bluuebunny/crossref_metadata_2025_split huggingface dataset:
Description of Atrazine Transport in Soil with Heterogeneous Nonequilibrium Sorption
Authors: Chen W. , Wagenet R. J. 
Published: July 2010

AbstractNumerous studies have shown that a single sorption rate constant is insufficient to describe nonequilibrium sorption and transport of organic solutes in soil. To investigate the effect of sorption rate (or, more generally, sorption site) heterogeneity on solute transport, we proposed a model assuming a γ distribution for both sorption rate and partitioning coefficient (abbreviated as GS for gamma‐distributed sites). The model was tested by a series of column leaching and batch sorption experiments conducted with atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) over various time scales. Observed asymmetry and a left‐hand shift of measured breakthrough curves (BTCs) with increasing flow velocity (0.51 to 21.3 cm/h) or decreasing column length (15.5 to 6.0 cm) were successfully predicted by GS with sorption parameters obtained from an independent experiment. However, two other distinct sorption site models, the two‐site first‐order sorption (TSFO) and the two‐site spherical diffusion (TSSD), were not able to describe the observed BTCs unless parameter values were adjusted for each case. In batch sorption experiments, increasing equilibration time (ranging from 1 to 237 h) was found to generally increase the isotherm‐derived partitioning coefficient (KD). The increasing trend was independently well‐predicted using the GS model with optimized parameters from the column studies. The TSSD was less successful and TSFO the least able to reconcile the entire range of change in KD. The weak time‐scale dependency of GS found in both column and batch experiments supports the assumption that a wide range of heterogeneous sorption sites or domains have been involved in the overall sorption process but to a variable degree as time elapsed. Potential alteration of soil sorption properties by γ irradiation was also observed.
Soil Erosion Effects on Soil Properties in a Highland Area of Central Kenya
Authors: Gachene C. K. K. , Mbuvi J. P. , Jarvis N. J. , Linner H. 
Published: July 2010

AbstractOne of the most important features that is neglected in many soil erosion studies in Africa is the monitoring of changes to the soil during the progress of the experiment. Objectives of this study were therefore to monitor runoff, soil loss, and enrichments of eroded soil material and to assess the effect of cumulative soil loss on soil chemical properties of an Alfisol in one of the high‐potential areas of Central Kenya highlands.Runoff, soil loss, and enrichments of eroded sediments were measured on newly opened ground from 1991 to 1992. Annual rainfall was 948 and 1125 mm for 1991 and 1992, respectively. Soil loss ranged from 0.8 to 247.3 t ha−1, and runoff ranged from 1 to 89 mm. No significant correlations were observed between enrichment ratios (ER) and soil loss. The ER were ≥ 1 and sediments were mostly enriched with P and Na. The P and Na concentrations were 4 to 10 and 2 to 3 times the source material, respectively. Sediment from the plots was 247 to 936% richer in P than the soil from which it originated. Changes in soil pH, percentage organic C, and percentage total N following erosion were significantly correlated with cumulative soil loss (r values of 0.77, 0.59, and 0.71, respectively, n = 20). The data indicated that nutrient loss due to erosion is one of the major causes of soil fertility depletion of Kenyan soils.
Effect of Growing Rice on Nitrogen Mineralization in Flooded Soil
Authors: Kundu D. K. , Ladha J. K. 
Published: July 2010

AbstractOnly a smally fraction of the total organic N in soils is mineralized to the plant‐available forms during a cropping season. The mineralization process and the availability of mineral N in soils are affected by various environmental factors and management practices, including the presence of growing plants. This study was conducted to determine the effect of rice (Oryza sativa L.) on mineral N availability in a flooded Maahas soil (Typic Tropaquept). Available N, extractable NH4‐ and NO3‐N in soil plus N accumulated in plants, referred to as mineral N availability, was significantly higher in planted than in unplanted soils. Increased N availability may result from reduced loss or enhanced supply of mineral N in the presence of growing plants. Average increase in mineral N supply in freshly flooded soil was 31% due to growing of rice through the first month (0–30 d) and 62% through the second month (30–60 d) of its life cycle. In soils under prolonged flooding, average increases in the mineral N supply due to 2 mo rice growing during the vegetative stage (10–70 d) were 14 to 47% depending on the initial mineral N status of the soils. The gain in mineral N achieved by growing rice plants was higher in soils with a low than a high initial mineral N content. Rice genotypes differed in their ability to increase mineral N availability in flooded soils, and the stronger influences were associated with higher dry‐matter yields of the plants (shoot plus root). Soil N availability to wetland rice, especially in soils with low mineral N supply, thus may be considerably enhanced by selection of efficient genotypes.
Modeling Organic Solutes in Peatland Soils Using Acid Analogs
Authors: White Jeffrey R. , Shannon Robert D. 
Published: July 2010

AbstractDissolved organic carbon (DOC) dominates the chemistry of porewaters in many peatland soils. Yet modeling its contribution to acid‐base chemistry and to anionic charge has not been attempted for peatland porewaters. Using 3 yr of field data, we investigated the effectiveness of four analog organic acid models in describing the acid‐base chemistry of DOC in porewaters from two acidic (mean pH = 4.0–4.2), high‐DOC (mean DOC = 4.2–5.4 mmol CL−1) peatlands in southern Michigan. Although developed for dilute lake waters, we applied these models to porewaters of peatland soils. All sites exhibited a large deficit in anionic charge (mean = 229 µmolc L−1), which was strongly correlated with DOC (r2 = 0.82) and accounted for 70 to 80% of the total anionic charge. We, therefore, used charge balance to evaluate the models. The four models varied in effectiveness; variations in model organic anion accounted for between 50 and 84% of the variation in anion deficit. Representing organic acid anions with a triprotic acid analog model yielded the best results (r2 = 0.84, slope = 0.96), while a monoprotic acid model was least effective (r2 = 0.50, slope = 0.91). Mean charge densities of the DOC pool (44–52 εmolc mmol−1 DOC) varied little with differences in site characteristics (i.e., water levels and emergent plant communities) and were consistent with other studies. The triprotic acid model appears to be an effective analog for the acid‐base and ionic charge‐contributions of DOC in porewaters of acidic peatland soils.
Evaluation of Nonequilibrium Models for Predicting Atrazine Transport in Soils
Authors: Ma Liwang , Selim H. M. 
Published: July 2010

AbstractModel evaluations are commonly undertaken using relatively sparce data, and the criteria for such evaluations are often not fully addressed. For instance, less effort has been made to evaluate models based on their prediction capability. In this study we compared several chemically and physically based nonequilibrium models for their predictions of atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) transport in a uniformly packed Sharkey soil (Vertic Haplaquept). The models compared were a nonlinear multireaction model (MRM), a second‐order model (SOM), and their coupled versions with a mobile‐immobile model (MIM), MRM‐MIM and SOM‐MIM. Model parameters were derived from kinetic batch experiments and were used to predict atrazine column breakthrough curves (BTCs) for different pore water velocities (0.52–2.17 cm h−1), aggregate sizes (0–2, 2–4, and 4–6 mm), flow interruptions (0, 4, and 16 d), and soil column lengths (10 and 15 cm). For each model, nine formulations reflecting various adsorption sites were evaluated. Based on root mean squared errors and sums of squared errors, considerable improvement in atrazine BTC predictions was achieved using SOM compared with MRM. Furthermore, SOM was more sensitive to different model formulations than MRM. Coupled MRM‐MIM did not improve atrazine BTC prediction. Although goodness of model predictions varied with individual columns, we concluded that SOM‐MIM with four parameters and a time‐dependent mass transfer coefficient (α) best described atrazine retention and transport in Sharkey soil.
Chemical Characterization of Soils of a Tropical Humid Forest Zone: A Methodology
Authors: Menzies N. W. , Gillman G. P. 
Published: July 2010

AbstractA methodology, based on a combination of routinely performed analyses and investigation of fundamental charge and anion sorption properties, was used to characterize the soils of the humid forest zone of Cameroon. In general, the soils have about 2 cmol kg−1 permanent negative charge, with about 1 cmol kg−1 from variable‐charge sources at current soil pH values. Furthermore, they are improverished with respect to Ca, Mg, and K, while Al frequently dominates the exchange complex. Thus, the ability of these soils to retain base cations is more limited than is suggested by the cation‐exchange capacity (CEC). Therefore we propose the concept of a degradation index (DI) defined as: DI = 100(CEC5.5 − sum of basic cations)/CEC5.5, where CEC5.5 is the CEC measured at pH 5.5. This index encompasses degradation a soil may have experienced from natural or man‐made causes. Extractable PO4 concentrations are considered very low and the soils have a moderate to high capacity to fix added PO4. Surface soil SO4 concentrations are considered marginal to deficient for plant growth, though adequate reserves of SO4 are held in the subsoil by SO4 sorption. The approach used demonstrated that the five morphologically different soil profile classes identified in the zone have similar chemical characteristics. Thus, the results of experimentation conducted on one of the soil profile classes will be applicable throughout the zone. Furthermore, the approach has provided a means of identifying comparable soil types in other parts of the world and will guide technology transfer. The analytical methods used in this study are relatively simple and require no specialized equipment, and are therefore within the capabilities of many laboratories in the developing world.
Consequences of Changes in Particulate Organic Carbon in Vertisols under Pasture and Cropping
Authors: Chan K. Y. 
Published: July 2010

AbstractSoil organic C levels are generally low in Vertisols and, under cropping, they decline rapidly, resulting in N deficiency limiting crop production. The pools of soil organic C lost during cropping of native pasture soils need to be identified so that management strategies can be developed to reverse this loss. Changes in particulate (>53‐µm) organic carbon (POC) under different histories of cropping and pasture were monitored in two Vertisols with contrasting C and N status in the semiarid subtropical area of Australia and the changes were related to N availability and aggregate stability. Results indicate POC was the form of organic C that was preferentially lost under cropping; on average it made up 70% of the difference in organic C between native pasture and cropped soils in the 0‐ to 5‐cm layer. It was also the form of organic C regained when cropped soils were returned to pasture. Particulate organic C was significantly related to N mineralization, indicating the importance of this fraction to N availability in the Vertisols. Particulate organic C was more significantly related to the water stability of the >250‐µm size fraction than that of the <50‐µm fraction and thus indicates the importance of POC in maintaining the stability of the macroaggregates of these soils. Regression analyses indicated that, for Vertisols, POC is equally sensitive to changes in these important soil properties under different management practices as TOC. Results also demonstrated the effectiveness of pasture in restoring POC and therefore its usefulness in maintaining and restoring the fertility of Vertisols.
Iron Oxide Sink Method for Extracting Soil Phosphorus: Paper Preparation and Use
Authors: Myers R. G. , Pierzynski G. M. , Thien S. J. 
Published: July 2010

AbstractSince the FeO‐sink method to estimate plant‐available P in soils was first introduced in 1983, modifications have continued to improve the procedure. Recently FeO‐coated paper circles (5.5‐cm diam.) were used in place of the traditional 2 by 10 cm strips. The objective of this study was to more clearly describe the preparation and use of the FeO‐coated circles. We used Whatman no. 50 hardened filter paper (2.7‐µm pore openings). Standard methods for FeCl3 treatment of the papers were used. After the papers had been air dried, one paper was secured between two 10 by 10 cm fiberglass screens. By simultaneously immersing stacks of 25 of these paper‐screen units in 2.7 M NH4OH for a 30‐s immersion time, 100 papers could be uniformly coated with FeO in about 10 min. Immersion times of 30, 60, and 180 s in NH4OH solution showed that papers immersed for 30 s in NH4OH solution extracted P as effectively as those immersed for longer times. One 5.5‐cm FeO circle was as effective as three circles in extracting P from most soils. A desorption model for soil P was used that can relate soil‐test P to desorption kinetics. In soils with maximum reversible P ranging from 25.1 to 106.5 mg kg−1, desorption constants ranged from 0.141 to 0.232 h−1 with a mean of 0.191 h−1. Low‐P soils released P slower than did high‐P soils. Such information may be of interest in assessing P availability in soils.
Estimating Long‐Term Drainage at a Regional Scale Using a Deterministic Model
Authors: Ould Mohamed S. , Bruand A. , Raison L. , Bruckler L. , Bertuzzi P. , Guillet B. 
Published: July 2010

AbstractThis study discusses the use of a deterministic model, at a regional scale, when the soils have small heterogeneity. Long‐term soil drainage was simulated on 3500 ha in Beauce (France), taking into account variation in soil thickness, agricultural practices, and climate characteristics for a 32‐yr period. The model was based on a numerical solution of Richards' equation, using a finite element method. Hydraulic properties were determined at four sites that are 4 km apart. The results show a small variability of hydraulic parameters, with coefficient of variation (CV) ranges from 1 to 16% for the α parameter, the empirical constant n, the saturated water content θs, and the residual water content θr, and from 60 to 75% for the saturated hydraulic conductivity Ks. Hence, the spatial and temporal variability of drainage are mainly related to soil thickness, agricultural practices, and climate characteristics. Assigning small spatial variability to hydraulic properties, we analyzed the role of soil thickness and initial water content (IWC), induced by agricultural practices and climate characteristics, on drainage prediction. Five IWC were defined: 100, 90, 80, 70, and 55% of field capacity (FC). Four soil thicknesses were studied: 30, 60, 100, and 150 cm. The IWC appeared as a significant factor in drainage prediction for 60% of the 32 yr, regardless of soil thickness. Soil thickness became the most significant factor (20% of the 32 yr) for low IWC. The model was spatially extrapolated by combining the calculated drainage (which varied with soil thickness and IWC) and the spatial distribution of crops and soil thickness classes. Simulated drainage was closely related (r = 0.90) to groundwater recharge during the 32 yr, indicating that the model could be applied to other areas with appropriate parameters.
On The History of the Ellipse Equation for Soil Drainage
Authors: van der Ploeg R. R. , Marquardt Maria , Kirkham Don 
Published: July 2010

AbstractColding from Denmark is considered to be the first who derived (in 1872) a drainage equation based on Dupuit‐Darcy theory. Because of the shape of the water table between the drains that is calculated, this equation is frequently called the ellipse equation. It has been believed that Rothe in 1924 in Germany, Kozeny in 1932 in Austria, Hooghoudt in 1937 in the Netherlands, and Aronovici and Donnan in 1946 in the USA independently developed the same equation. Such a coincidence, although possible, appears to be unlikely. Therefore, we decided to study the older European literature that formerly was not always easily accessible. The literature review shows that both Kozeny and Hooghoudt referred to Rothe in previous publications and hence were familiar with Rothe's work. Although less obvious, it appears that also Rothe, as well as Aronovici and Donnan, had knowledge of earlier work on the subject. Hence, it seems that the current view about a multiple, independent derivation of the Colding equation needs a revision. However, since each of the later researchers extended or modified the original Colding equation, all deserve some credit, especially Hooghoudt, who appears to be the first to use Dupuit‐Darcy theory to derive a ditch drainage equation.
Evaluation of Calibration Methods for Interpreting Soil Salinity from Electromagnetic Induction Measurements
Authors: Johnston M. A. , Savage M. J. , Moolman J. H. , du Plessis H. M. 
Published: July 2010

AbstractThe EM‐38 electromagnetic induction sensor of Geonics Ltd. (Canada) is a most useful instrument for rapid field identification and mapping of soil salinity. Interpretation of instrument measurements in terms of meaningful parameters of soil salinity is difficult, however, due largely to the non‐uniform response distribution with depth. Various models have been proposed that allow the conversion of measurements made on this instrument to the electrical conductivity of the bulk soil (ECa, as measured with the four‐electrode probe) or EC of the saturation extract (ECe). Seven of these models were evaluated in this study by comparing predicted with measured values. Four allow the estimation of ECa at 0.30‐m depth intervals down to 0.90 m, two allow the estimation of a single valued ECe, weighted for instrument response with depth, and one estimates ECe for 0.30‐m intervals down to 0.90 m. The performance of the models varied greatly, and likely reasons for poor prediction are discussed. For the model that produced the most accurate estimate of ECa, the estimated values were, based on 95% confidence limits, within 0.8 dS m‐1 of the values predicted using the regression equations. For the models that predict weighted ECe, the corresponding value was typically about 2.2 dS m‐1. While salinity measurements made with the EM‐38 are not highly accurate, the strength of the technique is that measurements of reasonable accuracy can be made very rapidly. Categories of soil salinity for large areas can be readily established, which represents useful information for salinity management and certain research applications.
Citrate‐Ascorbate as a Highly Selective Extractant for Poorly Crystalline Iron Oxides
Authors: Reyes I. , Torrent J. 
Published: July 2010

AbstractExisting methods for dissolving poorly crytalline Fe oxides (primarily ferrihydrite) in soils and mineral mixtures are simple and rapid but often lack selectivity. In this work, we tested a more selective, alternative ascorbate‐based extractant. Ascorbate combined with citrate was found to be highly effective in dissolving poorly crystalline Fe oxides while dissolving little goethite and hematite. Citrate‐ascorbate and oxalate extracted similar amounts of Fe from most of the soils and Fe‐rich materials studied. However, citrate‐ascorbate was more selective than oxalate, since it dissolved only negligible amounts of allophane or imogolite and magnetite. The recommended citrate‐ascorbate extraction procedure (0.2 M sodium citrate‐0.05 M sodium ascorbate, pH 6, 16 h) is simple to implement and relatively inexpensive, and uses nontoxic chemicals. Thus, it can be used on a routine basis for estimating poorly crystalline Fe oxides in soils. By subtracting citrate‐extractable Fe and Al from citrate‐ascorbate‐extractable Fe and Al values, respectively, one can estimate Fe and Al contained in poorly crystalline Fe oxides. The citrate‐ascorbate extraction, combined with others (oxalate, Tiron, hydroxylamine) can help detect and quantify other soil components such as allophane and magnetite.
Moist‐ and Dry‐Season Nitrogen Transport in Sierra Nevada Soils
Authors: Burcar S. , Miller W. W. , Tyler S. W. , Blank R. R. 
Published: July 2010

AbstractCharacterization of ion mobility is a first step in the understanding of nutrient flux relationships in alpine forested watersheds. Our purpose was to: (i) investigate the transport dynamics of inorganic N in Sierra Nevada soils by applying unspiked source water as a control, and a 1 mmolc L‐1 NH4NO3 spiked solution to two soil types (granitic and andesitic) under forest and meadow conditions via artificial rainfall during moist (spring) and dry (late summer‐early fall) seasons; and (ii) evaluate the presence of macropore or preferential matrix flow from characteristic profile distributions of the two N forms. Peak concentrations in surface flow discharge (runoff) of both N forms from control treatments occurred early for both soil types and were highest from the meadow areas (1.6–0.4 mg NO‐3‐N L‐1 meadow to forest for granitic soil and 0.3–0.1 mg L‐1 meadow to forest for andesitic soil; 0.75–0.37 mg NH+4‐N L‐1 meadow to forest for granitic soil and 0.25–0.18 mg L‐1 meadow to forest for andesitic soil). Both soils exhibited NH+4‐N adsorption, but only the soil of andesitic origin appeared to sorb NO‐3‐N. Andesitic soils of the Sierra Nevada may thus serve as a temporary sink for NO‐3‐N deposition, whereas meadow areas of both soil types appear to serve as a source. Higher initial soil moisture for the spiked treatments generally resulted in the transport of NH+4‐N to greater depths in both soils of forested cover (≈ 40 compared with 20 cm from spring to late summer‐early fall), and for NO‐3‐N (≈ 50 compared with 40 cm) as well. Wet‐season (spring) mobility must therefore be considered an important groundwater nutrient transport mechanism in Sierra Nevada watershed soils.
Nitrate Leaching from Cattle Urine and Feces in Northeast USA
Authors: Stout W. L. , Schnabel R. R. , Priddy W. E. , Elwinger G. F. , Fales S. A. , Muller L. D. 
Published: July 2010

AbstractManagement intensive grazing (MIG) is a grazing system in which animals at a high stocking density are rotated frequently through a series of paddocks in a manner that maximizes both forage yield and quality. Although MIG has the potential to increase dairy farm profitability in the U.S. Northeast, the uneven recycling of N through feces and urine can increase NO3‐N leaching. The extent to which NO3‐N can leach from beneath urine and fecal spots under soil and climatic conditions of the Northeast is not known. We conducted a field study to measure NO3‐N leaching loss from spring‐, summer‐, and fall‐applied urine and summer‐applied fecal beneath N‐fertilized orchardgrass (Dactylis glomerata L., cv. Pennlate) using 60‐cm‐diameter by 90‐cm‐deep drainage lysimeters. The study site was located in central Pennsylvania on a Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Averaged across the 3 yr of the study, NO3‐N losses were 1.17, 1.68, 22.0, 24.0, and 31.5 g m‐2 for the control, feces, and spring‐, summer‐, and fall‐applied urine, respectively. These losses represent about 2% of the N applied in the feces and about 18, 28, and 31% of the spring‐, summer‐, and fall‐applied urine N. If dairy farmers in the Northeast continue to increase the utilization of MIG, the amount of N leached to the groundwater from beneath pastures could become substantial if not mitigated by improved grazing management.