bluuebunny/crossref_metadata_2025_split huggingface dataset:
Near‐Saturated Hydraulic Conductivity in Soils of Contrasting Texture Measured by Tension Infiltrometers
Authors: Jarvis N. J. , Messing I. 
Published: July 2010

AbstractSoil structure is known to strongly affect water flow and solute transport, yet little information is available concerning soil hydraulic properties close to saturation. This study reports detailed measurements of near‐saturated hydraulic conductivity in undisturbed field soils. Steady‐state infiltration rates from tension infiltrometers were measured at the surface of six tilled soils of contrasting texture ranging from loamy sand to silty clay. Hydraulic conductivities (K) at supply pressure heads (h) in the range from − 100 mm to zero were obtained using Wooding's solution for infiltration from a circular source. The paired K,h data were summarized using the technique of functional normalization with three alternative models of K(h): a single exponential function (Gardner's model), a two‐line exponential model, and the Mualem‐van Genuchten model. The commonly used single exponential model was found to be inappropriate in all cases. Both the two‐line exponential and Mualem‐van Genuchten models satisfactorily described the data, with the former performing marginally better for five of the six soils. In the supply pressure head range − 100 mm to zero, K increased by three to four orders of magnitude in the finer textured soils and by about two orders of magnitude in two sandy soils. Estimates of field‐saturated hydraulic conductivity (Kfs) were largest in the fine‐textured soils, presumably because of the influence of continuous surface‐vented macropores. Spatial variability in measured K(h) was small to moderate for all soils. Predicting unsaturated K from soil water release data using Kfs as a matching point was shown to result in serious overestimations.
Fractal Parameters of Pore Surface Area as Influenced by Simulated Soil Degradation
Authors: Pachepsky Ya. A. , Polubesova T. A. , Hajnos M. , Sokolowska Z. , Józefaciuk G. 
Published: July 2010

AbstractFractal parameters of soils become increasingly important in understanding and quantifying transport and adsorption phenomena in soils. It is not known yet how soil degradation affects fractal characteristics of soil pores. We estimated pore surface area fractal parameters from Hg porosimetry data on samples of a Udic Argiboroll, a Typic Haploboroll, and a Ustolic Orthid before and after simulated soil degradation. Three or four distinct intervals with different fractal dimensions were found in the range of pore radii from 4 nm to 5 µm. This was attributed to differences in composition of soil particles of different sizes. The simulated degradation caused an increase in fractal dimensions in one or more fractal intervals, thus manifesting the increased roughness and irregularity of the pore surfaces. The interval of the smallest radii had the highest average fractal dimension, close to 3; some estimated values were >3, probably due to the compressibility of bulk material and air entrapment. Values of the fractal dimension in this interval increased after cyclic wetting‐drying but were not affected by organic matter oxidation. Smaller fractal dimensions were found in the next interval of radii. Here average fractal dimension increased markedly after organic matter oxidation and grew slightly after cyclic wetting‐drying, reflecting the loss of bonds between particles. The range of largest radii included two fractal intervals after cyclic wetting‐drying and one fractal interval for all other samples. Neither organic matter oxidation nor cyclic wetting‐drying significantly affected the boundaries between the fractal intervals.
Time‐Domain Reflectometry Measurements of Surface Soil Water Content
Authors: Nielsen D. C. , Lagae H. J. , Anderson R. L. 
Published: July 2010

AbstractSurface soil water content is an important parameter influencing such processes as residue decomposition, nutrient cycling, microbial activity, and weed seed germination and emergence. This experiment was conducted to determine if time‐domain reflectometry (TDR) could be used to measure water content in the 0‐ to 50‐mm soil layer. Wave guides were installed horizontally at a depth of 25 mm below the soil surface in field plots differing in current crop‐tillage history. The TDR system was interrogated hourly by a data logger. Daily average soil water contents from TDR were computed and compared with water contents obtained from gravimetric soil sampling. The TDR values were linearly related (r2 = 0.84) with gravimetric samples of soil water content when wave guides were at a depth of 25 mm, but not when wave guides were at a depth of 13 mm. Continuous measurements of surface soil water content can be obtained from an automated TDR system.
Nitrogen and Water Interactions in Trickle‐Irrigated Watermelon
Authors: Pier J. W. , Doerge T. A. 
Published: July 2010

AbstractRising water costs and concern for groundwater contamination by NO3 and other agricultural chemicals are forcing growers in arid regions to improve irrigation and N fertilization efficiency. Applying N and water through a subsurface drip irrigation system in conjunction with in‐season monitoring techniques for assessing crop water and N status has the potential to greatly improve water and N use efficiency. The objectives of this research were to: (i) investigate the interactive effects of water and N applied through a subsurface trickle irrigation system on watermelon [Citrullus lanatus (Thumb.) Matsum and Nakai var. lanatus] fruit yield and on the potential for leaching losses of NO3, and (ii) determine the optimum range of soil water tension for subsurface trickle‐irrigated watermelon. Field experiments were conducted during 1990 and 1991 on a reclaimed Casa Grande soil (fine‐loamy, mixed, hyperthermic Typic Natrargid) in southern Arizona. Levels of target soil water tensions and fertilizer N were arranged in a factorial design to determine fruit yield response surfaces. Tensiometers at 0.3‐ and 0.6‐m depth were used to monitor soil water tension throughout the growing season. Marketable watermelon yield showed a pronounced positive water × N interaction in both years of the study. Predicted marketable yields were 90 Mg ha−1 when mean soil water tension was 6 kPa and applied N was between 200 and 270 kg ha−1 in 1990 and a predicted yield maximum of 102 Mg ha−1 at 7.2 kPa and 336 kg N ha−1 in 1991. Scheduling of irrigations using feedback from tensiometers proved very useful in providing optimum amounts of water while avoiding conditions that favor N loss through leaching or denitrification.
Tillage and Traffic Influences on Water and Solute Transport in Corn‐Soybean Systems
Authors: Wu L. , Swan J. B. , Allmaras R. R. , Logsdon S. D. 
Published: July 2010

AbstractTillage management many influence water and solute movement throughout the root zone. To evaluate tillage effects on solute transport, parameters were estimated from breakthrough curves and directly measured macropores in no‐till (NT) and moldboard‐plowing (MBD) systems with traffic control on a Nicollet clay loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and a Rozetta silt loam (fine‐silty, mixed, mesic Typic Hapludalf). Ridge tillage recently imposed on long‐term NT (RT/NT) was compared with chisel tillage (CHT) on a Seaton silt loam (fine‐silty, mixed, mesic Typic Hapludalf) where manure was injected without traffic control. Breakthrough curves (Br− tracer) were measured in undisturbed soil cores from the Ap horizon (0–250 mm) and adjacent subsoil (250–500 mm) and were fitted to a physical, nonequilibrium two‐domain model to estimate mean pore‐water velocity of the mobile domain (Vm) and the fraction of water (v) participating in Br− transport. The Vm ranged from 0.10 to 10 mm s−1, while v ranged from 0.02 to 0.50. Means did not differ between the Nicollet and Rozetta soils in 1988, yet significant tillage × horizon interactions indicated more solute bypass in NT than in MBD. More macropores and a larger macropore conductivity (Km) were observed in NT than in MBD. Greater Vm and smaller v occurred (P < 0.05) in CHT than in RT/NT because RT/NT lacked secondary cultivation to remove compaction from manure injection. Traffic control in NT on the Nicollet and Rozetta soils produced high Vm and low v compared with RT/NT on the Seaton soil. Both Vm and v can be estimated from the more easily measured Km.
Calcium Salts and Mechanical Stress Effects on Water‐Dispersible Clay of Oxisols
Authors: Fontes M. P. F. , Gjorup G. B. , Alvarenga R. C. , Nascif P. G. S. 
Published: July 2010

AbstractIt can be hypothesized that clay dispersion as a function of lime application and mechanical stresses is an important factor in the deterioration of physical conditions of some Brazilian Oxisols. Therefore, a laboratory study was conducted to test the influence of these varaibles on clay dispersion. Different water‐dispersible clay (WDC) contents and incubation times varying from 0 to 50 d were tested. The Ca salts used were CaCl2, CaSO4, and CaCO3. The methodologies utilized to measure WDC and vary mechanical stresses were: (i) manual soil sample shaking for 1 min with a glass rod (low‐energy stirring system, LESS); and (ii) shaking in a reciprocating shaker for 3 h (high‐energy shaking system, HESS). The LESS did not yield significant amounts of WDC regardless of the Ca salt used. The HESS yielded approximately 120 to 311 g kg−1 of WDC by itself or when combined with CaCO3. Calcium chloride and CaSO4 yielded very low amounts of WDC in the range of 1 to 20 g kg−1.
Temperature Effects on Kinetics of Microbial Respiration and Net Nitrogen and Sulfur Mineralization
Authors: MacDonald Neil W. , Zak Donald R. , Pregitzer Kurt S. 
Published: July 2010

AbstractGlobal climate change may impact the cycling of C, N, and S in forest ecosystems because increased soil temperatures could alter rates of microbially mediated processes. We studied the effects of temperature on microbial respiration and net N and S mineralization in surface soils from four northern hardwood forests in the Great Lakes region. Soil samples were incubated in the laboratory at five temperatures (5, 10, 15, 20, and 25°C) for 32 wk. Headspace gas was analyzed for CO2‐C at 2‐wk intervals, and soils were extracted to determine inorganic N and S. Cumulative respired C and mineralized N and S increased with temperature at all sites and were strongly related (r2 = 0.67 to 0.90, significant at P = 0.001) to an interaction between temperature and soil organic C. Production of respired C and mineralized N was closely fit by first‐order kinetic models (r2 ≥ 0.94, P = 0.001), whereas mineralized S was best described by zero‐order kinetics. Contrary to common assumptions, rate constants estimated from the first‐order models were not consistently related to temperature, but apparent pool sizes of C and N were highly temperature dependent. Temperature effects on microbial respiration could not be accurately predicted using temperature‐adjusted rate constants combined with a constant pool size of labile C. Results suggest that rates of microbial respiration and the mineralization of N and S may be related to a temperature‐dependent constraint on microbial access to substrate pools. Simulation models should rely on a thorough understanding of the biological basis underlying microbially mediated C, N, and S transformations in soil.
Modeling Transport Kinetics in Clinoptilolite‐Phosphate Rock Systems
Authors: Allen E. R. , Ming D. W. , Hossner L. R. , Henninger D. L. 
Published: July 2010

AbstractNutrient release in clinoptilolite‐phosphate rock (Cp‐PR) systems occurs through dissolution and cation‐exchange reactions. Investigating the kinetics of these reactions expands our understanding of nutrient release processes. Research was conducted to model transport kinetics of nutrient release in Cp‐PR systems. The objectives were to identify empirical models that best describe NH4, K, and P release and define diffusion‐controlling processes. Materials included a Texas clinoptilolite (Cp) and North Carolina phosphate rock (PR). A continuous‐flow thin‐disk technique was used. Models evaluated included zero order, first order, second order, parabolic diffusion, simplified Elovich, Elovich, and power function. The power‐function, Elovich, and parabolic‐diffusion models adequately described NH4, K, and P release. The power‐function model was preferred because of its simplicity. Models indicated nutrient release was diffusion controlled. Primary transport processes controlling nutrient release for the time span observed were probably the result of a combination of several interacting transport mechanisms.
Effect of Water‐Soluble Phosphorus on the Effectiveness of Triple Superphosphate Fertilizers
Authors: Mullins G. L. , Sikora F. J. , Williams J. C. 
Published: July 2010

AbstractImpure phosphate rock results in the formation of P‐containing impurities having low water solubility in commercial triple superphosphate (TSP) fertilizers, which may influence their effectiveness. A greenhouse study was conducted to determine the level of water‐soluble P needed in TSP to maximize plant P uptake and yield when applied to a slightly acid soil (pH = 6.4). Fertilizer impurities were isolated from four commercial TSP fertilizers as a water‐washed fraction by washing the whole fertilizers with deionized water. Fertilizers with varying water‐soluble P were simulated by mixing reagent‐grade monocalcium phosphate (MCP; ≈ 100% water soluble) with water‐washed fertilizer fractions or reagent‐grade dicalcium phosphate (DCP; ≈ 1.2% water‐soluble P). The mixtures contained 0, 20, 40, 60, and 80% of the available P (available = water‐soluble + ammonium citrate soluble P) as MCP. An additional treatment received 100% water‐soluble P as MCP. Mixtures were applied to supply 50 mg available P kg−1 soil. Sorghum‐sudangrass [Sorghum bicolor (L.) Moench] was harvested 21 and 42 d after planting. Forage yield and P uptake were affected by P source and water‐soluble P content. Compared with using a 100% water‐soluble P source (MCP), individual TSP fertilizer materials required 52 to 66% water‐soluble P to attain 90% of the dry matter yield and 41 to 51% water‐soluble P to attain 90% of P uptake. Results of this study demonstrate that current levels of “water‐insoluble P” in commercial TSP sources are not affecting their performance when added to slightly acid soils.
Correspondence of Hydraulic Functions for Unsaturated Soils
Authors: Warrick A. W. 
Published: July 2010

AbstractThis study investigated the correspondence of hydraulic functions for unsaturated soils. The overall idea was to identify general properties and explore conditions for which alternative functions give the same or similar responses. Five commonly used empirical forms were examined in this context. The objective was to extend solutions based on particular forms of hydraulic models to more general conditions. For example, the commonly applied formula for steady‐state flow of a disk infiltrometer assumes a quasi‐linear form of Richards' equation. Another area of application is parameter identification and the choice of alternative models. In order for two sets of models to correspond, the zeroth and first moments of the soil water diffusivity, D, should be equal for the respective models. The zeroth moment is simply the integral of D with respect to water content across the range of interest and is closely related to sorptivity and capillary length. The first moment characterizes the shape of D.
Mobility of Anion Spin Probes in Hectorite Gels: Viscosity of Surficial Water
Authors: McBride M. B. , Baveye P. 
Published: July 2010

AbstractThe mobility of water adjacent to layer silicate clay surfaces and the spatial range of influence of these surfaces on the physical properties of water have been subjects of some controversy. In an attempt to further characterize the surficial water of clays, electron spin resonance (ESR) spectroscopy was used to determine the rotational mobility of an anionic nitroxide spin probe (3‐carboxy‐2,2,5,5‐tetramethyl‐1‐pyrrolidinyloxy) in hectorite gels of variable water content. There was a measurable decrease in average mobility of the anion probe only when the clay/water ratio exceeded 1 kg L−1. Because “negative adsorption” tended to exclude the anion from the near‐surface regions except at quite low water content, mobility of the anion probe was unaffected by adsorption processes and could be used to estimate the viscosity of water within 100 Å of the surface. The spin probe results indicate that, at low water contents, the addition or removal of water changes the rigidity of all the water, so that the viscosity of the interlamellar water cannot be estimated by averaging that of the adsorbed and added free water. The results place the maximum range of silicate surface influence on dynamic water properties at about five molecular diameters, with up to two monolayers of water at each surface being one to two orders of magnitude more rigid than free water.
Chemical Relaxation and Double Layer Model Analysis of Boron Adsorption on Alumina
Authors: Toner C. V. , Sparks D. L. 
Published: July 2010

AbstractBoron is a plant nutrient essential for adequate plant growth, yet the range between B deficiency and toxicity levels is rather narrow. Boron adsorption reactions with soil components, particularly sesquioxides, most often regulate the amount of B in the soil solution. The reaction mechanisms of B adsorption on oxides have not been fully characterized, however. Pressure‐jump relaxation experiments were conducted to measure the rates and determine the reaction mechanism for B adsorption on an alumina (γ‐Al2O3) surface from B(OH)3‐B (OH)−4 solutions. Relaxation times (τ) were measured from pH 7.0 to 9.7 in alumina suspensions with 0.012 mol L−1 total B. A plot of τ−1 vs. B(OH)−4 plus surface site concentration obtained from the triple layer model (TLM) assuming inner sphere B(OH)−4 adsorption yielded an adsorption rate constant (kintf) of 3.3 × 105 L mol−1 s−1 and a desorption rate constant (kintr) of 1.8 × 10−3 L mol−1 s−1. The ratio kintf/kintr yielded an equilibrium constant (log KintKIN) of 8.26, in agreement with the intrinsic equilibrium constant for B(OH)−4 adsorption (log KintBIS = 7.69) obtained from adsorption isotherms. Four additional surface complexation models were tested for their ability to model both the equilibrium and kinetic data simultaneously: the constant capacitance model, the diffuse layer model, a Stern model variant, and the TLM assuming outer sphere B(OH)−4 adsorption. Only the TLM, assuming both B(OH)3 and B(OH)−4 were adsorbed via ligand exchange on neutral surface sites, was successful. The TLM indicated that B(OH)−4 is the predominant adsorbed species throughout the pH range 7.0 to 10.8.
Laboratory Determination of Interrill Soil Erodibility
Authors: Truman C. C. , Bradford J. M. 
Published: July 2010

AbstractLaboratory soil pans and rainfall simulators have been used to study fundamental erosion processes affecting interrill soil loss. Problems exist when laboratory results are extended to those determined under field conditions. Experimental methodology influences a soil's interrill erodibility and interrill erodibility ranking among soils. We compared interrill soil loss and erodibility data from two erosion pans with field data from identical soils. Three plot size‐rainfall simulator methodologies were used: (1) 0.14‐m2 lab pan under a constant drop size (4.6 mm) rainfall simulator, (2) 0.32‐m2 lab pan with soil border areas under an oscillating nozzle (2.3 mm median drop diameter) rainfall simulator, and (3) 1‐m2 field plots under the same rainfall simulator as used in Method 2. Soil loss was measured at 5‐min intervals. Interrill erodibility (Ki) was calculated from two equations (E = KiiI2 and E = KiqIq) using measured soil loss (E), rainfall intensity (I), and flow discharge (q) values. The interrill erosion equation, methodology, time, and initial water content influenced calculated Ki values. Soil loss and Ki values from Method 1 did not correlate with and were greater than corresponding values from Methods 2 and 3. Soil loss and Ki values from Method 2 were correlated (r = 0.56 to 0.79) with corresponding values from Method 3. The Kiq values decreased with time and were a function of soil properties related to soil detachment and sediment transport. The Kii values (i) increased with time, (ii) were primarily a function of soil properties related to soil detachment only, and (iii) did not account for infiltration and runoff differences among soils.
Erosion‐Crop Productivity Relationships for Soils of Africa
Authors: Lal Rattan 
Published: July 2010

AbstractSoil erosion and land degradation are severe problems in Africa. Some quantitative information on the magnitude of soil erosion for different soils and ecoregions is available. However, quantitative data on effects of erosion on crop yields under different systems of management are available only for a few sites. The objective of this review is to use existing data on erosion rates and productivity relationships to estimate losses in crop yield due to past erosion at the continental level. The available information is also used to predict losses during the next 30 yr. Analyses of the available data indicate that yield reductions due to past erosion may range from 2 to 40%, with a mean of 8.2% for the continent and 6.2% for sub‐Saharan Africa (SSA). If accelerated erosion continues unabated, yield reductions by the year 2020 may be 16.5% for the continent and 14.5% for SSA. Annual reduction in total production for 1989 due to accelerated erosion in the continent was estimated at 8.2 million Mg for cereals, 9.2 million Mg for roots and tubers, and 0.6 million Mg for pulses. The reduction in total production in 1989 for SSA was estimated at 3.6 million Mg for cereals, 6.5 million Mg for roots and tubers, and 0.36 million Mg for pulses.
Soil Losses by Wind Erosion
Authors: Fryrear D. W. 
Published: July 2010

AbstractMeasurements of wind erosion from fields are limited, but with recently developed erosion samplers, it is possible to determine soil losses from natural winds. Erosion of soils by wind was measured in five states. The soil loss was dependent on wind velocity, storm duration, and soil surface characteristics. Average annual rainfall varied from 356 mm at Eads, CO, to 915 mm at Crown Point, IN. Field soil varied from 29% sand at Eads, CO, to 83% sand at Big Spring, TX. Soil losses from individual erosion events in 3.1‐ha fields varied from 0.050 kg m−2 at Big Spring, TX, to 7.007 kg m−2 at Elkhart, KS. Soil surface roughness, percentage of wind‐erodible aggregates on the soil surface, and percentage of the soil surface covered with nonerodible material such as crop residues are extremely important in controlling wind erosion. A ground cover of 4% reduced wind erosion losses 15% compared with bare soil. Ridging a smooth soil with 50‐ to 70‐mm ridges reduced soil erosion 98% on a sandy loam soil.