bluuebunny/crossref_metadata_2025_split huggingface dataset:
Secondary Manganese/Iron Ratios as Pedochemical Indicators of Field‐Scale Throughflow Water Movement
Authors: McDaniel P. A. , Bathke G. R. , Buol S. W. , Cassel D. K. , Falen A. L. 
Published: July 2010

AbstractThermodynamic models predict that Mn is a more mobile component of soil systems than is Fe and therefore subject to more extensive redistribution within soils and landscapes. This study was initiated to examine the accumulation of secondary Mn (Mnd) relative to that of secondary Fe (Fed) as influenced by field‐scale water movement. Secondary Mn and Fe were measured using a citrate‐bicarbonate‐dithionite (CBD) extract of genetic horizons of 60 soils sampled in an Ultisol‐dominated landscape of the North Carolina Piedmont. Soil water pressure was measured using tensiometers installed at each soil sampling site to infer water flow patterns. For all well‐drained soil borizons, Fed contents correlate well with clay content (r = 0.878***), suggesting that relatively little redistribution of Fe released through weathering has occurred within the landscape. In contrast, Mnd contents are extremely variable among genetically similar horizons and are not well correlated with clay content (r = 0.327***). These differences serve as the basis for using secondary Mn/Fe (Mnd/Fed) ratios as relative indicators of Mn accumulation. Total soil water potential contours for Ap and Bt horizons closely parallel elevation contours, indicating the strong influence of slope gradient and configuration on water movement. Secondary Mn/Fe ratios are highest in Ap horizons of soils occupying lower slope positions and concave areas of the landscape. Total soil water potential data indicate convergent throughflow occurs in these wetter areas of the landscape. In contrast, lower Mnd/Fed ratios are found in soils occupying more convex landscape positions where soil water potential data show that divergent throughflow occurs. Results indicate that the difference in mobility between Mn and Fe in these acid soil systems allows secondary Mn/Fe ratios to be used as pedochemical indicators of field‐scale water movement.
Cropping System and Consolidation Effects on Rill Erosion in the Georgia Piedmont
Authors: West L. T. , Miller W. P. , Langdale G. W. , Bruce R. R. , Laflen J.M. , Thomas A. W. 
Published: July 2010

AbstractConsolidation and changes in surface horizon properties induced by no‐tillage may reduce soil loss to levels beyond those attributable to surface residue alone. To evaluate effects of consolidation and surface horizon modification induced by long‐term no‐tillage on rill erodibility (Kr) and critical hydraulic shear (τc), simulated rainfall and inflow were applied to plots managed under conventionally tilled monocropped soybean [Glycine max (L.) Merr.], conventionally tilled monocropped grain sorghum [Sorghum bicolor (L.) Moench], and no till double cropped crimson clover (Trifolium incarnatum L.) and grain sorghum at three sites with differing surface horizon clay contents. All surface residue was removed prior to rainfall simulation, and conventionally tilled cropping systems were evaluated in both consolidated and freshly tilled conditions. Increases in organic C from 9.3 to 12.9 g kg−1 and water‐stable aggregates from 50 to 76% induced by no‐tillage resulted in a 60 to 70% decrease in Kr for the no‐till system, compared with conventionally tilled systems. No differences in Kr were observed for the two conventionally tilled systems. No differences in τc were observed among the tillage systems. Consolidation within the conventionally tilled treatments reduced Kr by ≈60% from that observed for freshly tilled soil. The reduction was attributed to greater resistance to detachment by flow associated with soil strength increases due to consolidation. Differences in Kr and τc among the sites were small and were not readily explained by any of the soil properties evaluated. These results indicate that consolidation and modification of surface soil properties under no‐till cropping systems are important factors that contribute to reduced rill soil loss observed under no‐tillage.
Assessment of Functions and Parameter Estimation Methods in Root Water Uptake Simulation
Authors: Rasiah V. , Carlson G. C. , Kohl R. A. 
Published: July 2010

AbstractLimited information is available on the influence of estimates of parameters of the root water uptake (RWU) function on RWU simulation in macroscopic RWU modeling. This study was conducted to assess the influence of (i) parameter estimation methods, linear vs. nonlinear, and (ii) the type of RWU functions, continuous vs. discontinuous, on the estimates of RWU parameters and RWU simulation. The model calibration and validation were carried out using the data for soybean [Glycine max (L.) Merr.] grown in large soil columns. The estimates of the RWU parameters varied with the estimation method used or the type of function used. The simulations in soil water content (θv) and RWU distribution across space and time varied with the estimates of the parameters used in the flow model. The simulations in θv produced with the estimates from the nonlinear estimation method agreed more closely with the corresponding measured values than did those produced with the estimates from the linear method. A similar trend was observed for the discontinuous vs. continuous functions. The differences in residual sum of squares between the linear vs. nonlinear estimation methods, and that between the continuous vs. discontinuous functions, were significant. The accuracy of the simulations in θv and RWU increased significantly using the nonlinear parameter estimation method and a discontinuous RWU function.
Leaching Effect on the Dissolution of Two Phosphate Rocks in Acid Soils
Authors: Hanafi M. M. , Syers J. K. , Bolan N. S. 
Published: July 2010

AbstractDissolution of phosphate rock (PR) in soil is a necessary prerequisite for the P in the PR to become plant available. The dissolution of two PR materials, Gafsa (GPR) and Christmas Island A (CIPR), in six acid, Malaysian soils (pH in water 3.0–5.4) was examined in closed‐incubation and open‐leaching systems. Dissolution was determined from the increase in either 0.5 M NaOH‐extractable P (ΔP) or 1 M BaCl2‐triethanolamine (TEA)‐extractable Ca (ΔCa) in soil amended with PR, compared with the control soil. In the closed‐incubation system, dissolution of the reactive GPR was higher (22–71%) than that of the less reactive CIPR (26–42%). Despite an adequate supply of protons, the extent of dissolution of both PR materials was very small at 50 d, after which there was a negligible increase in the amount of P released. Calcium released from the PR materials occupied most of the negatively charged exchange sites and there was an insufficiently large Ca sink for dissolution to continue. Although the extent of PR dissolution increased with increasing P‐retention capacity of the soil, in the closed‐incubation system the size of the sink for Ca determines the extent of PR dissolution in these high P‐sorbing soils. With one exception, the dissolution of both PR materials was larger (56–94%) in the open‐leaching system and there was less difference in the extent of dissolution between the two PR materials and among the various soils. Continuous leaching resulted in the removal of cations (between 4.2 and 29.9 mmolc kg−1 soil), thus providing new sites for the Ca released from PR. The renewal of the Ca sink during leaching was the main reason for the continued dissolution of PR under leaching conditions. Studies of PR dissolution in soils using a closed‐incubation system provide information that is less relevant to the field situation than do related studies involving an open‐leaching system.
Estimating In Situ Unsaturated Hydraulic Properties of Vertically Heterogeneous Soils
Authors: Shouse P. J. , Jobes J. A. , Sisson J. B. , Ellsworth T. R. 
Published: July 2010

AbstractThe majority of procedures for in situ measurement of the unsaturated hydraulic conductivity are variations of the instantaneous profile method. A vertically nonuniform soil requires the unsaturated hydraulic functions to be estimated at each horizon. Scaling systems have evolved in an attempt to reduce the number of hydraulic functions needed to characterize water flow through heterogeneous soils. In this study, we extended the concept of water content (θ) scaling to nonuniform soil profiles, tested the effectiveness of θ scaling for reducing apparent spatial variability, and estimated the unsaturated hydraulic functions for a naturally occurring loamy sand field site. Two instantaneous profile experiments conducted at Etiwanda, CA, provided soil water content and pressure head (h) data vs. depth (z) and time (t). Water retention, θ(h), and hydraulic conductivity, K(θ), functions fitted to data from the 15‐cm depth at Plot 1 were arbitrarily chosen as the reference hydraulic properties to which the other depths and plots were scaled. Based on a unit‐gradient analysis of the drainage data, the slope of the hydraulic conductivity function, dK/dθ, was estimated as z/t. Scaling other depths and plots to the reference location was done using an iterative procedure that provided least‐squares estimates of the two θ scaling parameters (δ and µ) and a corresponding transformed depth variable (z*). Scaled water content, θ*, plotted vs. z*/t, using data from all depths and plots, coalesced to a single curve. Scaling θ successfully coalesced heterogeneous soil hydraulic properties into unique functions for both θ(h) and K(θ).
Dispersivity Values Determined from Effluent and Nonintrusive Resident Concentration Measurements
Authors: Oostrom M. , Dane J. H. , Güven O. 
Published: July 2010

AbstractAs indicated in the subsurface contaminant transport literature, the longitudinal dispersivity values needed to predict salt concentrations become smaller if more details of the flow field are included in the calculations. One way of determining these small‐scale or local longitudinal dispersivities is from breakthrough curves using laboratory columns. A gamma radiation technique is presented that allows non‐intrusive, in situ (resident) salt concentration measurements in saturated sand columns. The technique is demonstrated by means of a series of vertical displacement experiments with deionized water and a NaI solution in a column containing a medium sand. Longitudinal dispersivity values derived from the resident concentration breakthrough curves determined with this technique were consistently smaller than those derived from conventional effluent concentration breakthrough curves. The density configuration of the liquids may affect the apparent dispersivities.
The Analysis of Soil Organic Matter by Pyrolysis‐Field Ionization Mass Spectrometry
Authors: Schnitzer M. , Schulten H. R. 
Published: July 2010

AbstractAt the present time, the analysis of organic matter (OM) in soils requires extraction of the OM, fractionation of the extract into humic acid (HA), fulvic acid (FA), and humin, and purification of each fraction prior to more detailed characterization by chemical, spectroscopic, and other methods. To obviate the need for these laborious and possibly damaging procedures, we examined the possibility of applying pyrolysis‐field ionization mass spectrometry (Py‐FIMS), a method that provides information at the molecular level on complex organic materials, to whole soils and HAs, FAs, and humins separated from these soils. In all materials, carbohydrates, phenols, lignin monomers and dimers, and, to a lesser extent, n‐fatty acids were the major components. Our data indicate that whole soils are the most suitable materials for the analysis of OM in soils. Thus, Py‐FIMS has an advantage compared with existing methods in that it permits soil chemists and other interested scientists to do comprehensive OM analyses on air‐dry soils, even ones with low OM contents, without any pretreatment.
Contrasting Selenate‐Sulfate Interactions in Selenium‐Accumulating and Nonaccumulating Plant Species
Authors: Parker D. R. , Page A. L. , Bell Paul F. 
Published: July 2010

AbstractThe shoots of primary Se‐accumulating plant species can accrue Se to several thousand micrograms per gram of dry weight, even when growing in gypsiferous soils, yet no detailed studies of the mutual antagonism between SeO4 and SO4 during plant uptake have been conducted with these species. In a comparative study, we grew a nonaccumulator (alfalfa, [Medicago sativa L.]) and a primary Se accumulator [Astragalus bisulcatus (Hook.) A. Gray] in identical nutrient solutions with varied SeO4 (2–80 µM) and SO4 (0.5–15.5 mM) concentrations for 21 (alfalfa) or 32 to 35 d (A. bisulcatus). Shoot S concentrations in alfalfa were increased by increases in solution SeO4, but only when shoot Se was above ≈20 µg g−1, suggesting that SeO4‐induced stimulation of S uptake may be a result of incipient Se toxicity. Similar stimulations of S uptake were less apparent in A. bisulcatus. Alfalfa shoot Se concentrations ranged from 4 to 154 µg g−1, while the same treatments resulted in shoot levels of 175 to 1200 µg g−1 in A. bisulcatus. Uptake of SeO4 by alfalfa was profoundly inhibited by increases in solution SO4, while Se uptake by A. bisulcatus was much less, although still significantly, affected. Comparison of molar Se/S ratios in plants and nutrient solutions indicated discrimination against Se by alfalfa, but preferential accumulation of Se by A. bisulcatus. A reevaluation of previously published results was in general agreement with our findings, and suggested that primary Se accumulators have a unique ability to accumulate SeO4 in the face of competition from SO4. These species could thus prove useful in efforts to remediate Se‐contaminated soils or sediments that are also enriched in SO4. Overall plant discrimination between SeO4 and SO4 may be related to (i) discrimination between the two analogues during initial absorption, or (ii) differential retranslocation of these elements to the root with subsequent afflux to the external solution.
Soil Carbon, Nitrogen, and Fine Root Biomass Sampling in a Pine Stand
Authors: Ruark Gregory A. , Zarnoch Stanley J. 
Published: July 2010

AbstractSpatial variability of soil properties can be great in forested settings. A study was conducted to determine the most efficient methodology for sampling surface mineral soils in a mature loblolly pine (Pinus taeda L.) forest for total C, total N, and fine root biomass to obtain stand level estimates. Specifically, we evaluated the variation within and among plots, the performance of small‐ and large‐diameter corers, the effect of stem proximity, the influence of fine roots on soil C and N estimates, and the effect of compositing samples. We concluded that (i) C and N levels always increased with proximity to stems; (ii) proximity to a stem did not affect mean fine root biomass estimates; (iii) variability of the estimates of C and N consistently decreased with increased distance from the stem, but no trend occurred for fine root biomass; (iv) for total stand estimates of N and fine root biomass, stratification with respect to tree stems does not yield a gain in precision, for C precision increased only slightly; (v) C associated with fine roots represented ≈5% of the total C in a core sample, while N in roots was < 2% of its total; (vi) for C and N estimates, the variation with a 1.8‐cm‐diam. core was similar to that obtained with a 6.1‐cm core; and (vii) chemical analyses could be reduced and precision maintained by compositing the soil core samples.
Soil‐Vegetation Relationships in Franciscan Terrain of Northwestern California
Authors: Popenoe J. H. , Bevis K. A. , Gordon B. R. , Sturhan N. K. , Hauxwell D. L. 
Published: July 2010

AbstractThis study sought to discover how soil and vegetation patterns are related in the mountains of northwestern California. Soils were compared by vegetation‐epipedon type and drainage class, with elevation as a covariate. Vegetation types were (i) open prairie, (ii) coniferinvaded prairie, (iii) oak woodland, (iv) conifer forest with umbric or mollic epipedon, and (v) conifer forest with ochric epipedon. The level of organic carbon (OC) was similar in the upper 10 cm of mineral soil under all vegetation types, but soils under forest and oak woodland had less cumulative OC and N, and a greater decrease with depth than soils under prairie. Ochric epipedons under forest had wider C/N ratios than umbric and mollic epipedons under other vegetation types. Exchangeable Ca2+ and base saturation decreased with increasing elevation. Exchangeable Ca2+ decreased with depth under oak woodland and forest, and pH decreased with depth under oak woodland. Under prairie, pH increased with depth, and Ca2+ exhibited little change. Soils under prairie and invaded prairie had lower exchangeable K+ in upper horizons than soils under forest or oak woodland. Drainage‐impaired subsoils had higher bulk density, pH, and exchangeable Ca2+ than well‐drained subsoils. Conifer invasion was restricted to well‐drained soils. Except for conifer‐invaded prairie, closely associated soil and vegetation patterns indicated that the vegetation mosaic has persisted for a long time.
Tillage Studies with a Corn‐Soybean Rotation: Hydrology and Sediment Loss
Authors: Edwards W. M. , Triplett G. B. , Van Doren D. M. , Owens L. B. , Redmond C. E. , Dick W. A. 
Published: July 2010

AbstractWhen soybean [Glycine max (L.) Merr.] is produced on sloping fields using conventional tillage and mechanical cultivation for weed control, potential soil losses are high, limiting production to relatively flat lands. With the advent of conservation tillage practices and herbicides for weed control, soybean production with tolerable soil losses on sloping fields has become technically possible. To evaluate soil loss under these new conditions, runoff and erosion were measured on six small watersheds that were farmed for 6 yr in a corn (Zea mays L.)‐soybean rotation with conservation tillage. Two of the watersheds were chiseled each year, two others paraplowed, and the other two received no‐tillage. A rye (Secale cereale L.) cover crop was established each winter following soybean. With average yearly rainfall of 930 mm, yearly runoff was 63.5 mm and varied between 28 and 108 mm. Average yearly soil loss for the 6‐yr period was 526 kg/ha, <10% of the allowable soil loss. Two storms caused most of the erosion, with a single storm accounting for 42% of the total measured soil loss. Earlier, these same watersheds averaged 5750 kg/ha of measured soil loss during the corn years of a corn‐wheat‐meadow‐meadow rotation with conventional tillage.
Tillage Studies with a Corn‐Soybean Rotation: Surface Runoff Chemistry
Authors: Owens L. B. , Edwards W. M. 
Published: July 2010

AbstractWhen soybean [Glycine max (L.) Merr.] is grown on sloping soils, there is a high potential for soil and nutrient losses. The purpose of this study was to compare nutrient losses in surface runoff across a range of watershed conditions when tillage practice was a variable. For 6 yr in east‐central Ohio, nutrient concentrations and transport in surface runoff were measured from six small (<1‐ha) watersheds planted to a corn (Zea mays L.)‐soybean rotation. Two watersheds were chisel plowed each year, two were paraplowed, and two received no‐tillage. Rye (Secale cereale L.) provided winter cover following soybean harvest. Nitrate‐N and K concentrations in surface runoff were greater during corn years than soybean years, but there was no significant difference among tillage treatments. There were no consistent differences between crops or among tillage practices for the transport of soluble P, soluble K, and total organic C (TOC). Most of the NO3‐N loss was in the runoff from a small percentage of runoff events. Although NO3‐N concentrations in surface runoff frequently exceeded 10 mg/L during the corn years, the actual amount of N lost was small. But because of year‐to‐year variation in runoff, which masked most of the differences resulting from cropping or tillage practice, there is a need for long‐term research (>6 yr) to assess the environmental risks associated with a particular management practice.
Long‐Term Nutrient Accumulation Rates in the Everglades
Authors: Reddy K. R. , DeBusk W. F. , DeLaune R. D. , Koch M. S. 
Published: July 2010

AbstractAnthropogenic nutrient inputs to the northern Everglades of Florida during the last three decades have resulted in alteration of vegetation and soil nutrient storage. Due to the nutrient‐limited status of this ecosystem, increased loading may have altered the capacity for long‐term nutrient accumulation. Our study was conducted to determine the potential long‐term nutrient accumulation rates for this ecosystem along a gradient of nutrient loading. Accumulation rates were calculated using the vertical peat accretion rates, as determined by 137Cs dating, and nutrient concentration profiles. Intact soil cores were obtained along a 15‐km transect and evaluated as a function of distance from the inflow structure. Soil cores were sectioned into 1‐cm‐depth increments and analyzed for 137Cs, P, N, C, and selected cations. Vertical accretion rates of peat decreased logarithmically with distance from the inflow, with rates of 1.1 cm yr−1 at 0.3 km from the inflow to about 0.25 cm yr−1 in unimpacted sawgrass (Cladium jamaicense Crantz‐dominated areas. Phosphorus, N, and C accumulation rates in soil and floodwater total P concentrations also showed similar relationships. The P accumulation rates ranged from 0.54 to 1.14 g P m−2 yr−1 in cattail (Typha spp.)‐dominated areas, and 0.11 to 0.25 g P m−2 yr−1 in sawgrass‐dominated areas. The C/P and N/P accumulation ratios increased with distance from the inflow, suggesting that a greater proportion of P accumulated in the system, compared with C and N. Similar P retention coefficients were obtained when calculated using either changes in surface water total P concentration, or the long‐term P accretion rates. These findings suggest that P was either directly adsorbed by soil or precipitated with Ca in the water column and deposited on the soil surface. This hypothesis was further supported by a highly significant correlation between P and Ca accretion rates, suggesting that Ca‐bound P controls equilibrium concentrations in this ecosystem.
Ammonium Oxidation and Nitrate Reduction in Sediments of a Hypereutrophic Lake
Authors: D'Angelo E. M. , Reddy K. R. 
Published: July 2010

AbstractInternal N cycling processes in sediments and the overlying water column may contribute to the eutrophication of lake systems. One of the major mechanisms for N loss in these systems is through biological oxidation and reduction of N species in the aerobic and anaerobic sediment zones, coupled with exchange processes between these zones. These mechanisms were measured using flooded, intact sediment columns and batch incubations with bulk sediments collected from a hypereutrophic lake. In continuously stirred batch incubations with aerated sediment, NH+4 oxidation to NO−3 (nitrification) showed two‐phase, zero‐order kinetics. The rapid first phase of nitrification (0.36 mg N L−1 h−1) was due to the oxidation of NH+4 initially present in the sediment, while the slower second phase (0.15 mg N L−1 h−1) was limited by the rate of production of NH+4 during ammonification of organic N. Denitrification as determined by the C2H2‐blockage technique was found to be limited by NO−3 availability. Under NO−3 nonlimiting conditions, the denitrification rate was 0.11 mg N L−1 h−1, but a fivefold decrease was measured at low NO−3 concentration (1 mg NO3 L−1). Denitrification was the major NO−3 reductive process in the surface 27‐cm sediment depth. Assimilatory 15NO−3 reduction into the organic 15N fraction was also a significant NO−3 loss mechanism at the sediment surface. Dissimilatory 15NO−3 reduction to 15NH+4 became the dominant NO−3 reductive pathway at sediment depths >27 cm. Losses of up to 90% of the floodwater 15NH+4 or 15NO−3 was largely attributed to sequential nitrification‐denitrification reactions.