bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stochastic Analysis of Soil Water Monitoring for Drip Irrigation Management in Heterogeneous Soils
Authors: Or Dani 
Published: July 2010

AbstractMany drip irrigation management schemes rely on frequent monitoring of soil water content and matric potential, using various sensors (e.g., tensiometers or time domain reflectometry probes). The soil water information is used either for irrigation scheduling or for adjusting schedules based on evapotranspiration measurements. Spatial variations in soil properties induce variations in wetting patterns about the drippers, which complicate the acquisition and interpretation of information on soil water status. The objective of this study was to quantify the effects of mild spatial variation in soil hydraulic properties on wetting patterns and the consequences on soil water sensor placement and interpretation. The soil hydraulic properties (saturated hydraulic conductivity, Ks, and the exponent α of the exponential unsaturated hydraulic conductivity function) were considered as random space functions. Small perturbation expansions were applied to analytical solutions of steady state flow from point sources. The resulting analytical expressions relate the variability of Ks and α to the expected variability in soil water pressure head (h) and relative saturation (S) about a point source. Comparisons of the analytical predictions with Monte Carlo simulations (for surface and buried sources) resulted in excellent agreement for coefficients of variation of ln(Ks) and α ≤ 0.3. The expressions may be used as first approximations to define regions with small uncertainty that may be most suitable for soil water monitoring and control in drip‐irrigated fields. Another application is for determining the minimum number of sensors needed to obtain estimates with a prescribed estimation error. The derived spatial covariance functions of S and h may be used to identify regions in the field with different wetting patterns or simply to interpolate measurements to unmeasured portions of the field.
Coprecipitation of Sodium, Magnesium, and Silicon with Calcium Carbonate
Authors: Levy D. B. , Amrhein C. , Anderson M. A. , Daoud A. M. 
Published: July 2010

AbstractCalcite oversaturation in soil solutions is often attributed to overestimations of Ca2+ (aq) and CO2−3 (aq) activities, organic matter mineralization, and the presence of metastable forms of CaCO3. Earlier research, however, has indicated that these explanations are often insufficient to explain the levels of calcite oversaturation observed in soil suspensions. This study was conducted to evaluate the solubilities of precipitates formed during evapoconcentration of synthetic irrigation waters. Solids precipitated from waters of various Mg and Si concentrations were redissolved in deionized water under controlled CO2 conditions. Ion activities were calculated from the solution composition using the geochemical speciation model MINTEQA2. X‐ray diffraction (XRD) and infrared absorption spectroscopy provided evidence for precipitation of poorly crystalline Mg silicates and hydrous Na‐Mg silicates (sepiolite [Mg2Si3O7.5(OH)·3H2O], loughlinite [Na2Mg3Si6 (OH)16·8H2O], stevensite [Na0.33Mg2.87Si4O10(OH)2], or magadiite [Na Si7O13(OH)3·3H2O]). Calcite, aragonite, gypsum, and amorphous SiO2 were also identified. The solubility of the solid phase was proportional to the amount of Si and Mg in the solid, and dissolution of the solids in deionized water under atmospheric CO2 yielded an average CaCO3 ion activity product value of 10−8.0. The maximum mole fraction of Mg (XMg) in the calcite determined by XRD was <0.03, while XMg values calculated from mass balance were up to 0.53. The high solubility of the solid phases and the high Ca2+ (aq) and CO2−3 (aq) activities are attributed to poorly crystalline Mg silicates and Na silicates similar in composition to sepiolite, loughlinite, stevensite, and magadiite.
Extraction of Manganese from Soils with Potassium Salts
Authors: Tu S. , Racz G. J. , Cho C. M. 
Published: July 2010

AbstractApplication of KCl usually increases the solubility of soil Mn and its bioavailability, yet the mechanisms of the phenomenon are not fully understood. The purpose of this study was to investigate the effects of KCl and salts such as KBr, KI, KNO3, K2SO4, K2CO3, K2HPO4, KH2PO4, Ca(NO3)2, Ca diethylenetriamine pentaacetic acid, and Cu(NO3)2 on the amount of Mn extracted from soils as affected by ionic strength, acidity of soil or extractant, and extraction time. The formation of anionic complexes of Mn and Cl in aqueous solution, using cation‐anion‐exchange resins, was also investigated. Amounts of Mn extracted by KCl from soils increased with increases in ionic strength and extraction time but decreased with increases in pH. The salts usually extracted more Mn from the noncalcareous than from the calcareous soils. The KI was capable of reducing MnO2 at normal soil pH, whereas Mn extracted by KCl was similar to Mn extracted by other neutral salts. The KCl‐extractable Mn was highly correlated with readily soluble [Ca(NO3)2‐extractable] Mn and weakly adsorbed (CaDTPA‐extractable) Mn fractions, but not to the specifically adsorbed [Cu(NO3)2‐extractable] Mn fraction. The Mn2+ in KCl solutions was shown to form anionic Mn‐Cl complexes. These complexes, along with ionic strength effects, were most likely responsible for the increases in solubility of soil Mn.
Mechanistic Simulation of Vertical Distribution of Carbon Concentrations and Residence Times in Soils
Authors: Elzein Abbas , Balesdent Jérôme 
Published: July 2010

AbstractWe developed a numerical simulation model of the decay and vertical transport of soil organic matter. Soil organic matter is divided into a number of compartments each with different decay rates but with similar migration parameters. Decay has been represented with first‐order processes. Two elementary forms of migration were explored: diffusive equations represent transport through soil mixing whereas translational convection simulates movement within the liquid phase. Coefficients of decay, diffusion, and convection were taken to be uniform with depth. Carbon input is both through the surface in the form of litter fall and directly underground from roots. Profiles of total C content and 14C content were measured for a temperate forest silt loam soil. Similar data for other forest soils, available in the literature, were also assembled. Statistical adjustment, through nonlinear regression, of decay, migration, compartment configuration, and plant production parameters, accurately simulated profiles of C and 14C. The rapidly decaying compartment was successfully likened to the 50‐ to 2000‐µm particle‐size fraction. Convection rates of ≈0.3 mm yr−1 and diffusion rates ranging from 1 to 15 cm2 yr−1 were obtained. Diffusive processes appear to be preponderant relative to convection. The model has proven sensitive to differences between temperate and tropical soils as well as textural variations.
Total and Light‐Fraction Carbon Dynamics during Four Decades after Cropping Changes
Authors: Bremer E. , Ellert B. H. , Janzen H. H. 
Published: July 2010

AbstractThe dynamics of soil organic C after a change in cropping practice are important in defining the potential impact of the new practice on soil behavior and net CO2 exchange. Our objective was to determine the duration and magnitude of a shift in soil organic C after a change in summer fallow frequency in spring wheat (Triticum aestivum L.) systems. Total organic and light‐fraction C in continuous wheat (W), fallow‐wheat‐wheat (FWW), and fallow‐wheat (FW) treatments were determined in soil samples collected periodically from 1954 to 1992 from a long‐term spring wheat study located in the northern Great Plains. Organic C concentrations in the 0‐ to 15‐cm depth were 11% lower in the FW and FWW treatments than in the W treatment from 1967 to 1992. Organic C concentrations in the 15‐ to 30‐cm depth were not affected by treatment, but varied among sampling years due to differences in effective sampling depth. Light‐fraction C concentrations were 38% lower in the FW and FWW treatments than in the W treatment from 1967 to 1992. Reduced light‐fraction C accounted for about one‐third of the decrease in total organic C due to inclusion of fallow in the crop rotation. The negative influence of fallow was primarily due to enhanced decomposition in the fallow year. We conclude that most losses of soil organic C due to introduction of a fallow system occur within two decades, and that further loss of organic C is negligible provided soil erosion is minimal.
Soil Acidification from Long‐Term Use of Anhydrous Ammonia and Urea
Authors: Bouman O. T. , Curtin D. , Campbell C. A. , Biederbeck V. O. , Ukrainetz H. 
Published: July 2010

AbstractAcidity generated by N fertilizers depends on factors such as the composition of the fertilizer, climatic and soil conditions, and the crops grown. Our objective was to quantify the acidifying effects of urea and anhydrous NH3 when used as fertilizers for cereal production in Saskatchewan, Canada. The fertilizers were injected annually (at 10‐cm depth) into a medium‐textured, moderately acid (pH ≈5.5) Typic Haploboroll, at rates of 0, 45, 90, and 180 kg N ha−1 for 9 yr. Soil acidity increased as N application rate increased, with anhydrous NH3 causing greater acidification than urea. Although pH values as low as 4.3 were recorded in soil treated with anhydrous NH3, KCl‐exchangeable acidity remained low. The major effect of acidification was a depletion of exchangeable Ca and Mg. The solubility of Mn (but not Al) increased substantially as pH decreased, with solution concentrations of almost 30 mg Mn L−1 being recorded 6 d after injection of NH3. Acidity generated by anhydrous NH3 compared well with values predicted assuming that all of the applied NH3 was oxidized to NO3− (with the production of 1 mol H+ mol−1 of N) and that these protons were partly neutralized by OH− released when NO3− was taken up and assimilated by plants. Acidification due to export of bases in grain was insignificant because wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) remove only a slight excess of cations over anions. Urea failed to realize its full acidification potential because of an apparent loss of urea‐N from the soil by NH3 volatilization.
An Alkaline Oxidation Method for Determining Total Arsenic and Selenium in Soils
Authors: Zhu Baojin , Tabatabai M. A. 
Published: July 2010

AbstractA simple, accurate, and precise method for determination of total As and Se in soils was developed. In this method, a mixture of soil and NaOBr solution was boiled to dryness in a sand bath (260–280°C), and the total amounts of As and Se were extracted with 1.25 M H2SO4 and determined by an atomic absorption spectrophotometer, equipped with a hydride generation system, after reducing As(V) to As (III) and Se(VI) to Se(IV). With 12 soils analyzed, the As values ranged from 5.0 to 14.3 mg kg−1 soil and the Se values ranged from 0.5 to 5.5 mg kg−1 soil. The average results by the proposed NaOBr oxidation method agreed closely with those obtained by the acid digestion methods of USEPA and USGS proposed for determination of As and Se in soils and geologic materials. The method gives quantitative recovery (96–103%) of As and Se in certified standard reference materials and of these elements added to soils (99–101%). Digestion of soil samples with NaOBr solution and determination of the extracted As and Se by hydridge‐generation atomic absorption spectrometry permit rapid analysis of a large number of samples at one time. Tests with 13 metals indicated that, at the concentrations normally expected in soils, none of those metals interfered with determination of As and Se by the proposed method. A single operator can complete the oxidation and analysis of one element in 40 samples in a normal working day.
Rapid Method for Accurate Determination of Colorless Siderophores and Synthetic Chelates
Authors: Shenker M. , Chen Y. , Hadar Y. 
Published: July 2010

AbstractA rapid, simple, and accurate method of determining concentrations of Fe‐chelating agents in solution was developed. The assay employs Cu‐CAS (chrome azurol S) complex as a testing agent and measures the equilibrium concentration of this complex in the presence of other Fe chelators. The Cu‐CAS was found to be advantageous in comparison to other compounds due to: (i) its high extinction coefficient (17 000 M−1 at pH 5.7) when complexed with Cu, and (ii) the rapid rate at which equilibrium was achieved. The color of the Cu‐CAS was measured at a wavelength of 582 nm, and the decrease in absorbance when the Cu is lost to other chelates was measured. Using this method, we successfully measured 50‐ to 100‐nmol quantities of the following chelates: ethylenediaminetetraacetic acid disodium salt (EDTA), ethylenediamine‐di(o‐hydroxyphenylacetic acid) (EDDHA), desferriferrioxamine‐B (DFOB), rhizoferrin, and mugineic acid (MA). We found the method to be accurate and useful in determining concentrations of chelates (not absorbing intensely at 582 nm) including phytosiderophores and microbial siderophores. This method is of particular importance for colorless chelates, which are very difficult to determine otherwise.
Rate of Nitrogen Mineralized from Incorporated Crop Residues as Influenced by Temperature
Authors: Vigil M. F. , Kissel D. E. 
Published: July 2010

AbstractMethods are needed to predict seasonal mineralization of N when crop residues are added to soils in order to assess N availability to crops. The objective of this investigation was to evaluate and develop methods for predicting the effect of temperature on the rate of N mineralization (Nmin) from crop‐residue‐amended soils maintained at near‐optimum soil water content. Unamended and crop‐residueamended soils were incubated at temperatures between 5 and 35°C to obtain Nmin rates for calculation of Q10 values, defined as the ratio of reaction rates at a temperature interval of 10°C. Measured Q10 depended on the C/N ratio of the residue and incubation time, indicating that for predictive purposes a single Q10 value is inadequate for describing the effect of temperature on crop‐residue Nmin. Temperature functions were developed from Nmin data collected from unamended soils incubated at four temperatures under laboratory conditions. These functions were then tested in the MINIMO model (a subroutine of CERES‐MAIZE) for residue‐amended soils at four temperatures for up to 160 d. Model‐predicted mineralizations was close to measured Nmin for most crop‐residue‐soil mixtures tested. The use of the new temperature equations improved the precision of the model, reducing the residual sum of squares (RSS) from 9797 to 5286. However, the modified model was not able to accurately predict Nmin for crop residues with a C/N ratio of 10 and 28. Inadequate prediction at these C/N ratios may be related to how the model allocates the pool sizes for soluble and insoluble plant N and the cellulose‐hemicellulose pool size of the crop residues.
Water Table Management Effects on Denitrification and Nitrous Oxide Evolution
Authors: Kliewer B. A. , Gilliam J. W. 
Published: July 2010

AbstractPrevious research suggested that using controlled drainage to elevate the water table reduces NO3− contamination of surface water by enhancing denitrification. The C2H2 inhibition technique was used to study denitrification and N2O evolution using 56‐cm‐long, undisturbed cores of Cape Fear loam (clayey, mixed, thermic Typic Umbraquult) maintained in the field and subjected to three static water table levels (15, 30, and 45 cm). Results showed that intermittent C2H2 exposure did not (i) affect soil inorganic N distribution between NH4+ and NO3−, (ii) diminish inhibition of N2O reduction during subsequent C2H2 exposure, or (iii) induce C2H2 decomposition. Denitrification from 1 Nov. 1993 through 21 Apr. 1994 (172 d) was 341 kg N ha−1 for the 15‐cm water table treatment, 260 kg N ha−1 for the 30‐cm water table treatment, and 86 kg N ha−1 for the 45‐cm water table treatment. Denitrification was maximum at the lowest monitored zone (36–54 cm) for each water table treatment. Total N2O evolution was 9 kg N ha−1 for the 15‐cm water table treatment, 4 kg N ha−1 for the 30‐cm water table treatment, and 2 kg N ha−1 for the 45‐cm water table treatment. Nitrous oxide evolution was positively correlated with mean soil temperature (10‐cm depth) until low NO3− levels appeared to limit denitrification. Since steady‐state diffusion was not reached, estimates of N2 evolution, using N2O evolution in the presence of C2H2, were underestimated 12‐fold. Evolved N2O‐N represented only 2% of denitrification in the soil core (0–54 cm) for each water table treatment. Drainage control to elevate the water table enhanced denitrification and N2O evolution, reducing the potential for N transport with subsurface drainage to surface water.
Temporal Patterns in Beech Forest Soil Solutions: Field and Model Results Compared
Authors: Johnson Dale W. 
Published: July 2010

AbstractThe applicability of cation exchange equations and the Nutrient Cycling Model (NuCM) to a beech (Fagus grandifolia Ehrh.) forest soil in the Great Smoky Mountains, North Carolina, was tested by examining temporal variations in soil solution chemical composition. Both field data and NuCM output implied that short‐term, local variations in exchangeable Ca2+ and Al3+ occurred, causing non‐ideal plots of pAl vs. pCa in soil solution. Thus, plots of pCa vs. pAl, with their inherent assumptions of constant exchangeable cations, do not provide an adequate test of the applicability of cation exchange equations to field conditions. A large NO3− pulse caused sequential peaks in soil solution Mg2+, Ca2+, and Al3+, which became more separated with soil depth. The NuCM model did not reproduce this pattern, showing instead simultaneous peaks of all cations in response to NO3− pulses. As a consequence, NuCM underestimated peak Al/Ca ratios. The disparity was probably due to the coarse scale at which NuCM and models like it represent the soil. A chromatographic model may be more appropriate for this time scale.
Iron and Aluminum Oxide Influence on Agronomic Effectiveness of Modified Phosphate Rocks
Authors: Menon R. G. , Chien S. H. , Hellums D. T. 
Published: July 2010

AbstractA greenhouse experiment was conducted to study the influence of Fe and Al oxide in phosphate rocks (PR) on partially acidulated phosphate rock (PAPR) effectiveness and to evaluate compaction of PR with soluble phosphates as an alternate method of utilizing PR with high Fe and Al oxide. Five PR with Fe + Al oxide ranging from 19 to 320 g kg−1 were acidulated with 50% of the H2SO4 (PAPR, 50% H2SO4) required to fully convert the PR to triple superphosphate (TSP) or were compacted with TSP so that 50% of the total P was in TSP form (PR + TSP). They were applied to Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.8) at rates 50, 100, 200, and 300 mg P kg−1. Two successive crops of maize (Zea mays L.) and one of rice (Oryza sativa L.) were grown. Biomass yield of the first crop from PAPR‐treated soils decreased from 86% of that from TSP to 16% and P uptake from 72 to 12% with increasing Fe and Al oxide from 1.9 to 32%. The decrease in effectiveness of PAPR was directly related to a decrease in water‐soluble P in PAPR with increasing Fe and Al oxide content. The compacted PR = TSP were 86 to 104% as effective as TSP in increasing biomass yield and 78 to 94% as effective in increasing P uptake. There were no great differences between PAPR and the compacted PR + TSP in terms of residual effect on the second crop of maize, except for Matongo PR. The difference in residual effectiveness between PAPR and compacted PR + TSP was not as pronounced for rice as for maize.
Characterizing Water and Solute Movement by Time Domain Reflectometry and Disk Permeametry
Authors: Vogeler Iris , Clothier Brent E. , Green Steven R. , Scotter David R. , Tillman Russell W. 
Published: July 2010

AbstractTo investigate a rapid, nondestructive way of characterizing solute transport properties, time domain reflectometry (TDR) and disk permeametry have been used in combination. Calibration measurements had previously related TDR measurements to both the volumetric water content and the pore water concentration of Cl‐. Laboratory measurements from a horizontal TDR probe were used to estimate transport parameters in a soil column by applying a one‐dimensional numerical model in an inverse sense. A vertical TDR probe was used to provide independent verification of these parameters. A repacked column of Ramiha silt loam (an Andic Dystrochrept) was used under unsaturated, transient flow conditions. The disk permeameter, set to a pressure head of −50 mm and containing a solution of 0.032 M KCl, was placed straight onto the repacked soil column, which had an initial water content of 0.32 m3 m‐3. The soil wet to 0.60 m3 m‐3. However, in the columns only an envelope of Cl‐ concentration could be obtained, due to exchange between the initially resident Ca2+ and the invading K+. This illustrates why cation exchange needs to be considered when TDR is used to infer solute dispersivity and the retardation were found to be 2.3 mm and 1.2, respectively. The retardation is shown to be due to the anion‐exchange capacity varying with the concentration of the invading soil solution.
Stability of Wetting Fronts in Dry Homogeneous Soils under Low Infiltration Rates
Authors: Yao Tzung‐mow , Hendrickx Jan M. H. 
Published: July 2010

AbstractOur understanding of unstable wetting phenomena in soils is limited. Therefore, lysimeter experiments were conducted in the laboratory to validate current wetting front instability theories. Four different grades of sieved and air‐dried perlite and quartz sand were used as the experimental material. Water was applied by a sprinkler system at rates within the range of natural precipitation rates in New Mexico. Experiments were conducted in small lysimeters (diameter 30 cm, height 50 cm) as well as a large one (diameter 100 cm, height 150 cm). The experimental results show that wetting front instability will cause fingering phenomena in a homogeneous soil system. This observation confirms experimental and theoretical results of other workers. The diameter of fingers was observed to be a function of the grain size of the sand. Small fingers (3–4 cm diameter) were found in coarse sand (grain size 1.41–0.84 mm); large diameter fingers (12 cm diameter) were observed in fine sand (grain size 0.42–0.25 mm). Our experimental results in the coarse sand show that, for infiltration rates varying between 0.3 and 12 cm/h, finger diameters remain more or less constant. This observation also agrees with existing theories. However, at infiltration rates lower than 0.12 cm/h, the coarse sand experiments show that the wetting fronts became stable. For rates between 0.3 and 0.12 cm/h, the wetting is semistable; that is, there is incomplete wetting without distinct development of fingers. A similar trend was observed in the experimental results of sands with grain sizes of 0.841 to 0.594 and 0.594 to 0.42 mm. This phenomenon has not been observed in previous experimental studies and is not predicted by current wetting front instability theories. Our experimental data under infiltration rates similar to natural precipitation intensities may explain why unstable wetting has rarely been observed in wettable field soils.