysis, the longitudinal dispersion coefficient was assumed to be a function of water content only. A computer simulation program using CSMP was used to solve the associated differential equations. A single program was found to be suitable as long as the Boltzman parameter (distance divided by the square root of time) was used as the independent variable throughout. An algorithm was developed to give successively better solutions of the soil water diffusion and hydrodynamic dispersion equations.

Infiltration experiments were carried out on a clay loam soil. Both the water and chloride content profiles preserved similarity in terms of the Boltzman parameter. Water and solute coefficients of the power series solutions were calculated from horizontal infiltration and hydraulic conductivity data and used to predict both the water and solute profiles during vertical infiltration. Good agreement between the vertical infiltration data and the theoretical predictions was obtained.
Phosphate Uptake by Corn as Affected by Soil Characteristics and Root Morphology
Authors: Schenk M. K. , Barber S. A.
Published: July 2010

Phosphate uptake by plants growing in soil is influenced by the P uptake properties of the root and the P supply characteristics of the soil. This system may be described by mathematical simulation models. The objective of this research was to determine if a model used successfully for describing K uptake by corn (Zea mays L.) could be used for describing P uptake. A growth chamber experiment with corn grain on six soils varying widely in physical and chemical characteristics was conducted. Three harvests were made and root morphology and P uptake were measured. The significance of the differences in root morphology and in soil P‐supply parameters of initial P concentration in soil solution, buffer power, and effective diffusion coefficient for P were determined by using them in the Claassen‐Barber simulation model which considers these soil factors, root morphology, and root physiology to predict P uptake by plants. The calculated P uptake, y was correlated (r = 0.93) with observed P uptake, x. The regression equation, y = 1.09x + 27.3 indicated a 9% overprediction of P uptake which was probably because the model did not consider root to root competition for P. The parameters used in this objective simulation model appear to be the important ones determining P absorption by plants from soil. In this study, root morphology varied with soil and was highly correlated with P uptake (r = 0.88). This simulation model should be a useful tool in P fertilization research.
Effect of Concentration on Decomposition of Some 14C‐labeled Phenolic Compounds, Benzoic Acid, Glucose, Cellulose, Wheat Straw, and Chlorella Protein in Soil
Authors: Martin J. P. , Haider K.
Published: July 2010

The decomposition of ring‐14C‐labeled anisic, ferulic, and benzoic acids and of O14CH3‐labeled ferulic acid at concentrations of 1 to 10,000 ppm and of UL cellulose, glucose, wheat straw and Chlorella protein at 1 – 50,000 ppm was followed in Chino loam (pH 5.6) and San Jacinto sandy loam (pH 8.0) over a 12‐week incubation period. A smaller proportion of the ring C of the benzenoid compounds and glucose was evolved as CO2 from the lower additions than from the higher applications. The range for C loss for ferulic acid was 40 to 79% for the acid soil and 22 to 33% for the alkaline soil as the concentration increased from 1 to 10,000 ppm. Comparable losses for glucose were 47 – 83 and 65 – 81%; for anisic acid 55 – 79 and 49 – 72%; for p‐hydroxycinnamic acid 54 – 81 and 21 – 53%; and for benzoic acid 68 – 77 and 50 – 79%. Loss of O14CH3 C of ferulic acid and of wheat straw, cellulose, and protein C was not influenced by concentration. Percentage C loss from ring‐14C ferulic and benzoic acids added to initially sterilized and reinoculated acid soil was about 82% and was not influenced by concentration.
Evidence for Clostridia as Agents of Dissimilatory Reduction of Nitrate to Ammonium in Soils
Authors: Caskey William H. , Tiedje James M.
Published: July 2010

Reduction of NO3‐ to NH4+ was studied in fresh and air‐dried soils which were amended with 15NO3‐ and glucose, acetate, or water and incubated anaerobically. Soils were either untreated or heat‐shocked at 68°C for 1 hour prior to amendment. Ammonium was produced rapidly after the onset of anaerobiosis, and thereafter was incorporated into organic matter. 15NH4+ plus 15N‐organic matter production was observed in glucose‐amended fresh soil in quantities up to 43% of added 15NO3‐ in untreated samples and 55% in heat‐shocked samples after 5 days incubation. In soils unamended with organic carbon, NO3‐ reduction to NH4+ was minor. Pretreatment of the soils either by air‐drying or heat‐shocking increased to a similar extent the amount of NO3‐ reduced to NH4+. The activity of clostridia during the NO3‐ reduction was indicated by the absence of any effect exerted by heat‐treatment, the production of H2 and CO2, and the presence of higher numbers of anaerobic sporeforming bacteria relative to denitrifying bacteria in the air‐dried soil. Also, the most common isolate capable of reducing NO3‐ to NH4+ was a Clostridium spp. The addition of washed spores of a NO3‐‐reducing Clostridium isolated from the soil increased the formation of 15NH4+‐N plus 15N‐organic N fourfold, an accumulation equivalent to 83% of added 15NO3‐‐N.

The reduction of NO3‐ to NH4+ in soils was not inhibited by NH4+ or glutamine, indicating that the mechanism of reduction was dissimilatory. This conclusion is supported by studies with several Clostrdium spp. isolated from the soils. The isolates were capable of reducing NO3‐ to NH4+ and exhibited increased cell yields when NO3‐ was included in the growth medium. These studies suggest that the potential for significant dissimilatory NO3‐ reduction to NH4+ exists in most soils, principally in the sporeforming genera of Clostridium and Bacillus, but that this potential is likely expressed only when soils become anoxic and are rich in C.
Corn Yield as Affected by Lime Rate and Type on a Coastal Plain Soil
Authors: Liebhardt William C.
Published: July 2010

Ground limestone rates of 0, 2.24, and 8.96 metric tons/ha as calcite, dolomite or a mixture of the two were applied to a Kalmia s1 (Typic Hapludult) in 1970 and 1973. Soil pH was 5.7 at the low rate and 6.4 at the high rate in 1977. Corn (Zea mays L.) yield was significantly lower at pH 6.4 compared to pH 5.7. At pH 6.4 dolomite resulted in lower corn yields than did calcite or a mixture of the two. Yield of corn was negatively related to soil pH and higher soil Mg and positively with plant Mn.

Extration of soil samples with the double acid extractant from 5 min to 48 hours showed that there was considerable non‐exchangeable Ca and Mg at the high lime rate (pH 6.4), but little or none at the low rate (pH 5.7). The nonexchangeable Ca and Mg appear to be reaction products from dolomite. The ratio of nonexchangeable Mg/Ca is 4.48 on a meq basis which is unfavorable for plant growth and indicates why continued use of dolomite on sandy Coastal Plain soil with a low CEC results in a yield decrease.
Phosphorus Transformations in Alternately Flooded California Soils: I. Cause of Plant Phosphorus Deficiency in Rice Rotation Crops and Correctional Methods
Authors: Brandon D. M. , Mikkelsen D. S.
Published: July 2010

Rice (Oryza sativa L.) is widely grown on soils continuously submerged during the annual growing season. Upland crops following rice culture often exhibit chlorosis, extremely slow growth, and low productivity. Phosphorus deficiency induced by drainage following soil submergence was shown to exist in crops following rice. Experiments were conducted to clearly define the problem in terms of crop response to P fertilizer on major California rice soils and to determine the most efficient methods of P fertilization.

Three field experiments were conducted on Myers, Willows, and Sacramento soils following variable years of annual rice production. Wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) were fertilized with P rates of 0, 29, 59, and 89 kg/ha applied as band‐placed TSP, broadcast TSP and band‐placed MAP. Phosphorus sources, rates, and method of application were evaluated by plant responses including seedling dry matter, plant total‐P and 2% HAc extractable PO4‐P, plant total‐N, grain yield, and 1,000‐kernel weight.

The differential severity of plant P deficiency between the three soils was Myers ⩾ Willows > Sacramento series. Severe plant P‐deficiency was observed in the Myers soil even though the soil NaHCO3‐extractable P level was 16.8 ppm. Soil submergence and drainage‐induced soil P transformations decreased soil P availability to wheat and barley following flooded rice.

The relative efficiency of P fertilizer sources and methods was band‐placed MAP > band‐placed TSP > broadcast‐incorporated TSP. Phosphorus band‐placed 3 cm directly below the seed was more efficient than broadcast‐incorporated P in wheat and barley after rice. Band‐placed P resulted in greater P uptake by plants probably because of less soil sorption of fertilizer P and greater P availability relative to broadcast‐incorporated P.
Holocene Soils in Eolian Sediments of Bailey County, Texas
Authors: Gile Leland H.
Published: July 2010

Three Holocene geomorphic surfaces and their associated soils and sediments are recognized in sandhills of Bailey County, Texas. Fairview sediments are related to the activities of man since about 100 years B.P. The Muleshoe (100–4,000 years B.P.) and Longview (4,000–7,000 years B.P.) sediments accumulated as a result of erosion initiated by severe droughts in the Holocene.

Typic Ustipsamments and Alfic Ustipsamments are the most common Holocene soils in the study area; Psammentic Haplustalfs also occur, but are less common. The Alfic Ustipsamments have two or more continuous clay bands and the Typic Ustipsamments do not. Clay bands occur sporadically in Muleshoe sediments, but continuously in Longview sediments. Argillic horizons and the Psammentic Haplustalfs occur in some of the Longview sediments and in all of the sediments next older than Longview, which may date from latest Pleistocene or earliest Holocene time. Muleshoe sediments 1‐ to 2‐m thick are underlain by buried argillic horizons in many places, and some soils in these areas have been classified elsewhere as Grossarenic Paleustalfs. Thus, some of the soils so classified actually consist in part of buried soils.

Clay in the clay bands is thought to have been deposited from clay in suspension on slowing of downward movement of the wetting front. Some clay apparently moves through the upper bands at times of deeply penetrating moisture and then accumulates in bands beneath as the wetting front slows its downward movement. Lateral movement of soil water is also important in the thickening and lateral spread of some bands. Clay accumulation in the bands gradually decreases soil permeability through time, and clay starts to accumulate between bands as well as in them. Since latest Pleistocene or possibly earliest Holocene time, enough clay has accumulated between some of the bands that they are partially obscured.
The Nature and Genesis of Some Salt‐Affected Soils in Iran
Authors: Mahjoory Ramez A.
Published: July 2010

Salt‐affected soils are distributed throughout arid to semiarid regions of Iran. They occupy about 15% of the area in the country, an amount equal to the total arable land. These soils are formed in level to depressional landform positions under the influence of a fluctuating ground water table. Three pedons representing different soil series were studied: Amir‐abad (pedon 1), Farsian (pedon 2) and Ahoo‐char (pedon 3). Pedon 1 was classified as a Haploxerollic Natrargid, pedon 2 as an Aquic Natrargid, and pedon 3 as an Aquic Natrargid.

The origin of salts is related to the parent materials that formed from saliniferous and gypsiferous marl deposits and carried by water and redeposited.

Saturated paste extracts are high in chlorides, sulfates, and carbonates in all three pedons, but increased in amounts from pedon 1 to pedons 2 and 3. ESP and SAR are more than 15 in all three soils studied. The average electrical conductivity (EC) values of pedon 1, 2, and 3 are 13, 16, and 32 mmho/cm, respectively. The pH values vary from 8 – 10.

X‐ray diffraction and chemical data indicate that the soils contain vermiculite (18–48%), clay mica (18–28%), interstratified vermiculite and/or chlorite‐clay mica, kaolinite, and quartz. Montmorillonite and attapulgite were found only in pedon 3.
Model for the Release of Urea by Granules of Sulfur‐Coated Urea Applied to Soil
Authors: Jarrell W. M. , Boersma L.
Published: July 2010

The 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

The 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

The 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

Contributions 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

The 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

Many 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

Winterkill 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

The 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

The 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

Potentiometric 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

The 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

Samples, 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

Equal 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

ESR 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

The 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

Studies 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

Spectral 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

Soils 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.
Crop Residue Influences on Soil Carbon and Nitrogen in a Wheat‐Fallow System
Authors: Rasmussen Paul E. , Allmaras R. R. , Rohde C. R. , Roager N. C.
Published: July 2010

Seven crop residue treatments were initiated in 1931 to measure long‐term residue management effects on soil organic matter in a wheat‐fallow cropping system on Pacific Northwest semiarid soils. There was evidence at this time of substantial organic matter (OM) loss during the first 50 years of wheat cultivation in the Great Plains. Organic carbon (C) and total (N) were measured at approximately 11‐year intervals over a 45‐year period to determine residue effects on the rate of change in soil OM content.

Only the addition of 22.4 metric tons of manure/ha to straw residue before incorporation prevented a decline in soil N and C. The addition of 45 or 90 kg fertilizer N or of 2.2 metric tons of pea vines/ha to straw residue before incorporation reduced N and C loss when compared to straw only incorporation. Burning of straw in the fall following wheat harvest accelerated the loss of N but not C. Burning of straw in the spring just prior to tillage had no effect on N or C loss.

Changes in N and C were primarily confined to the top 20 cm of soil. Soil C/N ratios in 1976 differed between treatments proportional to the rate of N loss; they were highest in burn or straw only treatments and lowest in the manure treatment.

In all treatments, changes in soil N were best described by a linear function of time; slope within the linear function depended upon residue treatment. This linear function of time over a 45‐year period following approximately 50 years of previous cultivation suggests that 100 or more years may be required before N levels become stationary. Residual effects confirm that the new stationary level will depend on past crop residue management practices.

Changes in soil C correlated highly with the amount of organic C supplied by each treatment, regardless of the different kinds of residue applied. Thus, changes in soil organic matter levels were controlled primarily by the amount of organic C supplied in crop residue. Regression equations indicate that approximately 5 metric tons of mature crop residue ha−1 year−1 are needed to maintain soil organic matter at its present level when cropped in wheat‐fallow rotation in this climatic zone.
Nitrogen Mineralization, Immobilization, and Nitrification Following Urea Fertilization of a Forest Soil Under Field and Laboratory Conditions
Authors: Johnson D. W. , Edwards N. T. , Todd D. E.
Published: July 2010

Following a 200‐kg urea‐N/ha fertilization in a loblolly pine stand (Pinus taeda), soil mineral N levels (almost entirely NH4+) declined from 200 ppm 20 days after fertilization to < 10 ppm within 161 days. Similar patterns had been previously observed following urea fertilization in a Douglas‐fir stand. After the decline in soil mineral N, 20% (40 ppm) of fertilizer N was mineralized within 4 weeks of aerobic incubation in the laboratory at 25°C. Nitrogen mineralization in control soils did not occur after 7 weeks incubation.

In contrast to field results, urea additions to control soils in the laboratory resulted in rapid net N mineralization. The difference between laboratory and field fertilization results is thought to be due principally to differences in available C supplies, i.e., large (> 2 mm) litter and roots were excluded from laboratory tests.

The maximum rate of nitrification during incubation was related to the supply of NH4+ substrate, whereas the delay period was probably related to the initial populations of nitrifiers.

Additions of 100 kg P/ha as triple superphosphate in the field and equivalent additions of NaH2PO4 in the laboratory had little or no effect on results.
Characterization of Hydroxy‐Aluminum Solutions
Authors: Bersillon J. L. , Hsu Pa Ho , Fiessinger F.
Published: July 2010

Hydroxy‐Al solutions were prepared and characterized with sulfate precipitation, resin treatment, and rate of Al‐ferron color development. The results suggest that the soluble Al species can be grouped into at least four categories: (i) high OH‐Al polymers — these have a residual positive charge of 0.33 or less per Al atom and are rapidly precipitable by Na2SO4, giving rise to the formation of noncrystalline basic aluminum sulfate; (ii) medium OH‐Al polymers — these form crystalline basic aluminum sulfate of composition Al(OH)2.50(SO4)0.22 · xH2O slowly and enter resin slowly; (iii) low OH‐Al polymers — these are not precipitable with Na2SO4, and they enter resin rapidly; and (iv) monomeric ions — these enter resin rapidly and react with ferron rapidly.
Some Accurate Numerical Solutions of the Soil‐Water Diffusion Equation
Authors: Braddock R. D. , Parlange J.‐Y.
Published: July 2010

Some accurate numerical solutions are obtained for the soil‐water diffusion equation. The method replaces the two endpoint boundary value problem with a standard initial value problem and uses iteration to select the appropriate initial slope. The results obtained are accurate to seven significant figures and the solution exhibits a wetting front with a sharp corner and foot at the leading edge of the front. The corner and foot highlights our ignorance of the processes by which water percolates the soil at low concentrations.
The Swelling of Clay: II. Montmorillonites
Authors: Low Philip F.
Published: July 2010

The water content at equilibrium was determined as a function of applied pressure for 35 different Na‐saturated montmorillonites by means of a miniature pressure membrane apparatus. Then the data were used to develop a general, empirical equation in which the swelling pressure of the montmorillonite depends exponentially on the water content. The parameters in this equation were shown to be functions of the cation exchange capacity and specific surface area of the montmorillonite. The data were also used to develop semiempirical equations in which the swelling pressure depends exponentially on the distance between the superimposed layers of the montmorillonite. Depending on the assumptions used in their development, the latter equations involve constant coefficients or coefficients that depend on the surface charge density of the montmorillonite. Analysis of these equations indicated that swelling is due primarily to interaction between the layer surfaces and water.
Analytical Properties of the Soluble, Metal‐complexing Fractions in Sludge‐Soil Mixtures: V. Amino Acids, Hexosamines, and Other Carbohydrates in Fulvic Acid
Authors: Holtzclaw Kenneth M. , Schaumberg Gene D. , LeVesque‐Madore C. S. , Sposito Garrison , Heick J. A. , Johnston Cliff T.
Published: July 2010

The quantitative distribution of amino acids, hexosamines, and other carbohydrates was determined for three representative, purified fulvic acids extracted from anaerobically‐digested sewage sludges. The amino acid content ranged from 5 to 9 wt % in the three fulvic acids and the distribution of acidic, neutral, and basic amino acids generally was similar to that in soil‐derived fulvic acids. The principal difference between the two types of fulvic acid was with the S‐containing amino acids, which were more abundant in the sludge‐derived fulvic acids. The content of galactosamine was very high in the three fulvic acids studied, with the result that the glucosamine/galactosamine ratio was about an order of magnitude lower in these fulvic acids than what is typical for soil‐derived fulvic acids. The content of neutral and acidic sugars ranged from 12 to 25 wt % in the fulvic acids, with a distribution of neutral sugars that was similar to what is found typically in natural soil organic matter. Thus the amino acid, hexosamine, and carbohydrate components of sludge‐derived fulvic acid may account for up to 50 wt % of this material. The major differences among these components between sludge‐derived and soil‐derived fulvic acids appear to be related to the high sulfur content of the sludge‐derived fulvic acids and their expected high content of anaerobic bacterial residues.
Factors Influencing Oxygen Consumption Rates in Flooded Soils
Authors: Reddy K. R. , Rao P. S. C. , Patrick W. H.
Published: July 2010

Thirty‐seven surface soil samples varying in physico‐chemical properties were incubated under reduced (anaerobic) conditions to study the factors influencing oxygen consumption rates. Oxygen consumption rates were measured after introduction of a known amount of oxygen into a reduced (anaerobic) soil system and following the disappearance of oxygen as a function of time.

The time dependence of oxygen consumption in all flooded soils could be described as a two‐phase first order reaction process. Rapid oxygen consumption during Phase I was followed by relatively slower consumption during Phase II. The first‐order rate coefficient (k1, hour−1) for Phase I was approximately the same for all 37 soils evaluated, whereas each soil was characterized by a different rate coefficient (k11, hour−1) for Phase II. The average value for k1 was 0.15 hour−1 (coefficient of variation = 20%) while the values of k11 ranged from 0.0027 to 0.054 hour−1. Step‐wise regression analysis of the data showed that NaOAc‐extractable Fe of a reduced soil was the single best predictor of k11 and also the fractional consumption associated with Phase I. Significant improvement in these regressions was obtained when total NH4‐N content of the reduced soil, in addition to reducible Fe2+ was considered.