摘要:

We measured hydraulic conductivity (saturated and unsaturated) on 127 soil cores, which were taken in different horizons of a wide variety of Belgian soil series. The hot air method (Arya et al. 1975) and the crust method (Bouma et al. 1983) were combined to obtain the complete range of hydraulic conductivity from saturation to air-dry.The textural composition in nine fractions, the organic carbon content, and the dry bulk density were determined for each of the sample horizons as well. Four different empirical models were evaluated on their performance in describing the measured hydraulic conductivity curves. The model parameters were estimated by linear and nonlinear regression techniques. It is concluded that the Gardner equation (1958) with three parameters best described the hydraulic conductivity for the given soils.Regression equations for estimating the Gardner parameters were established from simple soil properties, such as soil texture, carbon content, bulk density, and saturated hydraulic conductivity. We found that the three parameters can reasonably well be estimated from the textural composition and the saturated hydraulic conductivity. A one-dimensional sensitivity analysis indicates that the n parameter, representing the slope of the hydraulic conductivity pressure head relation in log-log scale, is most sensitive.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

In a Lagrangian material coordinate system, flow in a saturated swelling soil or slurry is governed by a nonlinear convection-diffusion equation. Analysis of the Lagrangian diffusivity function shows that typically, at moderate moisture levels, diffusivity depends weakly on moisture content though, at high moisture contents, it decreases strongly. In either case exact solutions may be found for some relevant analytic flow models. One of the spin-offs of these exact solutions is the direct analytic prediction of the time to incipient ponding under conditions of constant water supply rate, thereby extending previous analytic estimates that applied only to rigid porous media.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

The objective of this research was to improve upon current models used to predict the transport of nonsorptive solutes in the subsurface environment. We surveyed previous modeling efforts, including the familiar convection and dispersion equations, the micropore-macropore model, and the mobile-immobile zone model. The proposed model is a modification of an existing mobile-immobile zone model, which includes theoretical relationships useful in relating the process variables to each other. We verified some of these relationships with results of experimental studies in which tritiated water was used as a tracer in columns packed with selected sorbents. In addition, the model was used to successfully predict the results of other experiments in which the flow rate and column height were changed.According to our model, molecules of nonsorptive chemicals are transported by convective and dispersive mechanisms in the mobile zones and by random molecular diffusion in the immobile zones, where molecules in general are considered to move either toward the soil surface or toward the mobile zones. The flow in these forward and backward directions is a first-order process with two different rate constants. Also, partitioning of fluids between mobile and immobile zones is dependent on several variables, such as flow velocity, fluid viscosity, and soil-specific surface area. Although fitting individual break through curves can be accomplished by other models, our approach can be used to predict the transport of nonsorptive solutes under a variety of experimental conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Continuous fertilization for 40 years with N and P resulted in significant changes in soil pH, lime requirement, organic matter, Bray and Kurtz no. 1 P, and DTPA-extractable micronutrients. A pasture soil receiving up to 224 kg N.ha-1as ammonium nitrate and 45 kg.ha-1as superphosphate since 1946 was analyzed for soil test values as a function of depth. Soil pH values were observed to decrease when N applications exceeded plant requirements. In plots receiving continuous additions of 224 kg.ha-1, the pH decreased from 6.5 to 4.1. The lime requirement of the soils reflected pH changes. Organic matter was found to be unaffected by P fertilization, but increased with increasing N rate. Bray and Kurtz no. 1 P concentrations were extremely high in the surface 10 cm of P-fertilized plots, and increased concentrations were observed to a depth of 60 cm. DTPA-extractable Fe was negatively correlated with pH, and increased DTPA-Fe was observed to a depth of 20 cm. DTPA-Mn also tended to increase in soils with lower pH, and both total and DTPA-extractable Mn appeared to have leached from the 0− to 10-cm to the 10− to 20-cm increment in soils receiving the highest rate of N application. A strong interaction of N, P, and depth was observed for DTPA-Zn, but DTPA-Cu was unaffected by fertilization. In 1965, the plots were split, with one-half of each plot continuing to receive fertilizer and the other half having the fertilization permanently discontinued. The soil pH, lime requirement, Bray and Kurtz no. 1 P, and DTPA-extractable Fe and Mn all showed a significant response to discontinuation of fertilizer additions. The pH tended to increase, whereas the lime requirement, Bray and Kurtz no. 1 P, and DTPA micronutrients decreased during the 20 yr without fertilizer.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

The distribution of added potassium (K) in soil K forms (water-soluble, exchangeable, and nonexchangeable) as a function of clay mineralogy and taxonomy was determined using 102 soils from the continental United States and Puerto Rico, representing 10 soil orders. The soils were divided into three groups (kaolinitic, mixed, and smectitic) based on dominant clay mineralogy. A linear increase in water-soluble, exchangeable, and nonexchangeable K content of each soil was obtained after a 25-wk incubation with K (0 to 250 mg K kg-1). Slopes of these relationships represent water solubility (S), exchangeability (E), and fixation (F) indexes, with a significant decrease in S and increase in E and F observed from kaolinitic to mixed to smectitic soils. The indexes were closely related (r2= 0.75 to 0.96) to clay content for each group of soils. The K buffer capacity (KBC) was significantly greater for smectitic than mixed and kaolinitic soils and was closely related to clay, CEC, and K saturation for each group of soils. Using the relationship between clay content and S, E, F, and KBC, the distribution of fertilizer K in an independent set of 60 kaolinitic, mixed, and smectitic soils and published data was closely estimated. Differences in these relationships between each group of soils were consistent with K reaction mechanisms of the dominant clay minerals. Use of these relationships may allow prediction of fertilizer K disposition in soils of differing taxonomic and mineralogical properties and, thus, aid fertilizer K recommendations for certain soils.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Our objective was to determine the efficacy of surfactants as secondary recovery agents to enhance drainage from a previously dewatered sand column. Seventeen surfactants at concentrations of 0, 0.01, 0.1, 1.0, 10.0, and 100 g (solid) or ml (liquid) surfactant per liter of water were evaluated. Anionic, cationic, and nonionic classes of surfactants were represented. Surfactant solutions (150 ml) were added to the top of dewatered sand columns (0.1-m diameter by 0.5-m length), and column outflow was measured. Each treatment was replicated four times. Between surfactants additions, columns were cleaned with 500 ml of methanol and 750 ml of tap water. Outflow significantly increased as the log of surfactant concentration increased, but no surfactant class was significantly more efficient than any other class. Surface tension was significantly correlated with log of concentration (-0.73) and outflow (-0.42). This indicated that decreases in surface tension are associated with increases in column dewatering. Outflows from the less than 1 g or ml surfactant per liter of water treatment were not significantly different from the blank (no surfactant). Surfactant chemistry was additionally evaluated using several Igepal DM surfactants with differing numbers of ethyleneoxy (EO) units. Maximum outflow occurred at EO ratios of 15.3, indicating that surfactant chemical structure is also important. The high concentration of surfactant required to show significant benefits (1 g or ml per L) probably precludes use of surfactants as secondary recovery agents for water.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Soil microbial volatilization of selenium (Se) has been addressed as a potential bioremediation technique for saline Se-contaminated soils. The objective of this study was to determine the effect of salinization upon the addition of Na2SO4, NaCl, and CaCl2, up to 20 dS m-1, on the methylation of Se in soil. Los Banos, Panoche, and Panhill soils were amended with salts and 100 mg kg-1of labeled Se(IV) and incubated in a continuous air exchange system. Volatile Se was trapped on activated carbon and quantified radiometrically. Cumulative Se evolution over 34 d was inhibited from 0.6 to 73.0% at 20 dS m-1, depending on the soil series and salt species. In most cases, sodium salts exerted a stronger inhibitory effect than the calcium salts. Low levels of NaaSO4and CaCl2stimulated Se volatilization from the Panhill soil. Kinetic analyses were conducted in modeling the velocity of Se methylation from the experimental data using a nonlinear least-square method. The Seo(Se volatilization potential) ranged from 8 to 78 mg kg-1soil, with k (Se volatilization rate coefficients) ranging from 0.007 to 0.057 d-1. The rate coefficients were reduced by an average among soils of 16.8, 18.3, and 24.3%, by applying Na2SO4, NaCl, and CaCl2, respectively, at 20 dS m-1.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID