bluuebunny/crossref_metadata_2025 huggingface dataset:
Compaction Effect on the Gas Diffusion Coefficient in Soils
Authors: Xu Xia , Nieber J. L. , Gupta S. C.
Published: July 2010

Gas diffusion is important in determining the aeration status of soils for crop production and in providing estimates of transport of volatile chemicals at waste disposal or chemical spill sites. This study investigated the effects of compaction on the gas diffusion coefficient in four soils. The experiment involved equilibrating bulk loose soil to a known matric potential in a pressure chamber, compressing the equilibrated moist soil in metal cores at a given applied stress, and measuring the concentration of N2 diffusing through these cores into a diffusion chamber. The diffusion coefficient was calculated by fitting an analytical solution of the transient diffusion equation to the measured N2 concentration in the diffusion chamber as a function of time. The diffusion coefficient of N2 in four soils at four water contents and four applied loads varied exponentially as a function of air‐filled porosity and was nearly the same function for all four soils. At an air‐filled porosity of ≈ 10%, the diffusion coefficient was close to zero, reflecting a discontinuity in the pathways at an air‐filled pore space of 10% or lower. A model for predicting the diffusion coefficient of gases in soils based on the diffusion coefficient of individual soil constituents was tested with the data set. For known shape factors for soil solid and soil water, the model overpredicted the diffusion coefficient for all four soils. A reduction factor suggested in the literature to account for blocked air slightly improved predictions. The ratio of the measured to predicted diffusion coefficient vs. degree of air‐filled saturation suggests a second‐degree correction factor to account for blocked air in soils.
Organic and Inorganic Anion Effects on Reference and Soil Clay Critical Flocculation Concentration
Authors: Frenkel H. , Levy G. J. , Fey M. V.
Published: July 2010

Maintaining adequate soil permeability and favorable soil structure is largely dependent on the flocculation‐dispersion characteristics of the soil clay fraction. The critical flocculation concentration (CFC) of the clay fraction of three strongly structured clay soils from Natal (two dominated by smectite and one by kaolinite) was compared with that of smectite (bentonite from Wyoming) and kaolinite (from Georgia) in Na‐ and Ca‐saturated forms. The soil clays had much higher CFC than their reference mineral counterparts in both NaCl and CaCl2 systems. The addition of humic acid extracted from one of the soils and of citrate, formate, orthophosphate, carbonate, and silicate to the reference clays increased the CFC by as much as a factor of 50. Kaolinite was approximately 10 times more sensitive than bentonite to this dispersion effect of specifically adsorbing ligands. The results suggest that natural levels of soil humus, and possibly of certain inorganic anions, may be sufficient to impart a high degree of dispersion on the soil clay fraction. There is, therefore, some doubt as to the quantitative importance of clay mineral composition in the dispersion behavior of soils.
Reevaluation of Calcite Supersaturation in Soils
Authors: Suarez D. L. , Wood J. D. , Ibrahim I.
Published: July 2010

The calcite saturation status of soil‐water systems in semiarid regions was reexamined taking into consideration organic ligand alkalinity and Ca‐organic complexation. These factors have been forwarded as the reason for earlier reports of calcite supersaturation in soil‐water systems. We examined groundwaters beneath irrigated lands, soil‐water suspensions in the laboratory using four soils and two levels of CO2, and soil water extracted from the root zone of an irrigated, cropped field. Total alkalinity and net inorganic C alkalinity were determined by titration. Calcium activity values calculated from total concentrations using the speciation program WATEQ4F were compared with Ca2+ activity values measured with an ion‐specific electrode. In all our systems, total alkalinity and inorganic C alkalinity were almost equivalent and thus organic C alkalinity was negligible. Calculated Ca2+ activity was generally 5 to 25% greater than Ca2+ activity determined with an ion‐specific electrode. Although these data suggest the presence of additional Ca complexes not included in the speciation routines, the determined dissolved organic C values are too low for Ca‐organic complexes to be the cause of these differences in Ca2+ activity. Ion activity products based on either measured Ca2+ activity values or calculated Ca2+ activities indicated that all systems were supersaturated, with saturation ratios of two to three.
Calibration and Validation of a Soil‐Landscape Model for Predicting Soil Drainage Class
Authors: Bell James C. , Cunningham Robert L. , Havens Matthew W.
Published: July 2010

The soil‐landscape relationships frequently used for soil mapping activities are seldom documented. We developed a statistical model that relates soil drainage classes to eight landscape parameters describing slope morphology, proximity to surface drainage features, and soil parent material. Soil profiles and landscape parameters were described at 305 randomly selected sampling points within the Mifflintown 7.5‐min topographic quadrangle in the unglaciated ridge and valley physiographic province of central Pennsylvania. Variables defining the spatial structure of the landscape were derived from digitized 1:24 000 scale maps of streams and drainageways, surficial geology, bedrock geology, and a digital elevation model. These data were stored in a geographic information system and overlaid with the sampling point locations to define a database of 305 known soil‐landscape combinations. These soil‐landscape combinations were used to derive a statistical soil‐landscape model using multivariate discriminant analysis and class frequency information. For soil drainage class, a 74% overall agreement with field observations was found for the model using a cross‐validation approach, compared with 69% for the published soil survey. The model correctly predicted a majority of the observations within each drainage class and provided a consistent method of extrapolating point information about soils to the three‐dimensional landscape.
Plant Water Uptake Terms Evaluated for Soil Water and Solute Movement Models
Authors: Cardon G. E. , Letey J.
Published: July 2010

Two root water uptake terms, representative of the two major types commonly employed in soil‐based models of water and solute movement, were evaluated. Simulations were run to test the sensitivity of the two terms to salinity and water content and to investigate the details of their respective form and function. The two root water uptake terms tested were: (i) a mechanistic equation based on Darcy's law (Type I), and (ii) an empirical equation relating soil water potential to relative water uptake (Type II). The Type I term was insensitive to salinity where no reduction in transpiration was shown for increasing irrigation water salinity from 0.0 to 6.0 dS/m and applying water equal to potential transpiration. The Type II term was sensitive to salinity and showed a 35% reduction in water uptake by increasing water salinity from 0.0 to 6.0 dS m−1 and applying water equal to potential transpiration. Predicted reduction in water uptake due to matric potential was of the same magnitude as that due to salinity. The Type I term resulted in abrupt shifts in water uptake between full and zero transpiration, occasionally resulting in long periods of computed zero transpiration, uncharacteristic of conditions in the field. It was concluded that the Type I water uptake term may not be appropriate for models incorporating root water uptake, particularly under saline conditions.
Unconfined Compressive Strength of Some Streambank Soils with Herbaceous Roots
Authors: Kleinfelder Donald , Swanson Sherman , Norris Gary , Clary Warren
Published: July 2010

Streambank stability requires that bank strength exceed destabilizing forces, including compressive forces from sources such as trampling and foot traffic. This study was conducted to determine the unconfined compressive strength associated with herbaceously rooted streambanks, and whether greater compressive strength is developed from greater root‐length density (length of roots per volume of sample) or specific plant communities. The unconfined compressive strength, root‐length density, plant community, and engineering soil characteristics were measured on 122 samples from six meadow stream reaches. Sample compressive strength emulated an elastic condition in highly rooted samples, and developed negligible compressive strength in samples containing very small amounts of roots. Additionally, compressive strength was found to increase nonlinearly with increases in very fine root‐length density (herbaceous roots <0.5 mm in diam.), and reached an apparent asymptote at 50 kPa. The greatest compressive strength was derived from samples dominated by Nebraska sedge (Carex nebrascensis Dewey). Correlations between unconfined compressive strength and engineering soil properties were mostly insignificant, primarily because samples were derived from unconsolidated alluvium. Stream morphology parameters showed little correlation to compressive strength, root‐length density, or other independent variables, suggesting other unmeasured factors may have an equal or greater influence on stream morphology. Herbaceous roots appear to supply most of the compressive strength and soil stability found in meadow streambanks, especially those dominated by Nebraska sedge.
Preventing Irrigation Furrow Erosion with Small Applications of Polymers
Authors: Lentz R. D. , Sojka R. E. , Carter D. L. , Shainberg I.
Published: July 2010

Soil erosion is a serious problem threatening sustainability of agriculture globally and contaminating surface waters. The objective of this study was to determine whether low concentrations of anionic polymers in irrigation water would appreciably reduce irrigation furrow erosion on Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid), a highly erodible soil. Furrow slope was 1.6%, furrow length was 175 m, and irrigation rates ranged from 15 to 23 L min−1. Inflow during the first 1 to 2 h of the first 8‐h irrigation was treated. Subsequent irrigations were untreated. Polyacrylamide (PAM) or starch copolymer solutions were injected into irrigation water entering furrows at concentrations of 0, 5, 10, and 20 g m−3. Sediment loss from polymer‐treated furrows was significantly less than that of control furrows in the first (treated) and second (untreated) irrigations, but not in the fourth (untreated). The PAM provided better erosion control than the starch copolymer. Efficacy of PAM treatments varied depending on its concentration, duration of furrow exposure, and water flow rate. In the initial (treated) irrigation and at low flow rates, 10 g m−3 PAM reduced mean sediment load by 97% compared with untreated furrows. Residual erosion abatement in a subsequent irrigation, without further addition of PAM, was approximately 50%. The PAM increased net infiltration and promoted greater lateral infiltration. Effective erosion control was achievable for a material cost below $3 ha−1 irrigation−1.
Soil Salinity Assessment by Electromagnetic Induction of Irrigated Land
Authors: Hendrickx J. M. H. , Baerends B. , Raza Z. I. , Sadig M. , Chaudhry M. Akram
Published: July 2010

The purpose of this study was to characterize the variability and statistical distribution of electromagnetic induction measurements for salinity assessment on irrigated land. Such information is needed to optimize future sampling schemes. A detailed salinity survey was carried out with an electromagnetic device (Geonics EM38) in a representative experimental area of 37 ha near Faisalabad, Pakistan. The apparent electrical conductivity of the soil was measured at >3400 locations. In addition, a visual agronomic salinity survey was conducted. A linear relation between the standard deviation of the data and their means indicated that the salinity data were log‐normally distributed. Therefore, we recommend using log‐transformed data for statistical inferences. Geostatistical analysis of the log‐transformed data verified that the salinity of a field was principally determined by the irrigation management of the farmer. Significant salinity differences were found between abandoned, fallow, and cropped fields, but not between fields with different crops. We found that the electromagnetic induction meter (EM38) was in good agreement with the visual agronomic survey. The EM38 was superior because it had a better resolution, was more sensitive to salinity changes with depth and spatially, and could be conducted with or without a crop or at any stage of a crop. For random sampling schemes in our experimental area, the budgetary efficiency of the survey improved when entire fields rather than single points were selected for the survey. For salinity sampling with a stratified random sampling scheme, the strata can be based either on land use or on visually observed salinity status.
Soil Test Phosphorus Availability as Affected by Time after Phosphorus Fertilization
Authors: Esilaba A. O. , Eghball B. , Sander D. H.
Published: July 2010

The availability of fertilizer P in the soil decreases with time after fertilization. Routine soil tests or other estimates of plant‐available P should accurately reflect that change. The objective of this study was to determine the effect of the time fertilizer P is in contact with soil on the ability of commonly used soil tests to extract plant‐available P. Experiments were conducted to determine the relationship between available P as determined by A value and Bray and Kurtz P1 (BK), sodium bicarbonate (SB), and Mehlich no. 2 (ME) P soil tests. The A value was assumed to be the best available method of determining plant‐available P. Samples from an acidic Thurman loamy sand topsoil (sandy, mixed, mesic Udorthentic Haplustoll) and a calcareous Uly silt loam subsoil (fine‐silty, mixed, mesic Typic Haplustoll) were incubated with 0, 10, 20, 40, and 80 mg P kg−1 for 4, 8, and 20 mo at field‐capacity water content. After each incubation period, oat (Avena sativa L.) was planted and grown in the greenhouse with an additional 0, 10, and 20 mg P kg−1 labeled with 32P. The A value was determined for each incubation period and was correlated with the soil test results. Solubility products were also determined for each incubation P rate and period. After 4 and 8 mo of incubation, the BK, SB, and ME soil tests did not extract plant‐available soil P very accurately using the A value as a standard. After 4 mo of incubation, the SB soil test underestimated available P by as much as 50% on the Uly soil, while the BK soil test overestimated available P on the Thurman soil by 40%. Although there was no improvement after 8 mo of incubation, all three soil tests accurately extracted available P after 20 mo when fertilizer P and soil P appeared to have reached an equilibrium. Solubility equilibria analysis lacked adequate sensitivity to show different soil P compounds as affected by time of incubation. The results indicate large potential P fertilizer recommendation errors when soil samples are taken and analyzed prior to achieving equilibrium between applied fertilizer P and soil P.
On Particle‐Size Distributions in Soils
Authors: Wu Q. , Borkovec M. , Sticher H.
Published: July 2010

Measurements of soil particle‐size distributions have been performed down to 20‐nm radius using, beside classical methods such as sieving and sedimentation, mainly static and dynamic light scattering. The number of particles N per unit volume with a radius larger than r was found to follow a power law N α r−v with the exponent v = 2.8 ± 0.1. This exponent was observed in all soils investigated and can be interpreted as the fractal dimension of an underlying structure. The power law usually held over two to five decades of length scales. Below the lower cut‐off, typically located around 50 to 100 nm, the number of particles (≃ 1016‐1019 cm−3) remained roughly constant. Above the upper cut‐off, typically between 10 and 5000 µm, the distribution fell off much more steeply, possibly also like a power law with an exponent v = 5.4 ± 0.2.
Test of a Heat‐Pulse Probe for Measuring Changes in Soil Water Content
Authors: Bristow Keith L. , Campbell Gaylon S. , Calissendorff Kees
Published: July 2010

The maximum temperature rise measured at some distance from a line heat source can be used to determine the volumetric heat capacity and hence water content of porous media. We describe a simple heat‐pulse device for determining the volumetric heat capacity and hence water content of porous media. The device consists of three needle probes (0.813‐mm diam., 28 mm long) mounted in parallel. The heater probe contains a heating element while the sensor (mounted 6 mm from the heater) and reference probe (mounted 20 mm from the heater) contain thermocouples. The reference probe can be used to automatically correct for changes in background temperature. Measurements made at three depths during drying of a laboratory soil column yielded accurate changes in soil water content provided actual heater‐to‐sensor probe spacings were used in the calculations. We describe a simple procedure for checking on the probe spacings once the probes have been installed. These heat‐pulse devices should prove useful for monitoring wetting or drying changes in soil water under both laboratory and field conditions.
Unsaturated Transport Processes in Undisturbed Heterogeneous Porous Media: I. Inorganic Contaminants
Authors: Jardine P. M. , Jacobs G. K. , Wilson G. V.
Published: July 2010

Prolonged disposal of organic and inorganic waste in shallow land burial sites throughout the USA has prompted detailed investigations of subsurface contaminant transport processes. The fate and transport of contaminant leakage from pits, trenches, and cribs into the vadose zone via storm events is not well understood. The objective of this study was to investigate the thermodynamic and kinetic processes controlling the transport of inorganic contaminants in unsaturated, heterogeneous subsurface media. Large undisturbed columns were isolated from a proposed waste site consisting of fractured saprolite (weathered interbedded shale and limestone), and steady‐state nonreactive and reactive solute transport experiments were performed at a variety of pressure heads. Observed breaktbrough curves (BTC) for binary and ternary mixtures in the Co‐Sr‐Ca system were delayed relative to nonreactive Br BTC, indicating that the former tracers were adsorbed by the solid phase. Transport of the binary mixtures Co‐Ca and Sr‐Ca was predicted reasonably well with the equilibrium convective‐dispersive (CD) equation using independent measurements of all model parameters. However, application of the nonequilibrium or kinetic CD model to the observed Sr and Co binary data resulted in an improved description of contaminant transport. Cation‐exchange equilibria relationships on homogenized subsurface material, using both shake batch and miscible displacement methods, adequately described the thermodynamic processes that were prevalent during contaminant transport. These results suggest that preferential transport of reactive contaminants is negligible for the unsaturated conditions used in this study, and that the structured saprolite within the subsurface media is a chemically active constituent during reactive solute transport. Although the transport of contaminants in the ternary Co‐Sr‐Ca system exhibited many of the same features as the binary transport studies, an attempt to simulate the transport of contaminants in the ternary system as independent species was less than adequate.
Measurements of Free Zinc2+ Activity in Uncontaminated and Contaminated Soils Using Chelation
Authors: Ma Q. Y. , Lindsay W. L.
Published: July 2010

Measurement of free Zn2+ activity is important for understanding the mechanisms controlling Zn2+ solubility in soils. Free uncomplexed Zn2+ activities were measured using the chelation method in 12 uncontaminated soils and eight contaminated soils. The measured Zn2+ activities ranged from 10−9.97 to 10−6.49 M for the uncontaminated soils, and 10−8.11 to 10−2.26 M for the contaminated soils. They were inversely related to soil pH, with a correlation coefficient of 0.96 for the uncontaminated soils and 0.89 for the contaminated soils. The measured Zn2+ activities and pH for the uncontaminated and contaminated soils can be expressed as log(Zn2+) = (5.90 ± 0.24) − 2 pH and log(Zn2+) = (9.38 ± 0.74) − 2 pH, respectively. The measured Zn2+ activities in the uncontaminated soils were near that of franklinite (ZnFe2O4). The measured Zn2+ activities in the contaminated soils were close to those of Zn2SiO4 or ZnCO3 depending on the contaminated soils. Different solid phases may control Zn solubility in different soils depending on the sources of contamination and the soil.
Soil Organic Matter as Influenced by Crop Rotations and Fertilization
Authors: Campbell C. A. , Zentner R. P.
Published: July 2010

Few studies conducted in western Canada have assessed how crop rotations and fertilization influence soil organic matter content on land that has been cropped for many years. We monitored soil organic matter in the 0‐ to 0.15‐ and 0.15‐ to 0.3‐m depths of a 24‐yr crop rotation experiment conducted on a medium‐textured Aridic Haploboroll in southwestern Saskatchewan. Prior to the study, the land had been in a hard red spring wheat (Triticum aestivum L.)‐fallow rotation for ≈50 yr. Only the 0‐ to 0.15‐m segment showed significant treatment effects. Due to good weather and crop yields in the first 15 yr, soil organic matter had increased under well‐fertilized annually cropped rotations, and it remained constant under fallow‐containing rotations and under continuous wheat receiving inadequate N fertilizer. Because of several dry years in the final 9 yr of the study, all rotations except a well‐fertilized, fallow‐winter cereal‐wheat system lost organic matter. Changes in organic matter were directly related to the amount of crop residues produced by these systems and their ease of eroding. Soil organic matter was inversely related to apparent N deficit (i.e., N exported in grain minus N applied as fertilizer). The fallow‐flax (Linum usitatissimum L.)‐wheat rotation receiving N and P fertilizer had the lowest soil organic matter, partly due to low production of crop residues by flax, partly to greater leaching of NO3, and partly due to some loss of flax residues blown from the plots. Soil organic matter in the well‐fertilized fallow‐winter cereal‐wheat rotation remained constant because its shorter fallow period reduced soil erosion, and due to its more efficient use of N, as evidenced by minimal leached NO3‐N.
Carbon and Nitrogen Distribution in Aggregates from Cultivated and Native Grassland Soils
Authors: Cambardella C. A. , Elliott E. T.
Published: July 2010

Long‐term cultivation of grassland soils reduces soil organic C and N content and has been associated with a deterioration in the aggregate structure of the soil. This study examined the effects of bare fallow (moldboard plow), stubble mulch fallow (subtill), and no‐till fallow management on aggregate size distribution and aggregate organic C and N contents compared with a native (virgin) grassland soil. Aggregate size fractions were separated by wet sieving and the proportion of soil was quantified for each aggregate size class. Mineral‐associated (silt and clay) organic matter was isolated by dispersing aggregates in sodium hexametaphosphate and removing tbe sand and particulate organic matter (POM) by passing the dispersed aggregates through a 53‐µm sieve. The POM fraction is composed primarily of partially decomposed root fragments and has an average C/N ratio of about 16. A large proportion of the total soil dry weight (50–60%) was isolated in the small macroaggregate (250–2000 µm) size class. The native grassland soil was more stable than the cultivated soils when slaked, and the no‐till soil was more stable than the stubble mulch and bare fallow soil when slaked. Reduced tillage management is effective at increasing the proportion of macroaggregates and results in the accumulation of wheat (Triticum aestivum L.) derived POM within the aggregate structure compared with bare fallow soil. It has previously been shown that the POM fraction accounts for the majority of the soil organic matter (SOM) initially lost as a result of cultivation of grassland soils. The data reported in this study relates the loss of structural stability from cultivation to losses of organic C and N from the POM fraction.
Short‐Term Effects of Surface‐Applied Gypsum on Revegetated Sodic Bentonite Spoils
Authors: Schuman G. E. , Meining J. L.
Published: July 2010

The high clay content and saline‐sodic characteristics of bentonite mine spoils result in an environment that is not conductive to sustainable plant growth. Use of wood residue amendments have enabled revegetation of these materials; however, sodic conditions persist or worsen, threatening the long‐term sustainability of these revegetated lands. Gypsum, 56 Mg/ha, was surface applied to these revegetated ecosystems to evaluate its effectiveness in ameliorating the spoil sodicity under a natural precipitation environment. The gypsum treatment significantly reduced the exchangeable Na and the exchangeable Na percentage of the 60‐cm spoil profile 3 yr after treatment. The gypsum amendment also significantly increased the spoil‐water storage in the 60‐cm spoil profile. Gypsum treatment resulted in a significant increase in the spoil electrical conductivity; however, this increase did not detrimentally affect the vegetation. Surface‐applied gypsum amendment effectively ameliorated the revegetated bentonite mine spoil sodicity under natural rainfall conditions in a semiarid environment.
Urea Nitrogen Budget for a Subarctic Agricultural Soil
Authors: Knight C. W. , Sparrow S. D.
Published: July 2010

Urea is the predominant form of fertilizer N used in Alaska. However, little information is available on the N‐recovery efficiency (NRE) or the ultimate fate of urea‐N in subarctic soils. This study was conducted to determine the NRE and the ultimate fate of urea‐N applied in the spring for barley (Hordeum vulgare L.) production in interior Alaska. Urea and Ca(NO3)2 were applied at 100 kg N ha−1 and either incorporated into or left on the soil surface in each of three cropping years. Also, 15N‐labeled urea was applied to small plots. Ammonia traps and soil and plant samples were used to track the form and movement of the applied N. Ammonia volatilization losses were negligible. Deep soil samplings indicated negligible leaching of N. The NRE, as determined by the difference method, was estimated to be about 60% for urea and 73% for Ca(NO3)2. By the isotope dilution method, NRE for urea was calculated to be about 41%. An apparent added nitrogen interaction (ANI) accounted for an additional 16.5%. Approximately 43% of the applied urea‐N was recovered in the soil organic matter at the end of the season, 1% remained in the soil as inorganic N, and 15% was unaccounted for and assumed lost through denitrification. Grain yields did not differ due to N source or placement, but total plant N uptake was greater from the Ca(NO3)2 than from the urea source. Nitrogen placement did not affect N uptake. Fertilizer N cycling in this subarctic soil did not differ greatly from fertilizer N cycling in more temperate regions.
Optimization of Hydraulic Functions from Transient Outflow and Soil Water Pressure Data
Authors: Eching S. O. , Hopmans J. W.
Published: July 2010

Inverse solution techniques currently used for estimating unsaturated soil hydraulic functions from laboratory outflow experiments use cumulative outflow only in combination with initial and final soil water pressure head values. Additional soil water information is needed to improve the estimation procedure and to minimize uniqueness problems. It was the objective of this study to experimentally explore the feasibility of using both cumulative outflow and soil water pressure head data in the inverse solution for laboratory determination of soil hydraulic functions using both one‐step and multistep outflow experiments. Soil water pressure head was measured with a microtensiometer and pressure transducer. Desorption experiments were performed under both pressure and suction for the following soils: Yolo silt loam (fine‐silty, mixed, nonacid, thermic Typic Xerorthent), Panoche loam (fine‐loamy, mixed [calcareous], thermic TypicTorriorthent), Hanford sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent), and Oso‐Flaco fine sand (coarse‐loamy, mixed Typic Cryorthod‐fine‐loamy, mixed, mesic Ustollic Haplargid). Water retention curves optimized from cumulative outflow alone were compared with those obtained from outflow and soil water pressure head measurements for both one‐step and multistep outflow experiments. Computer optimization of the retention curve by the inverse solution technique using transient outflow experiments was greatly improved when cumulative transient outflow data were combined with simultaneously measured soil water pressure head data. Pressure and suction experiments yielded equally good results for one‐step and multistep desorption. Moreover, the addition of soil water pressure head data resulted in unique parameter values for the optimized soil hydraulic functions under our experimental conditions.
Sorption of Trace Organics to Colloidal Clays, Polymers, and Bacteria
Authors: Bengtsson Göran , Lindqvist Roland , Piwoni Marvin D.
Published: July 2010

Sorption to dissolved macromolecules and colloidal particles may enhance the transport of environmental contaminants in subsurface environments. Some properties of sorbent and solute that may influence the adsorption behavior, especially in saturated soils with low organic C concentrations, were examined in a series of stirred reaction cell experiments, using acetophenone and ionizable 4‐chloroaniline and pentachlorophenol as solutes and substituted bio‐ and geopolymers and suspended clays as sorbents. The distribution coefficient was most variable, by a factor of 5500 from one sorbent to another, for the anionic pentachloropbenol and least variable, by a factor of 250, for acetophenone. These variations could be ascribed to differences in binding properties of the solute and sorbent functional groups. Sorption to clay minerals was generally low and approximated sorption to an aquifer soil suspension; the exception was a local clay with 12% organic C, which increased sorption of the phenolate ion more than 30 times compared with the low‐organic‐C clays. The most efficient sorbent was cells of bacteria isolated from aquifer material. The linear distribution coefficient for sorption on bacteria varied from 0.5 × 103 mL g−1 for acetophenone to 5 × 104 mL g−1 for neutral pentachlorophenol. The implications of sorption varying with solute and sorbent functional groups on movement of solutes through an aquifer were examined by a transport model, which divides the mobile system into an aqueous and a colloidal phase. The relative mobility of pentachlorophenol associated with colloidal sorbents can vary by as much as 90% as a result of variations of the distribution coefficient to the polymers and clays examined.
Spatial Dependence of Geochemical Elements in a Semiarid Agricultural Field: II. Geostatistical Properties
Authors: Berndtsson Ronny , Bahri Akissa , Jinno Kenji
Published: July 2010

Experimental variograms may be used to infer the spatial structure of geochemical elements. This information is needed to control the transport of toxic elements through the unsaturated zone. Geostatistical properties of total soil contents for 20 major and trace elements were investigated for a soil in northern Tunisia. The analysis showed that all elements have a clear spatial structure. Several elements displayed a significant trend that was removed by fitting the raw data to a second‐order polynomial. Variograms for the residuals showed that most elements reach sills at ranges of ≈10 to 20 m. Exceptions are Co with a range of ≈1 m and Zn with a range of ≈5 m. The elements Be and Sr have larger ranges of ≈30 m. Calculation of direction‐dependent variograms showed that most elements depended on direction. Autocorrelation analysis of the residuals indicated no spatial correlation. The ranges found in this study can be used in sampling strategies to obtain independent values of geochemical elements.
Methodology for Determining Hydraulic Conductivity with Tension Infiltrometers
Authors: Logsdon S. D. , Jaynes D. B.
Published: July 2010

Tension infiltrometers have become a valuable tool for understanding infiltration in macropores and the soil matrix, but methodology varies. Our objective was to compare tension infiltrometer techniques and calculation procedures for determining unsaturated hydraulic conductivity, K(h), as a function of soil water pressure head (h). Field tension infiltrometer measurements were run to determine K(h) from: (i) steady‐state infiltration into an excavated one‐dimensional column, (ii) calculated sorptivity and measured change in soil water content for steady‐state three‐dimensional infiltration into dry soil, (iii) steady‐state three‐dimensional infiltration with two infiltrometer base sizes, and (iv) steady‐state infiltration for three negative heads at the same location using two different calculation schemes. For one scheme, a nonlinear regression method was used to fit α [a constant relating ln(K) and h] and K(0) from measured infiltration across three negative heads. The fitted α and K(0) were then used to calculate K(h) at each negative pressure head. Calculated K(h) by the nonlinear regression method from three‐dimensional infiltration measurements were 105% of measured one‐dimensional rates (from excavated columns), closer than any other method of calculation. More importantly, this method did not result in calculated K(h) less than zero or larger than three‐dimensional infiltration rates, as some calculation procedures did. The method did not depend on determinations of sorptivity or on initial or final soil water content.
Simultaneous Field Measurement of Nitrate‐Nitrogen and Matric Pressure Head
Authors: Moutonnet P. , Pagenel J. F. , Fardeau J. C.
Published: July 2010

Groundwater protection from NO3 pollution requires frequent measurements of potential water fluxes and NO3‐N concentrations. This study was conducted to improve researchers' abilities in managing these two parameters by using a new device. We developed a method allowing the researcher to simultaneously measure the hydraulic head and the NO3‐N concentration in the soil water solution. Measurements were made using the tensionic, in which a permeable porous ceramic cup allows the diffusion of NO3 from the soil to the water inside the cup. Diffusion is completed within 8 d. A system of capillary tubes allows this water to be extracted for measurement of NO3‐N, and it may be reinjected subsequently. An aliquot can be used for isotopic analysis. Tests carried out on a maize crop (Zea mays L.) in 1991 led to two conclusions: (i) on a 200‐m‐long transect of 50 tensionics (placed at 4‐m intervals and at a depth of 50 cm), statistical analysis made on the first three of the successive series showed the consistency of measurements with an 18% mean coefficient of variation (CV) for NO−3, whereas the mean CV for hydraulic head was 14%; (ii) in a battery formation (four probes located at depths ranging from 40 to 130 cm, with four sampling repetitions), the tensionics allowed easy monitoring of the distributions of hydraulic head and NO3‐N within the horizons of the soil profile.
Cadmium Sorption on Specimen and Soil Smectites in Sodium and Calcium Electrolytes
Authors: Zachara J. M. , Smith S. C. , McKinley J. P. , Resch C. T.
Published: July 2010

Although specimen smectities (e.g., SWy‐1) are often used as analogues of the exchanger phase in smectitic soils, few comparisons of metal ion sorption on specimen and soil smectites have been made. In this study, the sorption of Cd was measured on SWy‐1 and on clay‐sized separates from two smectitic subsoils to evaluate the selectivity of specimen and soil‐derived smectites for Cd. Sorption was measured in clay suspensions (≈1 mmolc L−1 equivalent charge concentration at pH 6.0) in Na+, Ca2+, and Na+‐Ca2+ perchlorate solutions across pH 4.5 to 8.5 and at ionic strengths (I) ranging from 0.005 to 0.1. Ionic strength and electrolyte cation valence strongly influenced Cd sorption by SWy‐1 and the soil smectites. Ion exchange dominated Cd sorption at low ionic strength in Na+ electrolyte (I = 0.005–0.014). Increasing Na+ concentrations to I = 0.1 or changing the electrolyte cation to Ca2+ at I = 0.003 to 0.006 suppressed ion exchange. When ion exchange was suppressed, Cd sorption to both specimen and soil smectites showed little dependence on ionic strength and increased with pH. Except at the lowest Na+ concentration (I = 0.005), conditional equilibrium constants (Kv) for Cd2+ exchange increased with increases in both ionic strength and pH. These increases were ascribed to Cd complexation reactions to edge sites on the layer silicates whose effects became evident only under conditions that suppressed ion exchange. At pH 6 and I = 0.05–0.01, SWy‐1 did not exhibit any preference for Na+, Ca2+, or Cd2+. The smectitic soil separates, in contrast, showed (i) sorption behavior that increased sharply with pH, (ii) preference for Cd in Na+ and Ca2+ electrolytes, and (iii) variation in Kv with ionic strength, pH, and surface coverage. The contrasting sorption behavior of the soil smectites was hypothesized to result from (i) a greater edge surface area, which increased the contribution of oxidelike complexation reactions to Cd sorption, and (ii) the presence of minor associated organic material and Fe oxides that functioned as co‐complexants for Cd.
New Evidence for the Origin of Ferrimagnetic Minerals in Loess from China
Authors: Fine Pinchas , Singer Michael J. , Verosub Kenneth L. , TenPas Jeff
Published: July 2010

The sequence of loess and interbedded paleosols of north‐central China has accumulated for the last 2.4 million yr. This offers a unique location to study pedogenesis. The paleosol units are easily differentiated from zones of unaltered parent material by their higher low‐field mass magnetic susceptibility (MS). We have studied the MS of 69 loess and paleosol samples to determine if MS could be used to understand more about pedogenesis in the loess column. The MS ranged from 11 × 10−8 m3 kg−1 in an unaltered loess to 324 × 10−8 m3 kg−1 in a paleosol. We present magnetic and chemical data that support the in situ formation of ferrimagnetic material during periods of pedogenesis. An inherited ferrimagnetic component, which is predominantly silt‐sized magnetite, is evenly distributed throughout the loess column with an average MS of 17 ± 4 × 10−8 m3 kg−1. This component is resistant to removal by citrate‐bicarbonate‐dithionite (CBD) extraction. A second ferrimagnetic component, with is CBD soluble, occurs predominantly in the clay (<2‐µm) fraction. We assume this material is a newly formed maghemite that has accumulated in the paleosols as a result of pedogenesis. This CBD‐soluble ferrimagnetic phase is enriched in the paleosols, as shown by the linear (P < 0.001) increase of the ratio of MS to Fe oxides and oxyhydroxides. The ferrimagnetic content, ferrimagnetic minerals, and particle‐size distribution of the ferrimagnetic phase in the paleosols are all related to the extent of pedogenesis in the loess column.
Effect of Landscape Position on Soil Water and Corn Silage Yield
Authors: Afyuni M. M. , Cassel D. K. , Robarge W. P.
Published: July 2010

Systematic variation in plant‐available water at different landscape positions is thought to be one of the most important factors controlling crop production. The objectives of this study were to evaluate variability in equivalent depth of soil water, plant‐available water, and soil water pressure as a function of landscape position and their effects on corn (Zea mays L.) silage production. Soil water content to a depth of 1 m and soil water pressure at depths of 30, 45, and 60 cm were monitored at 5‐m intervals on an 110‐m‐long transect, and at 10‐m intervals on an 80‐m‐long transect using neutron attenuation and tensiometers, respectively. Plant‐available water at a given time was calculated as field‐measured soil water content minus the soil water content at −1500 kPa. Corn silage yield was measured on 13.5‐m2 plots centered at 5‐ or 10‐m intervals and grouped by landscape position. The foot slope position had the lowest total water content on both transects, but the greatest amount of plant‐available water on the longer transect. Equivalent depth of soil water in the upper 1 m of soil decreased from the interfluve to the footslope position and was negatively correlated with silage yield. Soil water pressures were greater at the footslope than the other landscape positions and were positively correlated with silage yield in the shorter transect.
Hydraulic Conductivity of Saline‐Sodic Soil after Gypsum Application and Cropping
Authors: Ilyas M. , Miller R. W. , Qureshi R. H.
Published: July 2010

Slow internal drainage is a major problem in the reclamation of saline‐sodic soils. This field experiment was conducted on a low‐permeability, saline‐sodic soil (a fine‐loamy, mixed, thermic Typic Natrustalf) near Lahore, Pakistan, to compare field‐saturated hydraulic conductivities (Kfs) after various treatments. Treatments were: (i) deep‐rooted perennial alfalfa (Medicago sativa L.), (ii) sesbania [Sesbania bispinosa (Jacq.) W.F. Wright]‐wheat (Triticum aestivum L.)‐sesbania rotation, (iii) incorporated wheat straw at 7.5 Mg Ha−1, and (iv) a fallow control. These four treatments were each combined with and without 25 Mg ha−1 of gypsum, subsoiling to 0.45 m, and open‐ditch drainage. The Kfs of the soil under each treatment was measured in each 20‐cm increment to 120 cm after 6 mo and 1 yr. Gypsum applications increased the Kfs of the top 20‐cm soil layers. Compared with uncropped plots, Kfs of the 0‐ to 20‐cm depth on cropped plots with gypsum increased about twofold after 6 mo and about fourfold after 1 yr. The crop rotation significantly increased the Kfs of the 0‐ to 20‐cm (with and without gypsum) when compared with wheat straw or fallow treatments. The Kfs on plots with alfalfa plus gypsum were significantly greater to 80 cm than the Kfs on fallow plots. Neither subsoiling nor open‐ditch drains improved soil permeability. Gypsum plus sesbania‐wheat‐sesbania rotation most increased permeability of the surface layer; gypsum plus alfalfa was best to improve the permeability of the deeper layers.
Variations in Water Balance and Recharge Potential at Three Western Desert Sites
Authors: Gee G. W. , Wierenga P. J. , Andraski B.J. , Young M. H. , Fayer M. J. , Rockhold M. L.
Published: July 2010

Radioactive and hazardous waste landfills exist at numerous desert locations in the USA. At these locations, annual precipitation is low and soils are generally dry, yet little is known about recharge of water and transport of contaminants to the water table. Recent water balance measurements made at three desert locations, Las Cruces, NM, Beatty, NV, and the U.S. Department of Energy's Hanford Site in the state of Washington, provide information on recharge potential under three distinctly different climate and soil conditions. All three sites show water storage increases with time when soils are coarse textured and plants are removed from the surface, the rate of increase being influenced by climatic variables such as precipitation, radiation, temperature, and wind. Lysimeter data from Hanford and Las Cruces indicate that deep drainage (recharge) from bare, sandy soils can range from 10 to >50% of the annual precipitation. At Hanford, when desert plants are present on sandy or gravelly surface soils, deep drainage is reduced but not eliminated. When surface soils are silt loams, deep drainage is eliminated whether plants are present or not. At Las Cruces and Beatty, the presence of plants eliminated deep drainage at the measurement sites. Differences in water balance between sites are attributed to precipitation quantity and distribution and to soil and vegetation types. The implication for waste management at desert locations is that surface soil properties and plant characteristics must be considered in waste site design in order to minimize recharge potential.
Plant Response to Organic Amendments and Decreasing Inorganic Nitrogen Rates in Soils froma Long‐Term Experiment
Authors: Fauci Mary F. , Dick R. P.
Published: July 2010

To decrease the potential for adverse environmental impacts of N in agroecosystems, there is increasing emphasis on improving N efficiency of organic and inorganic sources. Greater reliance on organic N sources can cause short‐term crop yield decreases. Consequently, a study was conducted to determine the effect of decreasing rates of inorganic N during a transition from inorganic to organic N sources. The approach was to grow four crops of maize (Zea mays L.) during a period of 306 d in the greenhouse on soils that varied widely in organic matter and biological activity because of long‐term residue and fertilizer management. Treatments were arranged as a complete factorial with the following factors: four soils obtained from the Residue Utilization Plots (RUP), Columbia Basin Research Center, Pendleton, OR (beef manure or pea [Pisum sativum L.] vine residue, 0 or 90 kg N ha−1, applied biennially since 1931); four greenhouse amendments (pea vine, composted beef or poultry manure, or control); and four rates of N fertilizer (0–1600 mg N [2 kg]−1 soil as NH4NO3). In the absence of organic residue or N fertilizer, soil from the manure RUP produced greater dry matter yield (DMY) and plant N uptake than soil from the other RUP treatments. There was no net N mineralization from beef manure added in the greenhouse. Between 10 and 30% of the total poultry manure and pea vine N added was taken up by the four maize crops. Results showed that, by the fourth crop, when inorganic N applications had decreased to zero, plant productivity by organic residues was best maintained by pea vine residue or poultry manure.
Ammonia Volatilization from Urea Amended with Lignosulfonate and Phosphoroamide
Authors: Al‐Kanani T. , MacKenzie A. F. , Fyles J. W. , O'Halloran I. P. , Ghazala S.
Published: July 2010

Concern about losses of fertilizer N and pollution of the environment has stimulated research to find compounds that will reduce these problems by effectively inhibiting urease activity and nitrification. Laboratory studies were carried out to evaluate the effects of ammonium lignosulfonate (LS), thiophosphoric triamide (NBPT), and phenylphosphorodiamide (PPD) on NH3 loss from urea fertilizer. We examined NH3 losses from surface‐applied urea and from banded urea (2 cm below the soil surface) in samples of Ste. Rosalie clay soil (fine, mixed, nonacid, mesic Typic Humaquept) exposed to an initial water pressure of −0.01 MPa. Formulations of solution, physical dry blend, and tablets were used. Measurements of NH3 volatilization were carried out using an air train system. Ammonia loss from surface‐applied unamended urea ranged from 16 to 21% of urea‐N applied. Amending urea with LS induced between 46 and 85% reduction in NH3 losses compared with the unamended urea. For tablet and physical dry blend formulations, banding reduced NH3 loss compared with tbe surface application. There were no significant differences in NH3 losses between surface‐applied and banded treatments of solid fertilizer. Comparison of tbe effects of LS, NBPT, and PPD on NH3 volatilization showed that both NBPT and PPD were more effective in reducing NH3 loss than LS, but no significant differences between NBPT and PPD were found.