bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium Fixation and Charge Characteristics of Soil Clays
Authors: Bouabid R. , Badraoui M. , Bloom P. R.
Published: July 2010

Forty‐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

Adsorption 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

Currently 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

Intact 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

Many 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

Temperature 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

Many 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

Information 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

Maintaining 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

Water 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

Estimates 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

The 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

This 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

Saprolite 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

Some 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.
Bulk Density of a Sandy Loam: Traffic, Tillage, and Irrigation‐Method Effects
Authors: Meek B. D. , Rechel E. R. , Carter L. M. , DeTar W. R.
Published: July 2010

Modern crop production creates a cycle between soil compaction caused by traffic and alleviation of this condition by tillage or natural processes such as freezing and thawing. The objective of this study was to evaluate important management practices as they relate to changes in bulk density of a tilled sandy loam soil. Practices evaluated were irrigation method, time between tillage and traffic, tire pressure and wheel load of applied traffic, and controlled traffic. Relationships among bulk density, penetration resistance, and infiltration rate were determined. Experiments were conducted in the San Joaquin Valley of California, on a sandy loam soil (Entisol) with an organic‐matter content of <1%. After tillage, settling and trafficking of a soil resulted in rapid changes in its bulk density until a new equilibrium was reached. Tire pressure of 408 kPa and wheel weight of 2724 kg applied at moisture contents near field capacity resulted in a bulk density of 1.92 Mg m−3, compared with a value of 1.67 for no traffic. The time interval between tillage and traffic did not affect final bulk density. Drip irrigation, which did not saturate the soil, resulted in a bulk density of ≈0.1 Mg m−3 lower than flood irrigation, which saturated the soil surface. Wheel traffic in the furrow resulted in only small changes in the bulk density within the row. When tillage did not occur between cropping seasons, traffic caused high bulk densities in the furrow but only small changes in the row. An increase in bulk density from 1.7 to 1.89 Mg m−3 decreased the infiltration rate by four times and increased resistance to penetration at the end of the season by three times. Knowledge of how management practices affect bulk density can aid growers in reducing recompaction following tillage.
Transport in a Horizontal Flow Chamber
Authors: Sadeghi Ali M. , Starr James L.
Published: July 2010

A better understanding is needed of the factors that control the fate of chemicals that move laterally in shallow groundwater within fields to tile lines and drainage ditches and from fields to nearby streams or estuaries. A chamber was designed and used to simulate shallow groundwater flow in the field. The chamber, made of Plexiglas with dimensions 120 by 60 by 60 cm, was filled to a depth of 30 cm with sand. A multiport arrangement of 10‐mm‐diam. holes on a 5 by 5 cm grid on both end walls of the chamber provided a combination for quite uniform solute application at the inlet side, and allowed sampling simultaneously from all ports at the outlet side. As a first approximation, the flow and transport were assumed to be one dimensional, and a convective‐dispersive solute‐transport model was applied to the Cl breakthrough data of each of the 50 outlet ports in order to quantify the spatial distribution of the dispersion‐coefficient values at the outlet plate. Based on the inconsistency observed between measured and estimated pore‐water velocities and dispersion coefficients of each of the 50 outlet ports, it appears that the one‐dimensional model is not appropriate to adequately characterize transport parameter in this horizontal flow system.
State‐Space Approach to Spatial Variability of Crop Yield
Authors: Wendroth Ole , Al‐Omran A. M. , Kirda C. , Reichardt K. , Nielsen D. R.
Published: July 2010

Spatial crop yield variability complicates interpretation of field experiments if there is no information available about the spatial variability structure of the soil. Our objective was to determine, using a state‐space approach, the underlying process in a soil that caused spatial yield variability of a N2‐fixing crop and a nonfixing crop. On a heterogeneous soil, ryegrass (Lolium multiflorum L.) and alfalfa (Medicago sativa L.) were cropped on neighboring transects. Dinitrogen fixation, calculated with either the difference method or the 15N isotope dilution method and averaged across the transects, did not differ. But, as we examined locations along the transect, differences in amount of fixed N calculated by each method became apparent. Yields of both crops showed different variability structures along the transects. Local effective soil N content was related to local N uptake from soil and to soil symbiotic N2 fixation of alfalfa. In order to conclude this, the spatial distribution of the soil volume taken by stones in this partially rocky soil had to be considered. In stochastic (state‐space) models based on spatial dependence between observations, crop yield, effective soil N, and N2 fixation were identified as first‐order autoregressive processes moving through the transect. In other cases, state‐space models were useful tools for spatial interpolation of plant yield, except for large yield alterations between neighboring plots along a transect. This study showed that the spatial variability structure of yields could be explained from located field observations combined with state‐space models.
Genesis of Natriborolls (Solonetzic) in a Closed Lake Basin in Saskatchewan, Canada
Authors: Heck R. J. , Mermut A. R.
Published: July 2010

Morphological and chemical characteristics of seven soils (Aquents and Borolls), crossing four successive terraces, were studied to understand the genesis of Natriborolls (Solonetzic) and associated soils in a closed lake basin in the Saskatchewan prairies. Formation of these terraces may be associated with major climatic changes during the Holocene. Based on zirconium/quartz ratios and field observations, frequent lithological discontinuities were identified in the profiles. These discontinuities have influenced the morphology and chemistry of the soils. Differences between the lake water and underlying artesian aquifer reflect the influence of more soluble and weatherable minerals in the basin's deposits. The concentration and composition of soil solutions, the degree of carbonate dissolution, and the amounts of gypsum changed with increasing elevation. The sequence of anion leaching observed was: Cl‐ > SO2‐4 > HCO3‐ (or CO2‐3). Lateral capillary flow from the lake is the major mechanism of salination, but a limited redistribution of efflorescent salts by wind also occurs in the basin. Due to the high inherent shrink‐swell potential of the parent material, prismatic structure has formed at an early stage of profile development. Morphology of the soils on the younger terraces suggests that the eluvial horizons developed after the formation of the prismatic structure. The preservation of solonetzic morphology (stable columnar structure), despite changes in salinity, is attributed to the fine texture of the soil.
Alternative Soil Water Release Parameters for Distinguishing Tillage Effects
Authors: Powers William L. , Baer Jonathan U. , Skopp J.
Published: July 2010

Tillage effects on the water‐holding characteristics are frequently difficult to evaluate. This may partially be due to the insensitivity of the parameters selected to make the comparisons. This study was initiated to evaluate alternative parameters for assessing tillage effects on water‐holding characteristics. Corn (Zea mays, L.) was planted on a Crete silt loam soil (fine, montmorillonitic, mesic Pachic Argiustoll) which was subjected to conventional and no‐till management for four consecutive years. Water‐release data were obtained from undisturbed soil cores taken from the surface soil three times during the 1989 growing season and at harvest. The following parameters were calculated: the air‐entry value, ψe; the pore‐size distribution index, d; the transformed air‐entry value, c; the zeroth ordinary moment or porosity (OMO), the first ordinary moment or mean pore size (OM1), the second central moment or breadth of the pore‐size distribution (CM2), and the skewness (SKW) of the pore‐size distribution; and four volumetric fractions. Except for ψe and the volume fraction of pores with radii between 1.5 and 15 µm, VF3, all parameters showed an effect of tillage treatments at the 90% confidence limit as determined by an F test. Only the CM2 showed a significant effect of time. The above parameters were also calculated from data on three Iowa soils. For these data, two additional parameters, OMO and VF3, did not show a difference between selected tillage treatments. Stepwise discriminant analysis selected only OM1 as a discriminator for the data from the Crete soil, but several combinations of OM1, OM2, d, and VF3 were selected when the Iowa soil and Crete soil data were combined. Our recommendation for a single characterization of the pore‐size distribution is moment analysis.
Polymers' Effects on Infiltration and Soil Erosion during Consecutive Simulated Sprinkler Irrigations
Authors: Levy G. J. , Levin J. , Gal M. , Ben‐Hur M. , Shainberg I.
Published: July 2010

Impact energy of water drops from overhead sprinkler irrigation can cause seal formation, and an increase in runoff and in soil erosion. The effects of low concentrations (5, 10, and 20 g m−3) of two polymers, an anionic polyacrylamide (PAM) and a cationic polysaccharide (PSD), on soil permeability and erosion from a grumusol (Typic Chromoxerert) and a loess (Typic Haploxeralf), were studied during five consecutive irrigations of 60 mm each. The polymers were added to the irrigation water during the first three consecutive irrigations, and thereafter the soils were subjected to two additional irrigations of water only. During the first three irrigations, the final infiltration rates (FIR) of the soils were significantly higher than those of the untreated samples (control). In the subsequent two irrigations with water only, the FIR values of the treated samples decreased to values similar to those of the control. The low residual effect of the polymers was explained by erosion of the thin treated layer and an insufficient amount of the polymers. A lower concentration of PAM (10 g m−3) was needed for optimal effect on the FIR and cumulative infiltration, compared with PSD (20 g m−3). For the optimal treatments, infiltration parameters were generally higher in the PAM‐ than in the PSD‐treated soils. Soil losses in all the PAM treatments were significantly lower than those in the PSD treatments. Both polymers stabilized soil aggregates, but PAM also cemented aggregates together and increased their resistance to erosion.
Depth Profiles of Electrical Conductivity from Linear Combinations of Electromagnetic Induction Measurements
Authors: Cook P. G. , Walker G. R.
Published: July 2010

Within the past 10 yr, frequency‐domain electromagnetic (FEM) induction techniques have become more and more widely used in soil science and hydrology. Each measurement of apparent electrical conductivity represents a depth‐weighted average of soil electrical conductivity. However, the depth weighting corresponding to each measurement may be very different from that required by the user. The simultaneous use of multiple measurements (with different depth weightings) should allow some aspects of the depth distribution of electrical conductivity to be inferred. We illustrate a method for obtaining linear combinations of FEM measurements to estimate the soil electrical conductivity within the depth interval of interest. The method relies on the simple fact that the measurement‐system response is linear, so that a linear combination of apparent‐conductivity readings corresponds to a linear combination of response functions. One can seek a linear combination of response functions that has desirable characteristics. This sets up an optimization problem that can be solved by standard methods, which avoids difficulties encountered with layered inversions to resolve nonlayered systems. The approach was applied to GEONICS EM31, EM34, and EM38 instruments in three examples: (i) single frequency measurements at vertical and horizontal dipole configurations, (ii) frequency measurements using the EM34 at all six possible configurations, and (iii) frequency measurements using the EM38 held at varying heights above the ground. The derived linear combinations were applied to field data from southern Australia. Soil conductivity profiles predicted using linear combinations showed good agreement with profiles measured with a conductivity probe.
Dynamic Simulation of Phase Changes in Snowpacks and Soils
Authors: Grant R. F.
Published: July 2010

Phase changes of water in snowpacks and soils are controlled mainly by the short‐term dynamics of energy exchange with the atmosphere. The accurate reproduction of the exchange processes is thus necessary to the reproduction of freezing and thawing, and of consequent water movement, in ecosystem simulation models. In the model used for this study, energy exchange between the atmosphere and the surfaces of single‐layered snowpacks and multiple‐layered soils were calculated from recorded meteorological data and from measured physical properties of snowpacks and soils. The consequent absorption and transmission of energy through the snowpack and soil media were used to estimate the dynamics of phase changes in the snowpack and soil water. The hourly behavior of the model allowed it to reproduce, to within 50 W m−2, the diurnal patterns of energy exchange recorded over a melting snowpack and, to within 1 °C, the diurnal soil temperatures recorded at depths of 0.05 and 0.15 m in a thawing soil profile. The seasonal behavior of the model allowed it to reproduce overwinter patterns of accumulation and disappearance of a snowpack to within 50 mm, and those of maximum and minimum daily soil temperatures at depths of 0.05 and 0.15 m to within 1 °C. Models that function at this level of detail are useful in estimating the effects of slope, aspect, residue cover, and other surface characteristics on snowmelt and soil warming. With higher spatial resolution in parameterizing snowpack functions for hydraulic and thermal conductivity, these models may be used to represent multilayered snowpacks.
Electrophoretic Mobility of Illite and Micaceous Soil Clays
Authors: Lebron I. , Suarez D. L.
Published: July 2010

Examination of the colloid chemistry of clays may provide an increased understanding of the structural stability of soil clays under field conditions. Electrophoretic mobility (EM) gives specific information about the net charge of a particle at the shear plane. An evaluation was made of the effect of the important water quality variables, electrolyte concentration, sodium adsorption ratio (SAR), and pH on the EM of Silver Hill illite and three micaceous soil clays. Increases in electrolyte concentrationg enerally increased the mobility of the colloidal particles, contrary to double‐layer prediction. The EM behavior is thus not explained by the commonly used double‐layer theory of infinite plates; however, results can be explained if this double‐layer theory is extended to consider charge spillover into clay particle edges and changes in variable edge charge. The EM increased faster when the SAR increased from 5 to 20 (mmol L−1)0.5 than at higher values of this parameter. These results are in agreement with tactoid formation and demixing theory previously developed by others for smectites. The EM for micaceous soil clays and specimen Silver Hill illite was more sensitive to changes in pH as the electrolyte concentration increased. These results are consistent with observations on variable‐charge minerals where variable charge increases with increasing ionic strength. Removal of organic matter increased the EM in the pH 4 to 10 range studied.
Diffusion of Kjeldahl Digests for Automated Nitrogen‐15 Analysis by the Rittenberg Technique
Authors: Liu Y. P. , Mulvaney R. L.
Published: July 2010

Nitrogen‐isotope analysis by the Rittenberg technique requires N in the form of NH4. Conversion of organic N to NH4‐N is normally accomplished by the Kjeldahl method, which involves digestion with concentrated H2SO4. A diffusion method recently developed for isotope‐ratio analysis of inorganic N in soil extracts was modified for use with Kjeldahl digests. An aliquot of the digest (to 20 mL) containing 50 to 150 µg of N was neutralized by overturning a vial with 2 mL of 20 M NaOH in a 118‐mL specimen container sealed with a screw‐top lid, and the NH3 liberated was collected for 6 d at room temperature in a 7‐mm‐diam. glass‐fiber disk acidified with 10 µL of 1 M H2SO4. For automated Rittenberg analysis of the diffused NH3‐N by mass spectrometry, the glass disk was tranferred to a plastic sample tray (96 samples per tray), treated with 10 µL of 28.9 M (concentrated) HF, and dried in a desiccator over anhydrous CaSO4. Studies showed that diffusion was complete (>97%) and that, when correction was made for isotopic dilution by natural‐abundance N in reagents, isotope‐ratio analyses of diffused N (0.2–4.2 atom % 15N) were in close agreement with analyses using conventional steam‐distillation and concentration techniques.
Crop and Tillage Rotations: Grain Yield, Residue Cover, and Soil Water
Authors: Wagger M. G. , Denton H. P.
Published: July 2010

Information regarding crop yield response for different tillage and rotation systems is needed to determine regional or local suitability for a given production system. Our objective was to determine the effects of continuous and alternating tillage sequences in corn (Zea mays L.) monoculture and corn‐soybean [Glycine max (L.) Merr.] rotation on residue cover, soil water, and grain yield. Continuous conventional tillage (CT), continuous no‐tillage (NT), or CT and NT alternating every other year were evaluated during a 5‐yr period on a Rion (fine‐loamy, mixed, thermic Typic Hapludult)‐Pacolet (clayey, kaolinitic, thermic Typic Kanhapludult) sandy clay loam complex at a Piedmont location and an Eunola sandy loam (fine‐loamy, siliceous, thermic Aquic Hapludult) at a Coastal Plain location. The 5‐yr average NT corn grain yield was 27% (1.15 Mg ha−1) higher than CT at the Piedmont location, but only 4% (0.32 Mg ha−1) higher at the Coastal Plain location. Continuous NT at the Piedmont location also resulted in higher corn yields 2 out of 4 yr compared with NT following CT. The increase in corn yield with NT was associated with greater soil water availability, primarily attributed to surface residue cover from corn stover fostering greater infiltration on a crust‐prone soil. Soybean yield during the 5‐yr period was 5% higher with NT at the Piedmont location and unaffected by tillage at the Coastal Plain location. In general, crop rotation had no effect on corn yield at either location. Results indicate that continuous NT should be the system of choice on this upland Piedmont soil.
Alternative Farming System Effects on Profile Nitrogen Concentrations on Two Iowa Farms
Authors: Karlen D. L. , Colvin T. S.
Published: July 2010

There is a general lack of quantitative data to assess alternate farming systems. Our objectives were to quantify long‐term (20‐yr) effects of conventional and alternative farming practices on soil NH4‐N, NO3‐N, and total‐N concentrations. Contiguous soil map units of Clarion loam (fine‐loamy, mixed, mesic Typic Hapludoll), Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll), Canisteo silty clay loam (fine‐loamy, mixed [calcareous], mesic Typic Haplaquoll), and Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) were identified and used to compare long‐term farming system effects. Sixty‐four soil profile cores averaging 4.5 m in depth were collected from a 16‐ha conventional field and from a 16‐ha alternative field in April 1989 following a year in which total precipitation was ≈30% below normal (588 vs. 848 mm). In autumn 1990, 32 cores averaging 3.0 m in depth were collected from each of two other 16‐ha conventional and alternative fields just north of those sampled in 1989. Farming practice significantly affected total‐N, NH4‐N, and NO3‐N concentrations measured at the various sampling depths, but differences were small and inconsistent. Corn (Zea mays L.) grain yields averaged 9093 kg ha−1 in the conventional field and 8977 kg ha−1 in the alternative field in 1989. Comparing conventional and alternative fields, total aerial N accumulation 6 wk after planting averaged 203 and 123 mg plant−1, ear leaf N concentration averaged 26.6 and 20.6 g kg−1, and total N removed by corn grain averaged 91.6 and 85.7 kg ha−1. All measured differences were generally within the 95% confidence interval, and neither system was consistently better. We conclude that well‐managed conventional and alternative farming systems do not differ in their risk for groundwater N pollution in central Iowa.
Fractal Description of Macroporosity
Authors: Brakensiek D. L. , Rawls W. J. , Logsdon S. D. , Edwards W. M.
Published: July 2010

Much interest has been generated in the application of self‐similar power laws and fractal geometry principles to the description of soil properties. Fractal geometry is here proposed as a descriptor of macroporosity. Data on macropore counts‐sizes were used to investigate this possibility. The fractal Sierpinski carpet was assumed to compute two‐dimensional areal porosity. A tentative conclusion is that macropore count‐size distributions can be described by the carpet generator and the areal porosity can be calculated.
Catalytic Decomposition Kinetics of Aqueous Hydrogen Peroxide and Solid Magnesium Peroxide By Birnessite
Authors: Elprince A. M. , Mohamed W. H.
Published: July 2010

Peroxides are used as O2‐generating agents. The decomposition of H2O2 (aq) or MgO2(s) in the presence of synthetic birnessite [δ‐MnO2(s)] as a catalyst was observed by measuring the volume of O2(g) given off. The experimental data fit a first‐order kinetic law and the mechanism proposed by Habes and Weiss can explain the experimental results obtained for the decomposition of H2O2(aq). The applicability of the proposed mechanism involving H2O2(aq) was based on the following: (i) the activation energy was relatively high (82 ± 3 kJ mol−1); (ii) the rate constant (k) was pH dependent, indicating that H+ and OH‐ ions were formed in the process; (iii) a linear relationship (and not logarithmic) between k and the ionic strength indicated a reaction between an ion and a neutral molecule; and (iv) using birnessite with different fractional coverages of Co indicated that the reaction was heterogeneously catalyzed by Mnz+1/Mnz active centers. Regarding MgO2(s) decomposition, the experimental data obtained at pH 7.6 followed a rate law derived from a shrinking‐core model for fixed‐size particles. The rate of the reaction was controlled by diffusion through the Mg(OH)2(s) product layer rather than by chemical reaction at the core surface. Compared with ionic peroxides, MgO2(s) could be a potential O2‐generating agent for generating O2(g) during a relatively long period of time.
Noninvasive Time Domain Reflectometry Moisture Measurement Probe
Authors: Selker John S. , Graff Lynette , Steenhuis Tammo
Published: July 2010

Time domain reflectometry (TDR) has been shown to be a widely applicable method for determination of moisture content in soils and other geological and engineering materials. All TDR probes used to date have required penetration of the sample under study, which severely limits the utility of the method. We demonstrated that, by simply placing the probe wires against the surface of a sample and recalibrating the dielectric vs. moisture content response, the TDR method may be used to obtain moisture content without sample penetration. This expands the range of applicability of the TDR technique to such critical areas as hard rock drill cores and pavement measurements, as well as endurated soils. An example of such a noninvasive probe is shown to have the accuracy of previous probe designs (i.e., ± 2% m3 m−3 moisture content), without requiring penetration of the sample, with additional advantages including the ability to miniaturize the probe.