bluuebunny/crossref_metadata_2025 huggingface dataset:
Plant‐Available Nitrogen from Lentil and Wheat Residues during a Subsequent Growing Season
Authors: Bremer E. , van Kessel C.
Published: July 2010

Lentil (Lens culinaris Medikus) is being grown increasingly on the Canadian prairies as a pulse or green manure crop, and may increase N availability to a succeeding crop. This study was designed to compare the effects of lentil green manure, lentil straw, and wheat (Triticum aestivum L.) straw on plant‐available N during the growing season after application. The fate of 15N from fall‐applied (1988) lentil green manure, lentil straw, and wheat straw and spring‐applied (1989) fertilizer (NH4)2 SO4 was determined four times during the 1989 growing season at a field site located at Outlook, Saskatchewan, Canada, on a Bradwell sandy loam (Typic Boroll). Denitrification and leaching losses of 15N from added lentil and wheat straw were negligible, but 24 and 30% of the 15N in lentil green manure and fertilizer, respectively, were lost in the 6‐wk period after planting (8 May 1989). By wheat harvest (8 Aug. 1989), 7% of the 15N in lentil and wheat straw and 37% of the 15N in lentil green manure were mineralized. Addition of green manure increased net mineralization of indigenous soil N at the time of planting by 0.4 g m−2, equivalent to 10% of added green manure N. Immobilization of soil and fertilizer N was similar for lentil and wheat straw. The smaller fraction of 15N assimilated from green manure (19%) than from fertilizer (34%) by wheat was due solely to less net mineralization of green‐manure N rather than net immobilization of fertilizer N. Of the 15N added in lentil and wheat straw, 5.5% was assimilated by wheat. Thus, lentil straw was not a significant source of N in this study, while ≈40% of the N in lentil green manure was potentially available for plant uptake.
Estimating the Water‐Dispersible Clay Content of Soils
Authors: Brubaker S. C. , Holzhey C. S. , Brasher B. R.
Published: July 2010

Soil erodibility is influenced by several soil properties including the extent to which the clay fraction will disperse in water. Because early methods for estimating soil erosion were empirical methods and did not utilize water‐dispersible clay as a parameter, few data have been collected. The recent development of the Water Erosion Prediction Project (WEPP) model, a process‐based model for predicting water erosion that uses water‐dispersible clay in the algorithm for computing interrill erodibility, resulted in an increased demand for these data. In order to accommodate this and similar models, a method for estimating the water‐dispersible clay content of soils based on existing information is needed. Data collected by the National Soil Survey Laboratory in support of the WEPP were used to identify soil properties that were significantly correlated with water‐dispersible clay and to develop equations to estimate the water‐dispersible clay content of soils based on those properties. The property most strongly correlated with water‐dispersible clay is total clay. Other properties significantly correlated with water‐dispersible clay are the water content at 1.5 MPa, dithionite‐citrate‐extractable Fe and Al, the coefficient of linear extensibility, Wischmeier's M, the very‐fine‐sand content, the ratio of cation‐exchange capacity (CEC) to total clay, Bouyoucos' clay ratio, and the CEC. A simple linear regression of water‐dispersible clay vs. total clay revealed that, for the soils included in this study, approximately one‐third of the total clay was water dispersible. However, the model only had an R2 of 0.604. When the ratio of the CEC corrected for organic carbon (CCEC) to total clay was included in the model, the R2 improved to 0.723. However, sorting the data by the ratio of CCEC to total clay instead of including it in the model improved the overall fit of the model and increased the R2 to 0.879.
Miscible Displacement: An Interacting Flow Region Model
Authors: Skopp J. , Gardner W. R.
Published: July 2010

No existing microscopically based models of solute transport in porous media are completely satisfactory. In particular, it is difficult to a priori provide an estimate of the hydrodynamic dispersion coefficient. We developed a model of solute movement in saturated porous materials that starts with a continuous velocity distribution instead of an average velocity. The model allows transfer of solute between regions of differing velocity. This transfer is characterized by an interaction coefficient. An approximate solution for large interaction is obtained using the method of moments. This technique shows the equivalence of the model moments to those of the classical dispersion equation. The second moment yields the dependence of the dispersion coefficient on average velocity. The empirical dependence of dispersion on average velocity is recovered if the interaction is assumed to be a linear function of the average velocity. The model also predicts the increase in dispersion observed for heterogenous materials over that for a similar homogeneous material.
Improved Apparatus for Measuring Hydraulic Conductivity at Low Water Content
Authors: Nimmo John R. , Akstin Katherine C. , Mello Karen A.
Published: July 2010

A modification of the steady‐state centrifuge method (SSCM) for unsaturated hydraulic conductivity (K) measurement improves the range and adjustability of this method. The modified apparatus allows mechanical adjustments to vary the measured K by a factor of 360. In addition, the use of different flow‐regulating ceramic materials can give a total K range covering about six orders of magnitude. The increment of K adjustment is a factor of about 1.6. This makes it potentially useful for measuring targeted values of K or, through a trial and error procedure, of water content (θ). The range extension afforded by this modification has led to the lowest steady‐state K measurement to date: 1.1 × 10−11 m/s at θ of 0.068 m3 water/m3 for a sandy soil of the Delhi series (mixed, thermic Typic Xeropsamment).
Sample Size Consideration in the Determination of Soil Nitrate
Authors: Starr J. L. , Meisinger J. J. , Parkin T. B.
Published: July 2010

A prerequisite to increasing N‐use efficiency through the use of soil testing is the accurate determination of soil nitrate concentrations. This study was conducted to determine the influence of sample size on the magnitude and variability of NO3‐N concentrations in the surface horizon of a Beltsville silt loam soil (fine‐loamy, mixed, mesic Typic Fragiudult). Five different sized soil coring tubes, 1.7 to 5.4 cm in diam. (38–366 cm3) and one block sample of 8770 cm3 were used to collect soil samples. Thirty‐six of each sample size were collected twice before and twice after planting corn (Zea mays L.). Nearly all the NO3‐N values were lognormally distributed with the magnitude of skewness related more to concentration than to sample size, except for the largest sample size (8770 cm3), which was always minimally skewed. This study indicated that mean NO3‐N values could be accurately estimated using 36 of the smallest sized samples. The smallest sample size, however, was often unable to accurately estimate the spatial variability of soil NO3‐N. Further, a computer‐intensive random resampling procedure indicated that 20 to 50% more samples were required with the smallest sampler to achieve satisfactory estimates of the sample mean. This study did not provide a consistent basis for choosing between samplers with diameters of 2.15 to 5.4 cm (58–366 cm3).
Surface and Subsurface Soil Acidity: Soybean Root Response to Sulfate‐Bearing Spent Lime
Authors: Marsh Brian H. , Grove J. H.
Published: July 2010

Surface and subsurface acidity are of agronomic concern in the southeastern USA. The limits to crop production imposed by subsoil acidity need to be further defined for this region. Gypsum is being applied to ameliorate subsoil acidity and to overcome the problem of very slow lime movement from surface lime applications. Reduced crude conversion spent lime (RCCSL) containing anhydrite (CaSO4) was evaluated for use as a liming material with specific consideration given to the movement of SO2‐4 into the acid subsoil. Agricultural lime and RCCSL were applied at 0, 3.36, 6.72, and 10.08 Mg ha−1 to an acid Trappist silt loam (clayey, mixed, mesic Typic Hapludult). Soybean [Glycine max (L.) Merr.] was grown in the second year following lime application. Soil cores to 0.90 m were taken at growth stage R5 for root length measurement and soil chemical analyses. Yields were increased by the soil amendments and were well correlated with total root length (R2 = 0.84). Root growth below the surface limed layer was positively related to increased soil solution base cation (especially Ca) concentrations and SO2‐4 movement into the subsoil. Previously described solution Ca plus Al species activity models were not well related to field rooting responses. There remains a need for soil test procedures that predict the need for, and the amount of, subsurface acidity amelioration.
Land Use and Management Effects on Nonpoint Loading from Miamian Soil
Authors: Thomas M. L. , Lal R. , Logan T. , Fausey N. R.
Published: July 2010

Land use greatly affects soil and hydrological processes, which have major implications for environmental quality and agricultural sustainability. The objective of this study was to determine the effects of four land use systems — continuous alfalfa, forest, ridge‐till corn (Zea mays L.) and conventional‐till corn — on runoff, soil loss, and nutrient transport in runoff and sediment. Eight field plots (18.5 by 21 m), equipped with 0.3‐m H‐flumes and FW‐1 water‐level recorders, were established on Miamian silty clay loam soil (fine, mixed, mesic Typic Hapludalf) at the Ohio State University Agronomy Farm, Columbus, OH. Runoff samples, collected after erosive storms during the growing season in 1990, were analyzed for sediment concentration, NO3‐N, NH4‐N, PO4‐P, and dissolved organic C. Sediment collected from the flume base was analyzed for total Kjeldahl N and available P. A critical period was identified as the early stages of crop growth during which the soil was particularly vulnerable to erosion due to excessive runoff. Soil and nutrient losses were typically higher during the critical than during the noncritical period. Both N and P losses in runoff and sediment were higher for cropped treatments than for alfalfa (Medicago sativa L.) and forest. Losses observed for conventional tillage were, however, several orders of magnitude larger than uncropped treatments.
Soil‐Based Irrigation and Salinity Management Model: II. Water and Solute Movement Calculations
Authors: Cardon G. E. , Letey J.
Published: July 2010

The utility of a new model for irrigation and soil salinity management is based largely on the agreement between measured and predicted water and solute movement in the soil profile. Data suitable for comparison to model calculations is lacking in the literature. We conducted a greenhouse study designed to obtain detailed temporal salt and water distribution data under fluctuating shallow saline water table conditions, and compared simulated and observed data. Our model's calculations for water content and salinity agreed well with the observed distributions. Willmott's d index (a statistical index of agreement between measured and observed data) results ranged from 0.83 to 0.97 (perfect agreement = 1.0). Agreement was improved when potential evapotranspiration (PET) estimates were adjusted for data from individual treatment columns in the greenhouse experiment. The d‐index values, following adjustment of PET, increased to 0.94 or bigher, indicating the importance of accurate localized PET estimates for optimum model performance.
Immobilization and Uptake of Nitrogen Applied to Corn as Starter Fertilizer
Authors: Francis D. D. , Doran J. W. , Lohry R. D.
Published: July 2010

One goal of best management practices for N fertilization is to obtain high utilization of applied fertilizer. This experiment was conducted to determine plant uptake and the degree of microbial immobilization of NH4‐N and NO3‐N in fluid starter fertilizer applied to corn (Zea mays L.). In addition, two modifications of the fumigation‐incubation method for biomass C and N determinations were evaluated for their ability to quantify immobilization of fertilizer N by soil microbial populations. Starter fertilizers tagged with 14NH4NO3 or NH415NO3 were used to measure effects related to the fertilizer NH4 and NO3 components. Plant and soil samples were collected at the V3 and V8 growth stages. In both years, NO3 in the starter fertilizer was leached out of the emerging plant's root zone before it could be fully utilized. Ammonium underwent rapid nitrification and subsequently also was leached out of the topsoil, limiting immobilization and plant uptake. In the second year of the study, dicyandiamide (DCD) was included in the treatments, which maintained more N in the NH4 form, resulting in greater crop uptake and more microbial immobilization of fertilizer N. Under environments that tend to be conducive to leaching, it may be necessary to add a nitrification inhibitor to starter fertilizers to ensure that fertilizer N remains positionally available to young corn plants. The Shen, Pruden, and Jenkinson method for estimating biomass N gave immobilization values that were consistent with values anticipated from isotopic analyses of soil N. The Voroney and Paul technique appeared to overestimate biomass N by 1.5‐ to seven fold for our soils and climatic conditions.
Micromorphological Evidence of Polygenesis of Three Aridisols, Western Mojave Desert, California
Authors: Eghbal Mostafa K. , Southard Randal J.
Published: July 2010

Soils in arid regions are often polygenetically related to climatic variation. On a dissected alluvial fan in the western Mojave Desert, a Typic Durorthid (loamy, mixed, thermic, shallow; Alko series) and two Typic Haplargids (fine‐loamy, mixed, thermic; Neuralia and Garlock series) were selected for micromorphological investigation to determine the sequence of pedogenic events. The micromorphology of pedogenic silica, carbonate, and clay is described for duripans, duric horizons (Btqk), and underlying buried Bt horizons in these soils. In the Alko and Neuralia soils, rodent bioturbation has transported subsurface calcareous fragments, thereby enriching the soil surface with silica and CaCO3. These fragments are not completely removed from the surface by leaching under the present‐day climate. Clay illuviation and silicification occurred simultaneously in the lower duripan (40–150 cm) of the Alko, with subsequent accumulation of CaCO3 in seams and root channels. Silicification of the Btqk and buried Bt horizons in the Neuralia and Garlock soils occurred after clay illuviation. The complete cementation of the lower duripan in the Alko soil has apparently isolated the buried Bt, but the buried Bt, horizons in the Neuralia and Garlock soils have undergone further calcification and silicification. We speculate that the polygenesis of soils in the study area is related to climatic fluctuations since the mid‐Pleistocene and to bioturbation of surface horizons. Development of carbonate‐free argillic horizons probably occurred during pluvial periods, whereas calcification occurred during drier periods. Silicification appears to have been contemporaneous with both clay illuviation and calcification and, thus, may be related to pedochemical conditions rather than to climate.
High Intensity X‐Ray and Tensiometer Measurements in Rapidly Changing Preferential Flow Fields
Authors: Liu Yaping , Bierck Barnes R. , Selker John S. , Steenhuis Tammo S. , Parlange J.‐Yves
Published: July 2010

Synchrotron x‐rays at the Cornell High Energy Synchrotron Source (CHESS) and other available facilities provide a high‐resolution means of quantitatively studying rapid changes of fluid content in porous media. This technique is based on monitoring x‐ray absorbance changes in sand volumes traversed by an intense, highly collimated synchrotron x‐ray beam. The high intensity and brightness of synchrotron radiation permit acquisition of statistically significant x‐ray count data each second during the drying process of fingered flow. Simultaneous measurement of water pressure using tensiometers provides a reliable dynamic measurement of drying curves.
Predicting Saturated Hydraulic Conductivity Utilizing Fractal Principles
Authors: Rawls W. J. , Brakensiek D. L. , Logsdon S. D.
Published: July 2010

Preferential movement of surface‐applied chemicals to the groundwater has resulted in a great need to physically model the movement of water into and through the soil media. The objective of this study was to develop equations capable of predicting both matrix and macropore saturated conductivity and to relate the equation parameters to readily available soil properties. Equations for predicting the matrix and macropore saturated conductivity were developed by coupling fractal processes with the Marshall saturated conductivity formulation. The equation uses matrix and macropore porosity, maximum pore radius, and number of pore classes. Prediction equations were developed relating the number of pore classes and maximum pore radius to soil properties. The modified Marshall saturated hydraulic conductivity equation appears to provide reasonable estimates of matrix and macropore saturated conductivity and is applicable to a wide range of soil textures.
Soil Microbial Populations and Activities in Reduced Chemical Input Agroecosystems
Authors: Kirchner M. J. , Wollum A. G. , King L. D.
Published: July 2010

This study, conducted in the Piedmont of North Carolina, was initiated to determine how reductions in N fertilization and green‐manuring with crimson clover (Trifolium incarnatum L. cv. Tibbee) would affect populations and activities of soil microorganisms. Four continuous corn (Zea mays L.) treatments were used: no‐till (receiving herbicides and soil insecticides) with 0 or 140 kg N ha−1 as NH4NO3; conventionally tilled, receiving 140 kg N ha−1, but no pesticides; and conventionally tilled with a crimson clover green manure, but no fertilizer or pesticides. Populations were determined using selective media for culturable bacteria, gram‐negative bacteria, fungi, actinomycetes, Bacillus spp., and Pseudomonas spp. Microbial activities were estimated by enzyme assays for acid and alkaline phosphatase, arylsulfatase, and β‐glucosidase. Microbial biomass C was determined by a chloroform fumigation‐extraction procedure and levels of available N were measured after anaerobic incubation. Surface soil (0–7.5 cm) from the no‐till treatment receiving 140 kg N ha−1 contained significantly more fungi than did soil from the unfertilized, no‐till treatment. Microbial biomass C and available N were not affected by N addition, but levels of acid phosphatase and β‐glucosidase were significantly higher in the fertilized soil than in the unfertilized soil. Surface soil from a crimson clover‐corn rotation contained significantly larger populations of Bacillus spp. (260% more), actinomycetes (310% more), and culturable bacteria (120% more) than did soil from the well‐fertilized conventionally tilled, no‐pesticide treatment. Also, microbial biomass, available N, and levels of alkaline phosphatase, arylsulfatase, and β‐glucosidase were significantly higher in surface soil from the crimson clover treatment than the nonmanured soil. Although the soil biological properties changed significantly during the year, seasonal variations were similar across treatments. Microbial numbers and activities were high in the spring and fall and low during the late summer.
Spatial Dependence of Geochemical Elements in a Semiarid Agricultural Field: I. Scale Properties
Authors: Bahri Akissa , Berndtsson Ronny , Jinno Kenji
Published: July 2010

Information on the spatial structure of soil chemical elements in field soils is needed to evaluate potential environmental hazards. Basic spatial properties of total soil contents of 20 major and trace elements were investigated for three different scales in a soil in northern Tunisia. In total, 314 soil samples were taken on two adjacent 40 by 40 m2 plots (one plot sludge‐amended and one without sludge). Theoretical lognormal probability distributions best fit the empirical distributions for most of the elements. Assuming complete randomness, a relative error margin of 10%, and a probability level of 0.05, average values for the sampled scales can be estimated with a minimum number of samples, which are 25 for Cd and Cr, 10 for Al, Be, Ca, Fe, Mg, and Pb, and five for other elements. The elements Al, Ca, and Fe can be sampled irrespective of scale and location (sludge vs. no sludge) with a resulting similar variance. Elements like Cd, Cr, Mg, Na, Ni, Sr, and V have a variance independent of location but are dependent on scale. Other elements, Ba, Be, Co, Cu, K, Mn, P, Pb, S, and Zn, have a variance that depends on both scale and location.
Field Calibration and Monitoring of Soil‐Water Content with Fiberglass Electrical Resistance Sensors
Authors: Seyfried M. S.
Published: July 2010

Electrical resistance sensors, combined with data acquisition systems, offer a relatively inexpensive means of continuously monitoring soil‐water content (θ) at barely accessible remote sites. Fiberglass resistance sensors respond across the range of θ but require calibration. With field calibration, site‐specific soil conditions are implicitly accounted for, but calibration results have not been presented in the literature. The objectives of this study were to determine the accuracy and precision of field‐calibrated fiberglass resistance sensors and to demonstrate their application to monitoring at remote sites. Time domain reflectometry (TDR) was used for calibration. Sixteen individual sensor‐TDR calibrations and one overall calibration combining all measurements showed a strong log‐linear relationship between TDR‐measured θ and sensor‐measured resistance. Individual calibration 80% confidence intervals ranged from 0.02 to 0.045 m3 m−3. Calibration statistics did not appreciably drift during the study. These results, and subsequent measurements, were unaffected by soil freezing, indicating that the sensors respond to liquid water content. The overall calibration 80% confidence interval was 0.065 m3 m−3, due largely to high variability among sensors. However, changes in θ could be estimated with reasonably accuracy. Most (73%) of the resistance measurements made the year after calibration were within ±0.05 m3 m−3 of the TDR‐measured value. Sensor response time was shown to be within the 1‐h measurement interval. In this study, field‐calibrated fiberglass resistance sensors provided reasonably accurate estimates of θ at a high level of spatial and temporal resolution.
Stripper for Bubble‐Free Tensiometry
Authors: Miller Edward E. , Salehzadeh Amir
Published: July 2010

Unwanted formation of air bubbles in the liquid water inside soil water tensiometers has always been a major nuisance afflicting this simple, fast, and accurate device. The stripper, a plastic wall (usually just a tubing wall) between the tensiometer water and a wet vacuum (containing some droplets of liquid water), strips any dissolved air out of this water. Bubbles cannot grow, they will shrink and disappear, unless the water pressure inside the tensiometer is less than the vapor pressure of water (at the ambient temperature). Choices of desirable plastic materials and other considerations are based on 7 yr of development and employment of this method.
Characterization of Carbonaceous Adsorbents by Soil Fulvic and Humic Acid Adsorption
Authors: Johns M. M. , Skogley E. O. , Inskeep W. P.
Published: July 2010

Six porous carbonaceous adsorbents, selective for nonpolar organic adsorbates, were evaluated for dissolved soil humic adsorption and testing. Amberlite XAD 8 resin was similarly tested. Soil fulvic (FA) and humic (HA) acids were used as models for naturally occurring dissolved organic C in soil. The adsorbents were tightly packed as spherical capsules identical to previous studies using ion exchange resins for soil adsorption of plant nutrients. Static or passive adsorption from solution was applied. Kinetic studies (0–264 or 0–336 h) indicated a high initial adsorption rate followed by slower adsorption, common for porous adsorbents. Intraparticle diffusion was rate limiting. Adsorption differences between adsorbents are probably caused by molecular‐size exclusion effects due to pore size. The capsules of Carboxen‐Carbotrap resin mixture were capable of doubling adsorption, requiring no additional time, in response to doubling the FA (43–85 mg C L−1) or HA (46–90 mg C L−1) concentration. This effect was seen across the whole adsorption‐time range. The constant partitioning isotherm model described adsorption, indicating linear adsorption (r2 > 0.96, P < 0.01) with temperatures ranging from 13 to 50 °C, at pH 7.0, and within the concentration ranges of FA (9–126 mg C L−1) and HA (11–138 mg C L−1). This suggests a usefulness for these adsorbents at neutral pH and typical temperatures in waters for dissolved humic adsorption. Subsequently, initial solution concentrations of FA and HA were predicted from resin‐extractable C, indicating a potential for quantifying humic concentrations in solutions. Under identical conditions, XAD 8 resin did not demonstrate the testing attributes found with these carbonaceous adsorbents.
Residual Effects of No‐Till Crop Residues on Corn Yield and Nitrogen Uptake
Authors: Maskina M. S. , Power J. F. , Doran J. W. , Wilhelm W. W.
Published: July 2010

The residual effects of crop residues on N availability and crop growth are largely unknown. A field experiment was conducted from 1986 through 1988 at Lincoln, NE, to determine the residual effects on no‐till corn (Zea mays L.) production and N uptake of 0, 50, 100, and 150% of the amount of crop residues produced by the previous crop during the previous 5 yr. These effects were evaluated with and without tillage (disking), N fertilizer (60 kg N ha−1), and hairy vetch (Vicia villosa Roth ssp. villosa, ‘Madison’) winter cover crop. Increasing the previous crop residue rate increased organic C, total N, and NO3‐N in the upper 30 cm of soil as much as 10, 12, and 66%, respectively. Growth and N uptake by corn (3‐yr average) generally increased as previous residue rate increased. Corn grain and stover production was 17 and 25% greater for the highest compared with the lowest previous residue rate. Uptake of indigenous soil N, but not fertilizer N, also increased as previous residue rate increased. Cover crops generally increased growth and N uptake with no fertilizer, but had little effect with N fertilizer. Soil properties, crop growth, and N uptake generally were not affected by tillage or interactions among the variables. These results indicate that increasing no‐till crop residue rates increased the capability of this soil to provide N to growing crops for many years. It appears this effect is somewhat self‐perpetuating.
Water and Chemical Transport through Long‐Term No‐Till and Plowed Soils
Authors: Granovsky A. V. , McCoy E. L. , Dick W. A. , Shipitalo M. J. , Edwards W. M.
Published: July 2010

Flow in soil macropores has been implicated as a mechanism for accelerated movement of agrichemicals into groundwater under conservation tillage practices. Strontium bromide hexahydrate, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5 triazine), and alachlor (2‐chloro‐2′‐6′‐diethyl‐N‐[methoxymethyl]‐acetanilide) were surface applied to 18 undisturbed 0.3 by 0.3 by 0.3 m soil blocks collected from three Ohio soils subject to long‐term no‐till (NT) and moldboard plowing (MP). Two 30‐mm rains were applied to the block surface, and leachate was collected from 64 cells at the bottom of each block. Leachate volume, amount of chemicals leached, and visible pore area on bottom surfaces were determined for each cell. Semivariograms of cell leachate volumes revealed that water flow in both NT and MP soils is spatially uncorrelated at a scale of 30 to 300 mm. Principal component analysis at the cell level demonstrated that water flow in both NT and MP blocks followed preferential pathways. The NT blocks transmitted larger water volumes and chemical amounts than MP blocks; however, differences were rarely significant. Principal component analysis of transport in individual blocks suggested that the tillage differences resulted from a higher proportion of strongly preferential pathways in NT blocks. Discriminant analysis yielded significant separation in the soil hydraulic behavior as influenced by tillage and demonstrated the interaction in this behavior between soil type and tillage treatment. It has become clearer that rainfall timing and intensity following chemical application may overshadow tillage effects on water and chemical transport in soils.
Long‐Term No‐tillage Effects on Soil Properties and Continuous Corn Yields
Authors: Ismail Isro , Blevins R. L. , Frye W. W.
Published: July 2010

Lack of soil disturbance in no‐tillage changes some of the most important basic soil properties. Short‐term changes have been well documented by previous research, but little is known about long‐term changes. This study was to determine the effects of 20 yr of continuous corn (Zea mays L.) under no‐tillage (NT) and conventional moldboard plow tillage (CT) with 0, 84, 168, and 336 kg N ha−1 on soil properties and grain yields and, to the extent possible, compare 20‐yr results with previously published 5‐ and 10‐yr results. Soil organic C and N; extractable P; exchangeable Ca, Mg, and K; and pH were significantly higher with NT than CT in the 0‐ to 5‐cm depth. Below the 5‐cm depth, Mehlich III P; pH; and exchangeable Ca, Mg, and K were higher with CT than NT. Organic C and N increased with increasing N rates. Conversely, pH and exchangeable Ca and Mg declined with high N rates. Bulk density was not significantly different among NT, CT, and bluegrass sod (Poa pratensis L.), but increased with depth. Comparisons of 1989 results with those obtained in 1975 and 1980 revealed that the soil's organic C was restored to the level of the bluegrass sod following a decline of 19% with CT and 9% with NT between 1970 and 1975. Grain yields, which declined along with organic C, have not recovered. Changes in organic matter content, with their many ramifications, are probably the most important long‐term effects of tillage differences on basic soil properties.
Eliminating Nitrate Interference During Kjeldahl Digestion of Soil Extracts for Microbial Biomass Determination
Authors: Wyland L. J. , Jackson L. E. , Brooks P. D.
Published: July 2010

Nitrate interference in Kjeldahl digestion of soil and plant samples presents a significant problem in establishing N budgets in agricultural systems, where NO−3 is frequently abundant. During digestion, NO−3 can be reduced or it can cause volatilization of reduced N, resulting in either over‐ or under‐estimation of Kjeldahl N. A method has been developed to volatilize NO−3 from K2SO4 extracts of soil prior to Kjeldahl digestion for determination of microbial biomass N. Extracts were pretreated with H2O2 and H2SO4 at 97 °C for 48 h, and then were Kjeldahl digested using a procedure modified for microbial biomass extracts. This method volatilizes >99% of NO−3 in K2SO4 extracts, as determined by 15N recovery from spiked samples.
Synthesizing Bulk Density for Soils with Abundant Rock Fragments
Authors: Vincent Kirk R. , Chadwick Oliver A.
Published: July 2010

Bulk density is a fundamental soil property that is difficult to determine for gravelly to extremely gravelly soils because results vary significantly with sample volume. For such coarse soils, the representative volume (for whole‐soil bulk density) should be large, but guidelines for selecting an appropriate sample volume do not exist. We evaluated the representative volume for a soil with abundant rock fragments, by comparing measured properties of samples ranging in volume from 0.03 to 410 L. For whole‐soil bulk density determination, the representative volume is 4 L or larger for a soil horizon containing 34% (v/v) gravel and is between 5 and 50 L for a soil horizon containing 54% gravel. Intact samples of that size are prohibitively large, so we developed an alternative approach that starts with measurement of fine‐earth bulk density. For fine‐earth bulk density, the sample volume needed for representative results is between 0.2 and 1 L for gravelly to extremely gravelly soils. The alternative approach reliably synthesizes whole‐soil bulk density using (i) fine‐earth bulk density from modest‐sized samples, (ii) mass‐size distribution from large (>40 kg) representative disturbed samples, and (iii) rock fragment bulk densities. The mass and volume of rock fragments that should be in a sample are added to the mass and volume used to calculate fine‐earth bulk density. This method allows integration of lateral variability in the soil without the consequence of averaging properties across a large depth range.
Formation of a Transient Magnesium‐Aluminum Double Hydroxide in Soils of Southeastern Ohio
Authors: Smeck N. E. , Saif H. T. , Bigham J. M.
Published: July 2010

To assess the potential for Mg‐Al double hydroxide formation in acid, Al‐rich soils of southeastern Ohio under native conditions, laboratory studies were conducted to determine if Mg‐Al double hydroxide could be produced with Al‐saturated clays and soils of mixed mineralogy common to the region. Aluminum‐saturated clays suspended in dilute Mg solutions and titrated with NaOH to pH 9.5 yielded pronounced buffer regions between pH 8.3 and 8.5 attributable to the formation of Mg‐Al double hydroxide. Equilibration of the clays titrated to pH 9.5 for 55 d showed a gradual decline to pH 8.0 to 8.4. The decline was attributed to the precipitation of additional Mg‐Al double hydroxide caused by the slow release of interlayer hydroxy Al, which showed a correlation with the rate of pH decline. X‐ray diffractograms of the equilibrated clays yielded peaks at 0.78 and 0.39 nm that were indicative of Mg‐Al double hydroxide. Aluminum‐saturated soils equilibrated with Ca solutions at pH 8.4 retained only 50 to 70% as much added cation as soils equilibrated with solutions of combined but equal total quantities of Ca and Mg. Furthermore, the soils equilibrated with Ca and Mg retained 2.4 to 4 times more Mg than Ca. The enhanced retention of Mg was attributed to Mg‐Al double hydroxide formation. Sequential leaching of the equilibrated soils with NaOAc at pH 8.2, 7.0, and 5.0 and 0.05 M HCl indicated that Mg‐Al double hydroxide was not readily solubilized until the pH dropped below neutral. It was concluded that the pedogenic formation of an ephemeral Mg‐Al double hydroxide was a probable consequence of calcareous loess deposition on acid, residual soils during the Wisconsinan glaciation.
Emissions of Non‐Methane Organic Compounds and Carbon Dioxide from Forest Floor Cores
Authors: Hanson P. J. , Hoffman W. A.
Published: July 2010

Forest floor emissions of CO2 and non‐methane volatile organic compounds (NMOCs) were measured to determine their contribution to C losses from forests. Forest floor cores 19 cm in diameter and approximately 10 cm deep were obtained from beneath loblolly pine (Pinus taeda L.), oak‐maple (Quercus‐Acer), and yellow‐poplar (Liriodendron tulipifera L.) trees on the Walker Branch Watershed, Oak Ridge, TN. The cores were enclosed in an open system gas exchange instrument from which inlet and outlet concentrations of NMOC emissions were sampled. The NMOCs were quantified with a C trap/cryofocus/gas chromatography approach. Total NMOC emissions from the forest floor cores ranged from 15 to 90 nmol C m−2 s−1, and differed beneath each tree species. Cores from beneath yellow‐poplar trees had nearly an order of magnitude greater C equivalent efflux than cores from beneath either the pine or oak‐maple trees. Monoterpenes comprised virtually all of the NMOC emissions from the cores. The C equivalent efflux of NMOCs from the forest floor cores was one to two orders of magnitude less than rates of CO2 efflux (4–8 µmol m−2 s−1), indicating a very minor role for litter and soil NMOC emissions in stand C cycling.
Extractable Anions in Soils following Wildfire in a Sagebrush‐Grass Community
Authors: Blank Robert R. , Allen Fay , Young James A.
Published: July 2010

Field and laboratory research was conducted to measure changes in extractable anions following wildfire in sagebrush (Artemisia tridentata Nutt.)‐grass communities. Two sites were studied along the eastern Sierra Nevada front in northeastern California on coarse‐textured Haploxerolls and Haplargids formed from granitic parent materials. Soils were extracted with 0.15% KCl and analyzed with high‐performance anion exchange chromatography. Compared with unburned soils, significant (P ≤ 0.05) decreases in NO−3 and orthophosphate, and significant increases in SO2−4, acetate, formate, oxalate, and glycolate occurred immediately after wildfire in the surface 5 cm of under‐shrub soil. Concentrations of organic acids in burned under‐shrub soils increased significantly (P ≤ 0.05) in the weeks following a wildfire. In shrub interspaces, largely occupied by cheatgrass (Bromus tectorum L.), concentrations of anions were similar in unburned and post‐wildfire soils. Laboratory heating of under‐shrub soil indicated that maximum amounts of KCl‐extractable organic anions are produced at temperatures between 150 and 350°C, and that the length of time (up to 30 min) the soil was exposed to a given temperature considerably affected these amounts. Elevated concentrations of organic acids may influence seed germination, plant establishment, and mineral nutrition.
A Solute Transport Model for the Acid Leaching of Copper in Soil Columns
Authors: Montero Juan Pablo , Muñoz José Francisco , Abeliuk Roberto , Vauclin Michel
Published: July 2010

Modeling solution mining technique has recently received much attention in order to estimate metal recovery rates. We studied the acid leaching of Cu minerals found in mine tailings using a mathematical transport model and lab‐scale experiments on both batches and saturated soil columns. The model is a one‐dimensional macroscopic solute transport model that considers simultaneously (i) the convection, dispersion, and consumption of H2SO4, and (ii) the convection, dispersion, solubilization, and adsorption‐desorption of Cu. Time‐dependent batch experiments were carried out to understand the relationship between H2SO4 consumption and Cu extraction in tailing Cu materials under stagnant conditions. Additionally, miscible‐displacement experiments were conducted to obtain empirical data on Cu recovery in saturated soil columns that receive a constant pulse of H2SO4 and were designed to check the model's capability to simulate the transport phenomena. This was done by estimating the model parameters independently from the batch experiments. Since some findings from both experiments were consistent with each other, modeling assumptions, such as a second‐order kinetic relationship for Cu dissolution (by H2SO4) and a first‐order equilibrium isotherm for Cu, were appropriate in order to simulate the Cu recovery concentration at the outlet of each column. Finally, model equations were solved using finite differences and analytical solutions for Cu and H2SO4 transport equations, respectively, and model parameters were estimated using least squares techniques.
Oxide Surface‐Catalyzed Hydrolysis of Carboxylate Esters and Phosphorothioate Esters
Authors: Torrents Alba , Stone Alan T.
Published: July 2010

Pathways and rates of organic pollutant transformation may be altered through interaction with the surfaces of oxides and other soil minerals. We examined oxide surface‐catalyzed hydrolysis of representative carboxylate esters and phosphorothioate esters. Ester and hydrolysis product concentrations were monitored in acetate‐buffered suspensions containing 10 g L−1 oxide. Carboxylate esters found susceptible to catalysis in this work possess an auxiliary ligand donor group that, along with the carbonyl O group, form a chelate with surface‐bound metal atoms. Esters possessing an O‐donor auxiliary group (e.g., phenyl salicylate) are susceptible to catalysis by Al2O3, TiO2, and FeOOH surfaces. Esters possessing a N‐donor auxiliary group (e.g., phenyl picolinate) are no longer susceptible to catalysis by Al2O3, reflecting the poor affinity of N‐donor groups for Al complexation. Methyl chlorpyrifos is the most susceptible of the three phosphorothioate esters to oxide‐catalyzed hydrolysis; it possesses an auxiliary ligand donor group analogous to the carboxylate esters examined. Methyl parathion and ronnel, which do not possess a suitable auxiliary ligand donor group, are also susceptible to oxide‐catalyzed hydrolysis, indicating that chelate formation is not required in order for surface catalysis to occur. The presence of methanol and acetonitrile cosolvents diminishes the catalytic effect. The widespread use of these cosolvents in fate studies may have caused rates of oxide and mineral surface‐catalyzed hydrolysis reactions to be underestimated.
Organic Phosphorus Effects on Sink Characteristics of Iron‐Oxide‐Impregnated Filter Paper
Authors: Robinson J. Stephen , Sharpley Andrew N.
Published: July 2010

The effect of dissolved organic P (DOP) (p‐nitrophenyl phosphate, sodium myo‐inositol hexaphosphate, and β‐glycerophosphoric acid) on the ability of Fe‐oxide‐impregnated filter paper (Pi test) to act as a sink for dissolved inorganic P (DIP) was investigated. The efficiency of DIP recovery from strips equilibrated with DIP plus DOP was also studied. This information is needed to assess the accuracy of the Pi test to estimate bioavailable P (BAP) in soils and agricultural runoff containing high concentrations of DOP (up to 5 mg L−1). Iron‐oxide strips removed on average 100% DIP and 99% DOP during a 16‐h solution‐strip equilibration at 25°C. Thus, none of the DOP compounds affected the P‐sink characteristics of the Fe‐oxide strip. Recoveries of DIP by 0.1 M H2SO4 and 0.5 M NaOH, from strips equilibrated with DIP plus p‐nitrophenyl phosphate, averaged 95%; with DIP plus β‐glycerophosphoric acid, recoveries averaged 97%. However, amounts of DIP recovered by 0.1 M H2SO4 from strips equilibrated with DIP plus sodium inositol hexaphosphate were greater than those added. As 0.5 M NaOH did not hydrolyze sodium inositol hexaphosphate and DIP recovery averaged 95%, use of NaOH as strip extractant is recommended for soils and runoff samples containing high DOP concentrations.
Determining Root Activity Distribution by Measuring Surface Carbon Dioxide Fluxes
Authors: Ben‐Asher J. , Ephrath J. E. , Cardon G. E. , Phene C. J. , Peters D. , Rolston D. E. , Biggar J. W.
Published: July 2010

Methods for determining root characteristics and distributions are time consuming and tedious. Indirect approaches could decrease the effort required to obtain information on root distributions. The objectives of this study were to measure soil surface CO2 flux and to relate these measurements to root properties. Two chambers to measure CO2 fluxes at the soil surface were tested for use in root activity studies. One chamber was a 0.75‐L cylinder and the other was a 7.1‐L cubic chamber. The bottom edges of both chambers were inserted 1 to 2 cm into the surface soil. The increase in CO2 concentration in the chambers was measured with infrared gas analyzers. The following were used to evaluate the applicability of the approach for root studies: (i) test of the relationship between CO2 surface fluxes and root characteristics (length, area, mass, and number) in the root zone of a mature almond (Prunus amigdalus Batsch. cv. Butte) orchard and a corn (Zea mays L.) field, and (ii) evaluation of temperature and solar radiation effects on CO2 soil surface flux. The results showed that surface CO2 fluxes were proportional to the logarithm of root characteristics, i.e., large changes in root characteristics were associated with small changes in flux. Soil temperature had a distinct effect on measured CO2 surface flux. There was a clear diurnal cycle for soil surface CO2 flux, which peaked near solar noon and maximum solar radiation. Acceptable correlations between the major root characteristics and surface CO2 flux suggest that this approach can provide vital information on root activity.
Clay‐Fixed Labeled Ammonium as a Source of Available Nitrogen
Authors: Feigenbaum Sala , Hadas Aviva , Sofer M. , Molina J. A. E.
Published: July 2010

In soils low in organic matter but high in clay mineral content, the fixation and release of NH4 by soil clay may have a significant impact on available N, in addition to the organic N. The objective of this work was to evaluate the contribution that nonexchangeable NH4, newly fixed by clay minerals, may have in KCl‐extractable N in soil. The source of clay‐fixed NH4 was beidellite clay equilibrated with (15NH4)2SO4 and then washed with either KCl or CaCl2 solutions. Two calcareous soils were mixed with differently treated beidellite at a 2:1 ratio, mixed with sand, and incubated for 56 d at 30°C and 60% of water‐holding capacity. Periodically, NH+4 and NO−3 extractable in 1 M KCl and their 15N abundance were determined. Controls for each beidellite treatment were incubated without soil. Concentrations of KCl‐extractable N were considerably higher when beidellite was saturated with Ca than when it was saturated with K throughout the experiment. They increased with time in the presence of soil and remained unchanged in the controls. The recovery of beidellite‐15NH4 as KCl‐extractable N in soil showed a continuous release of clay‐fixed NH4 from K‐beidellite, from 4.8 and 6.5% of added NH4 at 1 d to 10.2 and 12.5% at 56 d in the two soils. The recovery of N from Ca‐beidellite was approximately 30% of added N already at 1 d, but the change with time was inconsistent in the two soils. The difference in the release of N from Ca‐saturated beidellite compared with that of K‐saturated beidellite was attributed to incomplete collapse of the mineral lattice in the Ca‐saturated clay, which enabled renewal of exchangeable NH4 and rendered the interlayer nonexchangeable NH4 more accessible to exchange with K or to biological activity. In K‐saturated clay, the interlayer nonexchangeable NH4 was trapped and, consequently, the release was slow.
Spatial Variability in Alluvium Properties at a Low‐Level Nuclear Waste Site
Authors: Istok J. D. , Blout D. O. , Barker L. , Johnejack K. R. , Hammermeister D. P.
Published: July 2010

Geological and statistical models for the spatial variability of soil properties are needed to predict field‐scale water flow and solute transport but only limited information is currently available on unsaturated soils below the root zone. Spatial variability of selected physical and hydrologic properties was quantified for fine‐ and coarse‐grained alluvial deposits at a low‐level nuclear waste disposal site on the Nevada Test Site. Gravimetric water content (w), bulk density (ρb), saturated hydraulic conductivity (Ks), and particle‐size distribution were determined for vertical and horizontal core specimens and bulk samples collected from 183‐m‐long horizontal transects in two existing waste disposal trenches located on a single alluvial fan. The transects were approximately aligned parallel and perpendicular to the principal direction of sediment transport. Properties were modeled as either normally or lognormally distributed random variables. Sample coefficients of variation were smallest for ρb and largest for log(Ks); a weak correlation was identified between log(Ks) and the grain‐size parameter d10. Particle‐size distributions for the fine‐ and coarse‐grained materials were different and significant differences in the natural logarithm of saturated hydraulic conductivity, log(Ks), existed between coarse and fine layers in an excavation aligned with the principal direction of alluvium deposition but not in a perpendicular direction. Differences in log(Ks) for vertical and horizontal cores were not significant. Sample variograms were described by combinations of pure nugget and spherical model structures with correlation lengths ranging from <2 to 61 m.