bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Variability of Water and Bromide Transport Through Variably Saturated Soil Blocks
Authors: Strock J. S. , Cassel D. K. , Gumpertz M. L.
Published: July 2010

Water and solute transport pathways through soil are very complex. Soil properties affecting solute transport vary spatially and temporally within a soil profile and across landscape positions. The objective of this laboratory study was to evaluate water and bromide (Br) transport through 38‐ by 38‐ by 60‐cm‐deep undisturbed blocks of Cecil soil (Clayey, kaolinitic, thermic Typic Kanhapludults) collected from three contrasting landscape positions (interfluve, linear slope, and foot slope) in the Piedmont region of North Carolina. Two replicate soil blocks from each position were placed on a grid lysimeter‐plate effluent collection system which facilitated collection of the effluent from 81 discrete cells under −2.5 kPa pressure. Each block was equilibrated for 5 d with a once daily application of 3.5 L of 0.005 M CaSO4 solution by a water drop applicator at a rate of 14 mm h−1 Four‐hundred mL of KBr solution (4000 g Br m−2) was uniformly sprayed onto the soil surface. Thereafter, 3.5 L of 0.005 M CaSO4 solution was applied daily for the duration of each experiment (19–33 d). Effluent volume and Br concentration in the effluent were measured daily for each of the 81 4 by 4‐cm cells. Cumulative water outflow and Br distribution plots, spatial distribution of cumulative effluent percent, frequency plots, and Br breakthrough curves (BTCs) showed that differences in preferential flow of water and Br occurred for soil blocks from different landscape positions. Differences in preferential flow of water and Br were attributed to soil horizon thickness, soil texture and structure, macroporosity, and slope gradient. Preferential flow of water and Br under variably saturated conditions was found to be highly variable within a given soil profile and that differences in the distribution and magnitude of preferential flow occurred across topographic positions.
Simultaneous Water Content, Air‐Filled Porosity, and Bulk Density Measurements with Thermo‐Time Domain Reflectometry
Authors: Ochsner Tyson E. , Horton Robert , Ren Tusheng
Published: July 2010

The partitioning of the soil volume between water, solids, and air strongly influences many soil processes. In this paper we demonstrate a new approach to nondestructively measure this partitioning. A thermo‐time domain reflectometry (thermo‐TDR) probe was inserted into sandy loam soil and used to apply thermal and electromagnetic pulses and to monitor the transport of these pulses through the soil. We used the resulting data to determine the soil water content, air‐filled porosity, and volume fraction of solids, as well as degree of saturation and bulk density. When calibrated for this soil, the standard errors between thermo‐TDR measurements and gravimetric measurements were 0.02, 0.07, and 0.05 m3 m−3 for water content, volume fraction of solids, and air‐filled porosity, respectively. The standard error for degree of saturation was 0.08 m3 m−3, and for bulk density was 0.18 Mg m−3 This technique has great potential for soil research and management, particularly if the accuracy of the bulk density measurement can be improved.
Numerical Analysis of Transport of Trifluralin From a Subsurface Dripper
Authors: Russo D. , Zaidel J. , Laufer A. , Gerstl Z.
Published: July 2010

The transport of a pulse of trifluralin (2,6‐dinitro‐N,N‐dipropyl‐4‐[trifluoromethyl] benzenamime) applied via a subsurfacedripper was analyzed numerically. Results of the analyses suggest that the movement and spread of trifluralin in the soil is considerably retarded by its strong adsorption to the solid phase of the soil. This is particularly so in soils which contain aconsiderable fraction of organic C and in fine‐textured (clayey) soils with low hydraulic conductivity and high water retentivity. Water uptake by plant roots and the resultant rapid decrease of water velocity with increasing distance from the dripper restricts further the downward movement of trifluralin and its potential to pollute the groundwater. The presence of dissolved organic matter (DOM) in the irrigation water may enhance both the movement and the spread of trifluralin in the soil, particularly in coarse‐textured soils with a relatively small fraction of organic C. Because of the strong adsorption of trifluralin to the soil, its concentration in the aqueous phase of the soil is very low and it decreases further with increasing time because of degradation and nonequilibrium sorption. This is particularly so in coarse‐textured soils with a relatively large fraction of organic C. Nevertheless, results of the analyses suggest that for soils of quite widely differing textures and organic C contents, a trifluralin concentration of may persist in the vicinity of the dripper for a relatively long period of time (90 d) even with relatively small applied mass (3 × 10−5 kg).
Freezing Effects on Carbon and Nitrogen Cycling in Northern Hardwood Forest Soils
Authors: Nielsen Caroline B. , Groffman Peter M. , Hamburg Steven P. , Driscoll Charles T. , Fahey Timothy J. , Hardy Janet P.
Published: July 2010

We evaluated the effects of freeze–thaw events on soil respiration, nitrogen mineralization, nitrification, and nitrous oxide production in soils from a northern hardwood‐dominated forest in New Hampshire, USA. Soil samples from three horizons (Oe, Oa, A) from nearly monospecific stands of sugar maple (Acer saccharumMarshall) and yellow birch (Betula alleghaniensisBritton) were placed in 200‐mL incubation vessels (microlysimeters), subjected to severe (−13°C) and mild (−3°C) freeze treatments for 10 d, and then incubated at laboratory temperature (20–25°C) for 3 wk. Evolution of CO2and N2O and concentrations of leachable NH+4and NO−3were measured at weekly intervals. Freezing increased rates of C and N cycling in these soils, but the effects varied with species, horizon, and freeze treatment. Whereas severe freezing stimulated respiration, N2O flux, and mineralization, mild freezing had very few effects. Nitrification did not appear to be affected by either freeze treatment, but increases in denitrification may have masked freeze effects on this process. Freeze effects were much more marked in maple than in birch soils and in the Oaand A horizons. Maple consistently had higher rates of nitrification and N2O production than did birch. The species and horizon differences were likely driven by higher levels of available C in the birch soils and Oehorizon at both sites. These results suggest that changes in climate and snow cover that influence soil freezing could increase N and C losses from northern hardwood forest ecosystems with potential effects on soil fertility and carbon storage, receiving water quality, and atmospheric chemistry.
Beneficial Effects of Humic Acid on Micronutrient Availability to Wheat
Authors: Mackowiak C. L. , Grossl P. R. , Bugbee B. G.
Published: July 2010

Humic acid (HA) is a relatively stable product of organic matter decomposition and thus accumulates in environmental systems. Humic acid might benefit plant growth by chelating unavailable nutrients and buffering pH. We examined the effect of HA on growth and micronutrient uptake in wheat (Triticum aestivum L.) grown hydroponically. Four root‐zone treatments were compared: (i) 25 μM synthetic chelate N‐(4‐hydroxyethyl)ethylenediaminetriacetic acid (C10H18N2O7) (HEDTA at 0.25 mM C); (ii) 25 μM synthetic chelate with 4‐morpholineethanesulfonic acid (C6H13N4S) (MES at 5 mM C) pH buffer; (iii) HA at 1 mM C without synthetic chelate or buffer; and (iv) no synthetic chelate or buffer. Ample inorganic Fe (35 μM Fe3+) was supplied in all treatments. There was no statistically significant difference in total biomass or seed yield among treatments, but HA was effective at ameliorating the leaf interveinal chlorosis that occurred during early growth of the nonchelated treatment. Leaf tissue Cu and Zn concentrations were lower in the HEDTA treatment relative to no chelate (NC), indicating HEDTA strongly complexed these nutrients, thus reducing their free ion activities and hence, bioavailability. Humic acid did not complex Zn as strongly and chemical equilibrium modeling supported these results. Titration tests indicated that HA was not an effective pH buffer at 1 mM C, and higher levels resulted in HA‐Ca and HA‐Mg flocculation in the nutrient solution.
Soil Water Retention as Related to Topographic Variables
Authors: Pachepsky Ya. A. , Timlin D. J. , Rawls W. J.
Published: July 2010

Digital elevation models were proposed and used as a data source to estimate soil properties. This study evaluated variability of texture and water retention of soils for a gently sloping 3.7‐ha field located in the long‐term precision farming research site at the Beltsville Agricultural Research Center, MD. The specific objectives of this research were (i) to characterize variability of water retention across the hillslope, and (ii) determine and describe any correlations of soil water retention with soil texture and surface topography. Soil was sampled along four 30‐m transects and in 39 points within the study area. Textural fraction contents, bulk density, and water retention at 0, 2.5, 5.0, 10, 33, 100, 500, and 1500 kPa were measured in samples taken from 4‐ to 10‐cm depth. A 30‐m digital elevation model (DEM) was constructed from aerial photography data. Slopes, profile curvatures, and tangential curvatures were computed in grid nodes and interpolated to the sampling locations. Regressions with spatially correlated errors were used to relate water retention and texture to computed topographic variables. Sand, silt, and clay contents depended on slope and curvatures. Soil water retention at 10 and 33 kPa correlated with sand and silt contents. The regression model relating water retention to the topographic variables explained more than 60% of variation in soil water content at 10 and 33 kPa, and only 20% of variation at 100 kPa. Increases in slope values and decreases in tangential curvature values, i.e., less concavity or more convexity across the slope, led to the decreases in water retention at 10 and 33 kPa. Results of this work show a potential for topographic variables to be used in interpretation of field‐scale variability of soil properties and, possibly, yield maps in precision agriculture.
Nitrogen and Water Stress Interact to Influence Carbon‐13 Discrimination in Wheat
Authors: Clay D. E. , Engel R. E. , Long D. S. , Liu Z.
Published: July 2010

The impact of interactions between water and N stress on 13C isotopic discrimination (Δ) is not well understood. The objective of this study was to determine the impact of N on Δ in wheat (Triticum aestivum L.) grown under low, moderate, and high water stress. In a field study located near Havre, Montana, USA (48° 30′ N lat. and 109° 22′ W long.), wheat grown under three different water stress environments (low, moderate, and high) was fertilized with three different N rates (none, moderate, and high). Each treatment was replicated four times. The grain N fertilizer use efficiency increased as water stress decreased. A differential response of Δ to N was observed. In general, if plants were grown under high water stress and N increased yield, then adding N to N‐deficient plants reduced Δ (−0.01‰ for every kg of N added); and if plants were grown under low water stress and N increased yield, then adding N had little or no impact on Δ. The break point between N impacting or not impacting Δ was ∼17.45‰. Under non‐N limiting (moderate and high N) conditions the equation relating Δ to yield was, yield (kg ha−1) = −11000 + 884 Δ, r = 0.92**. Wheat grown under N‐deficient conditions (0N treatment) did not fit this curve. By accounting for the impact of water and N stress on Δ, this variation could be explained. Results from this study suggest that Δ can be used to characterize N and water stress at different landscape positions in watershed studies.
Topographically Controlled Yield Response of Canola to Nitrogen Fertilizer
Authors: Pennock D. , Walley F. , Solohub M. , Si B. , Hnatowich G.
Published: July 2010

The effect of topographical position on the yield response of canola (Brassica rapavar. Maverick) to N fertilizer was evaluated in a 3‐yr field study in Saskatchewan, Canada. The hummocky, glacial till research site was stratified into three topographically defined landform complexes (convex, linear, and concave). Five N treatments (0, 0.5, 1.0, 1.5, and 2 times the recommended soil test rates; treatments will be referred to as 0×N, 0.5×N, 1×N, 1.5×N, and 2×N, respectively) were randomized in replicated blocks, and each block spanned the three landform complexes. Substantial yield differences occurred among the study years and were associated with year‐to‐year differences in spring soil moisture. Canola seed yields (averaged across years and treatments) increased from 0.53 Mg ha−1in convex complexes to 0.95 Mg ha−1in linear, and 1.42 Mg ha−1in concave landform complexes. The greatest yield responses to N occurred in the concave landform units in years where spring soil moisture was high. The N fertilizer rate required to achieve the economically optimum yield was significantly correlated to spring available moisture (required N rate [kilogram per hectare] = 40.9 + 14.87 [spring available water {in centimeters} water to 60‐cm depth],R2= 0.73, sig. = 0.003) but was not significantly related to spring (i.e., preseeding) available soil N. The results confirm earlier studies indicating the importance of spring available water for crop production in the northern Great Plains, and suggest that intensive spring sampling for soil moisture conditions may be the most useful diagnostic tool for the implementation of a variable rate N program in this region.
Dielectric Relaxation of Bound Water versus Soil Matric Pressure
Authors: Hilhorst M.A. , Dirksen C. , Kampers F.W.H. , Feddes R.A.
Published: July 2010

The electrical permittivity of soil is a function of the water content, which facilitates water content measurements. The permittivity of soil is also a function of the frequency of the applied electric field. This frequency dependence can be described by the relationship between the dielectric relaxation frequency and the activation enthalpy of the water, which in turn is related to the soil matric pressure. The activation enthalpy or soil matrix pressure is a measure of the binding forces acting on a water molecule in the soil matrix. Each water molecule is differently bound, varying from tightly bound to free water. The permittivity of the bulk soil results from the contribution of all the water molecules in the soil matrix. Therefore, the permittivity of soil as a function of frequency is related to the soil matrix pressure. It is realistic to consider hygroscopic water as ice like. A relatively sharp transition can be observed from free to hygroscopic water at matric pressure – 100 MPa corresponding to relaxation frequency fr ≈ 8 GHz. Therefore, for the interpretation of dielectric data using a dielectric mixture equation, the water content of soil can be split conveniently in “free” water and “hygroscopic” water.
Procedure for Determining the Biodegradation of Radiolabeled Substrates in a Calcareous Soil
Authors: Ström Lena , Godbold Douglas L. , Jones David L.
Published: July 2010

Calcareous soils are frequently typified by a low availability of plant nutrients due to poor solubility of these elements at high pH. Calcicole plants have recently been shown to release organic acids in response to the nutrient deficient conditions prevailing in these soils. It has been speculated, however, that the efficiency of this nutrient mobilization mechanism may be significantly reduced by microbial degradation of the organic acids. In conventional methods, root exudate degradation is typically determined by the addition of14C‐radiolabeled substrates to soil and subsequent tracking of their fate with time by trapping evolved14CO2in a strong alkali trap. However, in calcareous soils,14CO2and H214CO3produced by microbial decomposition may become trapped as Ca(H14CO3)2The aim of this study was to develop and validate an experimental procedure for the accurate quantification of14C‐labeled substrate degradation rates in calcareous soils. Conventional methods for determining14C‐labeled substrate decomposition rates in calcareous soils are inaccurate due to incomplete recovery of14CO2Up to 49% of the14CO2produced during microbial degradation of14C‐labeled organic acids (malate, oxalate, citrate) was trapped as carbonate in this calcareous soil (pH 7.58). For an acid soil (pH 4.32) no detectable amount of14CO2was trapped. We describe a simple, accurate, and reliable method, which includes a postincubation HCl addition, for the accurate determination of14CO2‐evolution and substrate degradation in calcareous soils.
Spatial Variability of Soil Properties and Weed Populations in the Mississippi Delta
Authors: Gaston L.A. , Locke M.A. , Zablotowicz R.M. , Reddy K.N.
Published: July 2010

Simulation models and precision agriculture practices may require more detail and certainty about soil spatial variability than provided by soil surveys. This study described soil and weed spatial variability in 50‐ha subareas of two sites included in the Mississippi Delta Management Systems Evaluation Areas project. Objectives were (i) to describe the spatial variability of soil properties and (ii) to determine relationships between spatially variable weed populations and soil properties. Surface soil samples were collected at nodes of 60‐m square grids prior to planting cotton (Gossypium hirsutumL.) in 1996. Field‐moist soil was analyzed for microbial activity. Air‐dried soil was used to determine soil organic C, pH, and texture. Fluometuron and either clomazone, metolachlor, or norflurazon were banded over the crop row at planting. Weed counts were taken 6 wk after herbicide application. The spatial variability of soil properties and weed populations was described using geostatistics. Soil microbiological activity exhibited limited spatial dependence, but pH, organic C, and texture semivariograms were well‐described with spherical models. Although short‐range (<60 m) variability was often high, the range of spatial dependence typically exceeded 120 m. Total weeds were spatially dependent both years; however, weeds susceptible to control by herbicide were not. Weed densities were significantly greater (P< 0.05) in areas that had higher organic C and finer texture. Areas of low organic C and coarse soil often had no weeds. Thus, more uniform weed control might be achieved by varying preemergence herbicide application rate. Acceptable weed control might be achieved with lower herbicide application rates in certain areas.
Comparison of soil water retention at field and laboratory scales
Authors: Pachepsky Yakov , Rawls Walter J. , Giménez Daniel
Published: July 2010

Water content and soil water matric potential are measured in different soil volumes and at different spatial scales in the laboratory and in the field. The objective of this work was to use a large database to compare field and laboratory water retention. The database consisted of 135 datasets for soil horizons of various textures. Coarse‐textured soils had the average difference between field and laboratory water contents close to zero. On the contrary, fine‐textured soils with the sand content <50% had field water contents substantially smaller than the laboratory water contents in the range of water contents from 0.45 to 0.60 cm3 cm−3 A quadratic regression explained 70% of variability in field water contents as computed from the laboratory data. A fractal scaling of the bulk density could contribute to the observed field–lab differences in volumetric water contents for the range of high water contents.
Comparison of Methods for Interpolating Soil Properties Using Limited Data
Authors: Schloeder C.A. , Zimmerman N.E. , Jacobs M.J.
Published: July 2010

Spatial interpolation methods are frequently used to characterize patterns in soil properties over various spatial scales provided that the data are abundant and spatially dependent. Establishing these criteria involved comparisons of abundant data from many fine‐scaled (<100 ha) investigations. In this study we investigated whether it was appropriate to use spatial interpolation methods with limited (n = 46), coarse‐scaled (1188 ha) soils data from a Vertisol plain. Methods investigated included ordinary kriging, inverse‐distance weighting, and thin‐plate smoothing splines with tensions. Comparison was based on accuracy and effectiveness measures, and analyzed using ANOVA and pairwise comparison t‐tests. Results indicated that spatial interpolation was appropriate when the data exhibited smooth and consistent patterns of spatial dependency within the study area and the selected ranges of estimation and weighting used in this investigation. Nine of twelve soil properties we investigated exhibited characteristics other than these, however, including independent data, variable and erratic behavior, and extreme values. Our sample design may have been an important factor as well. Ordinary kriging and inverse‐distance weighting were similarly accurate and effective methods; thin‐plate smoothing splines with tensions was not. Results illustrate that sample size is as important for coarse‐scale investigations as it is for fine‐scale investigations with most soils data. However, our ability to predict successfully with some of our data raises the question as to the exact nature of the relationship between accuracy, sample size, and sample spacing, and to what extent these factors are related to the property under investigation, particularly when data are limited.
Spatial Variability in Palustrine Wetlands
Authors: Stolt M.H. , Genthner M.H. , Daniels W.L. , Groover V.A.
Published: July 2010

Wetlands are complex ecosystems having considerable spatial variability. Understanding soil spatial relationships in wetlands is difficult because of the number of factors that affect soil properties. We established a nested sampling design within five small, forested and scrub‐shrub palustrine wetlands in Virginia to examine soil spatial variability within and among sites. Sampling was based on relative elevation intervals within each wetland and soil depth within each sampling unit. Soils were analyzed to determine variability in nutrient status, pH, organic C content, and particle‐size distribution (PSD). Elevation contributed the least amount to the total variability (variability among sites) for nearly every parameter. Depth from the soil surface explained the most total variability in regard to PSD, indicating that parent material stratification in these alluvial wetlands strongly influences soil physical properties. Most of the total variability in the soil chemical parameters was explained by site. Within sites, elevation trends were observed for particle‐size and chemical parameters in most of the wetlands. Elevation trends were related to water table levels and the depositional environment. Within elevation sampling units, particle‐size and chemical parameters were shown to be significantly related to depth from the soil surface (at the 0.05 level). These relationships could be attributed to the stratified nature of alluvial soils and the accumulation of organic matter at or near the soil surface. Pedon sampling locations were spaced ≈1 m apart and therefore showed less random variability than elevation sampling locations spaced throughout the 0.25‐ to 0.35‐ha study areas. Soils were classified as Endoaquepts, Humaquepts, Dystrudepts, Endoaquents, and Fluvaquents, depending on the wetland site.
Fine Root Productivity and Dynamics on a Forested Floodplain in South Carolina
Authors: Baker Terrell T. , Conner William H. , Lockaby B.Graeme , Stanturf John A. , Burke Marianne K.
Published: July 2010

The highly dynamic, fine root component of forested wetland ecosystems has received inadequate attention in the literature. Characterizing fine root dynamics is a challenging endeavor in any system, but the difficulties are particularly evident in forested floodplains where frequent hydrologic fluctuations directly influence fine root dynamics. Fine root (≤3 mm) biomass, production, and turnover were estimated for three soils exhibiting different drainage patterns within a mixed‐oak community on the Coosawhatchie River floodplain, Jasper County, South Carolina. Within a 45‐cm‐deep vertical profile, 74% of total fine root biomass was restricted to the upper 15 cm of the soil surface. Fine root biomass decreased as the soil became less well drained (e.g., fine root biomass in well‐drained soil > intermediately drained soil > poorly drained soil). Fine root productivity was measured for 1 yr using minirhizotrons and in situ screens. Both methods suggested higher fine root production in better drained soils but showed frequent fluctuations in fine root growth and mortality, suggesting the need for frequent sampling at short intervals (e.g., monthly) to accurately assess fine root growth and turnover. Fine root production, estimated with in situ screens, was 1.5, 1.8, and 0.9 Mg ha−1 yr−1 in the well‐drained, intermediately drained, and poorly drained soils, respectively. Results from minirhizotrons indicated that fine roots in well‐drained soils grew to greater depths while fine roots in poorly drained soils were restricted to surface soils. Minirhizotrons also revealed that the distribution of fine roots among morphological classes changed between well‐drained and poorly drained soils.
Evaluation of Pedotransfer Functions for Predicting the Soil Moisture Retention Curve
Authors: Cornelis Wim M. , Ronsyn Jan , Van Meirvenne Marc , Hartmann Roger
Published: July 2010

The soil moisture retention curve (MRC) is time consuming and expensive to measure directly. Several attempts have been made to establish a relation between readily available soil properties, like particle‐size distribution, organic matter content, and bulk density, and the soil moisture retention curve. Those relationships are referred to as pedotransfer functions (PTFs). The objective of this study was to evaluate some PTFs with respect to their accuracy in predicting the soil moisture retention curve. Five widely used and four more recently developed PTFs were selected for evaluation. Seven of the selected PTFs predict moisture retention function parameters, whereas the other two predict the moisture content at certain matric potentials. In order to quantify the prediction accuracy, the mean of the absolute value of mean differences (MAMD), the mean and the standard deviation of the root of mean squared differences (MRMSD and SDRMSD, respectively), and the mean of the Pearson correlation coefficient (Mr) were used. The evaluated PTFs were finally ranked based on these validation indices. The PTFs showed good to poor prediction accuracy with MAMD values ranging from 0.0312 to 0.0603 m3 m−3 and with MRMSDs between 0.0412 and 0.0774 m3 m−3 The SDRMSDs and Mrs ranged from 0.0212 to 0.0349 m3 m−3, and from 0.9468 to 0.9980, respectively. The validation indices computed by the PTF of Vereecken and coworkers gave the best results. Moreover, it predicts moisture retention function parameters, and therefore, this PTF is recommended most to predict the moisture retention curve from readily available soil properties.
Stability of Reduced Organic Sulfur in Humic Acid as Affected by Aeration and pH
Authors: Hutchison Kimberly J. , Hesterberg Dean , Chou Jeff W.
Published: July 2010

Reduced S groups in soil organic matter (OM) play an important role in the complexation of heavy metals. These complexation reactions are often studied using the humic acid component of OM. The objective of our study was to determine the effect of pH on humic acid yield and the effect of pH and exposure to O2on the oxidation of reduced organic S. Humic acid was extracted at pH levels between 11.5 and 13.0 from a soil collected from a salt marsh. Also, aqueous samples of humic acid at different pH levels were aspirated with CO2‐free air for 4 or 44 h. X‐ray absorption near‐edge structure (XANES) spectroscopy was used to determine changes in S oxidation states for the various treatments. With increasing pH, the yield of humic acid increased from 1.3 to 4.6 g humic acid kg−1soil, and the total S in these samples was 24 ± 1 g kg−1humic acid. Linear‐combination fitting of XANES spectra showed that all of these humic acid samples contained ≈70% (mol/mol) reduced S (modeled as benzyl disulfide) and 30% (mol/mol) oxidized S (modeled as sulfonate and ester sulfate). For humic acid exposed to aeration for 4 h at pH levels between 11.5 and 13.0, reduced organic S was oxidized only at pH 13.0 (15% [mol/mol] of total S). Samples exposed to aeration for 44 h between pH 3.5 and 12.4 showed no detectable change in reduced organic S.
Surface‐Induced Nickel Hydroxide Precipitation in the Presence of Citrate and Salicylate
Authors: Yamaguchi Noriko U. , Scheinost Andreas C. , Sparks Donald L.
Published: July 2010

Formation of surface‐induced precipitates may play an important role in the immobilization of Ni and other metals in nonacidic soils. To investigate the influence of commonly present organic ligands on precipitate formation, we monitored the uptake of Ni by gibbsite and pyrophyllite in the presence of citrate and salicylate for 4 wk and identified the Ni hydroxide precipitates with diffuse reflectance spectroscopy (DRS). In the absence of organic ligands, Ni uptake proceeded by formation of Ni–Al layered double hydroxide (LDH) precipitates. Citrate and salicylate generally decreased both the Ni removal from solution and the precipitate formation. The suppression by citrate was more pronounced than that by salicylate due to the stronger complexation of Ni by citrate. In the presence of citrate and salicylate, the precipitate phase was Ni–Al LDH on pyrophyllite, but predominately α‐Ni hydroxide on gibbsite. This difference can be explained by the differing Al solubilities of the two minerals. Pyrophyllite is relatively soluble, causing the rapid formation of amorphous Al hydroxide, which, in turn, is a necessary precursor for the formation of Ni–Al LDH. In spite of the complexation of Al by organic ligands, sufficient amorphous Al hydroxide was available to promote the formation of Ni–Al LDH. Gibbsite, on the other hand, is much less soluble, and the smaller amount of initially released Al may be fully complexed by citrate and salicylate. The subsequent lack of amorphous Al hydroxide prevented the formation of Ni–Al LDH, and, instead, α‐Ni hydroxide formed. Only after a longer period of 30 d and at a low citrate concentration did enough Al become available to transform α‐Ni hydroxide into the thermodynamically more stable Ni–Al LDH.
Sensitivity of Soil Manganese Oxides
Authors: Ross Donald S. , Hales Heidi C. , Shea-McCarthy Grace C. , Lanzirotti Antonio
Published: July 2010

The examination of soils by x‐ray absorption near‐edge structure (XANES) spectroscopy can provide valuable clues for determining the structure and composition of Mn oxides. XANES experiments can be conducted at ambient temperatures using field‐moist samples. This feature is attractive in the study of soil Mn because of the well‐documented effects of sample drying on reactivity. The present study was undertaken to determine whether the analysis of field‐moist soils by XANES spectroscopy has an effect on the oxidation state of the Mn. Repeated scans were taken on the same spot using seven medium‐ to high‐Mn soils. In all 10 experiments with untreated soils, the main absorption edge dropped in relative energy in successive scans, indicating reduction of Mn. The change in eV was as high as 1.7 eV after 150 min of exposure time. After a series of scans showing reduction, small movement of the sample in the x‐ray beam and reexamination showed no reduction, indicating that the effect was limited to the x‐ray spot. Modeling the change with Mn(II) was successful and showed increases in reduced Mn between 6 and 20% after three to five repeated scans. The slopes of eV change vs. exposure time were remarkably similar in most experiments, even with large differences in the density of photons between runs. Comparisons of initial moist scans with those of recently air‐dried samples found little difference, suggesting minimal reduction in a single XANES scan under our experimental conditions.
Effects of pH and Electrolytes on Inositol Hexaphosphate Interaction with Goethite
Authors: Celi L. , Presta M. , Ajmore-Marsan F. , Barberis E.
Published: July 2010

The pH and the nature of electrolytes are important factors affecting the sorption of anions by soil components. The effects of pH, K, and Ca on the interaction of inositol hexaphosphate (IHP) and inorganic phosphate (Pi) with goethite were investigated by sorption experiments. Laser Doppler Velocimetry‐Photon Correlation Spectroscopy was employed to determine zeta potential (ζ) and particle size before and after sorption. In the presence of KCl, the amount of adsorbed P decreased, with increasing pH, from 4.5 to 0.18 μmol P m−2 for IHP, and from 2.5 to 0.67 μmol P m−2 for Pi. A more pronounced decrease was observed in the amount of IHP adsorbed compared with Pi, because of the higher negative charge of IHP and to the lower tendency of phosphate groups of IHP to neutralize the OH− released from the surface during adsorption. In CaCl2, sorption increased from 4.5 to 4.9 μmol P m−2 for IHP, and from 2.7 to 4.8 μmol P m−2 for Pi with increasing pH. For both P compounds, however, the sorption increased even beyond the maximum adsorption capacity of the mineral. At the used concentrations of anions and Ca2+ and in a pure system, the reaction with goethite may involve adsorption at low pH, but precipitation of Ca salts at pH >5 must be taken into account. The sorption of IHP caused a high change of the surface charge that became negative at all pH values in K+, causing dispersion of particles, while in Ca2+ the slightly negative phosphated surface determined particle aggregation.
Managing Crop Residue with Green Manure, Urea, and Tillage in a Rice–Wheat Rotation
Authors: Aulakh Milkha S. , Khera T.S. , Doran John W. , Bronson Kevin F.
Published: July 2010

Most double‐crop grain farmers in South Asia remove or burn crop residue to facilitate seedbed preparation and to avoid possible yield reductions. This results in loss of soil organic matter (SOM) and nutrients. In this study, we determined whether incorporating wheat (Triticum aestivumL.) residue, rice (Oryza sativaL.) residue, and sesbania (Sesbania aculetaL.) green manure with urea fertilizer N in a rice–wheat cropping system can improve grain yields, N use efficiency, and SOM. We incorporated wheat residue (6 Mg ha−1, C/N = 94), rice residue (6 Mg ha−1, C/N = 63), or both, with and without green manure (20 or 40 Mg fresh ha−1, C/N = 19), in a field experiment with irrigated rice and wheat grown each year in rotation on a Tolewal sandy loam (Typic Ustochrept) in the Punjab of India. Rice and wheat residue did not affect grain yields of wheat and rice, but residue incorporation did result in reduced recovery efficiency of urea N and green manure N. Rice production was greater with wheat residue incorporation when an average of 86 kg N ha−1of a prescribed 120 kg N ha−1dose was applied as green manure N and the balance as urea N vs. 120 kg urea N ha−1alone. Despite wider C/N than rice residue, wheat residue additions to flooded rice resulted in greater C sequestration in soil than with rice residue or 40 Mg green manure ha−1These results demonstrate that a green manure crop and/or incorporating crop residue in a rice–wheat system has potential to increase SOM while maintaining high grain yields.
Simplified Method for Soil Particle‐Size Determination to Accompany Soil‐Quality Analyses
Authors: Kettler T.A. , Doran J.W. , Gilbert T.L.
Published: July 2010

Soil textural analysis is a key component of any minimum data set used for assessing soil quality and sustainability of agricultural‐management practices. However, conventional methods of soil textural analysis can be costly and time‐consuming. The objective of this study was to develop a rapid and simple method for evaluating soil particle‐size distribution, which could be employed as a tool for initial soil‐quality assessment. The method uses a combination of sieving and sedimentation steps and is designed to be used in conjunction with analysis of particulate organic matter (POM), or as a stand‐alone textural analysis. Soils of varied texture and organic‐matter content were collected from six sites in the Great Plains. Their sand, silt, and clay contents were determined using the proposed methods and standard hydrometer and pipette techniques. Averaged across all soils, absolute differences between the proposed and standard pipette analyses were <2% for sand, silt, and clay. Relative differences were 6, −1, and −4% for sand, silt, and clay, respectively. Coefficients of variation within soil samples averaged <5% for sand, silt, and clay fractions. Regression analysis between proposed and standard pipette methods produced coefficient of determination (r2) values of 0.99, 0.98, and 0.93 for sand, silt, and clay, respectively, and 0.98 across all particle‐size ranges. The method provides an inexpensive and reliable estimate of soil texture, useful in soil‐quality assessment.
Humus Forms in Mediterranean Scrublands with Aleppo Pine
Authors: Peltier Aline , Ponge Jean-François , Jordana Rafael , Ariño Arturo
Published: July 2010

Commonly reported effects of pine on topsoil include acidification, a decrease in biological activity, and an accumulation of surface organic matter. Such effects have not been documented for Mediterranean woodland and scrubland areas. This research evaluated humus profiles beneath pine and adjacent vegetation on the basis of previous knowledge on soil animal communities and vegetation. Two Mediterranean sites with aleppo pine (Pinus halepensis P. Mill.) and scrubland vegetation were compared, one in Spain (Navarre), the other in Italy (Sicily). Humus profiles were sampled under main vegetation types, comprising aleppo pine, rosemary (Rosmarinus officinalis L.), and bare ground in both sites, along transects with increasing pine influence. Quantitative morphological methods were used to analyze and compare humus profiles, and data were analyzed using correspondence analysis. In both sites the influence of aleppo pine on humus forms was well‐defined but minor, increasing the appearance of an Oe horizon characterized by intense activity of litter‐dwelling fauna and fungi. Under all vegetation types, and in both sites, the organo‐mineral A horizon was of the mull type, although the composition of the soil‐building fauna varied between Navarre and Sicily. There was more heterogeneity among vegetation types in Navarre, where aleppo pine was planted on derelict land, than in Sicily where aleppo pine was a component of natural vegetation (maquis). A decreasing influence of pine was perceptible in the inner edge of the pine plantation in Navarre, or under the crown of individual trees in Sicily.
Hydrologic Cycling of Mercury and Organic Carbon in a Forested Upland–Bog Watershed
Authors: Kolka R.K. , Grigal D.F. , Nater E.A. , Verry E.S.
Published: July 2010

The hydrologic cycling of total Hg (HgT) and organic C (OC) was studied for a 1‐yr period in a northern Minnesota forested watershed, consisting of an upland surrounding a bog peatland with a narrow lagg at their interface. Throughfall and stemflow contributed twice as much HgT and seven times as much OC to the forested watershed than atmospheric deposition in a nearby opening. Fluxes in upland runoff accounted for 16% of the HgT and 8% of the OC inputs to the lagg and were dominated by interflow transport. Bog runoff accounted for 57% of the HgT and 83% of the OC inputs to the lagg. For an annual cycle, upland soils were sinks for both HgT and OC, while bog soils were sinks for HgT but sources of OC. Fluxes to the lagg accounted for 184% of the HgT and 87% of the OC transported from the watershed outlet. We speculate that HgT was lost in the lagg by both volatilization and soil accumulation. Total Hg and dissolved organic C (DOC) are positively related in both throughfall and stemflow, with stemflow showing the strongest relationships. In the soil system, HgT–DOC relationships deteriorate and HgT–particulate organic C (POC) relationships dominate. Water residence time in contact with OC appears to be important in determining the relationships between HgT and OC. At the stream outlet, our data suggest that ≈70% of the HgT transported from the watershed is associated with POC, while 30% is associated with DOC.
Chemical Osmosis in Compacted Dredging Sludge
Authors: Keijzer Th. J. S. , Loch J. P. G.
Published: July 2010

Sediments of high clay content are known to exhibit semipermeable properties when compaction is sufficiently high, resulting in osmotically induced water and solute transport. The semipermeability of these materials is quantified by the reflection coefficient, σ. In the design of large dredging sludge depots in the Netherlands, osmotic transport is rarely taken into account. In a flexible wall permeameter, a bentonite and two dredging sludge samples were subjected to a chemical potential gradient to monitor water transport and to obtain values for σ. Chemical osmosis was observed in the bentonite and one of the sludge samples (∼56% clay), but was absent in the sludge with a relatively low clay content (∼26%). The measured σ are low in comparison with values obtained with the Fritz‐Marine Membrane Model (FMMM) and a model presented by Bolt. The discrepancy between the theoretical and experimental values is explained by the assumptions made in both models. Several of these assumptions do not hold for the samples. If the observed semipermeability of the sludge is applied to an existing depot, chemical osmosis induces a water flux close to the maximum allowed advective flux laid down in Dutch legislation.
Kinetics and Energetics of Phosphate Release from Tropical Soils Determined by Mixed Ion‐Exchange Resins
Authors: Agbenin John O. , van Raij Bernardo
Published: July 2010

Kinetic information on soil P release is required to optimize P fertilizer use efficiency in agricultural production and develop guidelines for the disposal of P‐rich wastes onto the land. We determined the kinetics and energy changes of P release from tropical soils by mixed ion‐exchange resin. Phosphate release patterns were determined with or without shaking and at three temperatures: 298, 308, and 333 K. Phosphate release patterns determined as P uptake by the exchange resins were best described by diffusion models. The nature of diffusional limitation was discriminated on the basis of activation energies (Ea), which ranged from 42.03 to 48.72 kJ mol−1The range ofEawas consistent with, and close to, 42.1 kJ mol−1for intraparticle diffusion‐controlled ion‐exchange reactions. The P diffusion coefficients ranged from 2.81 to 4.71 × to 10−13m2s−1under shaking conditions, but decreased to 1.42 to 2.68 × 10−13m2s−1for nonshaking conditions probably because of large films that developed around the resin beads under static or nonshaking conditions. The free energy of activation ΔGO‡and entropy of activation ΔSO‡were lower than those of soils studied by means of resin bags indicating favorable P exchange reactions and less stearic inhibition for the resins. The enthalpy of activation ΔHO‡for the overall P exchange reactions was strongly endothermic.
Microbiological Characteristics of a Vegetative Buffer Strip Soil and Degradation and Sorption of Metolachlor
Authors: Staddon W. J. , Locke M. A. , Zablotowicz R. M.
Published: July 2010

Numerous studies have documented efficacy of vegetated buffer strips (VBS) in removing herbicides from surface runoff. Little is known about the fate of herbicides after deposition in buffer strip soil. Soil samples (0‐ to 2‐cm depth) were collected from a buffer strip and an adjacent bare field (BF). Soil organic C was two‐fold higher in VBS than in BF, and VBS soil maintained about 0.7 log(10) greater propagule density of total fungi and bacteria and 2 log(10) greater gram‐negative bacteria and fluorescent pseudomonads. Corresponding with enhanced microbial populations, VBS exhibited higher endogenous levels of alkaline phosphatase, tetrazolium chloride dehydrogenase, aryl acylamidase, and fluorescein diacetate hydrolytic activity (1.6‐ to 3.8‐fold greater than BF). Batch studies of metolachlor[2‐chloro‐N‐(2‐ethyl‐6‐methyphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] sorption showed greater capacity to sorb metolachlor in VBS soil than in BF (Kd 2.25 vs. 1.60 mL g−1). Soil treated with 14C metolachlor (1.25 mg kg−1) was incubated for 46 d in a laboratory study. Limited mineralization (<4%) was observed for both VBS and BF. Less 14C (43%) was extracted from VBS samples 46 d after treatment. Extractable fractions consisted primarily of metolachlor, although increasing amounts of polar (e.g., sulfonic acid) and nonpolar metabolites were recovered over time, especially in VBS. Metolachlor half‐life was 10 and 23 d for soils from VBS and BF, respectively, attributed to higher levels of organic matter and microbial activity in VBS soils. Data suggest retention and enhanced degradation of metolachlor as it passes through VBS strips may limit further transport.
Residual Phosphorus Distribution and Sorption in Starter Fertilizer Bands Applied in No‐Till Culture
Authors: Stecker John A. , Brown James R. , Kitchen Newell R.
Published: July 2010

Banding fertilizer P in no‐till culture results in a heterogeneous soil P distribution for months to years. This study's objective was to quantify the spatial distribution and temporal dynamics of banded P to improve assessment of soil P availability. In three trials for no‐till corn (Zea maysL.) and from four replicated plots each, we collected a grid of 1.3 by 1.3 cm samples around 10 and 20 kg P ha−1starter fertilizer bands at ∼6, 12, and 18 mo after application. Soils were Mexico silty clay loam (Mollic Epiaqualf), Putnam silty clay loam (Vertic Albaqualf), and Dockery silt loam (Aquic Udifluvent). Band affected soil was defined as having a Bray‐1 P concentration of at least 1.5 times that of adjacent soil. Band dimensions varied from 5 to 8 cm (horizontal) and 5 to 12 cm (vertical), and tended to be largest at the 12‐mo sampling. Cross‐sectional area of bands ranged from 18 to 63 cm2Band P concentrations decreased logarithmically from the band center, and were largest at either 6 or 12 mo, and varied substantially along the direction of band application. Band P concentrations ranged from 100 to 313 mg P kg−1at 6 mo, 56 to 415 mg P kg−1at 12 mo, and 63 to 237 mg P kg−1at 18 mo (avg. of the six most concentrated samples of the 20 kg P ha−1bands). Soil in the band center was weakly buffered and appeared to be more easily extracted by the Bray‐1 extractant than nonband affected soil. Inclusion of bands in soil samples would increase the risk to overestimate available P to a crop.