bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind Erosion Control with Crop Residues in the Sahel
Authors: Sterk G. , Spaan W. P.
Published: July 2010

Mulching for wind erosion control in Sahelian farming systems is limited by low biomass production and use of crop residues for other purposes. The aim of this study was to test the effectiveness in soil protection created by two low amounts of crop residues. A field experiment was conducted in southwest Niger, on a Psammentic Paleustalf (sandy, siliceous, isohyperthermic) during the early rainy seasons of 1994 and 1995. Particle mass transport was quantified in two plots of 55 by 70 m. During the first storms of both seasons, the plots were without a mulch cover. Afterward, one plot was covered with flat pearl millet [Pennisetum glaucum (L.) R. Br.] stalks. The application rates were 1500 and 1000 kg ha‐1 during the first and second seasons, respectively. To quantify the mulch effect, mass transport rate differences between the two bare plots were quantified with a multiple linear regression model (R2 = 0.89), using wind speed (7.4–12.3 m s‐1), wind direction, and storm duration (464–3835 s). Total mass transport rates were reduced from 365.2 to 132.9 g m‐1 s‐1 (63.6%) with 1500 kg ha‐1, and from 325.1 to 188.0 g m‐1 s‐1 (42.2%) with 1000 kg ha‐1 of crop residues. Soil protection tended to decrease with increasing wind speed. Linear regression indicated that the reduction in mass transport becomes zero at wind speeds of 11.1 and 16.0 m s‐1 for the 1000 and 1500 kg ha‐1 covers, respectively. The 1000 kg ha‐1 cover even enhanced sediment transport by 6.5% during one storm with a wind speed of 11.3 m s‐1. The 1500 kg ha‐1 mulch cover reduced sediment transport from 49.7 to 80.2% during five storms with wind speeds varying from 8.3 to 10.6 m s‐1, and is therefore recommended as the better application rate for wind erosion control in the Sahel.
A Single, Continuous Function for Slope Steepness Influence on Soil Loss
Authors: Nearing M. A.
Published: July 2010

Recently proposed relationships for the effect of slope steepness on soil loss by water are linear functions of the sine of the slope angle. The Revised Universal Soil Loss Equation (RUSLE) uses two such functions: one for slopes <9% and another for slopes >9%. Recent research indicates that yet a different linear function is necessary for slopes greater than approximately 22%. The objective of this study was to develop a single slope steepness function that is representative of the data for all slopes. The resultant equation takes the form of a logistic function. It closely follows the RUSLE relationships for the slope steepness factor for slopes up to 22%, and also fits existing data for slopes greater than those from which the RUSLE relationships were derived.
Seasonally Precipitated Iron Oxides in a Vertisol of Southeast Texas
Authors: Golden D. C. , Turner F. T. , Sittertz‐Bhatkar H. , Dixon J. B.
Published: July 2010

The composition and crystallinity of Fe oxides in soils determines the reactivity and toxicity of Fe through redox and solubility reactions. The mineralogy and crystallinity of Fe oxides seasonally precipitating on ped surfaces and within soil pores and those forming around rice (Oryza sativa L.) roots were investigated by x‐ray diffraction, electron microscopy, and electron microprobe analyses. Iron oxides precipitated on exposed surfaces of the League soil (fine, montmorillonitic, hyperthermic Oxyaquic Dystrudert), which is flooded during rice production, differed from Fe phases precipitated around rice roots. Iron oxides precipitated on ped surfaces and within soil pores were relatively poorly crystallized while those precipitated on rice‐root surfaces were well crystallized. The presence of soluble Si and P during flooding may be responsible for precipitation of the less crystalline Fe oxides. Infrared and electron‐diffraction data on the precipitate suggest the presence of PO4 groups either adsorbed or coprecipitated with Fe oxide. Depletion of Si and P from the rhizosphere is believed to contribute to the formation of well‐crystallized lepidocrocite on root surfaces. The poorly crystalline Fe‐oxide precipitate that forms on ped surfaces upon draining and oxidation of the League soil has adsorbed or occluded Si and P. Thus, Fe oxides may influence the mobility of Si and P in alternately flooded and drained soils. Electron‐diffraction data suggests that some of the Fe may be precipitated as strengite. Upon reduction and dissolution, these oxides release Fe, Si, and P into the soil solution and influence the nutrient dynamics in the rhizosphere of the rice plant.
Aggregation and Aggregate Size Effects on Extractable Iron and Aluminum in Two Hapludoxs
Authors: Lima Jose M. , Anderson Sharon J.
Published: July 2010

Oxisols contain stable aggregates, and sorption and desorption kinetics for aggregates typically are slower than for disaggregated samples. The objectives of this research were to determine whether aggregation inhibits Fe and Al extraction more in large than small aggregates, and to determine whether aggregate composition differs between large and small Oxisol aggregates. Water‐stable 1‐ to 2‐ and 0.125‐ to 0.25‐mm aggregates were separated from two Oxisols that have similar total Fe contents but different goethite/hematite and kaolinite/gibbsite ratios. To assess the effect of aggregation on extractable Fe and Al, subsamples were disaggregated by sonication. Disaggregated samples and intact aggregates were then reacted with oxalate and dithionite‐citrate‐bicarbonate (DCB). In the larger aggregates, oxalate and DCB extracted 10 to 20% less Fe and Al from intact aggregates than from disaggregated samples. In the smaller aggregates, aggregation only caused a 5 to 10% decrease. Aggregation generally inhibited Fe and Al extraction by DCB more in B than A horizons. There also were small compositional differences between large and small aggregates. In A horizon samples, large aggregates contained more clay and had correspondingly greater extractable Fe and Al than did small aggregates, although the extractable Fe and Al in the clays themselves did not differ between large and small aggregates. Goethite/hematite ratios were 10 to 20% greater in clay from large than small aggregates. Thus, the rate and extent of sorption‐desorption reactions may differ between large and small aggregates not only because of physical differences, but also because of slight compositional differences.
Tikhonov Regularization of Electrical Conductivity Depth Profiles in Field Soils
Authors: Borchers Brian , Uram Tom , Hendrickx Jan M. H.
Published: July 2010

Electromagneetic induction is an established, noninvasive technique for measuring the apparent electrical conductivity of soils and contaminants in soils and aquifers. Nevertheless, the noninvasive determination of electrical conductivity depth profiles using only aboveground electromagnetic induction measurements remains difficult since it involves ill‐posed inverse problems. Tikhonov regularization is an established technique for the solution of ill‐posed linear inverse problems. We used Tikhonov regularization for estimating the electrical conductivity depth profile of the soil from aboveground electromagnetic induction measurements. Results from the inversion of sets of Geonics EM‐38 measurements are reported. It was found that this technique is superior to other inverse techniques previously reported in the literature.
Spatial Variability of Water Fluxes in Soil: A Field Study
Authors: Heuvelman W. J. , McInnes K. J.
Published: July 2010

Knowledge of spatial variability of soil properties is important for soil sampling and modeling water and solute transport through soil. A field study was conducted on a Silawa‐variant loamy fine sand (fine, mixed, thermic Udic Paleustalf) in Brazos County, Texas, to evaluate spatial variability and convergence and divergence of water fluxes through the soil profile. A 7 by 14 grid of interception cells (each 25 by 25 mm) was built to collect surface‐applied water at 0.3‐, 0.9‐, and 1.2‐m depth. The interception cells were installed on the ceilings of tunnels that had been hand dug horizontally into the walls of a large backhoe‐dug pit. Water was applied under a positive head of ≈50 mm in a 1.2 by 1.2 m infiltration square. Normal and lognormal probability functions were fitted to frequency distributions of intercepted fluxes from topsoil and subsoil, respectively, with correlation coefficients of 0.95 and higher. Most nonmatrix flow was found at 0.9 m in the Bt2 horizon. We speculate that fluxes were most heterogeneous in this horizon because of associated soil texture and structure. Compared with soil at 0.3 and 1.2 m, texture was finer, peds were larger, and clay films were more abundant at 0.9 m. This relationship with pedologic development suggests that descriptions of texture and structure might be used to predict spatial distributions of fluxes and design sampling schemes. Convergence of water flowpaths was observed from 0.3 to 0.9 m while divergence occurred from 0.9 to 1.2 m.
Miniature Rain Simulator for Field Measurement of Soil Infiltration
Authors: Ogden C. B. , van Es H. M. , Schindelbeck R. R.
Published: July 2010

In studies of erosion, runoff, and infiltration, high soil variability may demand many replicate measurements and rapid, inexpensive methodology. We developed a drop‐forming rainfall simulator in which flow through long, coiled capillary drip tubes is controlled by an adjustable Mariotte‐type bubbling tube. These rain simulators are inexpensive, rugged, simple to operate, easily transported, and require minimal maintenance. Responses to pressure head and water temperature changes were determined for two simulators using tap water. Flow response to pressure head changes corresponded closely to that predicted by Poiseuille's Law. Response to increasing water temperatures was somewhat less than predicted, due to formation of bubbles in the capillary tubes. Simulators incorporating long, coiled capillary tubes can provide combinations of low flow rates and large drop sizes, or a desired range of flow rates when appropriate drip tube diameters, lengths, and numbers of tubes per unit area are combined.
Organic Matter, Sodicity, and Clay Type: Influence on Soil Aggregation
Authors: Barzegar A. Rahman , Nelson Paul N. , Oades J. Malcolm , Rengasamy Pichu
Published: July 2010

Organic matter influences aggregation in non‐sodic soils, but less is known about its role in sodic soils. The purpose of this study was to examine the role of organic matter in aggregation and clay dispersion in soils with different levels of sodicity. Prepared soils with 15% clay (smectitic or illitic) and natural soil aggregates (from a smectitic clay soil [Pellustert] with 25 g kg−1 organic C and a pair of illitic loams [Rhodoxeralfs] with 15 and 29 g kg−1 organic C) were equilibrated with solutions having sodium adsorption ratios (SAR) of 0, 5, 15, and 30. Pea (Pisum sativum L.) straw was added at 50 g kg−1 to the prepared soils, which were then incubated. Changes in aggregation during incubation were similar irrespective of clay type. After 7 d incubation with no added straw at SAR 0 and 30, the amounts of spontaneously dispersible clay were 5.9 and 23.7 g kg−1 soil, and mechanically dispersible clay was 11.9 and 23.3 g kg−1 soil. Macroaggregation (>250 µm) was 125 and 41 g kg−1 soil at SAR 0 and 30. After 67 d incubation with pea straw, spontaneously dispersible clay contents were 2.1 and 5.4 g kg−1, mechanically dispersible clay contents were 9.0 and 17.7 g kg−1 soil, and macroaggregation was 533 and 416 g kg−1 soil at SAR 0 and 30. The effects of sodicity and organic matter on structural stability of the natural soil aggregates were similar to those in the prepared soils, but macroaggregation was less, and the smectitie clay soil was more sensitive to sodicity than the illitic loams. This work showed that organic matter has at least as great a role in aggregation in sodic soils as in non‐sodic soils.
A Landscape‐Scale Study of Soil Quality in Three Prairie Farming Systems
Authors: Boehm M. M. , Anderson D. W.
Published: July 2010

The relationship between farming practices and the quality or function of agricultural soils is difficult to characterize because of the complexity of soils and spatial variability within the landscape. This study in Saskatchewan, Canada, tested the hypothesis that soil quality differed among farming systems that varied in fallow intensity (crop‐fallow [fallow every second year], extended rotation [fallow every 3–5 yr], and continuous cropping [no fallow]) and that differences could be assessed using soil properties as indicators of soil quality. In 20 fields with coarse to fine loamy, glaciolacustrine soils (Typic Haploborolls), major landform elements were sampled. As years of continuous cropping and related fertilizer inputs increased, increases in organic C (by weight [Cw] 22%, by volume [Cv] 3%), aggregate size (24%) and stability (45%), microbial biomass (50%), resin‐sorbed N (503%) and P (227%), and nitrification potential (≈25%), decreases in bulk density (8%) and infiltration time (19%), and greater solum thickness (26%) were measured. We postulate that the changes in soil properties indicate an improvement in soil quality under the continuous cropping system and that the observed changes were caused by more frequent additions of crop residues (organic C), especially near the soil surface, which resulted in lower bulk density, more microbial biomass, and greater soil aggregation. It seems that the annual inputs of crop residues in conjunction with nutrients, such as N and P, resulted in the formation of an active and labile soil organic matter, increased availability of soil N and P, and a comparatively large pool of microbial C.
Carbon to Organic Matter Ratios for Soils in Rocky Mountain Coniferous Forests
Authors: Jain Theresa B. , Graham Russell T. , Adams David L.
Published: July 2010

Vegetation type, soils, climate, and conversion ratios influence estimates of terrestrial C. Our objectives were to (i) determine carbon to organic matter (C/OM) ratios for brown cubical rotten wood, litter, surface humus, soil wood, and mineral soils; (ii) evaluate the validity of using 0.58 and 0.50 ratios for estimating C in mineral and organic soil components, respectively; and (iii) determine if C/OM relationships were applicable across broad geographic areas. The study sites were located from the southern to northern Rocky Mountains. They differed in vegetation, soil parent material, and climate. The C/OM regression slopes we developed for organic components were quite consistent and relatively constant across vegetation types ranging from 0.43 to 0.51 and were similar to the 0.50 traditional ratio. The C/OM regression slopes for mineral soils ranged from 0.16 to 0.48 depending on vegetation type. These slopes were lower than the 0.58 ratio often applied. The reliability of simple ratios when used in estimating C as a function of organic matter is often overestimated. Error and bias can be introduced into C estimates when using simple ratios. This study refined C/OM regressions for mineral soils and provided regressions for organic soil components. Information developed in this study can be applied to improve regional and global C assessments.
Spatial Variability of Nitrogen Mineralization at the Field Scale
Authors: Mahmoudjafari M. , Kluitenberg G. J. , Havlin J. L. , Schwab A. P. , Sisson J. B.
Published: July 2010

Spatial variability of N mineralization represents a potential problem in predicting the quantity of N mineralized under field conditions. An understanding of mineralization variability is needed if prediction of potential mineralization is to be incorporated into fertilizer recommendation models. The objective of this study was to characterize spatial variability of N mineralization in a Kansas agricultural field. Intact undisturbed soil cores were collected at 108 locations within a 1.7‐ha field following wheat (Triticum aestivum L.) harvest. The undisturbed cores were incubated aerobically, and NO−3 was leached periodically as a measure of mineralization. Variability was characterized by examining the spatially distributed values of mineralization potential, N0, and mineralization rate constant, k, parameters of the classical first‐order mineralization rate model. Values of N0 were distributed normally with low variability (coefficient of variation [CV] = 15%) and weak autocorrelation. Values of k also followed a normal distribution with low variability (CV = 14%) but were spatially independent. Both N0 and k determined the spatial pattern of Nm, the quantity of N mineralized at a particular time. Variability in k controlled the spatial pattern of Nm earlier in the incubation period, and variability in N0 controlled the spatial pattern late in the incubation period. The incubation approach used in this study allowed characterization of the spatial patterns in N0, but the spatial variability of k observed in this study may not adequately represent field conditions because conditions of constant temperature and water content were used.
Preferential Transport of Solute through Soil Columns Containing Constructed Macropores
Authors: Li Yimin , Ghodrati Masoud
Published: July 2010

Implication of macropore flow in enhancing solute transport has prompted much research. The objective of this study was to characterize solute transport in constructed macropores in three soils of different water conductivities. The macropores were constructed by inserting metal rods into uniformly packed soil columns of 0.2‐m i.d. and 0.3 m long. A set of nine soil columns was prepared and a total of 52 displacement experiments was conducted using NO3 as a tracer. Significant preferential flow occurred in the silt loam containing seven continuous macropores of 3‐mm diam. even at fluxes <0.5K, where K is saturated hydraulic conductivity of a column matrix. At fluxes far smaller than those causing saturation, no preferential flow took place and the breakthrough curves (BTCs) displayed single peaks, indicating that only the matrix contributed to solute transport. As fluxes increased, BTCs exhibited double peaks, and the relative magnitudes and positions of the two peaks were flux dependent. These two‐curve or double‐peak BTCs may represent solute transport through the macropores and the matrix, respectively. Due to the difficulty in keeping macropores open in silica sand, especially at fluxes ≥K, little evidence of preferential flow was observed in this system. This was also ascribed to the porous and conductive nature of the medium. Preferential flow also occurred in the loamy sand, but a greater flux was needed to get the same degree of preferential flow as in the silt loam. In general, in the coarser soil, less preferential flow occurred even at similar normalized flow rates. Macropore continuity has been shown to be increasingly important in macropore flow when flux increases.
A Generalized Solution to Infiltration from Single‐Ring Infiltrometers by Scaling
Authors: Wu L. , Pan L.
Published: July 2010

Water infiltration into soil from a ring infiltrometer is an important issue for many scientific and engineering problems. Due to the complexity of the three‐dimensional water flow, no generalized solutions are available to describe the infiltration process from a finite ponding source. This study applied a scaling technique to three‐dimensional axisymmetric infiltration from a single‐ring infiltrometer to obtain a generalized infiltration solution and evaluated the effects of soil conditions and ring geometry on the scaled infiltration curves. A numerical model based on Richards' equation in the cylindrical coordinates was developed to simulate infiltration processes for three representative soils. By properly choosing length‐ and time‐scale factors, the infiltration curves of the three test soils representing different hydraulic properties were successfully scaled to essentially a single dimensionless infiltration curve. Tests showed that the dimensionless infiltration curve was not very sensitive to applied ponding head, ring diameter, ring insertion depth, and initial soil conditions. Finally a dimensionless infiltration equation in the form of i* = a + blt*0.5 was developed. The example showed that the generalized infiltration equation can predict the infiltration curve simulated by Richards' equation very well.
Scale‐Dependent Correlations among Soil Properties in Two Tropical Lowland Rice Fields
Authors: Dobermann A. , Neue H. U. , Goovaerts P.
Published: July 2010

Long‐term irrigated rice (Oryza sativa L.) cultivation is an important yet unstudied source of soil variation in tropical lowland rice fields. A field study was conducted to quantify spatial soil variability and to analyze correlations among soil properties at different spatial scales. Soil samples from the 0‐ to 20‐cm depth were collected from adjacent rice fields consisting of Typic Tropaquepts and Typic Tropaqualfs. Structural variogram analysis and factorial kriging (FKA) were used to describe the coregionalization of 14 soil properties. Coregionalization was described by a model comprising (i) a nugget effect, (ii) a spherical model with a range of 12 m, and (iii) a Gaussian model with a range of 36 m. Correlations among soil properties varied depending on spatial scale. Short‐range soil variation was caused by irrigation and land leveling, but results were not consistent for both fields. Similar autovariograms and high correlations between depth to the Cg horizon and extractable K in the Gaussian structure (ρ2uv = −0.95 to −0.99) revealed a strong influence of weathering of volcanic tuff on long‐range trends in K. Electrical conductivity (EC), Na, and B were spatially trended and correlated with depth to the Cg horizon (ρ2uv = 0.59–0.97) in the Gaussian structure. Subsurface water flow through cracks above an impermeable layer and surface water flow along the gentle field slope were sources of long‐range variation in EC, Na, and B caused by irrigation. The FKA provides quantitative measures of complex spatial process results and offers new ways for generating hypotheses about the phenomenon itself.
Light Nonaqueous‐Phase Liquid Movement in a Variably Saturated Sand
Authors: Oostrom M. , Hofstee C. , Dane J. H.
Published: July 2010

Numerical simulations with the multifluid flow simulator STOMP are compared with quantitative results of a detailed lighter‐than‐water nonaqueous‐phase liquid (LNAPL) infiltration and redistribution experiment in a 1.67‐m‐long, 1‐m‐high, and 0.05‐m‐wide flow cell. The experiment was performed to test the ability of commonly used non‐hysteretic and hysteretic constitutive relations between relative permeability (k), fluid saturation (S), and capillary pressure head (h) to describe multifluid flow in two dimensions. The fluid and sand parameters necessary to apply the constitutive relations were obtained independently. The flow cell was filled with a homogeneous sand mixture under saturated conditions. After partial drainage of the sand, the LNAPL was slowly injected for 12 h from a small source area located at the surface. A dual‐energy gamma radiation system was used to determine LNAPL and water saturations at 255 locations during infiltration and redistribution. The results show a reasonable match between the experimental and numerical data, indicating that the constitutive relations used are adequate to describe relatively slow LNAPL infiltration and redistribution. The differences between the nonhysteretic and hysteretic simulations are small. This implies that hysteresis, a result of nonwetting fluid entrapment and pore geometry, was not important in this experiment.
Gypsum Solubility at Subzero Temperatures
Authors: Marion G. M. , Farren R. E.
Published: July 2010

Gypsum is an important mineral in many terrestrial and marine environments. Despite numerous studies that estimated the gypsum solubility product at temperatures ≥0°C, there are no estimates at temperatures <0°C. The objectives of this study were to estimate, for the temperature range from ‐25 to 25°C: (i) the gypsum solubility product and (ii) the Pitzer‐equation parameters needed to define Ca‐SO4 interactions to high solute concentrations (ionic strengths >10 M). The gypsum solubility product was extrapolated to subzero temperatures by integrating the vant's Hoff equation using a published equation for the standard enthalpy of reaction for gypsum. A least‐squares regression technique was developed to estimate eight temperature‐dependent Pitzer‐equation parameters that describe ion interactions among Ca, SO4, Na, and Cl. The calculated Pitzer‐equation parameters were in reasonable agreement with published values. Calculated gypsum activity products were independent of ionic strength to concentrations >17 M. The resulting Pitzer‐equation parameters coupled with gypsum solubility data fit the theoretical gypsum solubility product equation reasonably well. The calculated eutectic concentration and temperature for a pure gypsum solution are 0.01293 M and −0.06°C. Gypsum is a common mineral in many cold region soils. According to the current paradigm for seawater freezing, sulfate should exclusively precipitate as mirabilite; however, there is evidence that gypsum can also precipitate during seawater freezing. The parameters developed in this study will allow, for the first time, the theoretical exploration of mechanisms such as freezing on gypsum geochemistry.
Changes in Soil Microbial and Chemical Properties under Long‐term Crop Rotation and Fertilization
Authors: Omay A. B. , Rice C. W. , Maddux L. D. , Gordon W. B.
Published: July 2010

With renewed interest in maintaining our soil resources, it is important to establish criteria that can describe and quantify the effect of different crop management practices on soil organic matter (SOM). We conducted this study to assess changes in SOM and other soil properties after long‐term (>10 yr) continuous corn (Zea mays L.; CC) and corn‐soybean rotation [Glycine max (L.) Merr.; C/SB] with and without fertilizer. Soil samples were collected from two furrow‐irrigated CC and C/SB rotations on a Crete silt loam (fine, montmorillonitic, mesic Pachic Argiustoll) and a Eudora loam (coarse‐silty, mixed, mesic Fluventic Hapludoll). Long‐term (350‐d) laboratory incubation at optimum moisture and temperature conditions measured potentially mineralizable C (PMC) and N (PMN) as a measure of the active fraction of soil organic C and N. Microbial biomass C (MBC) and N (MBN), organic C and N, pH, and texture also were determined. Crop rotations that included high‐residue‐producing crops such as corn and addition of fertilizer increased soil organic C and N. Crop rotation did not affect PMC in the Crete soil, but addition of fertilizer significantly increased PMC by 32%. The PMN in both soils was not affected by crop rotation or fertilizer addition. Inclusion of soybean in the rotation decreased the stable and active fractions of organic C and N. Changes in soil organic C and N in response to crop rotation and fertilizer addition were related to the estimated amount of crop residues returned to the soil and to soil texture.
Mineralization of Selenium‐Containing Amino Acids in Two California Soils
Authors: Martens Dean A. , Suarez Donald L.
Published: July 2010

Organic forms of Se as the selenoamino acids, selenomethionine (SeMet) and selenocystine (SeCys), are detected in plants grown on seleniferous soil, yet little is known about the speciation and distribution of Se upon decomposition of SeMet and SeCys in soil. To determine the mineralization rate of selenoamino acids in soil, three concentrations of SeMet, SeCys, methionine (Met), or cystine (Cys) were added to samples of a Panoche (fine‐loamy, mixed [calcareous], thermic Typic Torriorthent) or a Panhill (fine‐silty, mixed, thermic Typic Haplargid) soil and aerobically incubated at 22°C for up to 168 h. The amino acid concentrations were analyzed by high performance anion chromatography. Methionine additions closely followed first‐order reaction kinetics and SeMet additions followed pseudo‐first‐order kinetics, with order dependent on SeMet concentration. The time required for 50% mineralization of SeMet additions in the Panhill and Panoche soils was 23.5 and 3.2 h (5 mg Se kg‐1), 41.6 and 15.5 h (25 mg Se kg‐1), and 47.1 and 36.0 h (50 mg Se kg‐1), respectively. The majority of the SeMet and Met additions were recovered as volatile species (50–80%). In contrast to SeMet, SeCys was rapidly nonextractable (<6 h) from both soils, with little to no volatile Se detected and was initially recovered as phosphate‐soluble selenite and selenide after 6 h of incubation. These results suggest that Se present in seleniferous plant tissue as SeMet will not accumulate in soil due to extensive volatilization. In contrast, additions of seleniferous plant residues rich in SeCys will result in organic Se mineralization to inorganic Se forms in soil.
Isotopic Study of Environmental Change from Disseminated Carbonate in Polygenetic Soils
Authors: Connin Sean L. , Chamberlain C. Page , Virginia Ross A.
Published: July 2010

We evaluated the extent to which δ13C and δ18O values of disseminated carbonate preserve a signal of Holocene and modern vegetation changes in polygenetic soils of the Jornada Basin, New Mexico. Factors and processes influencing carbonate chemistry were constrained in a relict grassland community and recent mesquite [Prosopis glandulosa var. torreyana (L. Benson) M. Johnston] dunes, using 14C dates and δ13C data of soil organic matter (SOM) as independent measures of site history. Total‐profile carbonate contents ranged from 39 to 451 kg m‐2 due to local patterns of soil water infiltration and erosion. In grassland soils, 14C ages and δ13C values of disseminated carbonate in A and B horizons were influenced by the presence of older detrital carbonate, reworked from surrounding surfaces. As a result, carbonate isotopes did not record mid‐Holocene climate and vegetation changes, which were inferred from δ13C values of coexisting SOM. Shrub expansion during the past century was recorded by changes in the δ13C values of disseminated carbonate and SOM from mesquite dunes. Carbon‐14 data and mass balance estimates indicated that at least 80% of the dune carbonate (in C horizons) has been isotopically altered by dissolution and recrystallization processes in <100 yr. The modern carbonate is apparently forming from soil waters composed of nearly equal amounts of summer and winter rainfall, as evidenced by carbonate δ18O values. Our analyses indicate that disseminated carbonate can provide a meaningful environmental signal in polygenetic soils, when pedogenic contributions to isotopic variability are constrained.
Surface Roughness Changes as Affected by Rainfall Erosivity, Tillage, and Canopy Cover
Authors: Eltz Flávio Luiz Foletto , Norton L. Darrell
Published: July 2010

Surface roughness and canopy cover are important factors in preventing soil erosion. There is limited information on how soil surface roughness changes as a function of natural rainfall erosivity and canopy cover by plants. We hypothesized that canopy cover, tillage systems, and cumulative rainfall erosivity (CRE) would have unique effects on roughness. We tested this hypothesis on a Miami silt loam soil (fine‐silty, mixed, mesic Typic Hapludalf) using a portable laser microtopographer. Tillage treatments of conventional (moldboard plowing + disking), chisel plowing, and chisel plowing + dragging a chain produced three initial roughness levels. Surface cover was none (fallow) or soybean [Glycine max (L.) Merr.]. Random roughness (RR), standard deviation (SD), tortuosity (T), and fractal roughness functions, expressed by the fractal index (D) and the crossover length (l), were calculated from microtopography data. Chisel tillage had the greatest initial values of surface roughness, followed by chisel + chain and conventional tillage, as measured by the l index. All indices but D generally decreased with CRE. The RR and SD indices decreased quadratically with CRE, with decreases of 38 and 36%, respectively, from initial values after 200 units of CRE, while the T and l indices decreased exponentially, with decreases of 40 and 60%, respectively, from initial values after 200 units of CRE. Soybean cover lowered soil surface roughness 7% less than fallow, as measured by the l index. The l index was 50, 71, and 205% more sensitive to changes in CRE than RR, SD, and T indices, respectively. The fractal roughness functions, with D and l indices calculated, were the best approaches to characterize surface roughness at small scales, such as existing plant rows, mainly due to l index sensitivity to changes in CRE.
Electromelioration of a Sodic Horizon from an Illinois Natraqualf
Authors: Ahmad Efkar , Jones R. Lewis , Hinesly Thomas D.
Published: July 2010

Sodium‐enriched subsoils of Natraqualfs seriously limit crop production by impeding drainage on 150 000 ha in south‐central Illinois. We hypothesized that electromelioration of typical Natraqualf subsoils soils is feasible. Columns of natric material (subsoil of Huey silt loam, a fine‐silty, mixed, mesic Typic Natraqualf) were fitted with electrodes at either end of the column. Leachate generated by maintaining water at the column's top was collected at the bottom or cathodic end. Treatments were untreated soil or gypsum mixed with the natric material at rates of 38.5 and 77 Mg ha‐1. An additional column to which no potential was applied was prepared for each treatment. Fifty‐five volts direct current was maintained across the column, and current densities ranged from 0.04 to 0.35 mA cm‐2. Sodium leached rapidly from all treatments to which a potential was applied, but leachate was produced only in the treatment without potential and with the equivalent of 77 Mg ha‐1 of gypsum. Extractable Na reductions amounted to 96% in the column without added gypsum and 98% in each of the gypsum‐treated columns. Water required to leach Na was reduced by gypsum treatment from 138 cm for unamended columns to 84 and 55 cm for the 38.5 and 77 Mg ha‐1 treatments, respectively. Substantial changes in soil structure were observed at the end of the experiment. The power calculated to remove 96% of the extractable Na in 58 cm of natric material during 31 d of leaching amounted to 736 560 kW‐h ha‐1.
Rapid Determination of Hydraulic Conductivity in Clay Liners by Early‐Time Analysis
Authors: Odell B. P. , Groenevelt P. H. , Elrick D. E.
Published: July 2010

To predict the effects of water or leachate infiltration into unsaturated field soils requires measurements of both the field‐saturated hydraulic conductivity (Kfs) and the matric flux potential (ϕm). Measurement of these soil parameters commonly requires steady‐state infiltration rates, which, in the slowly permeable clay liners that are found underlying municipal landfills, can require several weeks or months to be attained. The transient, capillary‐dominated, early‐time method of determining Kfs and ϕm has been found to provide a much faster, yet still reliable estimate of these flow parameters. Here, an analytical solution was utilized for early‐time, one‐dimensional infiltration under the conditions of an initial constant head followed by a falling‐head phase. Six laboratory trials were conducted using precisely compacted clay cores to determine Kfs and ϕm during both early‐time and steady‐state flow domains. The results of these trials showed a favorable comparison between these two techniques, with the early‐time constant‐head and falling‐head methods producing Kfs estimates that were 60 and 75% of their respective steady‐state values. This suggests that the early‐time determination of Kfs and ϕm on slowly permeable media has a definite practical advantage over lengthy steady‐state analyses. A new, expeditious procedure for determining steady‐state Kfs values of highly compacted soil cores, involving use of a Mariotte‐equipped pressure plate chamber, was also developed and validated.
Modeling Mass Transfer Processes in Soil Columns with Pore‐Scale Heterogeneity
Authors: Haggerty Roy , Gorelick Steven M.
Published: July 2010

Removal of dissolved organic compounds from natural porous media is rate limited by multiple, simultaneous mass transfer processes, including slow diffusion from immobile zones of varying sizes and shapes, and rate‐limited sorption. We examined the variability in mass transfer rates and quantified the effects of multiple, simultaneous mass transfer processes on unsaturated column experiments using a diffusion model with a statistical distribution of diffusion rate coefficients. We examined the validity of conventional first‐order mass transfer and diffusion models to represent mass transfer in subsurface systems and compared this with a diffusion model with a lognormal distribution of diffusion rate coefficients. The main conclusions of our work are: (i) even in relatively homogeneous porous media, extreme variability (exceeding four orders of magnitude) in diffusion rate coefficients (Da/a2) must be invoked to represent mass transfer in the experiments we examined; (ii) models using a lognormal distribution of diffusion rate coefficients, while employing only one more mass transfer parameter than conventional models, generally represent mass transfer much better; (iii) single‐rate‐coefficient models (either first‐order or diffusion) very poorly represent mass transfer in all experiments examined, although some of this failure is attributed to our use of a linear isotherm; (iv) models with two diffusion rate coefficients, although containing twice as many estimated parameters, also offer poor representations of mass transfer.
Time Domain Reflectometry Measurements of Nitrate Transport in Manure‐Amended Soil
Authors: Nissen H. H. , Moldrup P. , Henriksen K.
Published: July 2010

To obtain more detailed information about N processes in agricultural soils, nondestructive measurement techniques with high spatial and temporal resolution are needed. The ability of time domain reflectometry (TDR) in combination with small polysulfone hollow fiber (PHF) solution samplers to follow NO−3 production and transport in soil fertilized with cattle slurry and exposed to different rainfall events was investigated. The experiments were conducted in minilysimeters using a coarse sandy soil and two different slurry application methods: (i) surface application followed by harrowing (homogenous incorporation) or (ii) direct injection (incorporation as a manure string). Comparison between soil‐water electrical conductivity (ECw) obtained with TDR and the sum of NO−3 and Cl− concentrations in the soil water measured with solution samplers showed a good agreement both with respect to concentration levels and temporal and spatial development. Except for an initial leaching of the natural ion content in the soil water when water application was started, NO−3 released from the manure was the dominating anion in the soil water and changes in NO−3 corresponded well to changes in ECw. Both slurry and water application strategy had a large effect on the temporal development in nitrification and NO−3 leaching. In the case of homogeneously incorporated slurry and constant water application for 3 wk, NO−3 formation and leaching started after 4 to 5 d, while it started after 9 to 10 d in the case of directly injected slurry. If water was applied only in the last (third) week to the directly injected slurry system, a large amount of the NH+4 in the slurry was oxidized to NO−3 before water application and subsequently leached. The TDR measurements of ECw with high spatial and temporal resolution combined with a few measurements of ion concentrations by PHF solution samplers is a new, valuable method for analyzing turnover and transport of nonconservative ions in soil.
Soil Dissolved Organic Matter Sorption as Influenced by Organic and Sesquioxide Coatings and Sorbed Sulfate
Authors: Kaiser Klaus , Zech Wolfgang
Published: July 2010

The sorption of dissolved organic carbon (DOC) and its fractions as influenced by organic C (OC), sesquioxides [amorphous Al(OH)3, ferrihydrite, goethite], and extractable SO2−4 was investigated by modifying the properties of the Bs horizon of an Entic Haplorthod. Coating the Bs material with OC extracted from the Oa horizon of a mor forest floor layer decreased the sorption of total DOC. The effects on the sorption of the hydrophobic DOC fraction were little, whereas the sorption of the hydrophilic fraction was strongly reduced. At the highest OC coating levels, a net release of hydrophilic DOC occurred, indicating a displacement of indigenous hydrophilic substances from the soil by the sorbing hydrophobic dissolved organic matter (DOM). Coating of the soil material with sesquioxides clearly increased the sorption of DOC and its fractions. The strongest effects occurred when amorphous Al(OH)3 was added, followed by ferrihydrite and goethite. Increased contents of extractable SO2−4 did not affect the sorption of DOC on soil material. With increasing addition of DOC, however, the concentrations of SO2−4 in the equilibrium solution increased. Adsorbing DOM seems to displace SO2−4 bound to soil materials. Thus, DOM shows a higher affinity to sorb on soil material than SO2−4.
Sorption of Atrazine and Simazine by Model Associations of Soil Colloids
Authors: Celis R. , Cornejo J. , Hermosín M. C. , Koskinen W. C.
Published: July 2010

The effect of association processes between single model soil components (i.e., Ca‐saturated montmorillonite [CaSWy], ferrihydrite [Ferrih], and soil and commercial humic acid [HA]) upon their association in binary and ternary CaSWy‐Ferrih‐HA systems on physicochemical properties (specific surface area, pH, and basal spacing) and on triazine herbicide sorptive behavior was determined. Ferrihydrite coatings on CaSWy increased the specific surface area of the clay and slightly decreased pH, whereas HA coatings on CaSWy and Ferrih decreased both specific surface area and pH. Further association of HA with the CaSWy‐Ferrih binary system decreased the specific surface area, but did not change the pH. Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) and simazine (2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine) sorption‐desorption data showed that the sorptive behavior of the associations is not the simple sum of the sorption on single components. The HA association with CaSWy increased sorption of both herbicides by the clay, as suggested by an increase in sorption capacity (Koc) for the CaSWy‐HA binary system. Although Ferrih did not sorb either triazine, Ferrih coatings on CaSWy increased sorption of both herbicides on the clay. The association of HA with Ferrih sorbed both triazines, but Koc decreased compared with HA alone. Further association of the CaSWy‐Ferrih binary system with soil HA decreased the sorption, whereas association with commercial HA increased it. Desorption isotherms of atrazine and simazine showed that sorption by the model associations was reversible.
Subsoil Characteristics and Landscape Position Affect Productivity of Reconstructed Mine Soils
Authors: Merrill Stephen D. , Ries Ronald E. , Power James F.
Published: July 2010

The placement of soil materials on minespoils during reclamation affects soil profile and landscape aspects of soil productivity. We hypothesized that the productivity of soil reconstructed by topsoil‐subsoil placement on sodic minespoil would be influenced by subsoil characteristics. A 1.4‐ha double wedge was constructed in west‐central North Dakota (annual precipitation 440 mm) from three subsoil materials (1.2‐m thickness at peak) placed in strips over smoothed minespoils so that north‐ and south‐facing slopes were 5 and 1.5%, respectively. Material mostly from B horizons of dominantly Argiboroll soils was used for subsoil treatments: (A) 50% clay; (B) 29% clay; and (C) 13% clay. Subsoils were covered with 0.2 m of mostly A horizon topsoil. Forage yields of crested wheatgrass [CWG, Agropyron desertorum (Fisch.) Schult.] were highest on C subsoil plots 4 yr out of 5 observed, and Russian wildrye [RWR, Psathyrostchys juncea (Fisch.) Nevshi] were highest on C subsoil plots 3 yr out of 4 observed. In contrast, 2 yr of spring wheat (Triticum aestivum L.) seed yields (824 kg ha−1 avg.) were 20 to 50% larger on A subsoil plots than on C subsoil, with B yields intermediate. Forage grass yields on north sideslopes of C subsoil plots averaged 1370 and 1040 kg ha−1 for CWG and RWR, about 20 to 60% greater than yields on other positions and subsoils. The largest spring wheat yields, 1068 kg ha−1, occurred on north sideslope positions of A subsoil plots. Sandy loam subsoils can enhance forage grass yields in rolling lands, while spring wheat yields can be increased by subsoils with greater water‐holding capacity.
High‐Resolution Bulk Density Images, Using Calibrated X‐ray Radiography of Impregnated Soil Slices
Authors: Bresson L. M. , Moran C. J.
Published: July 2010

Bulk density of undisturbed soil samples can be measured using computed tomography (CT) techniques with a spatial resolution of about 1 mm. However, this technique may not be readily accessible. On the other hand, x‐ray radiographs have only been considered as qualitative images to describe morphological features. A calibration procedure was set up to generate two‐dimensional, high‐resolution bulk density images from x‐ray radiographs made with a conventional x‐ray diffraction apparatus. Test bricks were made to assess the accuracy of the method. Slices of impregnated soil samples were made using hardsetting seedbeds that had been gamma scanned at 5‐mm depth increments in a previous study. The calibration procedure involved three stages: (i) calibration of the image grey levels in terms of glass thickness using a staircase made from glass cover slips, (ii) measurement of ratio between the soil and resin mass attenuation coefficients and the glass mass attenuation coefficient, using compacted bricks of known thickness and bulk density, and (iii) image correction accounting for the heterogeneity of the irradiation field. The procedure was simple, rapid, and the equipment was easily accessible. The accuracy of the bulk density determination was good (mean relative error 0.015). The bulk density images showed a good spatial resolution, so that many structural details could be observed. The depth functions were consistent with both the global shrinkage and the gamma probe data previously obtained. The suggested method would be easily applied to the new fuzzy set approach of soil structure, which requires generation of bulk density images. Also, it would be an invaluable tool for studies requiring high‐resolution bulk density measurement, such as studies on soil surface crusts.
Cadmium and Cobalt Desorption Kinetics from Soil Clays: Effect of Sorption Period
Authors: McLaren Ronald G. , Backes Clare A. , Rate Andrew W. , Swift Roger S.
Published: July 2010

Soil solution metal concentrations and hence metal bioavailability are controlled by sorption‐desorption reactions at the surfaces of soil colloids. Compared with the numerous studies on sorption of metals by soils, there are relatively few that examine desorption, and even fewer that have measured desorption kinetics. The objective of this study was, using techniques and models developed previously for studies with synthetic oxides, to examine the effect of sorption period on the subsequent desorption kinetics of Cd and Co from two natural soil clay fractions. Cobalt was less readily desorbed from the clay fractions than Cd, but with both metals and clay fractions, increases in sorption period were accompanied by substantial decreases in the proportions of sorbed metal desorbed. As with the oxides studied previously, desorption kinetics for Cd and Co sorbed onto clay fractions were found to be described well by both a two‐site first‐order model and a model involving a lognormal distribution of first‐order rate constants. Reaction half‐lives derived from the models suggested a movement of Cd and Co to slower desorption reactions with increasing sorption period. However, some caution should be used in interpreting such parameters.