bluuebunny/crossref_metadata_2025_split huggingface dataset:
Potassium Fixation and Charge Characteristics of Soil Clays
Authors: Bouabid R. , Badraoui M. , Bloom P. R. 
Published: July 2010

AbstractForty‐four soil clays and four reference phyllosilicate clays were used to establish qualitative and quantitative relationships between clay mineral characteristics and K fixation. The soil clays were obtained from Vertisols, Vertic Mollisols, Haploxerolls, Xerochrepts, and a Palexeralf, from three semiarid regions of northwestern Morocco. The soil clays contained beidellite, montmorillonite, vermiculite, and illite in widely varied abundances. Both total and tetrahedral cation‐exchange capacity (CEC) were measured. Octahedral CEC was calculated by difference. Tetrahedral CEC was determined after saturation with Li and heating at 300 °C to reduce octahedral charge to near zero. Potassium fixation was determined in both wet (1:4 soil/solution, 16 h on a shaker) and dry conditions (after drying for 24 h at 70 °C) using three different levels of added K. Total CEC was well correlated with tetrahedral CEC (r2 = 0.76, P < 0.001). About half of the smectitic and vermiculitic soil clays have >50% of their total charge due to tetrahedral charge. The amount of K fixed Increased with added K, whereas the percent K fixed relative to total added K decreased. The K fixation by the clays studied was best correlated with total CEC for a given amount of K added. It was also well correlated with tetrahedral CEC. Simple regression analysis did not show any significant effect of octahedral CEC. A multiple regression analysis, however, demonstrated that both components of total CEC, tetrahedral and octahedral, have a simultaneous effect on K fixation. Tetrahedral CEC explained more of the variation (64%) than octahedral CEC (36%). This greater effect was attributed mainly to the proximity of tetrahedral charge to the interlayer space of 2:1 phyllosilicate clays.
Trichloroethylene Vapor Sorption onto Soil Minerals
Authors: Ong Say Kee , Lion Leonard W. 
Published: July 2010

AbstractAdsorption of trichloroethylene (TCE) and water vapor onto five common soil minerals (montmorillonite, kaolinite, Fe oxide, silica, and Al oxide) and an organic phase (humic acid) was studied across a wide range of relative vapor pressures (0 to 90%). Dividing the amount of sorbate sorbed by the monolayer capacity for water and TCE (at 0% relative humidity [RH]) transforms this variable to values that are of the same magnitude. Normalizing the sorption data for monolayer capacity confirms that surface area serves as a good measure of the adsorptive capacity of the dry solids. The lack of complete convergence of the relative adsorption isotherms is attributed to specific sorbent‐sorbate interactions and the presence of micropores. The computed Brunauer, Emmet, and Teller (BET) surface areas, using TCE and water as sorbates, were different from the BET N2 surface area for a given sorbent. The differences in these surface areas may indicate sorbate packing arrangement for TCE and water that are different from the simple hexagonal close packing that is assumed for N2 molecules. Adsorption of TCE onto oven‐dried Al oxide was enhanced when the surface was coated with an organic phase (i.e., humic acid). Larger amounts of TCE were sorbed by humic acid at 80% RH than at 0% RH or under saturated aqueous conditions. Expansion of the humic acid due to hydration and exposure of internal surfaces/pore volume for sorption/condensation is proposed as an explanation for the higher uptake of TCE at high RH. In binary‐vapor (water plus TCE) sorption studies, isotherms for the total volume sorbed at different RH were coincident for porous solids such as Al and humic‐acid‐coated Al. This result strongly indicates that, at high TCE vapor pressures, vapor condensation plays an important role for porous sorbents in determining the amount of TCE sorbed.
Infiltration Patterns from Simulated Rainfall on a Semiarid Rangeland Soil
Authors: Seyfried Mark S. 
Published: July 2010

AbstractCurrently proposed approaches to the estimation of surface runoff and erosion are based on the Green‐Ampt equation. Processes controlling water movement in uncultivated semiarid rangelands, such as macropore flow for example, may be incompatible with assumptions fundamental to the Green‐Ampt equation. In this study, patterns of water and tracer (bromide, methylene blue, and alizarin red S) movement under two simulated rainfall intensities were compared with those consistent with the Green‐Ampt equation. Macropore flow was an important process at the site. The reasonably uniform and abrupt wetting front indicated that this was not necessarily incompatible with the use of the Green‐Ampt equation. Apparently the effective macropores were sufficiently close together and shallow that lateral movement effectively obliterated the effects of individual macropores at depths of about 0.3 m. Two other inconsistencies with the Green‐Ampt equation were observed. First, soil cover type strongly affected infiltration. Bare interspace areas in microtopographic lows had relatively low infiltrabilities and were hydraulically interconnected. These areas, therefore, control time to ponding and runoff initiation. Explicit consideration of these differences may improve runoff and infiltration estimation. Second, a contrasting argillic horizon appeared to inhibit water movement. Subsoil properties not usually considered in the Green‐Ampt equation may dominate infiltration under near‐field‐capacity soil moisture conditions and large rainfall events.
System for Collecting Undisturbed Cores from Surface Soils for Micromorphological Analysis
Authors: Rhoton F. E. , McChesney D. S. 
Published: July 2010

AbstractIntact soil cores are difficult to extract from reduced‐tillage plots using available equipment due to the tendency of cores to separate at planes of weakness. A split‐tube sampler was developed to minimize disruptions of the natural soil fabric that frequently occur as the core is removed from the sampling equipment. Construction details are provided that permit this equipment to be attached to standard hydraulically driven soil‐coring equipment. Use of this equipment, in conjunction with sample containers that are resistant to laboratory pretreatment procedures and impregnating resins, greatly reduced sample handling and the potential for creating structural anomalies.
Applications of a Laser Scanner to Quantify Soil Microtopography
Authors: Huang Chi‐hua , Bradford Joe M. 
Published: July 2010

AbstractMany transport processes on or across the soil surface boundary are controlled by surface microtopography, or roughness. How roughness affects the transport process depends on the length scale of the process. The most commonly used method of expressing soil surface roughness, the roughness length or random roughness, is contrained by the measurement technique and does not embody the concept of scale. The structural function, or variogram, plotted on a log‐log scale was used in this study to express the surface roughness at different scales. With the aid of a laser scanner, surface topography was measured down to 0.5‐mm grid spacing. Data collected from a variety of surface conditions showed that soil roughness can be quantified by a combination of fractal and Markov‐Gaussian processes at different scales. Potential applications of the roughness quantification were also discussed.
Soil Water Movement in Response to Temperature Gradients: Experimental Measurements and Model Evaluation
Authors: Bach L. B. 
Published: July 2010

AbstractTemperature gradients may have a significant effect on soil water movement under certain conditions, but inclusion of these effects adds complexity to the flow analysis. This study was conducted to help clarify the significance of nonisothermal water flow, and to examine theoretical and numerical descriptions of the transport processes. At initial water contents of 0.00, 0.049, 0.099, 0.151, and 0.282 m3 m‐3, isothermal and nonisothermal laboratory experiments were conducted to provide direct information on soil water movement in response to temperature gradients. These data were used to evaluate the numerical simulation model SPLaSHWaTr2, and to examine calculation of the thermal conductivity, λ(ϑ), the thermal vapor diffusivity, DTv(ϑ), and the temperature coefficient of the matric potential, Cψ, based on modifications to a theory proposed by Philip and de Vries in 1957. A statistically significant effect of the temperature gradient was found at an initial water content of 0.151 m3 m‐3, which corresponds to a pressure head of approximately ‐1.2 m of H2O. No effect of the temperature gradient was found at initial water contents of 0.00, 0.049, 0.099, or 0.282 m3 m‐3. Under isothermal conditions, the model provided simulated water‐content profiles that were in good agreement with measured profiles. Under nonisothermal conditions, profiles simulated by the model were in poor agreement with the measured data, using the original values of λ(ϑ), DTv(ϑ), and Cψ. Sensitivity analysis showed that λ(ϑ) and DTv(ϑ) had a negligible influence on nonisothermal water movement. On the other hand, Cψ had a significant influence on nonisothermal water movement. Adjusting Cψ from the original value of ‐0.0068 K‐1 to the value suggested by Philip and de Vries, ‐0.00209 K‐1, improved the agreement between simulated and measured water‐content profiles, particularly at an initial water content of 0.282 m3 m‐3. With the adjustment in Cψ, the model simulations were in good agreement with the measured data, indicating that the Philip and de Vries theory provides an adequate description of the nonisothermal transport processes.
Modeling Cation Amelioration of Aluminum Phytotoxicity
Authors: Grauer Ulrich E. , Horst Walter J. 
Published: July 2010

AbstractMany studies have demonstrated the role of cations in ameliorating Al phytotoxicity. Until recently, the role of pH on the expression of Al toxicity has always been discussed in the light of pH‐dependent change in Al speciation but not in the light of H+ as an ameliorative cation for Al toxicity. Several theoretical approaches have been proposed to characterize the ameliorating effects of specific cations. Based on the assumption that Al phytotoxicity is a function of the Al saturation of exchange sites in the root apoplast (AIS), a model is proposed with the general form:
urn:x-wiley:03615995:saj2sssaj199203615995005600010026x:equation:saj2sssaj199203615995005600010026x-math-0001 where Amj = ameliorating cations, Ali = Al species, and KAmj, KAmi = association constants of the respective ions with a ligand, L‐, that simulates the apoplastic binding sites, and braces denote molar activities. Association constants for Ca, Mg, and Al ions were estimated from cation‐exchange experiments with fresh roots of rye and yellow lupine, and ion speciation was calculated with the GEOCHEM‐PC program. Making a sensitivity analysis, we found that the Al saturation (AlS0) maximum is strongly dependent on both the choice of association constants, and the ion concentrations in the rooting medium. In contrast, the pH of maximum AlS0 is rather stable, and is predicted by the model to occur at pH 4.4 ± 0.4, a value that agrees with several reports of maximal Al toxicity at pH around 4.5. Cations were ranked for their competitiveness with Al3+ in the order H+ >> Ca2+ > Mg2+ >> K+. Limitations of the model, as well as prospects for improved understanding of genotypical differences in Al tolerance, are discussed.
Topsoil Depth and Desurfacing Effects on Properties and Productivity of a Typic Argiustoll
Authors: Gollany H. T. , Schumacher T. E. , Lindstrom M. J. , Evenson P. D. , Lemme G. D. 
Published: July 2010

AbstractInformation from desurfacing studies has been used to develop simulation models for assessing soil erosion‐productivity relationships. No attempt has been made, however, to directly compare the effect of desurfacing on soil properties and crop production with differences in topsoil depth arising from erosion or slower soil development. The objectives of this study were to determine the effects of topsoil depth on soil properties and continuous corn (Zea mays L.) yield for both a desurfaced summit and adjacent eroded backslope sites on a Beadle clay loam (fine, montmorillonitic, mesic Typic Argiustoll). Field studies were conducted for a 5‐yr period. Plots were established on a backslope position consisting of three topsoil‐depth classes (E1, E2, and E3). Plots were also established on an adjacent summit position consisting of three desurfaced classes (0, 30, and 45 cm of topsoil were removed in 1965). Prediction equations were developed from 16 variables. The selected equation, with three variables, explained 49% of the variability in grain yield. Depth to middle of the Bk horizon was the most important of the independent variables, explaining 23% of the yield variability, followed by soil water use, and the interaction of water use with depth to middle of the Bk. The equations for the desurfaced summit and eroded backslope plots were significantly different. A reduction in topsoil depth reduced yield more on the desurfaced summit compared with the eroded backslope. This effect was primarily a result of disproportionately higher yield potentials for the summit control plots due to landscape position and soil formation.
Infiltration in Response to Water Quality, Tillage, and Gypsum
Authors: Baumhardt R. L. , Wendt C. W. , Moore J. 
Published: July 2010

AbstractMaintaining adequate infiltration into cropped soils is a continuing problem in the Trans‐Pecos region of Texas due to the accumulation of electrolytes from irrigation water. The objectives of this study were to determine the effect of (i) number of years of irrigation, (ii) applied water quality, (iii) tillage, and (iv) surface‐applied powdered gypsum on field infiltration rate and amount. Infiltration rate into a Hoban silt loam (fine‐silty, mixed, thermic Ustollic Calciorthid) at Pecos, TX, was measured with a rainfall simulator in field experiments with different irrigation amounts and qualities of applied water treatments or tillage and powdered‐gypsum treatments. Electrical conductivities from the soil surface (0–50 mm) increased 300% after the first year's irrigation and remained relatively constant with continued irrigation. Infiltration rate and amount increased when the soil salinity and sodicity decreased or the salinity of the applied water increased. Tillage increased infiltration in the order of plow‐disk > double‐disk > compacted = control. The application of powdered gypsum to the soil surface increased infiltration amount by an average of 38% in tilled or compacted soil, where the surfaces had been disturbed. Powdered gypsum did not affect the infiltration amount where the soil surface was undisturbed. These data indicate that (i) sufficient electrolytes from irrigation water will accumulate in one growing season to reduce infiltration and (ii) field applications of powdered gypsum will increase the infiltration into tilled or disturbed soils.
Development of Seasonal Water Repellence under Direct Drilling
Authors: Chan K. Y. 
Published: July 2010

AbstractWater repellence was detected in an Oxic Paleustalf medium‐textured surface soil (27% clay,) under direct drilling but not under conventional cultivation. The phenomenon was apparently seasonal in nature, evident after the first rain in summer but disappearing after a period of relatively high rainfall. Water repellence was reproduced in the laboratory by slow drying soil cores under high relative humidity and was associated with fungal hyphae growing on the organic‐matter‐rich surface layer developed under direct drilling. Either rapid drying or wetting of the soil with a dilute thymol [5‐methyl‐2‐(1‐methylethyl) phenol] solution instead of water stopped the fungal growth and development of water repellence. Water repellence significantly slowed infiltration when water was applied at 40‐mm suction using a sorptivity tube. The seasonally developed water repellence found in the direct‐drilled soil was probably the result of enhanced fungal growth due to the absence of soil disturbance and presence of a permanent layer of organic matter.
Spatial Variability of Evaporation along Two Transects of a Bare Soil
Authors: Lascano R.J. , Hatfield J.L. 
Published: July 2010

AbstractEstimates of soil water evaporation are required for the assessment of soil water management practices. The purpose of this study was to investigate (i) the spatial and temporal changes in soil water evaporation along two transects in a bare soil, (ii) the spatial variability in soil properties, and (iii) the comparison of field‐measured and simulated evaporation. The study was conducted on an Olton sandy clay loam soil (fine, mixed, thermic Aridic Paleustoll) at Lubbock, TX. Two 50‐m transects were oriented in north‐south and east‐west directions with sampling positions marked at 1‐m intervals. A 150‐mm irrigation was applied and soil water evaporation was measured for the four succeeding days. Particle‐size distribution and bulk density were determined from each sample after the last measurement. Semivariograms were calculated for each parameter along with the population statistics. Evaporation values were isotropic between transects for the first 3 d of measurement and did not exhibit any particular range for the semivariograms. We conclude that random samples can be taken to quantify soil water evaporation rates within this bare field. Population statistics for the bulk density revealed that the populations were random, normal distributions with no spatial structure, and for particle size the populations were either normal or log‐normal. Values of soil water evaporation from the CONSERVB model were within one standard deviation of the mean of measured values when average soil hydraulic properties for the field were used. It is possible to use the average soil properties as input into a model for regional assessment of soil water evaporation rates.
On the Measurement of Soil Surface Temperature
Authors: Ham Jay M. , Senock R. S. 
Published: July 2010

AbstractThe temperature of the soil surface strongly influences physical, chemical, and biological processes at the surface. Field experiments were conducted to evaluate the accuracy and utility of several different methods for measuring soil surface temperature. Surface temperature of a bare soil was measured simultaneously with infrared thermometers (IRT), bare fine‐wire thermocouples (BFT), and soil‐encapsulated thermocouples (SET). The SET sensors consisted of fine‐wire thermocouples that had been encapsulated with soil from the measurement site of interest. Experiments were conducted on soils with silt loam and coarse sand textures. Continuous measurements were made throughout several drying cycles to test each measurement technique across a range of soil water and environmental conditions. All IRT measurements were corrected for surface emissivity and reflected longwave radiation. During the silt loam trials, both the SET and BFT measurements were lower than the IRT measurements during the day and greater than the IRT readings at night. Results suggest that both the SET and BFT sensors were measuring soil temperature below the immediate surface. On the average, however, the SET and BFT sensors were within ±0.8 and ±0.5°C of the IRTs, respectively. During the coarse sand trials, the SET and BFT measurements were consistently greater than the IRT measurements during both day and night periods. Results indicate that the low emissivity of the sand made it difficult to adequately correct the IRT measurements for emissivity and surrounding longwave radiation. During both silt loam and sand trials, the BFT and IRT measurements were in better agreement than the SET and IRT measurements. Nevertheless, data from a field study indicate that the SET sensors are reasonably accurate, and are capable of supplying continuous, long‐term data, despite irrigation and rain.
Solute Leaching in Crop Row vs. Interrow Zones
Authors: Timlin D. J. , Heathman G. C. , Ahuja L. R. 
Published: July 2010

AbstractThis was a pilot study to investigate overall differences in solute leaching from soil beneath row vs. interrow zones of a row crop. Overall leaching could be minimized by exploiting such differences. Strontium bromide was uniformly applied to two, 7.2 by 6 m plots on Bosville fine sandy loam (fine, mixed, thermic Albaquic Paleudalf) planted in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Within each plot, the surface soil texture varied from fine sandy loam to fine sandy clay loam. Soil water status was monitored with tensiometers. After the vegetative growth stage, soil samples were taken along five transects perpendicular to the crop rows at 0.2‐m intervals, to a depth of 0.5 m. Sampling locations corresponded to row, quarter‐row, and interrow positions. In the fine sandy loam half of the corn plot, there was significantly more leaching of Br below the 0.5‐m depth in the interrow positions than in the row positions. This appears to be related to the soil water status, since soil conditions in the fine sandy loam half of the corn plot were, on the average, drier under row positions than under interrow positions. Overall leaching was less under soybean than under corn. Simplified two‐dimensional simulations of solute transport in row‐interrow zones further enhanced our understanding of the effects of net flux differences between those zones, overall net flux, and soil and crop type. The simulations indicated that overall leaching could be slowed by enhancing the differences in evapotranspiration between the row and interrow zones.
Characterization and Genesis of Saprolite Derived from Gneissic Rocks of Virginia
Authors: Stolt M. H. , Baker J. C. , Simpson T. W. 
Published: July 2010

AbstractSaprolite is the most prevalent soil parent material in the Piedmont and Blue Ridge Highlands regions of Virginia. Soil‐saprolite‐land‐scape associations were examined in these regions in order to describe and characterize saprolite formed from gneissic rocks, and to study saprolite genesis on these landscapes. Three representative landscape associations were chosen as study sites, and soil and saprolite were examined at the summit, backslope, and footslope positions of each. Saprolite thickness decreased from summit to footslope. Greater thicknesses of saprolite at summits are apparently related to the relative stability of this position compared with associated backslopes and footslopes. Reconstruction results indicate that between 20 and 36% of the mass of the partially weathered rock, which is the precursor of saprolite, is lost during saprolite formation. From 73 to 82% of these losses are Al or Si. Initial soil formation occurs at a faster rate than saprolite formation. As profile development increases, the rate of soil formation and consequent increase in solum thickness is reduced. After soil formation is reduced to a rate below that of saprolite formation, and chemical weathering controls the rate at which the thickness of the regolith increases, saprolite begins to accumulate below the solum.
Water Retention of Soft Siltstone Fragments in a Ustic Torriorthent, Central Montana
Authors: Montagne C. , Ruddell J. , Ferguson H. 
Published: July 2010

AbstractSome soils in the western USA overlie or contain fragments of porous sedimentary rock. Estimations of plant‐available water that neglect water retained in the rock may be in error. Using pressure‐plate and newly modified tension‐table techniques, we measured the water retained at nine water potentials ranging from 0 to −1500 kPa in fissile siltstone fragments from the Cr horizon of a Ustic Torriorthent developed on the Fort Union formation in central Montana. The siltstone fragments held ≈0.10m3 m−3 plant‐available water, assuming −1500 kPa (−15 bar) as the lower limit of water availability.