bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological Properties of Surface Seals in Georgia Soils
Authors: Chiang S. C. , West L. T. , Radcliffe D. E. 
Published: July 2010

AbstractThe morphology of surface seals has not been extensively described for acid, sandy and loamy soils common in the U.S. Southeast. The objectives of this study were to: (i) evaluate evolution of seal morphological properties for seven soils in Georgia during the course of a rainfall event, and (ii) relate seal morphology and development to soil properties. Columns were packed with Ap horizons from seven soils in Georgia and subjected to simulated rainfall at 50 mm h−1 for intervals from 10 to 60 min. Seal morphological properties along with thickness and porosity were evaluated from thin sections. The most common feature of seals formed in all of the soils was a disruptional layer with 30 to 50% fewer pores >0.02‐mm diam. than unaffected soil. In readily sealed soils with sandy loam textures, low Fe contents, and high amounts of water‐dispersible clay, this layer formed within the first 10 min of rainfall, and thickness and porosity were constant at longer rainfall durations. In other soils, longer rainfall durations were required to form a disruptional layer. In addition to the disruptional layer, other morphological features observed in the seals included a thin layer of micromass concentration that occurred at the soil surface (skin seal). At intermediate rainfall durations in readily sealed soils, this layer was overlain by a layer of micromass‐depleted grains, which was removed by erosion at longer rainfall durations. Grain size and initial development in microtopographic lows suggest that the micromass‐depleted layer formed by transport and redisposition rather than in‐place disjunction of micromass.
Laboratory Measurements of Solute Transport Using Time Domain Reflectometry
Authors: Ward A. L. , Elrick D. E. , Kachanoski R. G. 
Published: July 2010

AbstractMeasurement of solute transport at different depths in layered soil columns provides more information than traditional outflow measurements. The objective of this study was to extend the time domain reflectometry (TDR) method of measuring soil water content, θ, and bulk electrical conductivity, σT, to the nondestructive measurement of resident concentration, CR, of an added electrolytic tracer. Calibration curves of CR vs. θ and σT were obtained directly, by mixing a sandy soil with different amounts of tracer and water and taking TDR readings of impedance. Similar soil was packed into a Plexiglas box fitted with curved TDR probes at different radial distances from one corner. A constant flux of water was applied at the corner of the box and a pulse of KCl tracer added. Measurements of θ and CR as a function of time and radial distance were made during the three‐dimensional flux experiment. In a one‐dimensional flux experiment, undisturbed soil columns (1.5 m long, 0.15‐m diam.) were instrumented with straight TDR probes installed horizontally at 0.10‐m increments. Indirect calibration of CR vs. θ and σT were obtained under steady‐flow conditions by using a step increase in tracer, and by numerically convolving measurements from a pulse application of tracer. The final value of σT was equated to the input concentration of the tracer to obtain the calibration relationship. The method overcomes many of the limitations associated with soil solution samplers, allowing frequent measurements at close spacings and low cost.
Calibration of Jointed Tube Model for the Gas Diffusion Coefficient in Soils
Authors: Freijer Jan I. 
Published: July 2010

AbstractModeling of gas and vapor transport in soils requires knowledge of the relative gas diffusion coefficient. The relative diffusion coefficient was determined as a function of air‐filled porosity, using a pore model based on two tortuous tubes of different radii joined in series. This model was fitted to measured relative diffusion coefficients on undisturbed samples of nine soil types at a wide range of water contents. It was found that model parameters vary with the soil types studied. Combined measurements of the water retention curve, air‐filled porosity, and relative diffusion coefficient were made to evaluate the effects of water distribution in the soil pores on the relative diffusion coefficient. After the samples were saturated with water, the residual air‐filled porosity ranged from 0.051 to 0.167 m3 m−3 and the relative diffusion coefficient was practically zero, which is due to pore blocking by soil water. At pressure heads corresponding to the air‐entry value in the water retention function, air‐filled porosity ranged from 0.095 to 0.256 m3 m−3 and the relative diffusion coefficient ranged from 0.002 to 0.013. From this point, with increasing air‐filled porosity, the relative diffusion coefficient increased rapidly to values ranging from 0.165 to 0.383 at zero water content. It was concluded that the air‐entry value is an important parameter, which indicates a priori the water content at which pore blocking becomes relevant.
Determining Nitrogen‐15 in Nitrite or Nitrate by Producing Nitrous Oxide
Authors: Stevens R. J. , Laughlin R. J. 
Published: July 2010

AbstractDetermining 15N in NO−3 or NO−2 is important when studying soil N transformations directly. Analysis of 15N in NO−3 by standard methods is time consuming and subject to errors such as cross‐contamination. The 15N content of NO−2 is determined conventionally as the difference between NO−3 + NO−2 and NO−3 alone. Since NO−3 concentrations are usually much greater than NO−2 concentrations in soil, determination of 15N in NO−2 has a poor detection limit. We developed new direct methods for determining 15N in NO−3 or NO−2 in 2 M KCl soil extracts, based on the production of N2O from NO−2 + NH2OH. For NO−2, N2O was produced by adding NH2OH at pH 1.7. For NO−3, NO−2 and NH2OH were produced as intermediates during the reduction of NO−3 by Cd‐Cu at pH 4.7. The 15N content of the N2O was determined by automated continuous flow isotope‐ratio mass spectrometry. Measured values of 15N in N2O were closely related to the theoretical values for 15N in NO−2 or NO−3. Five micromoles of NO−3 or 0.5 µmol of NO−2 at 0.1 atom % excess 15N could be determined with coefficients of variation of <4%. The new methods are fast, simple, and not subject to contamination from the atmosphere or from other samples. They should facilitate studies on the simultaneous measurement of gross rates of mineralization, immobilization, nitrification, and NO−3 reduction.
Tri‐ and Tetrafluorobenzoates as Nonreactive Tracers in Soil and Groundwater
Authors: Benson Carl F. , Bowman Robert S. 
Published: July 2010

AbstractSeveral fluorinated derivatives of benzoic acid (fluorobenzoate, FBA) have proven their usefulness as nonreactive soil and groundwater tracers. In this study, four previously untested trifluorobenzoates (TFBA) and two tetrafluorobenzoates (TEFBA) were examined for their suitability as water tracers in saturated and unsaturated environments. Negative log acid dissociation constants (pKa) determined by base titration ranged from 2.71 to 3.54 at 298 K. Some sorption of FBAs was observed in batch equilibration experiments with lower pH, high organic C fraction soils. An algorithm was developed for calculating a linear partition coefficient (KD) for each FBA isomer based on pKa, soil organic C, pH, and an average organic C‐based partition coefficient for protonated FBA (K*OC). K*OC was estimated to be 18 200 ± 6 300 L kg−1 when total FBA solution concentration is less than 5 mg L−1. Column mobility experiments in sandy media under saturated and unsaturated conditions yielded breakthrough curves for TFBA and TEFBA isomers that were indistinguishable from Br−. The results presented herein suggest that all 16 ring‐substituted FBAs can serve as nonreactive water tracers.
Predicting Increases in Extractable Phosphorus from Fertilizing Soils of Varying Clay Content
Authors: Cox F. R. 
Published: July 2010

AbstractThe change in extractable P due to fertilization should be quantified for reliable P recommendations, but this effect is dependent on the P buffering capacity of the soil. To determine this change, rates of fertilizer P were applied in six field experiments on Ultisols that varied in clay content. Mehlich‐3 extractable P (M3P) was measured annually, and an initial increase in M3P due to fertilization followed by an exponential decrease in M3P due to sorption were modeled. The change in extractable P after 1 yr at each site was calculated from the model. These data were combined with those from previous studies on two Ultisols in North Carolina and five Oxisols in Brazil to broaden the range in clay content observed. The increase in M3P per unit of applied P after 1 yr was 0.7 for soils with only 10% clay, and it decreased exponentially to <0.2 for soils with >50% clay. The results of this study were similar to conclusions from a P incubation study extracted with Bray‐1 in Natal, South Africa, on 54 soils from five U.S. taxonomic orders, including Ultisols and Oxisols. It appears there is a broad range of cultivated soils for which knowledge of the clay content would allow more reliable predictions of fertilizer P to keep extractable P at a level sufficient for optimum crop yields.
Effect of Variable Horizon Thickness on Solute Transport
Authors: van Wesenbeeck I. J. , Kachanoski R. G. 
Published: July 2010

AbstractSignificant variability of solute mass recovery, solute velocity, and dispersion occur in layered field soils. The effect of horizontally variable soil horzion thickness on vertical solute movement has not been examined in detail. The objective of this study was to determine the effect of varying B horizon thickness on solute transport. Steady‐state transport experiments were conducted on a Fox sand (a fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) in Ontario, Canada. A uniform pulse of KCl was applied at the soil surface on a 65‐m2 area and subsequently leached through the soil profile using a drip irrigation system and a constant surface flux density of water. After 13.1 cm of water had been applied, resident Cl− concentration distributions were measured by excavating a 10‐m‐long trench and sampling vertically every 0.1 m to a depth of 1.5 m and horizontally every 0.2 m. A total of eight parallel trenches, 0.15 m apart, were sampled. Moment analysis was used to calculate solute recovery, mean solute travel depth, and solute travel depth variance for each of the individual vertical samplings. Results indicate significant lateral movement of tracer resulting in greater recovery of tracer in deep B horizon tongue areas. The recovery and movement of solutes in this soil was largely controlled by the spatial pattern of B horizon depth, and the spatial variance structure of B horizon thickness was closely related to the scale dependence of in situ solute transport. The results suggest that the horizontal variability of horizon thickness should be taken into account for monitoring and modeling purposes in this soil.
Anion Exclusion‐Pore Water Velocity Interaction Affecting Transport of Bromine through an Oxisol
Authors: Melamed R. , Jurinak J. J. , Dudley L. M. 
Published: July 2010

AbstractThe transport of anions through soils is affected by both chemical and physical processes. We investigated how adsorbed phosphate affected the mobility of Br, at different pore water velocities (PWV), through saturated Oxisol soil columns. The PWVs were 2.9, 8.7, and 48.1 cm h−1. The addition of 16.2, 32.4, and 48.6 mmol P kg−1 phosphate reduced the pH of the point of zero charge from 6.0 (control) to 5.1, 4.6, and 4.3, respectively, as measured by potentiometic titration. The negative surface charge of the soil increased by 0.7 mmolc mmol−1 P added. The mobility of Br increased with P treatment because of Br exclusion induced by the P generated negative surface charge. At the highest P treatment, the exclusion volume of Br was 21% of the saturated water content. With increasing PWV, the P‐induced surface charge had a decreasing effect on Br mobility, whereas the influence of solute dispersion increased.
Soil Phosphorus Fraction Dynamics during 18 Years of Cultivation on a Typic Paleudult
Authors: Beck Michel A. , Sanchez Pedro A. 
Published: July 2010

AbstractTraditional soil P test methods estimate plant available inorganic P but ignore the less available inorganic and organic P pools. In low‐input systems where fertilizer P additions are very low to nil, these less available P pools may be a better measure of potential plant available P, particularly in highly weathered soils. The objectives of this study were to determine the size and changes in soil P pools in the nonfertilized and fertilized treatments of a long‐term continuous cultivation experiment established on a Typic Paleudult in Yurimaguas, Peru. A modified version of the Hedley et al. procedure was used to sequentially fractionate soil P into increasingly recalcitrant organic and inorganic pools. The use of path analysis highlights the interactions among P pools and the different roles of the pools in P cycling between the nonfertilized and fertilized system. For the fertilized system, the NaOH‐extractable inorganic P pool acts as a sink for fertilizer P but desorption is rapid enough to maintain high levels of plant available P. For this system, inorganic P pools explain 96% of the variation in the level of available P. Organic P is the primary source of plant‐available P in the nonfertilized system and explains 44% of the variation in available P. Available P, measured by anion exchange resin, is dependent on crop residue (b values ± standard error = 4.98 ± 3.57), whereas yield depends most strongly on the available P (0.16 ± 0.11) and on NaOH‐extractable organic P (−0.17 ± 0.11). The lack of stability in organic P levels in the first 10 yr illustrates the need for long‐term experiments. The presented results support the notion that traditional soil P tests are inadequate for low‐ to no‐input systems.
Phosphorus Transformations and Availability under Cropping and Fertilization Assessed by Isotopic Exchange
Authors: Morel C. , Tiessen H. , Moir J. O. , Stewart J. W. B. 
Published: July 2010

AbstractIn fertilized agricultural soils, both fertilizer and soil P are partly depleted by crop export, while residual fertilizer P reacts with the soil. As a result, P availability changes in complex ways that cannot be described by an available P pool. Our objective was to characterize the P availability in two long‐term field experiments on a Mollisol and an Alfisol (near Lethbridge and Breton, Canada), by using the soil solution P (Cp) and the time‐dependent isotopically exchangeable P (Et). The relationship of Cp to Et was further evaluated for short‐term reactions by incubating field samples for 1 d with increasing P rates. Both Cp and Et were related to changes in the soil P budget resulting from continuous cropping and wheat (Triticum aestivum L.)‐fallow rotations with and without fertilization, with lower Cp values in the more depleted soils. In the Alfisol, field variations in pH and texture affected both Et and Cp, obscuring relationships between the field P budgets and availability parameters. In the Mollisol, one single equation described the relationship between Et and Cp for both increases of Cp due to short‐term additions and decreases due to long‐term crop export, indicating that transformations of available P were fully reversible.
Field‐Scale Variability of Soil Properties in Central Iowa Soils
Authors: Cambardella C. A. , Moorman T. B. , Novak J. M. , Parkin T. B. , Karlen D. L. , Turco R. F. , Konopka A. E. 
Published: July 2010

AbstractSpatial distributions of soil properties at the field and watershed scale may affect yield potential, hydrologic responses, and transport of herbicides and NO−3 to surface or groundwater. Our research describes field‐scale distributions and spatial trends for 28 different soil parameters at two sites within a watershed in central Iowa. Two of 27 parameters measured at one site and 10 of 14 parameters measured at the second site were normally distributed. Spatial variability was investigated using semivariograms and the ratio of nugget to total semivariance, expressed as a percentage, was used to classify spatial dependence. A ratio of <25% indicated strong spatial dependence, between 25 and 75% indicated moderate spatial dependence, and >75% indicated weak spatial dependence. Twelve parameters at Site one, including organic C, total N, pH, and macroaggregation, and four parameters at Site two, including organic C and total N, were strongly spatially dependent. Six parameters at Site one, including biomass C and N, bulk density, and denitrification, and 9 parameters at Site two, including biomass C and N and bulk density, were moderately spatially dependent. Three parameters at Site one, including NO−3 N and ergosterol, and one parameter at Site two, mineral‐associated N, were weakly spatially dependent. Distributions of exchangeable Ca and Mg at Site one were not spatially dependent. Spatial distributions for some soil properties were similar for both field sites. We will be able to exploit these similarities to improve our ability to extrapolate information taken from one field to other fields within similar landscapes.
Energy Balance Model of Spatially Variable Evaporation from Bare Soil
Authors: Evett S. R. , Matthias A. D. , Warrick A. W. 
Published: July 2010

AbstractMost models of evaporation (E) provide estimates at one rather than many locations and thus cannot be used to describe the spatial variability of evaporation. An energy balance model (EBM) that estimates E at many locations was tested, improved, and validated, using daily evaporation measurements made with microlysimeters, giving an r2 value of 0.82 for regression of actual vs. estimated evaporation. The model is based on the surface energy balances of dry and drying soil. Data needed include only wind speed and soil surface temperature measurements obtained at a suitably small time interval (e.g., 0.5 h) with an automated weather station and reference dry soil at one location, and measurements of predawn and midday soil surface temperature made with a hand‐held infrared thermometer at as many locations as desired for evaporation prediction. The reference dry soil was established in a plastic bucket buried in the soil and protected from rain and irrigation. Model improvements included an easy method of accurately estimating continuous soil surface temperature at many points in a field. Also, an empirically fitted transfer coefficient function for the sensible heat flux from the reference dry soil showed that sensible heat flux from the relatively hot reference dry soil was dominated by free convection. Soil heat flux and reflected shortwave radiation terms are omitted in the EBM and this was shown to reduce model accuracy by as much as 9.2% of the measured evaporation. The model may prove useful for prediction of spatial variability of evaporation based on soil surface temperatures.
Stability of a Calcareous Saline‐Sodic Soil During Reclamation
Authors: Lebron I. , Suarez D. L. , Alberto F. 
Published: July 2010

AbstractGeneral guidelines to reclaim saline or sodic soils do not adequately consider variables such as pH and the presence of organic matter that are known to affect soil stability. Poor structural stability of sodic, saline‐sodic, and high‐pH soils adversely influences crop yields; promotes piping, tunneling, and slope erosion; and can accelerate the failure of water conveyance systems. We evaluated six soil tests, used to measure physico‐chemical properties, for their suitability to evaluate the structural stability of a calcareous, saline‐sodic soil under reclamation. The stability tests were wilting point, plastic limit, coefficient of linear extensibility (COLErod), water content at 0.03 MPa, liquid limit, and dispersion index. The range of electrical conductivity (EC) studied was 0.5 to 20 dS m−1, sodium adsorption ratio (SAR) 0 to 400 (mmol L−1)0.5, and pH 8.4 to 10.5. The results obtained indicate that the amount of water necessary for a soil to flow under standard conditions for the liquid limit test decreased an average of 25% when the EC decreased from 40 to 2 dS m−1. The liquid limit and EC showed a linear correlation (R2 = 0.785); therefore, the liquid limit was considered to be an appropriate index to evaluate the physical properties of a soil under a leaching process. Plasticity index and available water were more useful in the evaluation of the mechanical properties of the soil when we used amendments. Liquid limit combined with the water content of the soil at 0.03 MPa was the most useful tool for evaluating soil structural stability during reclamation.
Mechanisms and Control of Percolation Losses in Irrigated Puddled Rice Fields
Authors: Tuong T. P. , Wopereis M. C. S. , Marquez J. A. , Kropff M. J. 
Published: July 2010

AbstractThe low water use efficiency of irrigated lowland rice is partly due to water loss by percolation. Mechanisms of percolation losses were studied in a puddled rice field with a permeable subsoil using simulation models and field experiments. Inclusion of small nonpuddled areas (1.5 m2 per 100 m2 of puddled soil) within the field with 5‐cm ponding water depth (PWD) increased field water loss from 2.7 mm d−1 to 15 mm d−1. Under‐bund percolation rate (lateral movement of ponded water into the bunds, then vertically down to the water table) was about 10 mm d−1 in a 25 by 100 m field. A one‐dimensional mechanistic soil‐water balance model, SAWAH, accurately simulated the measured water losses in a homogeneously puddled rice field only when lateral flow toward nonpuddled spots and bunds was prevented. Maintaining shallow PWD did not significantly affect percolation loss through uniformly puddled soil but greatly reduced losses in nonpuddled spots and under‐bund percolation. Sealing the bund walls with puddled soil material will decrease the horizontal conductivity of the bunds and may further reduce under‐bund percolation.
Tracer Characteristics of Brilliant Blue FCF
Authors: Flury Markus , Flühler Hannes 
Published: July 2010

AbstractDyes are widely used to stain the travel paths of water and solutes in soils. Brilliant Blue FCF (C.I. Food Blue 2) is a valuable dye tracer for visualizing water flow patterns. Because this dye is nontoxic, it is particularly suited for field use. Depending on pH, the dye is either neutral or dissociates to a mono‐ or bivalent anion. The water solubility is 200 kg m−3. In this study, properties of the dye that characterize the adsorbing behavior in soil were determined. Batch adsorption experiments were carried out in the laboratory, and a field experiment was conducted to compare the mobility of Brilliant Blue FCF with that of I− and Br−. The batch studies gave distribution coefficients Kd of 0.19, 3.00, and 5.78 dm3 kg−1 for three different soils. The results of the batch studies suggest that the dye forms ion pairs with Ca2+. The field experiment showed that the dye is retarded compared with the conservative tracer Br−. A comparison between Brilliant Blue FCF and I− analyzed with the iodide‐starch method resulted in a relative retardation of 1.2 Brilliant Blue FCF compared with I−.