bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulating Nutrient Uptake by Single or Competing and Contrasting Root Systems
Authors: Smethurst P. J. , Comerford N. B. 
Published: July 2010

AbstractSimulation of nutrient uptake by competing root systems is necessary to assist in the quantitative understanding of these processes, to predict the consequences of competition for nutrients, and to prioritize future research on the mechanisms of nutrient competition. Our objective was to apply previously published concepts to a computer model based on solute transport theory that would have the ability to simulate nutrient uptake by root systems of one or two competing plant species. Analytical solutions were used for calculating the volume of soil allocated to each root system and the concentrations of solute at the root surfaces. We included in the model (i) a depletion zone that increased with time until it reached the no‐transfer boundary, (ii) an adjustment of the average concentration in the depletion zone to account for newly encountered solute as the zone increased in radius, (iii) a variable root‐absorbing power (α), and (iv) a routine to correctly account for all soil in simulations with two contrasting root systems. Predicted uptake for single‐species scenarios in soils of contrasting nutrient supply characteristics was verified against that predicted by the commonly used Barber‐Cushman model, NUTRIENT UPTAKE (maximum discrepancy was 23%), which utilizes a numerical solution. The ratio of uptakes predicted by both models was a function of α, root radius, effective‐diffusion coefficient, and buffer power in a more complex way than previously suggested in the literature. Sensitivity analysis indicated that, of all parameters, K uptake by slash pine (Pinus elliottii Engelm. var. elliottii) relative to competing grass would be most sensitive to variations in root‐length density of the grass, or in soil water content, if only soil parameters were examined.
Ferrihydrite, Lepidocrocite, and Goethite in Coatings from East Texas Vertic Soils
Authors: Wang H. D. , White G. N. , Turner F. T. , Dixon J. B. 
Published: July 2010

AbstractIron oxide coatings from ped surfaces and pores of three rice paddy soils and one non‐paddy soil near Beaumont, TX, provided samples for studying Fe oxide mineralogy and the relationship of extractable Fe to extractable Al, Si, and P. Analyses of Fe oxide coatings, concentrated by a combination of scraping, sonication, centrifugation, and magnetic separation, showed that these Fe oxide coatings cement clay minerals and quartz particles together. Iron oxide coatings in all soils contained lepidocrocite and smaller amounts of goethite. An improved differential x‐ray diffraction (DXRD) method, in situ DXRD on a nonreflecting quartz plate, allowed the identification of ferrihydrite, which is otherwise difficult to identify because of its poor crystallinity and low concentration. Most of the ferrihydrite was dissolved by 10 min in pH 3 ammonium oxalate in the dark (AOD). Sequential 10‐, 50‐, and 180‐min AOD treatments extracted lepidocrocite of progressively increasing particle size. The 180‐min AOD treatment extracted minimal amounts of goethite. The DXRD and chemical data indicate that the paddy soils have more ferrihydrite in relation to total Fe oxides than the non‐paddy soil. The P/Fe ratio decreased with each AOD treatment step for all soils. This study demonstrates that physical separation and in situ AOD treatment can be used with the DXRD method to identify ferrihydrite, lepidocrocite, and goethite in soil clays containing extractable Fe concentrations as low as 10 to 44 g/kg. We concluded that a short incremental AOD treatment (≈10–30 min) is a better approach to DXRD of ferrihydrite in <2‐µm fractions of seasonally reduced soils than the much longer treatment recommended in the past for soils.
Winter‐Associated Changes in Dry‐Soil Aggregation as Influenced by Management
Authors: Layton J. B. , Skidmore E. L. , Thompson C. A. 
Published: July 2010

AbstractChanges in surface soil structure during winter can increase soil erodibility. This study was conducted to examine winter‐associated changes in dry‐soil aggregation as influenced by crop, residue, and tillage system. These changes were studied at Hays, KS, on a Harney silt loam (fine, montmorillonitic, mesic Typic Argiustoll) in a winter wheat (Triticum aestivum L.)‐grain sorghum [Sorghum bicolor (L.) Moench]‐fallow rotation. Three tillage systems were used — clean tillage with residue buried, stubble‐mulch tillage, and zero tillage. Residue and crop cover present during the winter was wheat residue, sorghum residue, and winter wheat. Measurements of dry aggregate stability, aggregate‐size distribution as geometric mean diameter, and aggregate density were made before and after the winters of 1988–1989 and 1989–1990. Little difference occurred between clean and stubble‐mulch tillage systems, which were usually different from the zero‐tillage system. Greater changes in aggregation occurred during the 1989–1990 winter when precipitation was greater. Residue maintained higher surface water contents, decreased freeze‐thaw cycling and drying by sublimination, and decreased fluctuations in water content. Aggregates from plots with low residue cover decreased in stability more than aggregates from high residue treatments. Generally, differences in aggregation between tillage systems were maintained during the drier winter and minimized during the wetter winter. Soil aggregates were smaller, less dense, and less stable on the zero‐tillage plots in March 1989. Therefore, insufficient residue production for wind erosion control in a zero‐tillage system could lead to more erodible conditions than in a conventional tillage system.
Streamlines for Diffusive Flow in Vertical and Surface Tillage: A Model Study
Authors: Kirkham M. B. 
Published: July 2010

AbstractMethods of tillage must permit adequate flow of O2 to plant roots. The objective of this work is to calculate streamlines of O2 flow from chisel holes oriented vertically and horizontally (surface tillage) in the soil to plant roots. Streamlines are perpendicular to equipotential lines. They also have the property that the difference in value between two streamlines gives the quantity of fluid (in this case, O2) flowing between them. Therefore, streamlines are often more important than equipotentials. Streamlines for flow of O2 from the chisel holes in the soil to plant roots were calculated by use of the relaxation method, in which both a coarse grid (2.54 cm on a side) and a fine grid (1.27 cm on a side) were used. Transit times were calculated from the flownet resulting from the streamlines and equipotential lines. Calculations with the coarse grid showed that, for the vertical chisel case, 75% of the flow goes out of the side of the chisel opening closest to the sheet of plant roots and 25% of the flow goes out of the side of the chisel opening farthest away from the sheet of plant roots; for the fine grid, the values are 63 and 37% for the two sides of the chisel hole, respectively. For both the vertically and horizontally tilled cases, stagnant areas were identified in the soil. Transit times were short for both tillage cases (on the order of minutes), confirming the general assumption that diffusion is the major mechanism of gas transport in soil.
Phosphorus Uptake by Bahiagrass from Spodosols: Modeling of Uptake from Different Horizons
Authors: Ibrikci H. , Comerford N. B. , Hanlon E. A. , Rechcigl J. E. 
Published: July 2010

AbstractBahiagrass (Paspalum notatum Flugge), when grown on a Myakka fine sand in Florida (sandy, siliceous, hyperthermic Aeric Alaquod), did not respond to P fertilization even though Mehlich‐1 extractable P was low in the surface soil horizon. Previous research suggested that the Bh horizon was a potential source of P. The objective of this study was to evaluate the plant availability of P in the Bh horizon and to determine to what degree existing nutrient uptake theories explain the uptake of P by bahiagrass under greenhouse conditions. Sod and soil samples were collected from unfertilized bahiagrass growing on a Spodosol. Sod was replanted into soil samples. Plant and root samples were collected from unfertilized bahiagrass growing on a Spodosol. Sod was replanted into soil samples. Plant and root samples were collected at 18, 36, 61, and 90 d. Selected soil and plant model parameters were estimated at each harvest period. Bahiagrass was able to extract more P from the Bh horizon material than from Ap or E horizon materials. The COMP8 computer model was used to simulate uptake of P by bahiagrass. Observed and predicted P uptake by bahiagrass followed the same relative pattern (Bh > Ap > E). There was statistically good agreement between observed and predicted P uptake for 18‐d‐old plants, but less agreement at 90 d (within 20%) from the Bh horizon. Predicted P uptake values from the Ap and E were statistically lower than observed values at both harvest dates. Selected extraction procedures indicated that there was no P release from the mineral forms in the Ap horizon. Data suggest the plant‐induced mineralization was an important P supplying mechanism in this pot study.
Incorporating Variability into Soil Map Unit Delineations
Authors: Rogowski A. S. , Wolf J. K. 
Published: July 2010

AbstractPublished soil surveys comprise a nationwide soils data base available to users. Although adequate for farm planning and agricultural production, the surveys lack information on spatial and temporal variability of soil attributes. Such information is increasingly needed for modeling of water flow and contaminant transport, in geographical information systems (GIS) applications, and for environmental impact assessment. The proposed approach combines spatially interpolated distributions of measured values with soil map unit delineations within a GIS framework. Data analysis provides insights into the potential continuity and variability of attributes within and between the map units. The result is a map that preserves the map unit boundaries but incorporates spatial variability of attribute data into map unit delineations. The approach is illustrated using bulk density and hydraulic conductivity data for surface soil horizons at a farm scale. Semivariograms based on measured values are constructed and cross‐validated. Subsequently, GIS overlays of soil survey attributes and kriged overlays of measured data can be prepared. These GIS overlays can be combined pixel by pixel according to a simple rule. Results indicate that spatial distributions of bulk density and hydraulic conductivity are similar to original map unit delineations, but include aspects of the attribute continuity and variability from geostatistical analysis. Such combined representations of bulk density and hydraulic conductivity are superior, because they contain more information than either the soil survey map, or the kriged interpolation of discrete data.
Aluminum Influence on Iron Oxides: XVII. Unit‐Cell Parameters and Aluminum Substitution of Natural Goethites
Authors: Schwertmann Udo , Carlson Liisa 
Published: July 2010

AbstractAluminum‐iron substitution in goethites is a widely used parameter to characterize soil goethites and to gain information on the pedogenic environment. The extent of Al substitution is obtained from calibration curves consisting of linear relationships between the unit‐cell edge length c and the Al content of synthetic goethites. We derived calibration curves from natural goethites obtained from two contrasting genetic environments: 84 samples from tropical soils and 30 lake ore samples from Finland. Significant correlations between unit‐cell parameters and chemically determined Al (dithionite‐citrate‐bicarbonate‐extractable Al minus citrate‐bicarbonate‐extractable Al) were obtained for both groups. The negative slopes of the regressions for the tropical goethites were significantly greater and closer to the slope for 106 synthetic goethites, and to the Vegard line, than those of goethites from lake ores. This is tentatively attributed to the formation environment: the temperature is lower while the rate of formation and the presence of crystallization inhibitors are probably higher in the lake environment. The younger age may also have had some influence on crystal perfection.
Mineralogy of a Holocene Chronosequence on Andesitic Beach Sediments in Costa Rica
Authors: Nieuwenhuyse A. , Jongmans A. G. , van Breemen N. 
Published: July 2010

AbstractWe investigated weathering and neoformation of minerals in a Holocene (<5000 yr) soil chronosequence on sandy, andesitic, ocean beach ridges in humid tropical Costa Rica using micromorphological, mineralogical, and chemical analyses. Troposamments are present on the younger beach ridges and Hapludands are on the older ones. The parent materials of all soils are sands with similar mineralogical composition: andesitic rock fragments, plagioclase, and pyroxene dominate, with minor amounts of opaque minerals. None of the parent materials contained >13% (v/v) volcanic glass. Weathering and neoformation of minerals with increasing soil age is characterized by (i) increasing pellicular and linear alteration of sand grains and (ii) decrease of the sand fraction and concomitant increase of finer material. Andesitic rock fragments weather more rapidly than plagioclase and pyroxene mineral grains. The alteration rates of the latter two are similar. Clay content in the ≈ 2000‐yr‐old soil is several times higher than in soils developed in rhyolitic parent materials of similar age in New Zealand. Formation of allophane with Al/Si ratios ranging from 1.9 to 3.8 takes place mainly in the B horizons. Aluminum‐humus complexes, allophane, and Al oxides and hydroxides are mainly formed in the A horizons. Small amounts of gibbsite were noticed in soils older than 2000 yr. Small amounts of 2:1 and 1:1 clay minerals present in the clay fraction of all soils are thought to be inherited from the parent material, which contains sand‐sized bodies of clay and andesitic rock fragments with clay pseudomorphs, both consisting of 2:1 and 1:1 clay minerals.
The Upper Limit of Solute Dispersion and Soil Hydraulic Properties
Authors: Scotter D. R. , Ross P. J. 
Published: July 2010

AbstractCurrent theory inadequately describes the effects on solute movement of local variations in pore‐water velocity. A satisfactory theory for solute flow in structured soil has yet to be developed. As a possible starting point for such a development, we present a simple analytical description of the maximum amount of solute dispersion that can occur during steady water flow in a vertically uniform soil. The distribution of soil water velocities is found from the derivative of the unsaturated hydraulic conductivity‐water content relationship. With just this information, given the water flux and solute boundary conditions, the solute distribution can be described, assuming no mixing between water (and solute) flowing at different velocities in the soil. The analytical solution describes not only the upper limit of the dispersion that can occur, but also the maximum depth to which the leading edge of a surface‐applied pollutant can travel, given a steady water flux for a certain time. It is shown that the steeper the hydraulic conductivity curve, the greater the expected difference between the soil solution flux concentration (measured with a lysimeter) and resident concentration (measured by soil sampling). Transverse solute diffusion between water moving at different velocities reduces the dispersion below the upper limit described here. Incorporating a description of such diffusion into the approach given here may be a fruitful alternative to considering dispersion as enhanced longitudinal diffusion in soil water moving at a uniform velocity.
Unsaturated Hydraulic Conductivities of Fiberglass Wicks and Designing Capillary Wick Pore‐Water Samplers
Authors: Knutson John H. , Selker John S. 
Published: July 2010

AbstractPassive capillary samplers (PCAPS) use the capillary potential of fiberglass wicks to draw pore water from unsaturated soils. The sampling suction of a wick should be matched to the pressure head, h, in the soil in which the PCAPS will be installed. Currently there is no theoretically based procedure for matching wicks to soils, a problem this study solves. When matched, the top of a wick has approximately the same h as the soil across multiple fluxes. Unsaturated hydraulic conductivities, K(h), were measured in wicks. These data exhibited exponential behavior, and estimates of wick saturated conductivities, Ksat, ranged from 220 to 1380 cm/h. The Ksat values were compared with predictions from a capillary tube model (R2 = 0.85). Moisture contents, θ(h), were measured in wicks. Hysteresis was observed, and the draining curves were used to predict K(h) using the van Genuchten equation coupled with the Mualem conductivity model. The van Genuchten equation fit the draining θ(h) data well (R2 > 0.953), but Mualem's K(h) values did not reproduce the exponential predictions. A solution for unsaturated flow was used to calculate h in wicks given the flux, q, and length. Calculated values of h were within 25% of the measured values for high fluxes and within 5% of the measured values for low fluxes. A least‐squares procedure for matching the h vs. q curve of a wick to a soil was used to design PCAPS for application in two soils.
Water Content Effect on Denitrification and Ammonia Volatilization in Poultry Litter
Authors: Cabrera M. L. , Chiang S. C. 
Published: July 2010

AbstractPoultry litter is a mixture of excreta, bedding material, waste feed, and some soil that is removed from poultry houses and applied to soil as fertilizer. Because litter is commonly stockpiled outdoors before land application, losses of inorganic N may occur through denitrification and NH3 volatilization. This work was conducted to evaluate the effect of litter water content on denitrification and NH3 volatilization during storage. Litter samples from two broiler houses in northern Georgia were incubated (25°C) at four water contents for 13 d. Water contents used were 230 g H2O kg−1 in Litter A, 160 g H2O kg−1 in Litter B, and 800, 1200, and 2400 g H2O kg−1 in both litters. These water contents were equivalent to 8, 26, 40, and 79% water‐holding capacity (WHC) in Litter A and to 7, 33, 49, and 99% WHC in Litter B, respectively. Denitrification was evaluated by measuring N2O emission from samples incubated with 10 kPa C2H2, with and without additional NO−3 (15 mg Ng−1). Ammonia volatilization was evaluated by measuring NH3 evolved from samples incubated without C2H2. Denitrification was significant at the highest water content and increased with the addition of NO−3. Measured denitrification losses varied between 41 and 79% of the initial NO−3, although final NO−3 levels suggested that denitrification losses were larger (92–100%) and that part of the N2O produced remained entrapped in the litter. Ammonia volatilization losses ranged from 32 to 139% of the initial NH+4 and were increased by increasing water content. These results suggest that poultry litter should be stored under dry conditions to reduce N losses.
Thiosulfate Production in Cysteine‐Amended Soil
Authors: Zhong T. , Morra M. J. 
Published: July 2010

AbstractThiol‐labile compounds are produced in cysteine‐amended soil, as evidenced by the production of H2S following addition of reagents containing free sulfhydryl groups (−SH). Thiosulfate (S2O2−3) is a likely reactant candidate because it is an intermediate in biogeochemical S cycling and is reduced to H2S by ‐SH, but its presence in cysteine‐amended soils has not been documented previously. Four soils were amended with l‐cysteine (15 mmol kg−1 soil) incubated at 0.033 MPa soil water suction or under saturated conditions, and then extracted with 0.1 M LiCl. Colorimetric analysis of the extracts using cyanolysis with and without addition of a Cu2+ catalyst indicated the presence of S22−3 and a polythionate such as S4O2−6; positive interferences from the cyanolysis of S2− were minimal. Ion chromatographic analysis of the extracts showed a well‐resolved peak with the same retention time as S2O2−3 and yielded concentration estimates similar to those obtained by colorimetry, providing positive identification of S2O2−3 in cysteine‐amended soils. Thiosulfate production occurred under both saturated and unsaturated conditions, varied among soils from 0 to 35.2 mg S2O2−3‐S kg−1, and was nearly eliminated by autoclaving the soil before incubation or by addition of NaN3. Although the exact pathway for S2O2−3 production is unknown, it is likely that H2S formation and subsequent oxidation are responsible.
Prediction of Phosphorus Uptake by Field‐Grown Maize with the Barber‐Cushman Model
Authors: Lu Shen , Miller M. H. 
Published: July 2010

AbstractData collected from a field experiment conducted to determine the optimum P placement for maize (Zea mays L.) were used to test the Barber‐Cushman nutrient absorption model. Phosphorus absorption by maize predicted by the model was compared with that measured in a field experiment in which various rates of P were mixed with different volumes of soil. Shoot P content and root growth both in and outside the fertilized volume were measured at three times during early growth. Soil supply parameters were determined in the laboratory while literature values were used for plant absorption parameters. The ratio of predicted to measured absorption increased markedly as the P concentration in solution in the fertilized soil (Cli) increased, ranging from about 0.2 with low values of Cli (<0.03 mM) to as much as 2.0 with higher values of Cli (>0.06 mM). The ratio was highly sensitive to values of the maximum influx rate (Imax) at values of Cli >0.06 mM. Reducing the value of Imax eliminated the dependence of the predicted/measured ratio on Cli. With the lower value of Imax, predicted absorption ranged from 20 to 60% of that measured. This variation seemed due in part to the influence of vesicular‐arbuscular mycorrhizae on absorption. The sensitivity of the absorption model to Imax values at higher values of Cli indicates the necessity of measuring this parameter under conditions similar to those for which absorption is to be predicted.
Lateral and Vertical Bromide Ion Transport in a Piedmont Landscape
Authors: Afyuni Majid M. , Cassel D. Keith , Robarge Wayne P. 
Published: July 2010

AbstractVariation in soil physical properties and soil water transport can affect solute transport at different positions within a landscape. Our objective was to evaluate the magnitude of lateral and vertical transport of Br− under natural rainfall conditions as a function of landscape position. Potassium bromide was surface applied (300 kg Br−/ha) on three transects of Georgeville soil (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont of North Carolina. Each transect included a footslope, linear slope, and interfluve landscape position. The KBr was applied on alternate plots (5 by 2.7 m) on two transects and on contiguous plots on the third transect. Soil cores as deep as 3 m were collected after 140, 560, and 1460 mm of rainfall. Extent of lateral Br− transport was determined using cores from plots that did not receive surface application of KBr. After 140 mm of rainfall, the maximum Br− concentration remained in the upper 30 cm and some measurable lateral Br− transport occurred at all landscape positions. After 560 mm of rainfall, the maximum Br− concentration was above 60 cm, but some was detected at 150 cm on the footslope and interfluve positions. Lateral transport of Br− at the footslope and linear slope positions was 150 cm, but maximum concentrations occurred 10 to 45cm downslope. After 1460 mm of rainfall, most Br− disappeared from the footslope. Downslope lateral transport of Br− was 225 cm at all landscape positions. Both vertical and lateral Br− transport were greatest at the footslope. The variability in Br− transport is related to soil profile characteristics and hydrology at different landscape positions.