bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus Forms and Concentrations in Leachate under Four Grassland Soil Types
Authors: Turner Benjamin L. , Haygarth Philip M.
Published: July 2010

The transfer of P in water draining from agricultural land can contribute to eutrophication and the growth of toxic algae. Traditionally, research has focused on particulate P transfer in surface pathways, with transfer by subsurface pathways perceived as negligible. We investigated this by monitoring P in leachate draining through large‐scale monolith lysimeters (135 cm deep, 80 cm diam.) installed in a field site in southwest England. The lysimeters were taken from four grassland soil types with a range of textures (silty clay–sand) and extractable‐P contents (15–75 mg kg−1 NaHCO3 extractable P) and leachate was sampled over two drainage seasons. Export of total P was <0.5 kg ha−1 yr−1 for all soil types. Concentrations of total P in the leachate routinely exceeded 100 μg L−1 and remained relatively stable throughout the drainage season, except during the late spring period when maximum concentrations >200 μg L−1 were detected from all soil types. Physically, most of the leachate P was dissolved (<0.45 μm), although 21 to 46% occurred in the particulate (>0.45 μm) size fraction, most notably from the sandy‐textured soils. Chemically, the leachate was dominated by reactive (inorganic) P from all soil types (62–71%), although a large proportion was in unreactive (organic) P forms (29–38%). Reactive P occurred mainly in the <0.45 μm fraction, while unreactive P was predominantly in the >0.45 fraction. Unreactive P in the <0.45 μm fraction was greatest during the springtime (April–May), probably reflecting microbiological turnover and release of P in the soil. Our results indicate that (i) subsurface P transfer from soil to surface water can occur at concentrations that could cause eutrophication and (ii) unreactive and >0.45 μm P forms are important in subsurface P transfer.
Changes in Soil Mineralogy and Texture Caused by Slash‐and‐Burn Fires in Sumatra, Indonesia
Authors: Ketterings Quirine M. , Bigham Jerry M. , Laperche Valérie
Published: July 2010

We investigated the effect of fire intensity from slash‐and‐burn agriculture on the mineralogy of Oxisols in the Sepunggur area, Jambi Province, Sumatra, Indonesia, in both field and laboratory experiments. Samples were collected from two depths (0–5 and 5–15 cm) at locations exposed to 100, 300, 600, and >600°C surface temperatures during the burns. Soils under forest and slashed vegetation were collected as controls. The pre‐burn soil mineralogy was dominated by kaolinite, gibbsite, anatase, and goethite. Changes in soil properties with burning were most pronounced in the 0‐ to 5‐cm layer. Burning the topsoil led to coarser textures, especially at temperatures exceeding 600°C. Heat reduced the gibbsite and kaolinite concentrations and converted goethite into ultra‐fine maghemite, thus increasing the magnetic susceptibility of the samples. The conversion of goethite did not take place until water in the samples had vaporized. Addition of organic matter to soil with a low organic C content before heating increased the magnetic susceptibility, indicating that organic matter was necessary (and limiting) for the complete conversion of goethite. Coarse‐grained magnetite particles were present prior to and after the burning and, therefore, were not pyrogenic. Magnetic susceptibility measurements were highly discriminatory among heat treatments, whereas x‐ray diffraction (XRD) was much less sensitive to fire‐induced changes in mineralogy. Our research showed that severe burning had drastic effects on soil mineralogy, but changes should also be expected at lower fire intensities. Further research is needed to determine how important these changes in soil mineralogy are for nutrient availability in the growing season after the burn.
Soil Particle Concentrations and Size Analysis Using a Dielectric Method
Authors: Starr G. C. , Barak P. , Lowery B. , Avila-Segura M.
Published: July 2010

Limitations of traditional methods for particle‐size analysis warrant the investigation of new techniques. An alternative method based on the difference between the dielectric constant of soil solids (≈4) and dispersing solution (≈81) was developed. We determined changes in suspended sediment concentrations (C) using a coaxial probe placed on the surface of a dispersed soil suspension by monitoring changes in the apparent dielectric constant with time following complete mixing. A single‐point calibration for each sample was obtained using the known initial concentration. A refractive index (n) model of the suspension dielectric properties gave the slope of a C vs. n curve for changes in silt‐size (0.002–0.05 mm) particles. A magnetic stirring rod was used to homogenize the dispersion, and temperature changes were minimized given the rapid measurement time. Using the dielectric method, particle‐size distributions were measured on a 1‐ to 2‐g sample with 400‐s settling time because the effective depth of measurement was only 1.5 mm. Wet sieving was used to remove the sand fraction. Comparisons between the silt and clay fractions obtained using the dielectric and pipette methods were in agreement. The combination of speed, automation, small sample size, and nearly continuous data should be balanced against the higher cost of the equipment necessary for the dielectric method.
Soil water content determination using a network analyzer and coaxial probe
Authors: Starr G. C. , Lowery B. , Cooley E. T.
Published: July 2010

A small‐volume dielectric constant and soil water content sensor would be desirable in many laboratory experiments. Phase shift of the reflection coefficient in soil and various solutions was measured with a coaxial probe (CP) and a network analyzer operating at a frequency of 795 MHz. The CP had a measurement depth <1 cm. Five soils, varying widely in texture, bulk density, and organic matter content, were tested and comparison was made with other dielectric methods. Synthesized time domain reflectometry (TDR), resonant waveguide, CP, and conventional TDR measurements were in agreement for the sand. A simple mixing model for known dielectrics accurately predicted measurements of the apparent dielectric (Ka) for mixed solutions. A linear function , fit for the water content of all soil data, had a single measurement root mean square error The uncertainty improved when individual linear soil calibrations (singe measurement to 0.99) were used and further improved when repeated measurements were averaged The CP method for measuring Ka is fast, simple, linear, easily repeated, and reasonably accurate, indicating that this instrumentation is useful for studying dielectric behavior of soil and various solutions and for rapid determination of soil water content in a small sample.
Quantitative Characterization of Humic Substances by Solid‐State Carbon‐13 Nuclear Magnetic Resonance
Authors: Mao J-D. , Hu W-G. , Schmidt-Rohr K. , Davies G. , Ghabbour E. A. , Xing B.
Published: July 2010

The compositions of humic acids (HAs) from various Histosols in North America and Europe, of similarly treated plant‐extracted materials (PEMs), of coal‐extracted humic acids, and of International Humic Substances Society (IHSS) Florida peat were quantified by solid‐state 13C nuclear magnetic resonance (NMR). In order to obtain quantitative intensities, the peak areas in direct‐polarization 13‐kHz magic‐angle spinning (DPMAS) 13C NMR spectra were corrected for incomplete relaxation by factors measured in cross‐polarization spin‐lattice relaxation time (CP/T1) experiments with total sideband suppression (TOSS). The elemental compositions (%C, %H, %O + N) of a peat sample, 8 HAs and 2 PEMs were estimated from the NMR results and compared with chemical analyses, as well as solution NMR for two of the HAs. The results are in good agreement, which shows that DPMAS corrected by CP/T1–TOSS permits quantitative characterization of HAs and PEMs. The compositions of the PEMs deviate significantly from those of the Histosol HAs. The compositions in terms of nine types of chemical groups were computed. The investigated HAs consist of more than 60% of aromatic and CO carbons (including both carbonyl and carboxyl groups). Previous cross‐polarization magic‐angle spinning (CPMAS) NMR experiments have significantly underestimated the ratio of sp2– to sp3–carbons; in particular, the true COO carbon fraction is a factor of two larger than estimated by CPMAS NMR. In spite of their wide range of geographical origins, the compositions of the Histosol HAs appear to be relatively uniform, suggesting that the search for a general model of Histosol HA structure is worthwhile. Eight models proposed in the literature do not reproduce the experimentally determined compositions, but a few models show promising partial agreement.
Biochemical Quality of Crop Residues and Carbon and Nitrogen Mineralization Kinetics under Nonlimiting Nitrogen Conditions
Authors: Trinsoutrot I. , Recous S. , Bentz B. , Linères M. , Chèneby D. , Nicolardot B.
Published: July 2010

Statistical relationships were established between the fate of C and N from 47 types of crop residues and their biochemical characteristics during a soil incubation at 15°C. The incubations were carried out under nonlimiting N in order to differentiate the effects of biochemical characteristics of residues from those of soil N availability. Depending on the residue, the apparent mineralization of residue C after 168 d varied from 330 to 670 g kg−1 of added C. Mineralization kinetics were described using a two‐compartment decomposition model that decomposes according to first‐order kinetics. Amounts of C mineralized after 7 d and the decomposition rate coefficient of the labile fraction were related mainly to the soluble C forms of the residue. No statistical relationship was established between the N concentration of residues and their decomposition in the soil. The incorporation of crop residues into soil led to various soil mineral N dynamics. Two residues caused net N mineralization from the time of their incorporation, whereas all the others induced net N immobilization (1–33 g N kg−1 of added C). After 168 d, only residues with a C/N ratio <24 induced a surplus of mineral N compared with the control soil. The mineral N dynamics were related mainly to the organic N concentration of the residues and to their C/N ratio. At the start of incubation, these dynamics were also influenced by the presence of polyphenols in the plant tissues. Finally, this study showed the need to include the biochemical quality of crop residues in any C and N transformation models that describe decomposition. In contrast, the N concentration or C/N ratio of the residues are sufficient to predict the net effects of crop residues on soil mineral N dynamics.
Distribution and Variability of Surface Soil Properties at a Regional Scale
Authors: Brejda John J. , Moorman Thomas B. , Smith Jeffrey L. , Karlen Douglas L. , Allan Deborah L. , Dao Thanh H.
Published: July 2010

Information on the probability distribution and variability of soil properties at a regional scale could improve the ability of the USDA‐Natural Resources Conservation Service (NRCS) to monitor soil condition using the National Resources Inventory (NRI). Our objective was to evaluate the hypothesis that the probability distribution of 17 physical, chemical, and biological soil properties are: (i) normally distributed, or (ii) log‐normally distributed at a regional scale, and to estimate the magnitude of change that may be detected assuming either a normal or log‐normal distribution. Samples were collected irrespective of soil series from two Major Land Resource Areas (MLRAs) (no. 9 and 105), and from the Ascalon (fine‐loamy, mixed, superactive, mesic Aridic Argiustoll) and Amarillo (fine‐loamy, mixed, superactive, thermic Aridic Paleustalf) soils in MLRA 67 and 77, using the NRI sampling design. Most soil properties were non‐normally distributed, with the frequency of non‐normality varying between MLRAs. Confining sampling to a single soil series did not consistently improve the precision with which soil properties were estimated. Loge transformation resulted in normal distributions for most soil properties and reduced variability two‐ to threefold. However, a few soil properties remained non‐normally distributed. Soil pH may be monitored at the regional scale with a high degree of precision. Small changes in soil C content (3–8% of the regional mean) may be detected using loge transformed total organic C as the indicator. Sampling soil properties as part of the NRI should improve NRCs' ability to monitor soil condition on a regional scale.
Defining Geographic Soil Bodies by Landscape Position, Soil Taxonomy, and Cluster Analysis
Authors: Young F. J. , Hammer R. D.
Published: July 2010

The key Soil Taxonomy is based upon the idea that certain properties can be used to define populations of soils from the soil continuum. The soil mapping paradigm is that similar soil populations exist within landforms. High taxonomic variability has been reported within numerous soil mapping units. The hypotheses in this paper are that for large scale mapping (i) Soil Taxonomy creates classes that are only partially related to landform and (ii) more homogeneous soil classes exist if different defining constructs are used. The objectives are to: (i) classify a sampling of soils within a 40‐ha upland pasture using both Soil Taxonomy and cluster analysis, (ii) identify the distinctness and relationships of these samples to landforms, and (iii) compare the geographic distributions of soil classes identified by Soil Taxonomy and cluster analyses. Ninety‐four soil properties were measured from 257 pedons along point transects. Cluster analysis identified three pedologically and geographically distinct groups. A single cluster group was identified for soils within the “ridge” landform, whereas the “backslope” landform was a mixture of all three groups. A significant relationship was found for soil attributes and slope profile curvature within the backslope landform, but predictive value was low. Soil Taxonomy produced 13 geographically indistinct classes that were partially related to cluster groupings. Cluster analysis appears to be useful for revealing patterns of soil homogeneity and for identifying relationships among soil properties and landforms. Numerical analysis may be a helpful supplementary method for correlating soil surveys with large soil databases, or for defining those soil attributes which distinguish mappable bodies from the soil continuum.
Hydraulic Gradient and Wetting Rate Effects on the Hydraulic Conductivity of Two Calcium Vertisols
Authors: Moutier M. , Shainberg I. , Levy G.J.
Published: July 2010

Understanding the combined role of intrinsic (e.g., clay content) and extrinsic soil conditions in determining the saturated hydraulic conductivity (K) is a key factor in improving soil and irrigation management. Hydraulic gradient effects on K have been investigated on two Ca vertisols (Chromic Haploxerert) from Yizreel and Kedma, Israel. Samples were packed in columns and subjected to two prewetting rates (4.5 and 70 mm h−1) and two hydraulic gradients (2.8 and 11.6 for Yizreel; 3.1 and 13.6 for Kedma). Saturated K was determined during leaching with CaCl2 solutions having total electrolyte concentrations (TEC) of 0.5, 0.01 M Cl−, and deionized water (DW). The average hydraulic conductivity at the end of the leaching with the 0.5 M solution K0.5 of the two vertisols increased with a decrease in prewetting rate. The effect of prewetting rate was more pronounced in Yizreel, where the high clay content (70.3% clay) resulted in a more stable structure. Upon leaching with the 0.01 M solution, Kr0.01 first decreased and then increased. This increase in Kr0.01 was explained by cohesive bond formation, which increased with an increase in soil clay content and with increased proximity between the clay particles. High hydraulic gradient enhanced clay to clay contacts, and a steep increase in Kr0.01. Following fast prewetting, the effect of the hydraulic gradient on cohesive bond formation was more pronounced in Yizreel than in Kedma (46.5% clay). Leaching with DW decreased the KrDW, regardless of the prewetting treatment or soil clay content, suggesting that swelling was the governing mechanism in the reduction of KrDW.
A Thermal Wave Approach for Heat Transfer in a Nonuniform Soil
Authors: Karam Mostafa A.
Published: July 2010

A novel thermal wave model is developed for studying heat transfer in nonuniform soils. The model, which is based on the wave‐like characteristics of periodic heat flow, discretizes the soil into sublayers. The total thermal reflection and transmission coefficients at the interfaces of those sublayers are formulated and then employed to construct the soil temperature and heat flux profiles from their values at the air–soil interface. Numerical simulations showed that the thermal wave model could predict the predictions of two exact analytic models for the temperature profiles and their derivatives.
Elastic Wave Velocities in Partially Saturated Ottawa Sand
Authors: Velea Doru , Shields F.Douglas , Sabatier James M.
Published: July 2010

A theoretical model is needed to predict the macroscopic mechanical properties of soil from the size, shape, and elastic properties of its constituent particles. To test one such model, we compared measured and calculated values of compressional and shear wave velocities in Ottawa sand. The sand was packed in a cylindrical tank ≈0.9 m in diameter and 0.9 m deep. The velocities were measured in the horizontal direction as a function of depth as the zero tension level of the water in the sand was slowly raised. In the air‐dry sand the velocities varied nonuniformly with depth, reaching a maximum value about two‐thirds of the way to the bottom of the tank. When water was introduced into the bottom of the sand, the nonuniform depth dependence was removed. At higher saturations, the velocities gradually decreased until the zero tension level was at the top of the sand. The nonuniform depth dependence in the dry sand has been attributed to the tank wall supporting part of the gravitational stress in the material. A modified Digby (1981) model was found to adequately account for the results in the wet material. A lumped parameter combining the contacts per grain, size, and the grain roughness was used to fit the data. In terms of the model, it is concluded that the water in the contacts between the grains had little effect on the normal contact stiffness, but reduced the tangential contact stiffness to zero.
Transient Flow from Tension Infiltrometers I. The Two‐Parameter Equation
Authors: Vandervaere Jean-Pierre , Vauclin Michel , Elrick Dave E.
Published: July 2010

Tension disk infiltrometer experiments are generally conducted until apparent steady state is reached because most of the methods of analysis are based on Wooding's solution for steady state flux. However, the time necessary to reach steady state may be a penalizing aspect for soils with low permeability and the information contained in the transient stages is not utilized. Moreover, these methods assume homogeneous soil and a uniform initial water content, which may be unrealistic when a large volume of soil is sampled. In this series, we propose and compare several new methods of analysis that are based on the transient stage of axisymmetric infiltration. In the first part, we show that a two‐parameter equation—one term linear in square root of time and one term linear in time—adequately describes the transient flow from the disk infiltrometer for both simulated and laboratory tests. The technique used for the determination of the two coefficients must meet two criteria; it must verify the validity of the two‐term equation throughout the duration of the experiment, and it must account for the early‐time perturbation that is induced by the sand‐contact layer placed between the disk and the soil. We show that the best technique consists in linearizing the data by differentiating cumulative infiltration with respect to the square root of time. Direct nonlinear fitting on cumulative infiltration or infiltration flux is likely to lead to unacceptable errors, either because of the undetected invalidity of the two‐parameter equation or arising from the influence of the contact layer.
Transient Flow from Tension Infiltrometers II. Four Methods to Determine Sorptivity and Conductivity
Authors: Vandervaere Jean-Pierre , Vauclin Michel , Elrick Dave E.
Published: July 2010

In Vandervaere et al. (2000) it was shown that the transient regime of axisymmetric infiltration can be described by a two‐term equation with one term proportional to the square root of time and the other term proportional to time. The two corresponding coefficients, C1 and C2, are functions of the hydraulic conductivity, K, and the sorptivity, S In this paper we propose four different methods to achieve the determination of S and K The four methods differ by the number of disk radii and the number of supply pressure head values which are utilized. We show that the accuracy of a given method is highly dependent on the combination of S and K values obtained. Three situations can be distinguished, depending on the disk radius: (i) the flow is dominated by the lateral capillary term; (ii) the flow is dominated by the gravity term; (iii) lateral capillary and gravity terms have equivalent weights. The seven model soils tested here all correspond to the first situation with usual disk radius values. This tends to show that a precise estimation of K is unlikely from disk infiltrometer data. We introduce a new time scale, tstab, which generalizes the concepts corresponding to the two well known time scales tgrav and tgeom We propose a guideline for the investigator to choose between all existing methods of analysis that use steady or transient flow. Finally, the four new methods are tested against numerically simulated tests with Grenoble sand and Yolo light clay.
Soil Thermal Conductivity Effects of Density, Moisture, Salt Concentration, and Organic Matter
Authors: Abu-Hamdeh Nidal H. , Reeder Randall C.
Published: July 2010

The thermal conductivity of soil under a given set of conditions is most important as it relates to a soil's microclimate. The early growth and development of a crop may be determined to a large extent by microclimate. The effect of bulk density, moisture content, salt concentration, and organic matter on the thermal conductivity of some sieved and repacked Jordanian soils was investigated through laboratory studies. These laboratory experiments used the single probe method to determine thermal conductivity. The soils used were classified as sand, sandy loam, loam, and clay loam. The two salts used were NaCl and CaCl2, while addition of peat moss was used to increase the organic matter content. For the soils studied, thermal conductivity increased with increasing soil density and moisture content. Thermal conductivity ranged from 0.58 to 1.94 for sand, from 0.19 to 1.12 for sandy loam, from 0.29 to 0.76 for loam, and from 0.36 to 0.69 W/m K for clay loam at densities from 1.23 to 1.59 g cm−3 and water contents from 1.4 to 21.2%. The results also show that an increase in the amount of added salts at given moisture content (volumetric solution contents θ ranged from 0.03–0.12 m3 m−3 for the sand and from 0.09–0.30 m3 m−3 for the clay loam) decreased thermal conductivity. Increasing the percentage of soil organic matter decreased thermal conductivity. Finally, it was found that the sand had higher values of thermal conductivity than the clay loam for the same salt type and concentrations.
Quantifying Preferential Flow by Breakthrough of Sequentially Applied Tracers Silt Loam Soil
Authors: Kung K.-J. S. , Kladivko E. J. , Gish T. J. , Steenhuis T. S. , Bubenzer G. , Helling C. S.
Published: July 2010

Field experiments were conducted on tile‐drained plots at the South East Purdue Agricultural Center in Butlerville, Indiana, to quantify contaminant transport via preferential flow paths in a silt loam soil. Breakthrough patterns of three fluorobenzoic acids (pentafluorobenzoic acid [PFBA], o‐trifluoromethylbenzoic acid [o‐TFMBA], and 2,6‐difluorobenzoic acid [2,6‐DFBA]) in a preliminary study indicated that they were transported as conservatively as is bromide (Br−). These four tracers were then sequentially applied, in an adjacent plot, during simulated precipitation (3 mm h−1 intensity, 10‐h duration). Bromide was sprayed shortly before irrigation started, while PFBA, o‐TFMBA, and 2,6‐DFBA were applied at 2, 4, and 6 h thereafter, respectively. Tile flow began increasing at around 3 h, and Br− appeared in tile drain flow ≈4 h after irrigation started, yet benzoic acids, PFBA, o‐TFMBA, and 2,6‐DFBA, were detected in the tile drainage at 102 min, 42 min, and 18 min after their applications, respectively. Tracer mass recovery from tile drainage was Br− (7.04%), PFBA (13.9%), o‐TFMBA, (18.7%), and 2,6‐DFBA (19.7%) of applied mass. The faster arrival time and greater recovery of sequentially applied tracers confirmed that water movement and contaminant transport shifts toward increasingly larger pores of the preferential flow paths as soil becomes wet during a precipitation event. The breakthrough patterns of these tracers can be used to quantify the water flux distributions of preferential paths. Because ≈90% of the chemical leached from this precipitation event occurred during the first day, it was critical to intensively monitor contaminant transport during the first 24 h after a rainfall. A soil sampling protocol based on collecting soil cores at random locations once every several days is unsuitable for determining the deep leaching under field conditions.
Solute Transport for Steady‐State and Transient Flow in Soils with and without Macropores
Authors: Vanderborght J. , Timmerman A. , Feyen J.
Published: July 2010

The effect of flow rate and flow regime on solute transport in two soils, a sandy‐loam (Glossudalf) and loam (Udifluvent), was investigated. For each soil type, leaching experiments were carried out in two large undisturbed soil columns (0.3‐m i.d., 1‐m length) for three different steady‐state flow rates and three (sandy loam), or two (loam) transient flow regimes. Solute concentrations were measured in the drain water, cf, and in situ, cr, using time domain reflectometry (TDR). In order to approximate the transient by a steady‐state flow transport process, a solute penetration depth coordinate, ζ, was used. Breakthrough curves (BTCs) of cr and cf were used to optimize parameters of the convection–dispersion equation (CDE). In the sandy loam, the CDE described transport for steady‐state and transient flow conditions well and relevant CDE model parameters could be derived from BTCs of cr. In the loam soil, due to the activation of macropores, lateral solute mixing decreased with increasing flow rate, which resulted in an increase of dispersivity with increasing depth for higher flow rates. Since bypass flow and transport through macropores is barely apparent in time series of concentrations measured in situ, cr, CDE parameters derived from BTCs of cr were inconsistent with parameters derived from BTCs of cf when bypass flow was important. The dispersivity increased with increasing flow rate in both soil types and an effective or flux‐weighted average flow rate rather than a time‐averaged flow rate was used to derive the relation between the dispersivity and the flow rate.
Deriving Transport Parameters from Transient Flow Leaching Experiments by Approximate Steady‐State Flow Convection–Dispersion Models
Authors: Vanderborght J. , Jacques D. , Feyen J.
Published: July 2010

The applicability of two different steady‐state flow approximations of the convection–dispersion equation (CDE) to derive transport parameters from time series of concentrations or breakthrough curves (BTCs) that are observed during transient flow leaching experiments was evaluated. In the first often‐used approximation, the time coordinate was transformed to a cumulative drainage coordinate, I, assuming that the water content remained constant during the leaching experiment. In the second approximation, the time coordinate was transformed to a solute penetration depth, ζ, assuming that the flow rate and water content remained constant with depth across the solute displacement front. Comparisons of numerical solutions of the CDE for transient flow conditions with analytical solutions of the approximate steady‐state models revealed that the first approximate model underestimates the dispersion of the BTC when the water content fluctuates considerably during the leaching experiment. Alternatively, fitting this model to a BTC as a function of I results in an overestimation of the dispersion coefficient D and the dispersivity Since the second approximate model described the simulated BTCs well, good estimates of D and λ were obtained when this model was fitted to a BTC as a function of ζ. If λ is a function of the flow rate Jw, the fitted λ could be related to an effective or flux‐weighted average flow rate so that the soil specific relation λ(Jw) could be defined.
Predicting Boron Adsorption by Soils Using Soil Chemical Parameters in the Constant Capacitance Model
Authors: Goldberg Sabine , Lesch Scott M. , Suarez Donald L.
Published: July 2010

The constant capacitance model, a chemical surface complexation model, was applied to B adsorption on 17 soils selected for variation in soil properties. A general regression model was developed for predicting soil B surface complexation constants from easily measured soil chemical characteristics. These chemical properties were cation‐exchange capacity (CEC), surface area, organic carbon content (OC), and inorganic carbon content (IOC). The prediction equations were used to obtain values for B surface complexation constants for 15 additional soils, thereby providing a completely independent evaluation of the ability of the constant capacitance model to fit B adsorption. The model was well able to predict B adsorption on the 15 soils. Incorporation of these prediction equations into chemical speciation–transport models will allow simulation of soil solution B concentrations under diverse environmental and agricultural conditions without the requirement of soil specific adsorption data and subsequent parameter optimization.
Polyacrylamide, Sediments, and Interrupted Flow Effects on Rill Erosion and Intake Rate
Authors: Sirjacobs D. , Shainberg I. , Rapp I. , Levy G. J.
Published: July 2010

The reduction in the intake rate (IR) during interrupted irrigation is difficult to predict. Sediments in irrigation water decrease the effect of interrupted irrigation on IR. Polyacrylamide (PAM) reduces rill erosion, but its effect on IR is controversial. The effects of water quality (tap water, tap water containing sediments, and 10 g m−3 PAM solution) and interrupted flow on IR and rill erosion in an Alfisol (Calcic Haploxeralf) and a Vertisol (Typic Chromoxerert) were studied using laboratory miniflumes. Rill erosion in both soils was eliminated by the PAM treatment in both continuous and interrupted flow. The PAM application reduced IR in the Alfisol and increased it in the Vertisol. In the Alfisol, interrupted flow reduced IR of the PAM solution by 37% compared with only 18% for tap water. In the Vertisol, interrupted flow reduced IR only slightly and the decrease was not affected by the polymer. When the water contained sediments, cumulative infiltration was reduced by 22% for the Vertisol and 59% for the Alfisol in comparison with tap water. These reductions were attributed to depositional seal formation. The IR of the Alfisol was more susceptible to depositional seal formation than the Vertisol. The presence of sediments in water was effective in reducing rill erosion. The effects of interrupted flow with PAM on reducing IR were explained by partial blocking of the conducting pores leading to greater suction and compaction of the soil surface. For sediment‐laden irrigation water, interrupted flow had no advantage over continuous flow in reducing IR because of depositional seal formation associated with the sediments in the water.
Measuring Hydraulic Properties Using a Line Source II. Field Test
Authors: Zhang Z.Fred , Kachanoski R.Gary , Parkin Gary W. , Si Bingcheng
Published: July 2010

We designed and tested a field method to measure unsaturated soil hydraulic properties using multi‐purpose time domain reflectometry (TDR) probes below a surface line source with constant flux of water. The surface line source was produced with a moving irrigation system at a field site sheltered from precipitation. Two hundred multi‐purpose TDR probes were vertically installed in the soil beneath the line source to measure soil water pressure head (ψ), water storage (W), and tracer travel time (T). The soil hydraulic properties, the inverse macroscopic capillary length (α), hydraulic conductivity at saturation (Ks), and soil water content at saturation (θs) were estimated by inverse procedures with new analytical expressions. Five combinations of measurement sets, namely W‐only, ψ and W, ψ and T, and W and T, and ψ and W and T were used. Approximate confidence contours in the α–Ks plane were calculated to show the precision of the parameter estimates. For comparison, hydraulic properties were also measured by means of the Guelph Permeameter (GP) and the modified Guelph Pressure Infiltrometer (GPI) systems. Hydraulic parameters estimated from only W measurements were similar to those estimated from the combinations of W and ψ, or W and T, or W and ψ and T The estimated hydraulic parameters were similar to those obtained with three‐dimensional (3‐D) infiltration measurements by means of the GP and GPI systems.
Recharge from a Subsidence Crater at the Nevada Test Site
Authors: Wilson G.V. , Ely D.M. , Hokett S.L. , Gillespie D.R.
Published: July 2010

Current recharge through the alluvial fans of the Nevada Test Site (NTS) is considered to be negligible, but the impact of more than 400 nuclear subsidence craters on recharge is uncertain. Many of the craters contain a playa region, but the impact of these playas has not been addressed. It was hypothesized that a crater playa would focus infiltration through the surrounding coarser‐grained material, thereby increasing recharge. Crater U5a was selected because it represented a worst case for runoff into craters. A borehole was instrumented for neutron logging beneath the playa center and immediately outside the crater. Physical and hydraulic properties were measured along a transect in the crater and outside the crater. Particle‐size analysis of the 14.6 m of sediment in the crater and morphological features of the crater suggest that a large ponding event of ≈63000 m3 had occurred since crater formation. Water flow simulations with HYDRUS‐2D, which were corroborated by the measured water contents, suggest that the wetting front advanced initially by as much as 30 m yr−1 with a recharge rate 32 yr after the event of 2.5 m yr−1 Simulations based on the measured properties of the sediments suggest that infiltration will occur preferentially around the playa perimeter. However, these sediments were shown to effectively restrict future recharge by storing water until removal by evapotranspiration (ET). This work demonstrated that subsidence craters may be self‐healing.
Generalized Transfer Function Model for Solute Transport in Heterogeneous Soils
Authors: Zhang Renduo
Published: July 2010

The convection‐dispersion (CDE) equation and stochastic–convective models are the most commonly used process representations for predicting solute transport in the field. The convection–dispersion equation assumes that the solute is perfectly mixing in the lateral direction, whereas the stochastic–convective model assumes that the solute moves at different velocities in isolated stream tubes without lateral mixing. However, solute transport in heterogeneous porous media cannot always be conceptualized as being either a convective–dispersive or a stochastic–convective process. In this study, a generalized transfer function model (GTF) was proposed to describe various solute transport processes in heterogenous soils. The model is similar to the convective lognormal transfer function model, but two parameters, λμ and λσ, are introduced to characterize the depth‐dependency of the mean (μ) and standard deviation (σ) of the logarithm of travel time, respectively. The GTF can describe well the two extremes of solute dispersion, the convective–dispersive and stochastic–convective processes, and transport processes between the two extremes. In addition, the GTF can be used to characterize other solute transport processes in heterogeneous soils, such as those in which the mean of travel time increases with depth nonlinearly, and those in which the dispersivity is a scale‐dependent function of the travel distance with any power values.
Water Holding Capacity of Ironstone Gravel in a Typic Plinthoxeralf in Southeast Australia
Authors: Brouwer Joost , Anderson Heather
Published: July 2010

Water retention by coarse fragments in the soil is often ignored in agronomic and water balance studies. Following the calculation of inexplicably high water retention by the fine earth fraction, water contents at −20 and −1500 kPa and apparent bulk density were determined for remnant pisolithic ironstone gravel samples isolated from soils on the Dundas Tableland in southeast Australia. The volumetric water content of the ironstone gravel at −1500 kPa was found to vary between 0.12 and 0.24 m3 m−3, while at −20 kPa it varied between 0.16 and 0.36 m3 m−3 Available water holding capacity (AWHC) of the ironstone gravel varied between 0.03 and 0.15 m3 m−3 Both the AWHC and the water content at −1500 kPa of the ironstone gravel showed significant increases with depth. Magnetic ironstone gravel, found almost exclusively in the A and E horizons, was much denser than nonmagnetic ironstone gravel (average 3.38 vs. 2.64 Mg m−3), but had similar water retention characteristics. Ignoring the water retention characteristics of the ironstone gravel would have led to overestimation of the AWHC of the bulk soil by a factor 1.08 to 1.67 for various horizons. For the combined top 1.0 m of the soil, ignoring the water held by the ironstone gravel would have led to an estimated AWHC of 162 mm, while in fact it was only 129 mm. Water balance studies of soils with ironstone gravel clearly need to take into account the water holding characteristics of that gravel.
Solid‐Phase Iron Characterization During Common Selective Sequential Extractions
Authors: La Force Matthew J. , Fendorf Scott
Published: July 2010

Selective chemical extractions provide semiquantitative information on elemental partitioning within operationally defined soil fractions. In this study, the efficiency of common extraction steps was determined for a mining‐impacted soil by analyzing Fe transformations in the solid phase using x‐ray diffraction, scanning electron microscopy, and x‐ray absorption near edge structure (XANES) spectroscopy. Extractions involve the isolation of operationally defined double‐deionized water (soluble), magnesium chloride (exchangeable), sodium hypochlorite (organic matter), sodium acetate–acetic acid (carbonate), hydroxylamine‐hydrochloride–nitric acid (Mn‐oxides), ammonium oxalate in the dark (AOD) (noncrystalline material), hydroxylamine‐hydrochloride–acetic acid (Fe oxides), potassium perchlorate–hydrochloric–nitric acid (sulfidic), and hydrochloric–nitric–hydrofluoric acid (residual) fractions of the solid phase. Ferric Fe remained in the solid phase throughout the extraction sequence until its removal by hydrochloric–nitric–hydrofluoric acid (residual fraction). The hydroxylamine‐hydrochloride (1.0 M in 25% [v/v] HOAc) extraction may underestimate Fe associated with crystalline materials. Thus, selective sequential extractions need to be optimized for a given soil prior to implementation and should be used in conjunction with spectroscopic techniques, when possible, to fully ascertain elemental partitioning within the solid phase.
Effectiveness of Phosphate and Hydroxide for Desorption of Arsenic and Selenium Species from Iron Oxides
Authors: Jackson Brian P. , Miller W. P.
Published: July 2010

Phosphate and OH− are often used for the extraction of As and Se from soils, either as single extractants or as part of a sequential extraction scheme. However, the recovery of As and Se species and the integrity of the resulting solution speciation merit investigation. In this study the relative effectiveness of PO4 at 0.1 and 0.5 M and pH values of 3 and 6.7 and 0.1 M OH− to extract As(III), As(V), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), p‐arsanilic acid (p‐ASA), roxarsone (ROX), Se(IV) and Se(VI) sorbed to goethite and an amorphous Fe oxide were compared, and the speciation in the resulting extract was determined. The extent to which 0.1 M PO4 added to 0.25 M NH2OH·HCl or 0.175 M Na oxalate/0.1 M oxalic acid prevents readsorption of As(V) or Se(IV) to goethite during the dissolution of an amorphous Fe oxide was also assessed. Hydroxide was the most effective extractant for desorption of all species except As(III) from both oxide surfaces. Arsenite was extracted most efficiently by 0.5 M PO4 at low pH; however, amorphous Fe oxide exhibited a strong affinity for As(III) with a maximum of 18% of As(III) extracted by 0.5 M PO4 at pH 2.8. Partial oxidation of As(III) to As(V) occurred in all extractions where an Fe oxide solid phase was present, but only in the hydroxide extract in the absence of a Fe solid phase. Addition of 0.1 M PO4 to extractants used for the dissolution of the amorphous Fe oxide prevented the readsorption of As(V) and Se(IV) to goethite.
Factors Controlling Soil Carbon Levels in New Zealand Grasslands Is Clay Content Important?
Authors: Percival Harry J. , Parfitt Roger L. , Scott Neal A.
Published: July 2010

Soil organic matter is a major component of biogeochemical cycles and is important in maintaining soil quality. We investigated relationships between soil organic C and various soil and site properties that may influence long‐term soil C accumulation across a range of soil orders in New Zealand. We used pedon and climatic data for 167 pedons under permanent grass, and carried out regression analysis between soil C (0–200 mm) contents (t ha−1) or concentrations (g kg−1) and climatic and soil properties, namely, precipitation, temperature, and contents or concentrations of sand, silt, clay, pyrophosphate‐extractable Al (Alpy), Fe oxide, and allophane. Soil clay content or concentration explained little of the variation in soil C across all soils (R2 < 0.05) and within each soil type. Likewise, mean annual precipitation and temperature explained little variation in soil C content or concentration (R2 < 0.15 for precipitation, for temperature). Allophane content or concentration was unrelated to soil C in the soils of volcanic origin; Alpy, however, correlated strongly with both soil C content and soil C concentration across all soil types (, respectively). When all factors were combined in a multiple regression analysis, the combination of Alpy and allophane contents explained the greatest amount of variation in soil C content , whereas the combination of Alpy, Fe oxide, allophane, and clay concentrations explained the greatest amount of variation in soil C concentration Our results suggest that in New Zealand soils, chemical stabilization of organic matter is the key process controlling soil C accumulation, and that clay content relates poorly to long‐term soil organic C accumulation.
Effects of Freeze–Thaw and Soil Structure on Nitrous Oxide Produced in a Clay Soil
Authors: van Bochove Eric , Prévost Danielle , Pelletier France
Published: July 2010

Freezing and thawing have been shown to cause significant soil physical and biological changes. The increase in denitrification following thawing may be attributed to the diffusion of organic substrates newly available to denitrifiers from disrupted soil aggregates. The objective of this study was to evaluate the effect of freezing and thawing on N2O production in a clay soil under contrasting crop rotations and tillage practices. Laboratory experiments were conducted in soil slurries to favor substrate diffusion, in macroaggregate fractions separated by wet sieving to characterize the biologically active soil organic matter (SOM) pool, and in undisturbed soil cores to simulate field conditions. In slurries, a freezing and thawing cycle increased denitrification rates by 32%. Soil slurries from no‐tillage under rotation (NT–R) exhibited denitrification rates 92% higher than those from conventional till under continuous cereal (CT–C). Macroaggregates fractions (0.25–2 and 2–5 mm) from both management systems increased their rates of C mineralization and denitrification activity by 95% following freezing, but the increases tended to be greater (57%) in small than in large macroaggregates. Higher rates of denitrification (55%) found in both aggregate fractions of NT–R system were attributed to the higher mineralizable organic C content. Undisturbed soil cores sampled in November showed increased N2O production by 220% after thawing. This thawing effect was also significantly higher in cores from NT–R than in those from CT–C.
Organic and Biodynamic Management Effects on Soil Biology
Authors: Carpenter-Boggs L. , Kennedy A. C. , Reganold J. P.
Published: July 2010

Biodynamic agriculture is a unique organic farming system that utilizes, in addition to the common tools of organic agriculture, specific fermented herbal preparations as compost additives and field sprays. The objective of this work was to determine whether biodynamic compost or field spray preparations affect the soil biological community in the short term, beyond the effects of organic management. Four fertilizer options: (i) composted dairy manure and bedding (organic fertilization), (ii) the same material composted with biodynamic compost preparations, (iii) mineral fertilizers, and (iv) no fertilizer were investigated with and without the biodynamic field spray preparations. Both biodynamic and nonbiodynamic composts increased soil microbial biomass, respiration, dehydrogenase activity, soil C mineralized in 10 d (MinC), earthworm (Lumbricus terrestris) population and biomass, and metabolic quotient of respiration per unit biomass (qCO2) by the second year of study. No significant differences were found between soils fertilized with biodynamic vs. nonbiodynamic compost. Use of biodynamic field sprays was associated with more MinC and minor differences in soil microbial fatty acid profiles in the first year of study. There were no other observed effects of the biodynamic preparations. Organically and biodynamically managed soils had similar microbial status and were more biotically active than soils that did not receive organic fertilization. Organic management enhanced soil biological activity, but additional use of the biodynamic preparations did not significantly affect the soil biotic parameters tested.