bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Transport of Atrazine Under Irrigation with Effluent
Authors: Graber E. R. , Gerstl Z. , Fischer E. , Mingelgrin U. 
Published: July 2010

AbstractEnhanced transport of atrazine (2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine; C8H14CIN5) applied to a corn (Zea mays L.) field was observed after irrigation with secondary effluent. Cores to 4 m were obtained from 10 effluent‐irrigated and 10 high‐quality water‐irrigated plots after two growing seasons and two winter rainy seasons. In most of the effluent‐irrigated cores, atrazine was widely distributed with depth, with an average center of atrazine mass at 115 ± 39 cm and a mean variance around the center of mass of 142 cm. In the high‐quality water‐irrigated cores, atrazine was concentrated in the upper soil horizons with an average center of mass at 63 ± 64 cm and a mean variance around the center of mass of 58 cm. The mean centers of atrazine mass in the effluent‐irrigated profiles and high‐quality water‐irrigated profiles are significantly different (Student's t‐test, P = 0.06). The equilibrium sorption isotherm for atrazine in the presence of high‐quality water was nonlinear, with a Freundlich n of 0.87 and a distribution coefficient (Kf) of 1.07. The atrazine isotherm in the presence of effluent had a similar n (0.86) but a significantly lower Kf of only 0.93. Atrazine at a rate of 4 mg/kg−1 was added to soil columns filled with the < 1‐mm size fraction of the 0 to 30‐cm horizon of soil from an uncultivated site adjacent to the field site. Three replicate columns were leached with 0.85 pore volumes of either secondary effluent or 0.005 M CaCl2 solution at constant head. Atrazine in the effluent‐treated columns was more strongly leached from the upper columns and peaked at higher concentrations lower in the columns.
Soil Water Bypass and Solute Transport under Irrigated Pasture
Authors: Prendergast J. Bernard 
Published: July 2010

AbstractDownward water flow through soil transports solutes and suspended matter. The velocity of flow can be critical in the process of groundwater pollution, and can determine how effectively this water leaches the root zone of crops. This study quantifies fast soil water fluxes (bypass), and provides some insight into the effectiveness of this bypass in leaching of salt. Three water salinity treatments were imposed on replicated 75‐m2 plots growing irrigated pasture. A tritium‐labeled irrigation was applied to the plots to quantify bypass flow. Penetration of tritium‐labeled water decreased with increased salinity treatment (P < 0.01) for up to 50 d after irrigation application, despite a greater leaching fraction under saline conditions. Bypass decreased with increased salinity because there was higher antecedent water content (P < 0.02) due to lower crop water use, resulting in less soil cracking under saline conditions. Bypass flow was also calculated from a model that used the profile of Cl− concentration below the root zone. However, calculations from the model failed to agree with the experimental results, including the direct measurement of bypass made from recovery of the applied radiotracer. The model failed because it assumed that bypass was of low salinity, whereas the experiment indicated that bypass contributed to leaching. Therefore it was concluded that bypass is best defined in hydraulic terms, rather than in terms of salt leaching. It was also concluded that the Cl− concentration in bypass flow reflected the concentration in the soil matrix. Therefore total water loss below the root zone was adequately quantified by a leaching model of the Cl− mass balance, incorporating the volume‐averaged soil water Cl− concentration.
Determining Manganese Oxidation State in Soils Using X‐ray Absorption Near‐Edge Structure (XANES) Spectroscopy
Authors: Schulze D. G. , Sutton S. R. , Bajt S. 
Published: July 2010

AbstractThe redox chemistry of soil Mn is important in Mn uptake by plants, the movement of trace elements absorbed on or occluded in Mn‐oxides, and the etiology of some soil‐borne plant fungal diseases. The objectives of this study were to develop calibration curves for determining Mn oxidation states in moist soil samples using micro‐x‐ray absorption near‐edge structure spectroscopy and to test the method on selected soils. Oxidation‐state standards were prepared by mixing dry powders of MnSO4·H2O (Mn2+) and a synthetic Na‐birnessite, Na4Mn14O27·9H2O (Mn4+) to obtain various Mn2+ mole fractions, f(Mn2+), where f(Mn2+) = Mn2+/(Mn2+ + Mn4+). Corundum (α‐Al2O3) was used as a diluent to prepare mixtures containing 50, 1000, and 100 000 mg Mn kg−1. Quantitative analysis of Mn oxidation state is possible using either the energy of the pre‐edge peak at 6540 eV or a ratio based on the intensity of the Mn2+ white line peak at 6552.6 eV divided by the intensity of the Mn4+ white line peak at 6560.9 eV. The white line intensity ratio is more sensitive, with an estimated lower detection limit of 20 mg Mn kg−1 using a 300 by 300 µm spot, and predicts f(Mn2+) with an accuracy of ±0.1 mole fraction (95% confidence interval) through most of its range. The f(Mn2+) for four air‐dried Indiana surface soils ranged from 0.26 to 0.44 ± 0.1. Saturation and reduction for 5 d resulted in complete reduction of Mn in the soil matrix.
Pyrite Enhancement of Phosphorus Availability from African Phosphate Rocks: A Laboratory Study
Authors: Lowell K. , Weil R. R. 
Published: July 2010

AbstractPhosphate rock (PR) and pyrite deposits, indigenous to many African countries, may be useful to resource‐poor farmers for increasing the P and S fertility of highly weathered tropical soils. Combination of PR and pyrite was examined as a means to increase the availability of P from five PR of African origin. Pyrite and PR were combined in several ratios (P/S) and incubated. Mixtures were periodically leached on a vacuum extractor with 0.01 M KCl for a 6‐mo period. Soluble P and pH of the leachate were measured. The pH of the leachates decreased with increasing levels of pyrite. In all cases, soluble P measured in the leachate increased with increasing levels of pyrite. Soluble P measured in the leachate was greatest from Togo and Uganda PR mixtures, much less from Zimbabwe PR, and virtually nil in all but the highest pyrite treatments for both Tanzania and Malawi PR mixtures. Citrate‐soluble P was a less reliable predictor of P release than total P and the percentage of CO2, Al, and Fe in the PR and associated minerals. High pyrite levels with low‐quality rocks generated P release comparable with that from untreated high‐quality rocks. The addition of Fe from the pyrite apparently did not lead to precipitation of substantial amounts of P as it was released from PR. The rocks responded very differently to the pyrite treatment. Although the method is promising for some rocks (Togo and Uganda), it is obviously not useful for other rocks (Malawi).
Influence of Soil Properties on the Biogeochemistry of a Beaver Meadow Hydrosequence
Authors: Johnston C. A. , Pinay G. , Arens C. , Naiman R. J. 
Published: July 2010

AbstractPrevious research about the biogeochemistry of beaver (Castor canadensis Kuhl) impoundments has generally overlooked the influence of soil type on solutes. In this study, soils derived from glacio‐lacustrine and glacio‐fluvial parent materials in northern Minnesota beaver meadows (i.e., former beaver ponds that have drained and revegetated) were studied to: (i) describe soil morphology, (ii) analyze soil and solute chemistry, and (iii) statistically evaluate the relative influence of hydrology and soil type on solute chemistry. With decreasing depth to groundwater, soils in both hydrosequences were increasingly reducing; redox potentials were consistently negative in the Borosaprist. Differences in soil morphology associated with increasing wetness included: (i) increasing thickness of O and A horizons, (ii) decreasing thickness of the Bt horizon (glacio‐lacustrine hydrosequence), (iii) disappearance of E and Bk horizons (glacio‐lacustrine hydrosequence), and (iv) decreasing depth to redoximorphic features. In the glacio‐lacustrine hydrosequence, depth to subsurface concentrations of oxalateextractable Fe (≥800 g m−3) decreased with increasing wetness. Two‐way ANOVA indicated that differences in water chemistry among soils were due to moisture, parent material, and their interaction. Increasing moisture was associated with increased concentrations of Fe2+, Ca2+, and Mg2+ and decreased concentrations of SO4‐S. Glaciolacustrine soils contained higher concentrations of base cations (K+, Ca2+, and Mg2+) than did glacio‐fluvial soils, and so did their soil water. There were pronounced seasonal variations in cation concentrations and significant interannual differences for NH4‐N, total N, and K+. Nitrate concentrations were consistently low and did not differ significantly among any of the groupings.
The Soil Freezing Characteristic: Its Measurement and Similarity to the Soil Moisture Characteristic
Authors: Spaans Egbert J. A. , Baker John M. 
Published: July 2010

AbstractA soil freezing characteristic (SFC) represents the relationship between the quantity and the energy status of liquid water in frozen soil. The SFC is the analogue to the soil moisture characteristic (SMC) and is essential to modeling the transport of water, heat, and solutes in frozen soil. This paper presents a new, automated technique to measure an SFC in situ, for which there has previously been no method. Liquid water content in frozen soil was measured with time domain reflectometry. The corresponding energy status was inferred from accurate soil temperature measurements with a generalized form of the Clapeyron equation. Since both SFC and SMC describe water retention properties in soil, their similarity was investigated. The SMC and SFC agreed to within 1% moisture content across a wide range of matric potentials. Determination of the SMC is reliable at high matric potentials but becomes increasingly inaccurate and time consuming as soil dries. By contrast, the SFC determination becomes more accurate and rapid at lower matric potentials. We thus propose that water retention properties at high matric potentials are best obtained from draining and at low matric potentials from freezing.
Errors in Converting Time Domain Reflectometry Measurements of Propagation Velocity to Estimates of Soil Water Content
Authors: Hook W. R. , Livingston N. J. 
Published: July 2010

AbstractThe determination of soil water content by time domain reflectometry (TDR) involves the measurement of the propagation velocity of a radio frequency (RF) pulse in soil and the conversion of this measurement to an estimate of soil water content. The objective of this study was to quantify errors in this conversion. A comprehensive error analysis can only be carried out if a well‐defined measurement procedure is followed. We define and recommend such a procedure and identify the physical origin and the magnitude of each of the error sources in the procedure. Total measurement errors are calculated as the root mean square sum of each of the individual errors. We express propagation velocity measurements in terms of time intervals, that is, the travel time of an RF pulse in soil (T) relative to that in air (Tair). Our measurement and error calculation procedure is based on an analysis of our own and published data for nonclay soils, which reveals that in all cases, there is a linear relation between T/Tair and volumetric water content (θv) with a mutually independent slope and intercept. A theoretical explanation for this observation is presented. We show that the dominant measurement error source is the transition time of the TDR reflection, which in turn is a function of θv. Absolute measurement errors range from 0.015 to 0.028 m3 m‐3 if the T/Tair vs. θv intercept is known and increase to 0.023 to 0.034 m3 m‐3 if a nominal value (1.55) is used. We recommend that a T/Tair vs. θv slope value of 0.1193 (5% less than theory) be used for measurements in nonclay agricultural soils. This leads to little loss in accuracy. Measurement resolution is primarily a function of the time base error of the TDR instrument and can be as good as 0.0018 m3 m‐3.
Self‐Similitude and Fractal Dimension of Sand Grains
Authors: Barak Phillip , McSweeney Kevin , Seybold Cathy A. 
Published: July 2010

AbstractFractal theory postulates that geological materials possess a noninteger, fractal dimension describing length‐surface‐volume relations and particle‐size distribution. We examined sand grains, composed largely of quartz, from several horizons of Wisconsin soils derived from glacial outwash for fractal dimension using image analysis of reflected light micrographs with NIH Image software. No evidence was found to support other than a Euclidean, i.e., regular dimension, relating the geometric properties of: (i) measured particle perimeter as a function of magnification or (ii) particle area and perimeter. In addition, particle‐size distributions were better fit by lognormal distribution than by a fractal fragmentation dimension. Fractal theory would not appear to provide a useful description for these soil materials.
Metal and pH Effects on Adsorption of Poly(vinyl alcohol) by Silicon Oxide
Authors: Schulthess C. P. , Tokunaga S. 
Published: July 2010

AbstractThe adsorption of pentanol onto a smectite shows an adsorption edge at pH 10. Because adsorption similarities between smectites and Si oxides have been noted in the literature, we anticipated that poly(vinyl alcohol) (PVA) would also display an adsorption edge near pH 10 on a Si oxide (SiO2). Adsorption edges between pH 9 and 10 on Si oxide were confirmed when using two PVA polymers of 98 and 88% hydrolysis (MW = 11 000 and 10 000 g mol‐1, respectively). The decrease in adsorption at high pH is attributed to the interference of Na+ adsorption on the Si oxide. The addition of aqueous metals (Al3+, Pb2+, Cu2+, Mg2+, and Ba2+) significantly modified the adsorption envelope of PVA on the Si oxide in various ways. Three mechanisms are proposed: metals may modify the Si surface, interact with the PVA while in the aqueous phase, or form an additional independent surface that can adsorb the PVA polymer. New PVA adsorption envelopes were observed at high pH in the presence of Mg, Cu, and (adsorbed) Pb. The presence of metals also increased the amount of PVA (98% hydrolysis) adsorbed at low pH, but caused no change in, or decreased, the amount of PVA (88% hydrolysis) adsorbed on a mass per area basis. Because of this, we suggest that the metals can modify the effective thickness of the polymers on the surface. The adsorption of Pb and Al on the Si oxide modified the solubility of Si, suggesting a chemisorption reaction with the surface.
Analysis and Field‐Evaluation of the CERES Models' Soil Components: Nitrogen Transfer and Transformations
Authors: Gabrielle Benoît , Kengni Lucas 
Published: July 2010

AbstractFor estimating N losses in soil‐crop systems with the simple and functional CERES models, we evaluated their N modules and compared them with the more complex SLIM (for solute transport) and NCSOIL (for N mineralization) models. SLIM is based on the concept of immobile and mobile water regions in soil, and CERES on a piston‐flow hypothesis. In NCSOIL, the soil organic matter (SOM) mineralizes through two active pools, whereas in CERES the SOM decomposes as a whole with a gross decay rate. We used data on mineral N dynamics under bare soils (silt loam, loam, and sandy loam) from 1‐yr‐long experiments at three locations in France, including measurements of weekly NO3 leaching fluxes. The original CERES mineralization submodel did not correctly simulate N supply from potentially degradable SOM. When using NCSOIL instead, the simulations improved and CERES predicted NO3 leaching reasonably well, with a root mean square error of 6 to 21 kg N ha‐1, representing 5% of the yearly flux. The SLIM model performed as well, and better simulated the intense NO3 percolation regime that occurred in wintertime. Its immobile water fraction parameter had to be calibrated, however, or the yearly leaching flux was underestimated. When linked to NCSOIL, the CERES model showed a good potential for estimating N dynamics in soil, even if its piston‐flow type of NO3 transfer was not always relevant. In such case, SLIM was a more appropriate approach, although it required a site‐specific calibration.
Comparison of Three Methods to Obtain the Apparent Dielectric Constant from Time Domain Reflectometry Wave Traces
Authors: Timlin D. J. , Pachepsky Ya. A. 
Published: July 2010

AbstractA calibration of time domain reflectometry (TDR) probes to measure soil water in a particular soil is desirable since no consistent relationship between water content and apparent dielectric constant (Ka) has been found. We compared three procedures to compute Ka from TDR traces: a manual method that uses a plot of the wave trace, a derivative‐based computer algorithm, and fitting a simulated TDR trace to a measured one with a simple multiple reflection model. We added a model of inertia to the multiple reflection model to approximate the rise time of the cable tester. The TDR traces were measured in situ with a Tektronix 1502B cable tester (Tektronix, Inc., Wilsonville, OR) on samples from two soils with contrasting textures, Beltsville silt loam (fine‐loamy, mixed, mesic Typic Fragiudult) and Rumford loamy sand (coarse‐loamy, siliceous, thermic Typic Normudult). Ten‐centimeter probes with three rods were used. The water contents were measured gravimetrically with soil cores. Calibration with apparent dielectric constants obtained from the derivative‐based algorithm had the smallest standard error for both soils, and the manual method was better than the wave simulation method. The intercepts and slopes of the calibration equations for the manual and derivative methods were not significantly different from each other for both soils. The wave simulation method, which gives physically meaningful values for Ka, and characteristic impedances can be a useful tool for theoretical studies.
The Characterization of Water in Peat
Authors: McBrierty V. J. , Wardell G. E. , Keely C. M. , O'Neill E. P. , Prasad M. 
Published: July 2010

AbstractThe functionality and ultimate use of peat are intimately bound up with the way in which absorbed water behaves in the host matrix. Control of the amount of absorbed water, the dynamics of water loss in drying, and the gain of water in rewatering are important determinants in its commercial exploitation. We examined the nature and behavior of water in a range of different Irish peat samples by exploiting the combined capabilities of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and proton nuclear magnetic resonance (NMR). Up to four different forms of water were detected in heavily hydrated peat: absorbed or tightly bound water, which is non‐freezable and behaves like a glass at low temperatures; two forms of loosely bound water; and bulk water. Increasing temperature across the subambient regime revealed the sequential onset of mobility of the different forms of water. The transitions are well‐defined in terms of both water concentration and the temperature at which motion sets in. Unlike hydrated polymers, NMR estimates of the maximum amounts of bound water at low temperatures depend on overall water content, reflecting the extent to which the peat matrix can restructure and swell when hydrated. The TGA, which maps out the loss of water under controlled conditions of temperature and atmosphere, offers additional evidence on the mechanism of dehydration, indicating that drying on a small scale under laboratory conditions is not grossly impeded by internal barriers. The gratifying consistency between the data from the three experimental techniques used, along with pertinent data in the literature, give additional insights into the role of water in peat.
Two‐Dimensional Model for Water, Heat, and Solute Transport in Furrow‐Irrigated Soil: I. Theory
Authors: Noborio K. , McInnes K. J. , Heilman J. L. 
Published: July 2010

AbstractBecause of salinity, many areas with irrigated farmland have suffered from reduced food and fiber production, especially where irrigation water or soil contains large amounts of soluble salts. In those areas, ridge‐furrow tillage is a common practice and furrow irrigation is a popular irrigation method. Effects of water content, temperature, and solute concentration on transport phenomena in soil are hard to predict without complex models. The geometry of a ridgefurrow surface contributes to complexities in heat and vapor transport, and hence, in the distribution of water, temperature, and salt in soil. To improve understanding of water, heat, and solute transport in furrow‐irrigated and salt‐affected soil, we developed a two‐dimensional mechanistic model using the Galerkin finite element method (FEM). The model was designed to consider interactive effects of water content, temperature, and solute concentration on water, heat, and solute transport. To simulate field conditions, an energy balance equation was applied to the ridge‐furrow surface to provide boundary conditions for water and heat transport. To utilize a single FEM solver, equations governing transport of water, heat, and salt in soil were generalized as a diffusive‐convective type equation. Numerical schemes for the model were tested by comparing simulated results with analytical or semianalytical solutions. Good agreements between FEM and analytically calculated soil water content, temperature, and solute concentration were obtained.
Role of Redox Potential in Chemical Transformations of Selenium in Soils
Authors: Jayaweera Gamani R. , Biggar James W. 
Published: July 2010

AbstractIrrigated agricultural areas with high levels of soil Se face the dilemma of elevated Se levels in drainage and groundwater systems, which will adversely affect the environment and the wildlife. The release of Se from soils to water systems is dependent on the speciation of Se, which is primarily governed by the redox potential. This study describes the dynamics of redox transformations of naturally occurring Se in a soil matrix as a continuous function of time during a sequence of oxic‐anoxic‐oxic transition. An experimental setup where a solution stream is continuously passed through a soil column in a closed loop to reach an equilibrium between the soil and the solution was used. The pH and redox potential (Eh) were recorded and the solution was analyzed over time for various Se forms and Mn2+. During soil reduction, the total soluble Se and SeO2−4 decreased, while the SeO2−3 and other Se forms (organic Se, elemental Se, and selenide) increased initially, then decreased. Both soluble Se and SeO2−4 decreased during the anoxic phase, slowly at first, then more rapidly, and were characterized by first‐order rate constants. During reoxidation, the total soluble Se and SeO2−4 increased, SeO2−3 initially increased followed by a decrease, and other Se forms decreased. Decrease in SeO2−3 during reduction may be partly due to the precipitation of MnSeO3. This study showed that the soil Eh plays an important role in mobilizing Se into water systems.