bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Phosphorus Release from Spodosols: Effects of Oxalate and Formate
Authors: Fox T. R. , Comerford N. B. , McFee W. W. 
Published: July 2010

AbstractOrganic anions have been implicated in the release of P to soil solution and may thus increase the availability of P to plants. Oxalate and formate have been identified as the most prevalent low‐molecular‐weight organic anions in the soil solutions in Spodosols under forest vegetation in northern Florida. The purpose of this study was to investigate the effect that these two organic anions have on the kinetics of inorganic‐ and organic‐P release from the A, Bh, and Bt horizons of a representative forested Spodosol. Soil samples were equilibrated for various periods of time with solutions of either oxalate, formate, or water. The extracts were analyzed for pH, inorganic P, organic P, Al, and organic acids. Results showed that oxalate had little effect on P release in the A horizon. This was due to the lack of Al oxides to hold P. Conversely, oxalate greatly increased solution P in the Bh and Bt horizons. In the subsoil horizons, the release of P was rapid, followed the disappearance of oxalate from solution, and was coincident with an increase in pH. These facts suggested that P was released via a ligand‐exchange reaction. A longer term reaction was consistent with the reprecipitation of the P as an amorphous Al phosphate when oxalate was either totally sorbed or degraded. The presence of formate did not increase P release.
Ammonia Volatilization from Flooded Soil Systems: A Computer Model. I. Theoretical Aspects
Authors: Jayaweera G. R. , Mikkelsen D. S. 
Published: July 2010

AbstractAmmonia volatilization from flooded rice (Oryza sativa L.) is a major mechanism for N loss and poor fertilizer use efficiency. Ammonia volatilization is influenced by five primary factors: NH4‐N concentration, pH, temperature, depth of floodwater, and wind speed. This NH3‐volatilization model is based on chemical and volatilization aspects. The chemical aspects of the model deal with the NH4/NH3(aq) equilibrium in floodwater. Ammonium ions undergo dissociation with a first‐order rate constant, while NH3(aq) and H undergo a diffusion‐controlled association reaction with a second‐order rate constant. The transfer of NH3 across the water‐air interface of flooded soil systems is characterized by a first‐order volatilization rate constant. By utilizing the chemical dynamics of the NH4/NH3(aq) system in association with transfer of gaseous NH3 across the interface, an equation was derived to determine the rate of NH3 volatilization from flooded systems as a function of the five primary factors. The chemical aspects of the model include the derivation of association and dissociation rate constants. The volatilization aspects of the model, which is based on the two‐film theory, allows it to compute the volatilization rate constant for NH3. Expressions are derived to compute the Henry's law constant, gas‐phase and liquidphase exchange constant, and the overall mass‐transfer coefficient for NH3.
Defining Soil Buffer Power: Implications for Ion Diffusion and Nutrient Uptake Modeling
Authors: Van Rees K. C. J. , Comerford N. B. , Rao P. S. C. 
Published: July 2010

AbstractVarious definitions of the nutrient buffer power of soils, based on ion‐exchange isotherms, have been proposed in the literature. However, incorrect definitions can result in erroneous estimations of solute diffusion coefficients and nutrient replenishment of soil solution, hence, rates of nutrient supply for plant nutrient uptake. This note presents conditions under which each definition of buffer power is valid, and situations where inherent assumptions may not be valid.
Statistical Parameters Characterizing the Spatial Variability of Selected Soil Hydraulic Properties
Authors: Ünlü K. , Nielsen D. R. , Biggar J. W. , Morkoc F. 
Published: July 2010

AbstractThe knowledge of the statistical parameters of the variance, σ2, and the correlation scale, λ, characterizing the spatial structures of the log of the saturated hydraulic conductivity, lnKs, pore size distribution parameter α, and the specific water capacity, C, is required in stochastic modeling in order to understand the overall response of large‐scale heterogeneous unsaturated flow systems. These parameters are estimated assuming second‐order stationarity and an exponential semivariogram model with nugget effect. Methods of ordinary least squares (OLS), maximum likelihood (ML), and restricted maximum likelihood (RML) are used for estimating σ2 and λ, while methods of cross‐validation (kriging) and uncorrelated residuals are used to validate the semivariogram model with estimated σ2 and λ. The objectives of this study were to evaluate the sensitivity of σ2 and λ to the estimation methods and to discuss the implications of the analysis in view of the stochastic modeling. The significance of the results of parameter estimation and model validation in relation to the stochastic modeling of large‐scale transient unsaturated flow is demonstrated with two examples involving the variance of soil‐water pressure head, σ2h, and the vertical component of effective hydraulic conductivity, K*11. Results show that the estimated values of σ2 and λ are highly dependent on the estimation method. Although the majority of the estimated parameters pass the validation tests, the RML estimates of σ2 and λ used in estimating σ2h and K*11 significantly reduce the prediction uncertainties.
Microwave Radiation and Incubation Effects on Resin‐Extractable Nutrients: II. Potassium, Calcium, Magnesium, and Phosphorus
Authors: Yang Jae E. , Skogley Earl O. , Schaff Bernard E. 
Published: July 2010

AbstractThe phytoavailability soil test (PST) is a resin‐extraction methodology being developed for use on fresh soil samples. Mineralization or other nutrient conversions during shipment of samples to a soil‐testing laboratory are of concern with this soil‐test approach. The objective of this research was to investigate microwave‐radiation (MWR) treatment of soil samples to arrest microbial conversions of nutrients during incubation of fresh samples. Fresh samples from three Ap horizons of Montana soils (Haploborolls) were subjected to MWR for 0 to 4 min and then incubated at 20 °C for 0 to 12 d. Subsamples were also dried before being subjected to the same treatments. Nutrients were extracted with mixed‐bed ion‐exchange resin extractors placed in saturated pastes of each sample. Standard soil tests were also conducted on dried soil samples. Results for K, Ca, and Mg indicate increased resin extractability with increasing MWR, and incubation without MWR caused both increases and decreases in extractability, depending on length of incubation. Neither MWR nor incubation resulted in consistent changes in resin‐extractable P. Results from dried soil were generally similar, except one soil did not produce significant changes in resin‐extractable cations due to MWR or incubation. Extractable cations by standard soil tests were not influenced by MWR, but P levels increased with length of MWR. These results support those for N and S, providing additional evidence that MWR should not be recommended for soil samples intended for soil testing by either standard or PST methods.
Characteristics and Taxonomy of Sodic Soils as a Function of Landform Position
Authors: Seelig B. D. , Richardson J. L. , Barker W. T. 
Published: July 2010

AbstractSodic soils in central North Dakota are related to landform position in relation to the water table and plant communities. Classification problems are commonly encountered when field observations are compared with established taxa. This study focused on relating soil and plant characteristics to differences in soil water regime. Soils at three landform positions, designated as upland, intermediate, and wetland, were sampled at regular intervals. The sampling pattern at each position formed a grid (49 pedons/grid). Each pedon was described and classified. Selected pedons were analyzed for major cations, electrical conductivity (EC), and dispersible clay. Water‐table observations were made from wells with perforated casings at each area sampled. Plant composition was determined by the point‐frame and quadrat methods. Landform position and plant communities reflected variations in sodic soil properties and soil water regime. The highest amounts of dispersible clay and lowest Ca/Mg ratios were in the sodic soils at the two lowest positions. The highest sodium adsorption ratios (SAR) were in soils at the intermediate position. These soils were associated with a plant community dominated by inland saltgrass [Distichlis spicata ssp. stricta (Torrey) Thorne] in the intermediate position. Sodic soils from the upland position were drier than the sodic soils at the two lower positions and were not so severely affected by Na.
Modeling Water Balance and Grass Production
Authors: de Jong R. , Kabat P. 
Published: July 2010

AbstractThe previously developed soil water‐crop production model SWA‐CROP was adapted and tested for grassland production under the weather conditions and management practices encountered on sandy soils in the Netherlands. The model, which required soil physical and crop properties as input, was driven by meteorological data. The main output of the soil water balance module (SWATRE) included actual transpiration and the distribution of soil water contents and pressure heads over depth and time. The crop production module (CROPR) calculated dry‐matter yields of roots, stubble, and harvestable sward. The CROPR module was also used to calculate leaf‐area index and soil cover, which formed feedback loops with the soil water balance. After initial calibration, 85% of the predicted soil water contents in the root zone fell within 10% of the measured data. Seasonal accumulated grass yield, predicted by the model under non‐stressed conditions, was within 10% of the measured yield, but yields during dry periods were overestimated. Discrepancies between measured and predicted yields under irrigated and nonirrigated conditions were attributed to the model's inability to simulate growth and death rates of individual plant organs.
Fertilizer Effects on Dinitrogen, Nitrous Oxide, and Methane Emissions from Lowland Rice
Authors: Lindau C. W. , DeLaune R. D. , Patrick W. H. , Bollich P. K. 
Published: July 2010

AbstractDinitrogen, N2O, and CH4 emissions were measured from a Louisiana flooded rice (Oryza sativa L.) field. Field experiments were conducted on a Crowley silt loam soil (a fine, montmorillonitic, thermic Typic Albaqualf) to determine the effect of fertilizer types and rice plants on evolution of N2, N2O, and CH4 to the atmosphere. Highly labeled (60–74 atom% 15N) urea, (NH4)2SO4, and KNO3 fertilizers were applied into the floodwater at the four‐ to five‐leaf stage to maximize N loss. The direct emissions of N2, N2O, and CH4 were measured at 1, 3, 5, 7, 9, 11, 13, 15, 17, and 21 d after N application. Maximum N2 fluxes from the planted rice plots were 254, 516, and 3 330 g ha−1 d−1 for the urea, (NH4)2SO4, and KNO3 treatments, respectively. Dinitrogen fluxes from the urea, (NH4)2SO4, and KNO3 unplanted plots were 264, 484, and 1 720 g N2 ha−1 d−1, respectively. Nitrous oxide emissions due to fertilizer addition to the soil were low. No increases in N2O emission above control values were recorded for any of the sampling intervals after urea addition. Maximum N2O flux from the (NH4)2SO4 treatments was 4 g ha−1 d−1 on Day 17 and 122 g ha−1 d−1 for the KNO3‐treated plots measured on Day 1. Peak CH4 emissions from the planted and unplanted urea‐treated plots were 75 and 22 g ha−1 d−1, respectively. Fluxes of CH4 from the (NH4)2SO4 and KNO3 plots were much lower and did not exceed 9 and 18 g ha−1 d−1, respectively, over the 21‐d sampling period. This study shows that the type of fertilizer N and presence of rice plants affects the evolution of N2, N2O, and CH4 from a flooded‐rice soil to the atmosphere.
Hydroxy‐Aluminum's Effect on Permeability of Clay‐Sand Mixtures
Authors: Keren R. , Singer M. J. 
Published: July 2010

AbstractThe effect of the hydroxyl‐Al synthesis method on the hydraulic conductivity (HC) of a clay‐sand mixture in the presence of hydroxy‐Al was studied. Hydroxy‐Al precipitates were formed by adding Al(NO3)3 and NaOH solutions to continuously stirred smectite suspension. Aluminum nitrate was added either before or after NaOH. When the mixtures were leached with deionized water, HC reduction was much less when Al(NO3)3 was added prior to rather than after NaOH. Dispersion and transport of clay from the clay‐sand mixture occurred only when the NaOH was added prior to Al(NO3)3. The differences in behavior between the two systems is due to the location of hydroxy‐Al. When Al(NO3)3 is added to the clay followed by NaOH, hydroxy‐Al polymers interact with the clay particles to reduce swelling and dispersion. When clay and NaOH are mixed, followed by Al(NO3)3, precipitates form as a separate phase from the clay platelets.
Cropping and Sulfur Fertilization Influence on Sulfur Transformations in Soil
Authors: Castellano S. D. , Dick R. P. 
Published: July 2010

AbstractThe dynamics of S cycling in soils are not well understood. A 2‐yr field study was conducted to determine the effects of two S fertilizers (CaSO4·2H2O [CS] or elemental S [ES]) at two fertilization rates (0 or 50 kg S ha−1 yr−1) on the temporal distribution of soil S fractions (inorganic SO4, ester sulfate, and C‐bonded and residual S), arylsulfatase activity, and microbial‐biomass C and S in soil. The soil studied (a fine‐silty, mixed, mesic Aquultic Argixeroll) was cropped with winter rape, Brassica napus L. var. napus or left uncropped. Sulfate levels (0–15 cm depth) were significantly (P < 0.01) affected by S‐fertilizer treatment. During the rainy winter season, SO4 levels ranged from 7 to 13 mg kg−1 in CS plots, compared with 2 to 7 mg kg−1 in control plots. In the months from March to May, biomass S increased and SO4 levels decreased (<6 mg SO4‐S kg−1 soil), indicating S immobilization was occurring in the spring. Ester sulfate and residual S varied seasonally, whereas C‐bonded S showed minimal seasonal fluctuations. Cropping significantly increased biological activity (arylsulfatase activities and biomass C) over uncropped treatments. Subsoil SO4 appeared to be both a source (upward movement during high evapotranspiration) and a sink for S in surface soil, with extractable SO4 in the 60‐ to 90‐cm depth being significantly affected by cropping and S fertilization. The limitations of using extractable SO4 as a soil test were shown by wide variations in SO4 over time (2–14 mg SO4 kg−1 soil) in control plots, even though there was a seed yield response to S.
Water Quality Effects on Soils and Alfalfa: II. Soil Physical and Chemical Properties
Authors: Costa J. L. , Prunty Lyle , Montgomery B. R. , Richardson J. L. , Alessi R. S. 
Published: July 2010

AbstractSalt accumulation can occur in northern Great Plains soils during irrigation with saline water. The objective of this study was to quantify effects of salinization produced in Barnes loam (fine‐loamy, mixed Udic Haploboroll), Parshall loam (coarse‐loamy, mixed Pachic Haploboroll), Svea loam (fine‐loamy, mixed Pachic Haploboroll), and Williams loam (fine‐loamy, mixed Typic Argiboroll) soils by irrigation with seven water qualities during 21 mo of greenhouse alfalfa production in undisturbed columns. Eight physical and chemical soil properties were evaluated and related to soil, water quality, and depth in the soil. Saturation percentage (SP) of the soil increased 0.2% for each unit increase in soil‐extract sodium adsorption ratio (SARe). Saturation‐extract electrical conductivity (ECe) increased with depth, at rates dependent on water quality, to maximums of 1 to 17 ds m−1. Parshall was the soil most susceptible to dispersion as SARe increased. From the surface to 15‐cm depth, bulk density was reduced 0.04 to 0.06 Mg m−3 by the water that resulted in the highest soluble‐Ca concentration. Significant regression models were developed for SP, ECe, SARe, and salt precipitation. Parshall, the most irrigable soil, was the most detrimentally affected, as judged by dispersion, ECe, and SARe, indicating a need for further investigation. Barnes, Svea, and Williams soils proved more suited to irrigation than previously believed.
Broadcast and Subsurface‐Banded Urea Nitrogen in Urea Ammonium Nitrate Applied to Corn
Authors: Maddux L. D. , Barnes P. L. , Raczkowski C. W. , Kissel D. E. 
Published: July 2010

AbstractLower yields of corn (Zea mays L.) have been reported in northeastern Kansas when urea ammonium nitrate (UAN) solution is broadcast incorporated rather than subsurface banded. Broadcast incorporated and subsurface‐banded 15N‐tagged urea in UAN were evaluated in 1982 and 1983 for N uptake by irrigated corn and N immobilization by a Eudora silt loam (coarse‐silty, mixed, mesic Fluventic Hapludoll). Uptake of N in corn plant components and residual inorganic and immobilized tagged urea N were measured, and an N balance calculated. Recovery of tagged urea N by all plant components was 61 and 68% for banded UAN in 1982 and 1983, respectively, but only 39 and 44% for broadcast incorporated UAN. The amount of tagged urea N immobilized in the top 90 cm of the soil profile was 58 and 14% greater with the broadcast incorporated than with the banded treatment for 1982 and 1983, respectively. Tagged urea N that was unaccounted for was 62 and 200% greater, respectively, for the 2 yr with the broadcast than with the banded applications. The difference in unaccounted‐for tagged N between treatments was attributed to variations in loss by leaching. The differences in uptake of tagged urea N were attributed to a combined effect of greater soil immobilization and loss by leaching with the broadcast incorporated application.
Hydraulic Resistance of Soil Surface Seals in Irrigated Furrows
Authors: Segeren Antonius G. , Trout Thomas J. 
Published: July 2010

AbstractSoil surface seals resulting from overland flow in irrigation furrows reduce infiltration rates. A method was developed to quantify the hydraulic resistance of furrow seals. Infiltration was measured with a recirculating infiltrometer on two southern Idaho soils, Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid) and Bahem loam (coarse‐silty, mixed, mesic Xerollic Calciorthids). Surface sealing was prevented on half the furrow test sections with cheesecloth laid on the furrow perimeter. Subseal soil‐water potential was measured with a recording tensiometer. A two‐dimensional finite‐difference infiltration model with measured flux as the wetted perimeter boundary condition calculated matric potential directly beneath the seal. Seal resistance was then calculated by Darcy's law from the measured flux and calculated potential. Surface sealing on the bare furrows decreased infiltration by an average of 46% compared with the cloth‐covered furrows. The seal conductivity values, based on a constant seal thickness, decreased rapidly during the initial 100 min and reached 0.1 to 8% of the conductivity of the soil underlying the seal after 300 min. Potential gradients across the seal were inversely related to infiltration rate and the conductivity of the seal. The procedure successfully calculated seal conductivity changes with time and can be used to evaluate the effects of management practices on seal formation.
Noncrystalline Phosphates in Florida Phosphatic Soils
Authors: Wang H. D. , Harris W. G. , Yuan T. L. 
Published: July 2010

AbstractSix Florida soils formed over phosphoritic deposits were analyzed by horizon to verify the presence of noncrystalline P and to determine the P forms associated with Ca, Fe, and Al. Each soil contained only one phosphate mineral, as detectable by x‐ray diffraction (XRD): carbonate‐fluorapatite, wavellite, or crandallite. Some horizons contained no detectable crystalline P, despite the presence of appreciable total P. Quantities of fluorapatite and wavellite, determined by XRD and thermal analysis, respectively, were insufficient to account for total P. Higher proportions of noncrystalline P near the surface were substantiated by a decrease in ratios of oxalate‐extractable P to total P with depth. Oxalate‐extractable P was higher for most samples than for standard minerals. Oxalate was more effective than dithionite‐citrate‐bicarbonate (DCB) in extracting P associated with Al, but DCB extracted more P associated with Fe. Endothermic differential scanning calorimetry peaks (90–100°C) were reduced in size or eliminated by oxalate or DCB extractions, suggesting that the peaks originated from the dehydration of noncrystalline Al and Fe with which some P could be associated. The fraction of total P extracted by soil‐testing reagents (Mehlich I and Olsen) was generally higher for horizons containing appreciable noncrystalline P associated with Al and Fe. Crandallite was resistant to dissolution by all extractants.
Kinetics of Sulfate Retention on Soil as Affected by Solution pH and Concentration
Authors: Schnabel R. R. , Potter R. M. 
Published: July 2010

AbstractKnowledge of the time dependence of chemical retention by soil is crucial to a full understanding of how retention is affected by solution variables and to accurately simulate the fate of soil‐applied chemicals. The kinetics of SO2‐4 retention by and release from soil were examined in a continuously stirred reactor tank. The concentration‐time histories were processed with a number of commonly used kinetic equations. Of those tested, an equation that was first order in available retention sites consistently gave the best fit to the data. Sulfate‐retention kinetics were strongly influenced by SO2‐4 concentration and the presence of PO3‐4 in solution, but unaffected by a change in pH from 3 to 4. For example, when SO2‐4 concentration was doubled from 0.313 to 0.625 mM in the retention phase of the experiment, the average first‐order forward rate constant increased from 0.07 to 0.24 min−1. The addition of PO3‐4 to the solution increased the forward rate constant to 0.13 min−1 and decreased equilibrium retention from 8.1 mmol/kg when PO3‐4 was not present to 5.2 mmol/kg. In the release phase of the experiment, the presence of PO3‐4 increased the estimated reverse rate constants by an order of magnitude, and an even greater increase in the reverse rate constant was estimated when the initial sulfate concentration was increased from 0.313 to 0.625 mM. Although the data was closely approximated by first‐order kinetics, changes in the rate coefficients for the different influent solutions indicate that commonly determined kinetic parameters have limited applicability beyond the particular conditions of the experiment.