bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrite Transformations during Soil Extraction with Potassium Chloride
Authors: Stevens R. J. , Laughlin R. J. 
Published: July 2010

AbstractNitrite is a key intermediate in both NH+4 oxidation and NO−3 reduction. There is increasing concern over its origin and significance in food and water. Measuring NO−2 concentrations in soils requires extraction procedures, KCl (2 M) being the most commonly used extractant. We investigated the effect of soil/extractant ratio, extraction procedure, shaking time, and pH on the transformations of 15NO−2 from a range of grassland soils. We measured the recovery of NO−2 and 15N as 15NO−2 or 15NO−3. Nitrite destruction and pool dilution occurred at 1:10 and 1:1 soil/extractant ratios. Using a 1:1 soil/extractant ratio, average 15NO−2 recovery for six soils was 86% with a blending procedure (10 min), and 32% with a shaking procedure (70 min). About two‐thirds of the 15NO−2 lost during extraction appeared as 15NO−3. When the pH of the soil suspension was adjusted with KOH to 7.8, recovery of NO−2 was not significantly less than 100% for reaction times up to 40 min. Pool dilution and decomposition of NO−2 appeared to be due to chemical rather than microbial reactions. When 20 soils were tested using the blending procedure and extractant pH of 8.0, 14 gave recoveries >97% and an additional six gave recoveries >90%. One of the mineral soils giving >97% recovery was extracted at two pH values, and NO−2 stability measured in filtered extracts during 28 d of storage at 4°C. Nitrite was more stable in extracts at pH 5.6 than 8.0. To ensure at least 95% recovery of 15NO−2, extracts at pH 8.0 had to be filtered through a 0.7‐µm filter and analyzed within 2 d of extraction.
Influence of pH on Phosphorus Retention in Oxidized Lake Sediments
Authors: Olila O. G. , Reddy K. R. 
Published: July 2010

AbstractDiel pH changes in lake waters resulting from high photosynthetic activity may regulate water‐soluble P concentration (WSP) and P sorption by suspended sediments in shallow eutrophic lakes. Laboratory studies were conducted to determine the pH effect on P fractions and P sorption kinetics in oxidized sediment suspensions from two subtropical lakes (Lake Apopka and Lake Okeechobee, Florida). The P sorption rate was calculated for sediment suspensions adjusted to various pH levels: 6.5, 7.0, 8.5, 9.5, and 10.5 for Lake Apopka and 6.5, 7.0, 8.5, 9.5, and 10.5 for Lake Okeechobee. A decrease in pH increased the WSP concentrations in Lake Apopka sediment suspensions but had no effect on WSP concentrations in Lake Okeechobee sediment suspensions. Lake Apopka sediment suspensions at pH 7.0 (ambient) and below did not show net P uptake. Phosphorus uptake for Lake Apopka occurred only when pH was increased to ≥8.5 and when P treatments were increased to ≥27 mmol P kg−1, which resulted in supersaturation with respect to octacalcium phosphate. Phosphate solubility diagrams and mineral equilibria calculations suggest that P uptake by Lake Apopka sediment suspensions at pH ≥8.5 was due to P coprecipitation with CaCO3 and probable formation of nonapatitic Ca‐P compounds. Phosphorus sorption on Lake Okeechobee sediment suspensions followed first‐order kinetics for all pH levels studied, with rate constants (k) ranging from 0.003 to 0.75 h−1. High P uptake by Lake Okeechobee sediment suspensions could be attributed to two reactive components: (i) amorphous or poorly crystalline Fe and Al oxyhydroxides at pH <7.5, and (ii) Ca/Mg carbonates and other minerals at pH ≥7.5.
Precision of Neutron Scattering and Capacitance Type Soil Water Content Gauges from Field Calibration
Authors: Evett S. R. , Steiner J. L. 
Published: July 2010

AbstractSoil water content gauges based on neutron scattering (NS) have been a valuable tool for soil water investigations for some 40 yr. However, licensing, training, and safety regulations pertaining to the radioactive source in these gauges makes their use expensive and prevents use in some situations such as unattended monitoring. A capacitance probe (CP) gauge has characteristics that would seem to make it an ideal replacement for NS gauges. We determined the relative precision of two brands of NS gauges (three gauges of each) and a brand of CP gauge (four gauges) in a field calibration exercise. Both brands of NS gauges were calibrated vs. volumetric soil water content with coefficients of determination (r2) ranging from 0.97 to 0.99 and root mean squared errors (RMSE) <0.012 m3 m−3 water content. Calibrations for the CP gauges resulted in r2 ranging from 0.68 to 0.71 and RMSE of 0.036 m3 m−3 water content. Average 95% confidence intervals on predictions were three to five times higher for the CP gauges than for the NS gauges, ranging from 0.153 to 0.161 and 0.032 to 0.052 m3 m−3, respectively. Although poorly correlated with soil water content, readings were reproducible among the four CP gauges. The poor correlation for CP gauges may be due to small‐scale soil water content variations within the measurement volume of the gauge. The NS gauges provide acceptable precision but the CP gauge has poor precision and is unacceptable for routine soil water content measurements.
Phosphorus Sorption at Field Capacity and Soil Ionic Strength: Kinetics and Transformation
Authors: Agbenin J. O. , Tiessen H. 
Published: July 2010

AbstractAn array of kinetic equations has been used to describe time‐dependent sorption of P by soils. In these studies, soil/solution ratios and ionic strengths of the equilibrating solutions did not mimic real field conditions. We investigated the time‐dependent P sorption and transformation of five benchmark soils from the semiarid part of northeast Brazil with the aid of rival kinetic models and sequential extraction. Our objectives were to ascertain whether commonly employed kinetic models can describe slow P sorption at field moisture capacity and soil ionic strength, and to determine the changes in labile and nonlabile P with time. The time‐dependent P sorption was described by the rival kinetic models in the order: Elovich equation = fractional power function > apparent first order > parabolic diffusion, all of which are indicative of diffusion kinetics with a slow chemical reaction, involving possible ligand exchange between H2PO−4 or HPO2−4 and OH−. Sequential P extraction by the modified Hedley procedure indicated that 60 to 90% of sorbed P was in the labile form. Anion‐exchange resin extractable P (AER‐P) correlated negatively with dithionite‐citrate‐extractable AL (ALd). An improved correlation between AER‐P and Ald with the time (r = −0.53 [P = 0.05] at 10 d, r = −0.55 [P = 0.01] at 100 d, and r = −0.60 [P = 0.01] at 200 d) is consistent with diffusion kinetics. Most likely, the slow P sorption involved surface‐adsorbed P diffusing to vacant sites in the micropores of Al oxides or Al‐substituted Fe oxides. Such internal sites may not be directly accessible to soil solution P.
Heavy Metal Release from a Serpentine Soil Using a pH‐Stat Technique
Authors: Kaupenjohann Martin , Wilcke Wolfgang 
Published: July 2010

AbstractSerpentine soils show high contents of Cr and Ni. Acidification may convert the metals bound in silicate structures into bioavailable forms. The effects of mineral acids on a serpentine‐derived Typic Hapludoll were examined in column studies. Cadmium and Pb were also examined. One end of the soil‐packed column was placed in 1 mM HCl solution and constant pH was maintained by pumping the acid through a H‐saturated cation‐exchange resin. The experiment was conducted for 100 d, after which the soil column was vertically sectioned. Chemical and mineralogical analyses showed steep vertical gradients in the sectioned columns. Base saturation decreased by about 60% at the contact of the column with the acid; exchangeable Fe, Cr, Pb, and Al increased while Ni decreased. Cadmium exhibited a differential behavior in that it increased in concentration in the middle of the column. Extracts using ethylenediaminetetraacetic acid (EDTA) gave similar results. X‐ray diffraction indicated chlorite dissolution by acid loading. The resin‐based pH‐stat technique is a useful method in simulating soil weathering.
CERES‐N Model Predictions of Nitrogen Mineralized from Cover Crop Residues
Authors: Quemada M. , Cabrera M. L. 
Published: July 2010

AbstractWinter annual cover crops, widely used in no‐till systems, can be an important source of N for the subsequent crop. Because many factors affect net N mineralization from cover crop residues, computer models can be powerful tools to predict it. The CERES models, which are some of the most widespread models for simulating the whole crop‐soil system, have a common submodel (CERES‐N) that describes N transformations. The objectives of this study were to determine decay rate constants under nonlimiting conditions for the carbohydrates and cellulose pools (CARB and CELL) of CERES‐N for residues that decompose on the soil surface, and to test if two modifications to CERES‐N could improve the simulation of N mineralization. The two modifications were to: (i) allow the user to vary the relative size of the residue pools (CARB, CELL, and lignin), and (ii) allow stems and leaves to decompose separately, having a common point of interaction through the inorganic N pool. Results of a 6‐mo laboratory incubation experiment with four cover crop residues were used to adjust rate constants and test the effect of model modifications. The decay rates obtained were 0.14 and 0.0034 d−1 for CARB and CELL, respectively. Allowing the user to vary the relative size of residue pools greatly improved the simulation of net N mineralized (root mean square error of the model decreased from 1.0 to 0.28 g m−2), whereas modeling the separate decomposition of leaves and stems only caused a slight improvement in the prediction of net N mineralized.
Residue Decomposition Effects on Nitrogen Availability to Corn following Corn or Soybean
Authors: Green C. J. , Blackmer A. M. 
Published: July 2010

AbstractRates of N fertilization required to attain maximum yields of corn (Zea mays L.) usually are less for corn grown after soybean [Glycine max (L.) Merr.] than for corn grown after corn, but the reason for the difference in N fertilizer requirement has not been clearly established. We studied immobilization and mineralization induced by various management histories and residue treatments to learn about the causes of differences in N fertilizer requirements. Soil samples were collected at five sites in the fall of 1990 from plots that had been planted to soybean and plots that had been planted to corn receiving various N rates. The soil samples were incubated for 42 wk after treatment with 15N‐labeled NO−3 and with crop residues. All treatments showed a period of net immobilization followed by a period of net mineralization. Net amounts of N immobilization induced by soybean residue were approximately equal to those induced by corn residue from plots with the higher rates of fertilization. However, the soybean‐induced immobilization was much more rapid. Rates of mineralization of nonlabeled N were not greater from soils having soybean residue than from soils having corn residue. Because soybean produces less residue under field conditions, the results suggest that differences in N fertilizer requirement are better explained by differences in amounts of N immobilized during residue decomposition than by mineralization of biologically fixed N associated with the soybean.
Variation of Soil Water Storage across a Sand Plain Hillslope
Authors: Tomer M. D. , Anderson J. L. 
Published: July 2010

AbstractAlthough landscape variations in soil properties and productivity are often attributed to soil water conditions, landscape‐scale studies of soil water are rare. This study describes variability of soil layering and soil water storage on a sand plain hillslope. According to a nested grid (with spacings from 2 to 16 m), soil cores were collected by horizon, and soil water profiles were measured with a neutron probe during the 1992 growing season. Particle‐size analysis was conducted on the soil samples. A topographic survey of the hillslope was conducted, and elevation, slope, and slope curvature maps were constructed. Fine aeolian sand overlies medium sand of alluvial origin. The fine sand is thickest at upland positions, indicating the hill is a dune remnant. Lamellae only occur in the finer upland soils. Surface water storage (0–0.7‐m interval) is greatest at the toeslope, where the epipedon is mollic. Subsurface storage (0.7–1.7‐m interval) is greatest at upland positions, where perching of soil water is associated with lamellae and the depositional discontinuity. Regression modeling showed that combinations of elevation (cubic trend), slope, and plan curvature explain 51 to 77% of the variability in profile water storage, depending on depth interval. When topographic trends are removed, spatial correlation of water storage only occurs within distances <6 m. Topographic trends can be used to model variability in soil water storage for this landscape, even though surface runoff is not significant.
Reassessment of Polynov's Ion Mobility Series
Authors: Hudson Berman D. 
Published: July 2010

AbstractPolynov (1937) calculated the relative mobilities of important elements in landscapes: Cl > SO4 > Ca > Na > Mg > K > Si > Fe > Al. This series depicts a general weathering sequence that is essential to understanding many aspects of soil genesis and soil geography. It is argued on tbeoretical grounds that Ca and Na are out of proper sequence in Polynov's series. Polynov estimated ion mobilities by comparing the average content of elements in igneous rock to the average content of the same elements in river waters. However, an estimated 80% of the rocks at the earth's surface, which supply most of the leachate to rivers, are sedimentary. Accordingly, Polynov's mobility series was recalculated after adjusting rock chemical composition for the dominance of sedimentary rock types at the earth's surface. By using the elemental composition of igneous rocks in his calculations, Polynov greatly overestimated the amount of Na relative to Ca in rocks providing leachate to rivers. As a result, he significantly underestimated the mobility of Na relative to Ca. It is recommended that Polynov's ion mobility series be modified to the following: Cl > SO4 > Na > Ca > Mg > K > Si > Fe > Al. This study showed that Na is much more mobile (relative mobility 18.0) than Ca (8.1), Mg (5.4), or K (3.5). Therefore, it is recommended that Na be placed in a distinct mobility phase (II) second in relative mobility to Cl and SO4 (I).
Effects of Cultivation and Abandonment on Soil Organic Matter in Northeastern Colorado
Authors: Ihori Tamiko , Burke Ingrid C. , Lauenroth William K. , Coffin Debra P. 
Published: July 2010

AbstractThe influence of climate and soil texture on soil organic matter losses due to cultivation are rarely addressed due to lack of appropriately paired sites. In addition, soil organic matter recovery on previously cultivated fields is not well understood. In this study, we identified seven sites that have native and abandoned fields and five sites that have native, abandoned, and cultivated fields. All sites are in the northeastern Colorado shortgrass steppe, crossing a precipitation range from 320 to 370 mm, and have sand contents from 36 to 67%. Historical cultivation reduced soil C and N across this region by between 16 and 42%. Although variation in native soil C and N at these sites correlates with climate and soil texture, variation among sites in soil losses due to cultivation is not explained by these variables. We used a statistical model and a simulation model to estimate patterns of soil loss across sites; neither model predicted variation among sites adequately (P > 0.05). We suggest that local‐scale variability in organic matter losses due to cultivation are strongly dependent on management practices. With a simulation model and the data from native, abandoned, and cultivated fields, we estimated that 25 to 120 g C m−2 have been recovered on the abandoned fields during the past 50 yr. Such rates of recovery are small compared with loss rates due to cultivation. Rates of soil organic matter recovery are constrained by natural pedogenic processes, which cannot reverse disturbance processes at a comparable rate in this semiarid environment.
Relationship between Buffelgrass Survival, Organic Carbon, and Soil Color in Mexico
Authors: Ibarra‐F. Fernando A. , Martin‐R. Martha H. , Cox Jerry R. , Crowl Todd A. , Post Donald F. , Miller Raymond W. , Rasmussen G. Allen 
Published: July 2010

AbstractT‐4464 buffelgrass (Cenchrus ciliaris L.), a perennial bunchgrass from Africa, has been extensively seeded throughout Mexico. After establishment and grazing, T‐4464 either persists with time and actively invades surrounding areas (spreads), persists with time but does not increase (persists), or declines with time and all plants die (dies). To help land managers select high‐potential seeding sites, we classified 139 seeding sites in three survival regimes: (i) spreads, (ii) persists, and (iii) dies. In previous research, we identified a relationship between plant survival and organic C. This research was designed to identify relationships between organic C and soil color. Single comparisons between organic C and Munsell hue, value, chroma, and reflectance in dry and moist soils were poor predictors of plant survival. To predict buffelgrass survival among the three survival regimes and between spreads and dies, we used discriminant function analyses. In dry soil, a model including value and chroma correctly classified 53% (Wilke's λ = 0.8) of the seeding sites in the three survival regimes, while in moist soils, value and reflectance components correctly classified 61% (Wilke's λ = 0.7) of the seeding sites. A dry soil model including value, chroma, and reflectance correctly classified 81% (Wilke's λ = 0.7) of the seeding sites between spreads and dies, while a moist soil model, including the same components, correctly classified 83% (Wilke's λ = 0.6) of the seeding sites. Survival regime selection with multiple soil color components prior to brush control and sowing will reduce adverse economic and environmental consequences and enhance long‐term beef production.
Water Management Effects on Mineralization of Soil Organic Matter and Corn Residue
Authors: Kimmelshue J. E. , Gilliam J. W. , Volk R. J. 
Published: July 2010

AbstractWater table control is being used on large areas of poorly drained Atlantic Coastal Plain soils during the winter to reduce N losses to surface waters. This study was conducted to determine the effect of water table depth (WTD) and control on N mineralization of added corn (Zea mays L.) residue. Soil columns (15‐cm‐diam.) were extracted to 70‐cm depth from a Portsmouth loam (fine‐loamy over sandy or sandy‐skeletal, mixed, thermic Typic Umbraquult), placed in polyvinyl chloride (PVC) water table columns, and buried even with the surrounding soil surface. Labeled corn residue (18.01 atom % excess 15N) was incorporated in the upper 15 cm of the PVC columns and WTDs of 0, 15, 30, and 45 cm maintained. Soil microsamples were taken over time for N analyses. After 209 d, approximately 8 to 13% of the inorganic N came from the N added as plant residue, even though the added N was only 1.1% of the total soil N. Although the 0‐ and 15‐cm WTD treatments accumulated little 15NO3‐N, they contained appreciable 15NH4‐N. In contrast, the 30‐ and 45‐cm WTD treatments accumulated primarily 15NO3‐N as inorganic N accumulation increased with time and rising soil temperatures. It was concluded that WTD control could be used during the winter to promote denitrification of available NO3‐N and thus to minimize NO3‐N lost to drainage water.
Land Subsidence in Drained Histosols and Highly Organic Mineral Soils of California
Authors: Rojstaczer Stuart , Deverel Steven J. 
Published: July 2010

AbstractThis study was conducted to determine historical trends in subsidence in the Sacramento‐San Joaquin Delta and their environmental controls. Historical subsidence was determined by measuring soil surface elevation loss near electrical tower foundations and by evaluating survey data between 1922 and 1981. The data indicated that subsidence slowed with time. In the western Delta, average subsidence rates were 2.3 cm yr−1 from 1910 to 1988 and 1.5 cm yr−1 from 1952 to 1988. Spatially variability in subsidence was correlated with organic matter content of the soil (r2 = 0.62), which in turn was related to the depositional and drainage history of the Delta. Subsidence rates appeared to be independent of crops grown.
Nitrogen Mineralization in Humid Tropical Forest Soils: Mineralogy, Texture, and Measured Nitrogen Fractions
Authors: Motavalli P. P. , Palm C. A. , Elliott E. T. , Frey S. D. , Smithson P. C. 
Published: July 2010

AbstractChemical and physical stabilization of soil organic matter by the interaction of organic compounds with soil clay minerals may affect N mineralization in tropical forest soils. Nitrogen mineralization rates during long‐term incubation were determined on soils of several mineralogies collected from native forests in Costa Rica, Colombia, Peru, and Brazil. Amounts of N mineralization were related to soil mineralogy, texture, and N fractions in order to determine the effects of these soil components on N mineralization and to evaluate measurements of these components for their use as potential N availability indices. Allophanic soils produced higher cumulative levels of mineralized N and had higher initial levels of several N fractions than soils with smectitic, oxidic, and kaolinitic mineralogies. This mineralogical effect was attributed to greater initial N stabilization in allophanic soils followed by greater N release after the addition of nutrient solution during incubation. Total soil N had the strongest correlation with N mineralization among the N measurements considered in this study. The active N pool, as calculated by a two‐pool regression model of cumulative mineralized N, had the highest positive relationships with NH+4‐N evolved in a 1‐wk anaerobic incubation and soluble N. The stable N pool had the strongest correlations with total N and light‐fraction N. The relationships between soluble N or NH+4‐N evolved after a 1‐wk anaerobic incubation and N mineralization were affected by soil mineralogy, which suggests the need for further evaluation of potential N availability indices for the effects of soil mineralogy.
Co‐Occurrence of Hydrophobicity and Allelopathy in Sand Pits under Burned Slash
Authors: Everett Richard L. , Java‐Sharpe Bonnie J. , Scherer George R. , Wilt F. Martin , Ottmar Roger D. 
Published: July 2010

AbstractPrescribed burning of slash following tree harvest is a standard practice to reduce fire hazard and prepare seed beds for planting conifers. This study examined the co‐occurrence and intensity of hydrophobic and allelopathic layers created in sand pits under burned slash piles and broadcast slash. Following slash burning, 24 sand cores were taken from the sand pits and analyzed for water repellency and allelopathic effects on germination, emergence, and height growth of a bioassay species, blue wildrye (Elymus glaucus Buckley). Water drop penetration that was instantaneous in untreated sand cores was delayed in sand cores from burn treatments for 5 to 90 s in seven cores and for >270 s in five cores. Seedling emergence and height of the bioassay species declined in both the created hydrophobic sand layer and in an allelopathic zone of wettable sand immediately below the hydrophobic layer. Lack of allelopathic response when free water was present suggests that allelopathic effects are exhibited only under unsaturated soil conditions. Results indicate that nonwettable soils and allelopathy effects will act in unison to reduce water penetration and slow plant establishment following wildfires or prescribed burns.