Soil Science Society of America Journal
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Simulation of Profile Water Storage as Related to Soil Hydraulic Properties Abstract A previously published numerical model of soil‐water dynamics was used to simulate the separate and combined processes of infiltration, drainage, and evaporation, as determined by hydraulic properties. Three hypothetical soils were compared: sand, loam, and clay. Typical soil moisture characteristic functions were assigned to each, and the respective hydraulic conductivity functions were calculated. Uniform profiles of these soils were then subjected to various sequences of rainstorms and dry periods. The sandy soil provided the least evaporation and the most rapid downward flow. This resulted in the most effective storage under a relatively dry regime. The situation was reversed in the case of the clay soil, which stored the most water under a relatively wet regime, while the loam exhibited intermediate behavior. Some consequences of this pattern affecting arid zone ecology are discussed.
Soil Science Society of America Journal - Tập 40 Số 6 - Trang 807-815 - 1976
Estimating Bulk Density from Organic‐Matter Content in Some Vermont Forest Soils Abstract A close relationship between organic‐matter content and bulk density was found in the acid till forest soils of the Green Mountains of Vermont. Reasonably good estimates of bulk density can be made from determinations of organic matter content. Thus, the difficulties of direct determination of bulk density in these stony soils can be avoided. A method of determining bulk density, including a correction for stone content, is described for use in these stony soils.
Soil Science Society of America Journal - Tập 28 Số 2 - Trang 285-286 - 1964
Slope Length Effects on Soil Loss for Steep Slopes Empirical soil erosion models continue to play an important role in soil conservation planning and environmental evaluations around the world. The effect of hillslope length on soil loss, often termed the slope length factor , is one of the main and most variable components of any empirical model. In the most widely used model, the Universal Soil Loss Equation (USLE), normalized soil loss, L , is expressed as a power function of slope length, λ, as m , is 0.2, 0.3, 0.4, and 0.5 for different, increasing slope gradients. In the Revised Universal Soil Loss Equation (RUSLE), the exponent, m , is defined as a continuous function of slope gradient and the expected ratio of rill to interrill erosion. When the slope gradient is 60% and the ratio of rill to interrill erosion is classified as moderate, the exponent m has the value of 0.71 in RUSLE, as compared with 0.5 for the USLE. The purpose of this study was to evaluate the relationship between soil loss and slope length for slopes up to 60% in steepness. Soil loss data from natural runoff plots at three locations on the Loess Plateau in China and data from a previous study were used. The results indicated that the exponent, m , for the relationship between soil loss and the slope length for the combined data from the three stations in the Loess Plateau was m was greater for intense storms than for less intense storms. These experimental data indicate that the USLE exponent,
Soil Science Society of America Journal - Tập 64 Số 5 - Trang 1759-1763 - 2000
Surface Clogging in an Intermittent Stratified Sand Filter Accumulation of biomass and deposition of suspended solids at the surface of a sand filter can lead to clogging of the filter media. A laboratory intermittent sand filter column, which included three sand strata, was operated for a period of 806 d before failure occurred through surface clogging. Upon dismantling the column, the cause and effects of the surface clogging were investigated. The main mechanism responsible for sand clogging appeared to be biomass buildup. Maximum loss on ignition of filter media samples was 2.35%, and it occurred in the upper 0.01 m of the sand. There was a reduction in field‐saturated hydraulic conductivity in the top 0.01 m of the upper sand stratum from a value of 1.9 × 10−3 ± 1.7 × 10−4 m s−1 (for virgin sand with an effective size, d 10 , of 0.45 mm) to 3.5 × 10−5 ± 7.5 × 10−6 m s−1 The soil‐water characteristic curve, which relates the volumetric water content (θv ) to the soil suction, also reflected the changes in the filter media due to clogging. The water‐holding capacity greatly increased as biomass accumulated in the filter media. Scanning electron microscopy (SEM) confirmed the existence of a clogging organic layer on the surface of the top sand layer.
Soil Science Society of America Journal - Tập 68 Số 6 - Trang 1827-1832 - 2004
Numerical Evaluation of Static-Chamber Measurements of Soil-Atmosphere Gas Exchange: Identification of Physical Processes
Soil Science Society of America Journal - Tập 60 Số 3 - Trang 740-747 - 1996
Routine Procedure for Rapid Determination of Soil Carbonates Abstract A procedure is presented for the routine determination of soil carbonates based on the following reaction: CaCO3 + 2 HC2 H3 O2 → Ca2+ + 2 C2 H3 O2 ‐ + H2 O + CO2 (g) A known quantity of acetic acid is added to a known quantity of soil. The pH of the reaction mixture is then determined following complete dissolution of CaCO3 . Calcium carbonate content is determined empirically from a standard curve relating pH to known CaCO3 content according to the equation: pH = K + n log [CaCO3 /(T − CaCO3 )], in which T equals the total amount of calcium carbonate which could be completely dissolved by the acetic acid added to the system, and K and n are constants. Several possible sources of error exist in the procedure; however, potential errors may be minimized by the maintenance of optimum working conditions. Results obtained by the acetic acid procedure compared favorably with results obtained by the Chittick procedure. The proposed procedure has the advantage of simplicity and offers a rapid alternative for routine determination of soil carbonates.
Soil Science Society of America Journal - Tập 48 Số 5 - Trang 1030-1033 - 1984
Soil Salinity Using Saturated Paste and 1:1 Soil to Water Extracts Saturated paste (SP) and 1:1 soil/water extractions (1:1) are commonly used to assess soil salinity for field remediation. Correlation of electrical conductivity (EC) and other analytes between the SP and 1:1 extraction methods have been documented, except the relationships were based on limited soil types and require further examination to be adequately evaluated. This study examined these relationships using 170 soils from petroleum and agriculture production sites. Saturated pastes and 1:1 extracts were prepared and analyzed for EC, major cations (Na+ , K+ , Mg2+ , Ca2+ ), and major anions Cl− , SO4 2− Relationships of all analytes were established between the two methods using linear regression. Saturated paste extract EC (ECSP ) was highly correlated with that of 1:1 extract EC (EC1:1 ) (r 2 = 0.85, P < 0.001). Significant relationships also existed (r 2 > 0.73, P < 0.001) between different ions in SP and 1:1 extracts. An independent validation set of 22 soils showed that the slopes of the regressions between predicted EC, Na+ , and Cl− of SP equivalents from 1:1 extract measurements and direct SP extract measurements were very close to 1.0 suggesting that the regressions developed can accurately assess soil salinity in salt affected soils using 1:1 extract analysis instead of using the more expensive and time‐consuming SP extraction.
Soil Science Society of America Journal - Tập 69 Số 4 - Trang 1146-1151 - 2005
Soil Sorption of Nickel: Influence of Solution Composition Abstract Sorption/desorption isotherms were used to evaluate the effects of solution composition on the retention of nickel (Ni) by soils of varying physical and chemical properties. Soils examined included agricultural soils of New Mexico, as well as soils from potential chemical waste disposal sites. Sorption of Ni from 0.01N CaCl2 was extensive for all samples: more than 99% of added Ni was sorbed in some cases. Desorption in 0.01N CaCl2 was slight (extreme hysteresis). Ability to extract sorbed Ni with diethlyenetriaminetetraacetate (DPTA), however, indicated that Ni sorption was not completely lrreversible. Increasing the CaCl2 concentration to 0.1N lowered Ni sorption by up to 40%. This was due primarily to direct sorption competition by Ca, rather than to increased Ni‐Cl complex formation, as shown by parallel experiments using Ca(ClO4 )2 . Presence of small amounts of ethylenediaminetetraacetate (EDTA) in the equilibrating solution lowered Ni sorption by up to 98%. The extent of the chelate effect depended upon whether EDTA was present in the Ni solution before or after contact with soil.
Soil Science Society of America Journal - Tập 45 Số 5 - Trang 860-865 - 1981
Kinetics of Fixation of Iron and Zinc Applied as FeEDTA, FeHDDHA and ZnEDTA in the Soil Abstract The disappearance of zinc and iron from soil solution after their addition as soluble metal chelates is attributed to adsorption and fixation. The value of the adsorption coefficient, Kd , was estimated from a batch experiment but because of the inaccuracy involved they were evaluated from the breakthrough curves of column experiments using Rehovot sand. FeEDDHA was neither adsorbed nor was its iron fixed by the soil to any significant extent. The fixation of iron applied as FeEDTA was found to be a first order reaction. Assuming that the fixation reaction kinetics is similar in both the solution and the solid phase, then the reaction rate constant can be expressed as k = (k 1 θ + k 2 ρKd )/(θ + ρKd ), where k 1 and k 2 are the reaction rate constants in the liquid and solid phases, respectively. θ is the volumetric water content and ρ is the bulk density. By using 5 different soil/water ratios, the values of k 1 and k 2 were found to be 0.0096 h‐1 and 0.087 h‐1 , respectively. The value of k was also estimated from the breakthrough curve in a column experiment by using the relative effluent concentration under steady state condition (C/Co )s The adsorption of ZnEDTA was negligible under the present experimental conditions. Thus k = k 1 and is independent of the water content and bulk density. This was shown by comparing the results of the two experimental techniques. The value of k 1 thus found was 0.084 h‐1 . The first order model of the fixation reaction of zinc applied as ZnEDTA is applicable for time periods up to 8 to 10 hours.
Soil Science Society of America Journal - Tập 39 Số 1 - Trang 55-58 - 1975
Effect of pH and Redox on Predicted Heavy Metal‐Chelate Equilibria in Soils Abstract Metal‐chelate stability diagrams were developed as a function of pH and redox to predict the behavior of DTPA, EDTA, CDTA, EGTA, and HEDTA in soils. The metals evaluated include H+ , Fe3+ , Fe2+ , Al3+ , Mn2+ , Ca2+ , Mg2+ , Zn3+ , Cu2+ , Cd2+ , Pb2+ , and Ni2+ . In acid systems, Ni2+ at 10−5 to 10−7 M was the predominant ligand species for all chelating agents. Similar results were obtained in alkaline systems when NiCO3 controlled Ni2+ solubility. In the absence of Ni2+ , either Cd2+ or Pb2+ ligand species dominated at alkaline pH for all chelating agents. In acid systems, Cu, Pb, Fe, and Zn are the major chelated species. In acid soils, the chelating agents EDTA, EGTA, and HEDTA deserve further study as extractants for metals and as reagents for determining metal ion activities through competitive equilibria. The results identify ligands which may be useful in determining various metal ion activities in soils. The DTPA soil test appears to have a sound theoretical basis for evaluating plant available Pb, Cd, and Ni in soils.
Soil Science Society of America Journal - Tập 43 Số 1 - Trang 39-47 - 1979
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