bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organic Matter Fractions from Organically and Conventionally Managed Soils: II. Characterization of Composition
Authors: Wander M. M. , Traina S. J. 
Published: July 2010

AbstractDiffuse reflectance Fourier transform infrared (DR‐FTIR) spectroscopy was used to investigate the effects of organic and conventional management practices on soil organic matter (SOM) chemistry. We characterized physically and chemically isolated SOM fractions collected from Rodale's Farming Systems Trial (FST) experiment and used ratios of reactive (O‐containing) and recalcitrant (C, H and/or N) functional group heights to characterize SOM fraction composition. Based on peak ratio comparisons, we determined that humic acid (HA) in the manure‐amended organic rotation was more reactive than HA isolated from crop‐residue‐amended soils. Reactive/recalcitrant (O/R) peak ratios indicated that fulvic acid (FA) and particulate organic matter or light fraction (LF) isolated in April were most reactive in the organic cash‐grain‐based rotation. By June LF reactivity had changed; O/R ratios of LF and litter (LT) fractions isolated from the conventional and organic cash‐grain soils were greater than the manure‐amended soil's ratios. We did not draw any conclusions about management impacts on SOM composition from spectra of fine‐clay‐(FC) and sand‐ (S) sized fractions. Using DR‐FTIR we were able rank SOM fraction reactivity; average O/R ratios were FA > LT > HA > LF > FC. No consistent link between SOM fraction O/R ratios and reported C/N ratios or biological availability was made. Humic acid O/R ratios were most consistent with other estimates of overall SOM biological activity. More research is needed to clarify the relationship between the composition of specific SOM fractions and their functional significance in mineral soils.
Soil Organic Carbon Pools of Two Tropical Soils Inferred by Carbon Signatures
Authors: Hsieh Yuch‐Ping 
Published: July 2010

AbstractLabile and stable soil organic carbon (SOC) pools of two tropical soils of Belize, Central America, as influenced by land use management, were investigated using a combination of 14C and 13C techniques. The sizes and mean residence times (MRT) of the labile pools were found to be in the range of 1.5 to 59.8 g/kg and 5 to 8 yr, respectively, and those of the stable SOC pools, 25.1 to 65.2 g/kg and 250 to 388 yr, respectively. Both the labile and stable SOC pools have significantly shorter MRT than those of the temperate soils. The labile SOC pools of sugarcane (Saccharum officinarum L.) in continuous management averaged 12.9 and 19.8 g/kg, respectively, for Xaibe (Lithic Ustropept) and Louisville (Typic Pellustert) soils. Continuous sugarcane management reduced the labile pool to about one‐third the size of the corresponding secondary forests. The labile SOC pools is sensitive to changes in management practices and its size represents the intrinsic sustainable soil productivity. A radiocarbon single‐plot approach to study the dynamics of SOC pools was developed using the 14C and 13C signatures of the soil and those of the CO2 evolved. The results of the single‐plot method and that of the paired‐plot method agree well within the range of the experimental errors.
Isotope Discrimination during Decomposition of Organic Matter: A Theoretical Analysis
Authors: Ågren Göran I. , Bosatta Ernesto , Balesdent Jérôme 
Published: July 2010

AbstractStable isotope composition is a powerful characteristic of the development of soil organic matter, but there is a need to understand the causes of and to predict the changes in isotopic composition during organic matter decomposition. We used the continuous quality theory to derive a set of equations to analyze how properties of the litter interact with properties of the decomposers to produce different patterns of isotopic composition. The distribution of isotopes between different chemical fractions in the litter is in itself such that it should lead to increasing depletion of 13C during the course of decomposition. Isotope effects on decomposer growth rate, efficiency, and dispersion in quality increase, on the other hand, 13C concentration. The magnitudes of these effects have to be, in relative terms, considerably greater than that of initial litter chemical composition. The equations derived were also successfully tested on experimentally observed patterns of changes in C isotopic composition in an agricultural soil and some forest soils.
Determination of Microbial Biomass and Nitrogen Mineralization following Rewetting of Dried Soil
Authors: Franzluebbers A. J. , Haney R. L. , Hons F. M. , Zuberer D. A. 
Published: July 2010

AbstractRoutine soil testing procedures that are rapid and precise are needed to evaluate agricultural surface soils for their potential to mineralize C and N. Our objectives were to determine the optimum preincubation time after rewetting of dried soil for estimating soil microbial biomass (SMB) and to identify a quick, reliable biochemical predictor of soil N mineralization potential. Biochemical determinations of SMB were screened on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) having five levels of soil organic C (SOC) as a result of long‐term management. Determinations used (i) field‐moist soil and (ii) soil that was air dried, rewetted, and preincubated for 0.2, 1, 3, 6, 10, and 15 d. Biochemical determinations included arginine ammonification, substrate‐induced respiration (SIR), cumulative C and net N mineralization, and SMBC using the chloroform fumigation‐incubation (CFI) method. Preincubation periods of 1 and 15 d prior to fumigation gave estimates of SMBC using CFI most similar to those determined on field‐moist soil. Arginine ammonification and SIR determinations on dried soil were highly variable, making longer preincubation periods necessary. Carbon mineralization during all preincubation periods was highly correlated to (i) SMBC using CFI determined on field‐moist and dried soil with all preincubation periods and (ii) net N mineralization during 21 d for the Weswood soil, as well as for seven additional soil series each having five to eight levels of SOC. The CO2‐C evolved during the first day after rewetting of dried soil is recommended for rapid estimation of SMBC and potential N mineralization because of its simplicity and precision.
Pore Size Distribution and Hydraulic Conductivity Affected by Tillage in Northwestern Canada
Authors: Azooz R. H. , Arshad M. A. , Franzluebbers A. J. 
Published: July 2010

AbstractTillage management can affect crop growth, in part by altering the pore structure and hydraulic properties of soil. We hypothesized that water retention, pore size distribution, and unsaturated hydraulic conductivity (k) differed under conventional tillage (CT) and no tillage (NT). We evaluated this hypothesis on a Donnelly silt loam (fine‐loamy, mixed, frigid Typic Cryoboralf) and a Donnelly sandy loam (coarseloamy, mixed, frigid Typic Cryoboralf) in northwestern Canada. Soil cores were collected from the 0‐ to 300‐mm depth in 75‐mm increments. Water retention was measured at 10 pressure levels from ‐2 to −400 kPa to calculate pore size distribution and k. Both soils retained 0.04 to 0.09 m3 m−3 more water under NT than under CT. The volume fraction of total porosity with pores <7.5 µm in diameter (effective pores for retaining plant‐available water) in the silt loam averaged 0.49 and 0.58 m3 m−3 under CT and NT, respectively, and in the sandy loam averaged 0.39 and 0.51 m3 m−3 under CT and NT, respectively. In contrast, the volume fraction of total porosity with pores >150 µm in diameter (pores draining freely with gravity) in the silt loam averaged 0.29 and 0.23 m3 m−3 under CT and NT, respectively, and in the sandy loam averaged 0.35 and 0.24 m3 m−3 under CT and NT, respectively. Conventional tillage appeared more likely to interrupt capillaries than NT, since large differences in k between tillage regimes were observed below a depth of 75 mm with increasing moisture deficit. Continuous NT management increased water storage of both silt loam and sandy loam soils in this cold, semiarid region.
Organic Carbon Characteristics in a Spruce Swamp Five Years after Harvesting
Authors: McLaughlin James W. , Liu Guo , Jurgensen Martin F. , Gale Margaret R. 
Published: July 2010

AbstractForest harvesting and regeneration may cause changes in soil and solution chemistry that adversely affect environmental quality. Organic C content in the forest floor and mineral soil, and dissolved organic carbon (DOC) fractions in the soil solution and groundwater were investigated in a black spruce [Picea mariana (Miller) BSP] swamp 5 yr after the application of two silvicultural prescriptions: whole‐tree harvest only and whole‐tree harvest followed by site preparation bedding. Soil organic carbon (SOC) content in the forest floor of both treatments were significantly lower than that of an uncut control stand. However, SOC in the upper 50 cm of mineral soil of the bedded treatment was similar to that of the control, while both were about 20% higher than SOC in the harvest‐only treatment. Total DOC concentrations ranged from 12 to 87 mg/L in the soil solution and 6 to 46 mg/L in the groundwater and did not differ among treatments. Hydrophobic acids were the dominant DOC fraction across all treatments, but the proportion of hydrophobic strong acids increased at the expense of hydrophilic acids in the harvest‐only treatment. Carboxyl content of hydrophilic acids in the soil water was 7.0 mmol/g hydrophilic compound in the control stand and 4.4 mmol/g in the treatments. Hydrophobic acid carboxyl content across treatments was 4.6 mmol/g hydrophobic substance. Relative to C loss and changes in water chemistry, these results indicate that 5 yr after whole‐tree harvesting, this forest site has not yet fully equilibrated.
Characterization of Miller‐Similar Silica Sands for Laboratory Hydrologic Studies
Authors: Schroth M. H. , Istok J. D. , Ahearn S. J. , Selker J. S. 
Published: July 2010

AbstractThe use of well‐characterized porous media can simplify and improve the efficiency of laboratory subsurface flow and transport experiments. The objective of this study was to present a comprehensive set of hydrologically relevant properties for a unique set of commercially available silica sands. Features of sands selected for characterization included high sphericity, high batch‐to‐batch consistency, Miller‐similarity, and availability in large quantities. Samples of four different sand grades (12/20, 20/30, 30/40, and 40/50 sieve sizes) were characterized for physical properties, chemical composition, water retention, three‐phase air‐non‐aqueous‐phase liquid (NAPL)‐water saturation‐pressure relationships for water and a model NAPL, Soltrol 220, and saturated and unsaturated hydraulic conductivity. Properties common to all sand grades included high chemical purity and low organic matter content. Water retention curves featured well‐defined air entry pressures and the Miller‐similarity of the media was demonstrated for both static and dynamic properties. During water retention measurements, we determined that the common assumption of a uniform vertical water content distribution in retention cells can result in significant errors in uniform porous media. A numerical correction procedure was developed and successfully applied to correct fitted water retention curve parameters, illustrating that potential errors of up to 70% in volumetric water content are made without proper analysis. The characterization data for the four sand grades presented here should facilitate their use in a wide range of laboratory flow and transport studies.
Spatial Structure of Solute Transport Variability in an Unsaturated Field Soil
Authors: Ellsworth T. R. , Boast C. W. 
Published: July 2010

AbstractThree solutes were applied in series under steady, unsaturated flow to determine the spatial scale dependence of transport. Twenty‐seven days after solute application, a 2 by 2 by 2 m3 field plot was excavated using two measurement scales, 22.2 by 22.2 by 10 cm3 (scale L) and 7.4 by 7.4 by 10 cm3 (scale l), providing two sets of 81 samples for each 0.1‐m layer to a depth of 2.0 m. For each chemical and for each scale, vertical moment analysis was performed on the data for each of the 81 vertical columns. Evidence of enhanced local horizontal mixing with increasing mean travel time was observed in two ways: (i) a decrease in mass recovery variance at scale L for NO−3 (center of mass at 80‐cm depth) vs. Br− (46‐cm depth of center of mass), and (ii) a horizontal correlation range in solute concentrations in individual 0.1‐m‐thick layers, which was lowest between 70 and 130 cm deep. Point variograms of the vertical moments for each solute were estimated by simultaneous deconvolution of the two observed (at scales l and L) area‐averaged variograms. Dispersion variance analysis (based on these point variograms) characterized the variability within the plot of mass recovery and center of mass depth as a function of sample size. Several approaches for characterizing plot‐ or field‐scale transport features from soil‐core scale measurements were evaluated. The horizontal dependence of the vertical variance increased with mean travel time. For each tracer, this dependence was reasonably characterized as the sum of the dispersion variance in the center of mass and the average L‐scale vertical variance.
Uranium(VI) Adsorption on Goethite and Soil in Carbonate Solutions
Authors: Duff M. C. , Amrhein C. 
Published: July 2010

AbstractElevated concentrations of U are found in agricultural drainage waters from the San Joaquin Valley, CA, which are often disposed of in evaporation basins that are frequented by waterfowl. To determine the factors that affect aqueous U concentrations in the basins, sorption experiments with U(VI) were performed at various CO2 partial pressures, dissolved Ca, Mg, and P concentrations, and carbonate alkalinities. Synthetic waters, comparable in inorganic constituents to irrigation and drainage waters, were prepared, spiked with 0.1 (soil) and 2 mg U(VI) L−1 (synthetic goethite), and analyzed for U, P (when applicable), and major ions. Total chemical analyses were input into the computer program FITEQL to determine U(VI) speciation and generate U(VI) adsorption constants with the diffuse layer model (also referred to as the two‐layer model). Maximum adsorption occurred in solutions with low carbonate alkalinities (≤3 mmol L−1), ionic strengths (≤0.03 M), Ca concentrations (≤4 mmol L−1), and P concentrations (<0.005 mmol L−1 for soil). Lesser and negligible adsorption was attributed to the predicted formation of highly soluble, negatively charged U(VI) carbonates [UO2(CO3)2−2 and UO2(CO3)4−3] that did not strongly adsorb to soil surfaces. Calcium and, to some degree, Mg competition with positively charged U(VI) species for surface sites was observed at low carbonate alkalinities (<3 mmol L−1 for goethite; <14 mmol L−1 for soil). At high carbonate alkalinities, carbonates competed with anionic U(VI) species for adsorption sites. Study results suggest that elevated U concentrations in the drainage waters are due to the speciation of dissolved U(VI) into negatively charged carbonate complexes.
Nitrification of Ammonium Nitrogen in Soils Treated with XDE‐474
Authors: Kpomblekou‐A K. , Killorn Randy 
Published: July 2010

AbstractRetardation of NH+4 nitrification constitutes one means to conserve fertilizers applied to soils. A new nitrification inhibitor, XDE‐474, has been developed by DowElanco Chemical Company (Indianapolis, IN) and needs to be evaluated. Laboratory studies evaluated the effect of nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] and XDE‐474 on nitrification rates in five Iowa soils varying markedly in organic C (OC), pH, and texture. A 10‐g sample of surface soil treated with 1 mL of solution containing 2 mg N as either NH4OH or (NH4)2SO4 and 4 µg a.i. g−1 soil of nitrapyrin or XDE‐474 was incubated at 20 ± 1°C for 0, 7, 15, 30, 45, and 60 d. First‐order equations were used to calculate the maximum nitrification rate (Kmax), duration of lag period (t′), period of maximum nitrification (Δt), and duration of lag plus maximum nitrification period (ts). Nitrification rates were significantly affected by N sources and inhibitors used. In the Okoboji soil (43.0 g kg−1 OC), nitrification of NH4OH was 19.5 mg kg−1 d−1 NO−3‐N in the control soil but reduced to 15.2 or 4.43 mg kg−1 d−1 NO−3‐N when nitrapyrin or XDE‐474 were added, respectively. Extension of the lag period due to the inhibitors varied from 0.73 d in the Okoboji soil to 18.8 d in the Storden soil (11.0 g kg−1 OC). Multiple regression equations expressing the dependence of Kmax on OC, pH, and clay showed that only OC and pH were significant in accounting for the variation in Kmax. The resulting three‐dimensional response surface indicated that XDE‐474 was less affected than nitrapyrin by changes in OC and pH.
Small‐Scale Heterogeneity of Aluminum and Heavy Metals in Aggregates along a Climatic Transect
Authors: Wilcke Wolfgang , Amelung Wulf 
Published: July 2010

AbstractConcentrations and forms of AI and heavy metals in aggregate core and surface fractions of forest soils in Central Europe differ significantly. The objectives of this study were to (i) test if there is a similar small‐scale metal heterogeneity in topsoils of the native North American prairie and (ii) investigate the influence of climatic parameters on this heterogeneity. Aggregates of eight A horizons along a climatic transect in the North American prairie were separated into core and 0.5‐mm‐thick surface fractions. Seven forms of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined in the aggregate fractions using a sequential extraction procedure. The differences of metal concentrations between aggregate surface and core fractions are 1 to 25% of the total concentrations of the core fractions. The percentages of easily extractable metals are up to 120% higher in the aggregate surface than in the core fractions. The percentages of the mainly silicate‐bound metals (extractable only with strong acids) are up to 25% lower than in the core fractions. These results support the hypotheses that (i) preferential weathering of aggregate surfaces causes a shift from strongly to more weakly bound metal forms and (ii) atmospheric metal input is sorbed preferentially at the aggregate surfaces, and (iii) this input is weakly bound only. Lead is significantly enriched in the surface fractions compared with the cores, indicating ubiquitous input of Pb to the soils. The depletion of the mainly silicate‐bound metals in the aggregate surface fractions compared with the core fractions correlates with the mean annual temperature and the mean annual precipitation, which both favor silicate weathering.
Phosphorus Retention as Related to Morphology of Sandy Coastal Plain Soil Materials
Authors: Harris W. G. , Rhue R. D. , Kidder G. , Brown R. B. , Littell R. 
Published: July 2010

AbstractPhosphorus retention in sandy coastal plain soils can be low enough that surface water quality is jeopardized by agricultural P loadings. Objectives of this study were to: (i) determine if discrete morphological characteristics could effectively differentiate sandy soils with respect to P retention and (ii) test the efficacy of a rapid chemical assessment of relative P adsorption (single‐point isotherm) for sandy materials. Soil samples from 96 surface and subsurface horizons of randomly selected Alaquod, Quartzipsamment, and Paleudult pedons were used. These pedons had previously been described, sampled, and characterized as part of the Florida Cooperative Soil Survey Program. Two groups of uncoated Quartzipsamments (<5% silt plus clay) were distinguished: those having “clean” (coating‐free) and “slightly coated” grains. Eluvial horizons from Alaquods were also designated as clean because of a dominance of coating‐free sand grains. Single‐point P adsorption isotherms were obtained for all samples, and multipoint adsorption and desorption isotherms for 21 of the 96 samples. Single‐point isotherms effectively arrayed sandy material with respect to relative P adsorption. Sand‐grain coatings significantly enhanced P adsorption and resistance to desorption. All clean samples readily desorbed P regardless of origin or amount adsorbed. Thus clean sands pose a greater hazard for P leaching than sands with grain coatings. Clay content was closely related to P adsorption, but silt content was not. The P‐retention distinction between clean and other Quartzipsamments is more marked than the “uncoated vs. coated” USDA family criterion, the latter being confounded by the inclusion of silt content.
Water and Solute Movement under Conventional Corn in Central Spain: I. Water Balance
Authors: Román R. , Caballero R. , Bustos A. , Díez J. A. , Caballero A. , Cartagena M. C. , Vallejo A. 
Published: July 2010

AbstractPartitioning temporal changes in soil water storage to water balance components (evapotranspiration [ET], drainage) under field conditions remains a vexing task. An in situ protocol using neutron probes and tensiometers was established on a sandy loam (Typic Xerofluvent) under irrigated, conventional corn (Zea mays L.) with the objectives to separate ET from deep drainage and to improve the accuracy of estimating the water balance components. An experimental research site (0.4 ha) at La Poveda Field Station near Madrid (Spain) was divided into 24 plots of 9 by 11.1 m each. The heterogeneity of the research site had been previously determined and the experimental field was instrumented accordingly. Vacuum soil‐water extractors were placed in all plots, but neutron probe and tensiometers were installed in only eight plots based on soil texture. Plot management included nine furrow irrigations of 404 mm and rainfall of 250 mm throughout the growing season. Measurements of water flow and soil water storage for periods of a few days allowed the determination of ET and drainage with the soil water balance equation. Four water flow patterns and six water balance cases were identified. Results showed a cumulative ET of 532 ± 70 mm and total drainage of 75 ± 22 mm below the 1.4‐m soil depth. Peak drainage took place 20 d before maximum ET and represented 19% of total irrigation water.
Corn Residue Age and Placement Effects on Evaporation and Soil Thermal Regime
Authors: Sauer Thomas J. , Hatfield Jerry L. , Prueger John H. 
Published: July 2010

AbstractDifferentiation between tillage‐ and residue‐induced effects on soil moisture and thermal regimes is necessary to improve residue management practices. The objective of this research was to quantify the influence of corn (Zea mays L.) residue age and placement on evaporation from and heat flow in two soils. Soil temperature, thermal conductivity, heat flux, and moisture content were monitored in duplicate monoliths (0.45 [length] by 0.35 [width] by 0.5 [height] m) of Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and Monona silt loam (fine‐loamy, mixed, mesic Typic Hapludoll) in a controlled environment chamber. Mass changes of one monolith of each soil were measured with load cells to estimate evaporation. Surface cover types consisted of a bare soil surface (B), fresh residue (F), weathered residue (W), and weathered residue with a 0.15‐m‐wide bare strip (S). Bare‐soil evaporation averaged 9.97 ± 0.66 mm for both soils during a 96‐h period and was reduced to an average of 5.76 ± 0.70 mm with residue cover. Nicollet soil with weathered residue had an average evaporation rate of 1.33 to 1.4 mm d−1. By comparison, evaporation rates measured in a field having Nicollet and associated soils with weathered corn residue averaged 1.37 and 1.11 mm d−1. Residue cover had no significant effect on thermal conductivity measured at 0.15 m that averaged 1.22 and 1.35 W m−1 K−1 for the Nicollet and Monona soils, respectively. Phase shift in soil temperature and average daily conductive soil heat flux were similar for field and chamber measurements but the amplitude of the soil temperature wave and conductive soil heat flux were much greater in the field.