摘要:

Using an instantaneous profile (IP) method we generated in situ distributions of volumetric water content, &thetas;(z, t), and water suction head,h(z, t), in two field profiles of Candler sand during a cycle of soil-water redistribution. With these data, we then calculated hydraulic conductivity,K, values over the narrow suction head range 0 <h< 80 cm of water. Field-determined values for saturated hydraulic conductivity,Ko, exceeded 100 cm h−1for this very coarse-textured soil.Values ofKdetermined by the IP method were used to evaluate two methods commonly used to predict unsaturated hydraulic conductivity. The two methods utilized field-determined soil-water characteristic curves, &thetas;(h), experimentally determined values of saturated hydraulic conductivityKo, and Poiseuille's equation for flow in cylindrical soil pores to calculate unsaturated hydraulic conductivity. For values of &thetas; > 0.10 cm3cm−3andh< 40 cm of water,Kvalues predicted by each of the methods agreed well with values determined in situ by the IP method. However, for lower water contents (i.e., &thetas; < 0.10 cm3cm−3), values ofKdetermined by both predictive methods overestimated those obtained by the IP method.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The infiltration equation with a time-dependent surface flux is solved numerically for nonlinear conductivities, using first-integral and shooting techniques. The diffusivity and conductivity are both taken as power laws. The relative accuracy of the numerical technique is obtained by comparison with the case of linear conductivity, where an exact analytical solution exists. An approximate analytical result is given and compared with the solution for nonlinear conductivities from the shooting technique. It is found that the approximate analytical result is an excellent approximation to the exact numerical solution. It is also suggested that the solution obtained here can be used to validate the numerical solution of Richard's equation for arbitrary soil properties and arbitrary boundary conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A kinetic-mechanistic model is P sorption in calcareous soils was developed. Model construction was based on batch sorption experiments in which three forms (phases) of sorbed P were defined: Pwe, water-extractable sorbed P; Pbic, bicarbonate-extractable sorbed P; and Pn, nonextractable sorbed P. The form Pwewas associated with equilibrium sorption and described by a Freundlich-type equation. Pbicwas shown to consist of a fast, irreversible sorption term and a time-dependent precipitation reaction of slightly soluble Ca-P compounds (e.g., DCPD, DCP, or OCT). Pnswas also shown to consist of a fast sorption term and a time-dependent term associated with precipitation of sparingly Ca-P compounds, e.g., HA. The precipitation reactions in the calcareous soil were assumed to be controlled by the Ca-P-CO2system.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

This paper describes a method by which the antimony in soil samples can be determined spectrophotometrically, employing 3,5-br2-PADAP and emulsifier OP. The optimum acidity of the color reaction is in the range of 0.12 to 0.25Mhydrochloric acid. The blue-green complex formed exhibits an absorption maximum at 630 nm with a molar absorptivity of 5.2 × 104L. mol−1cm−1. Beer's law is obeyed in the range of 0 to 25 μg of antimony per 10 ml of solution. The effect of experimental variables and interferences of foreign ions are reported. The digestive method of soil samples has also been studied. The method has been successful for determining antimony in soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We conducted laboratory experiments to determine urea-N transformations in four rice soils maintained under oxidized and reduced conditions. Urea hydrolysis rates differed significantly between oxidized and reduced soil suspensions. Urease activity showed considerable variation with flooding, and for three soil suspensions hydrolysis rates were faster under aerobic conditions. Urea hydrolysis followed first-order kinetics, and rate constants in oxidized acid soil suspensions ranged from 0.054 to 0.094 h−1(t1/2= 7.4 to 13.8 h) and under reducing conditions from 0.028 to 0.062 h−1(t1/2= 11.2 to 24.8 h) after urea application of 50 μg N g−1soil. For the calcareous soil, disappearance of urea was faster under a reducing environment (0.403 h−1), compared with the oxidized rate (0.369 h−1). Ammonium production under reducing conditions ranged from 0.50 to 4.74 μg NH4+-N g−1h−1, and nitrification in oxidized soil suspensions showed a significant linear relationship over initial sampling periods, and rates ranged from 0.16 to 0.72 μg NO3−-N g−1h−1.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Residual quantities of methyl salicylate, sprayed on sand, red loam, and heavy loam soils, were estimated by measuring evaporation rates in a laboratory simulation setup.Methods for homogeneous dissemination of liquid on the surface and for controlling and measuring droplet size and surface concentration were developed. A flow system was built for measuring the time dependence of the vapor concentration in a wind tunnel, at various flow rates.Our experiments have demonstrated that the efficiency of soil spraying is affected by droplet size—the highest residuals were obtained with the biggest droplet diameter.It is clear, however, that the final determination of the optimal droplet size is a function of soil type and agricultural requirements.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Extensive areas of cultivated soil develop crusts that impede seedling emergence. In a laboratory study, we tested the effectiveness of several polymer types and a latex emulsion for enhancing seedling emergence, reducing crust hardness, and improving aggregate stability. Guar (G) and polyacrylamide (PAM) polymers, which were either cationic (C), nonionic (N), or anionic (A), were investigated at applied solution concentrations of 0, 10, or 50 mg L−1. Arlington soil (coarse-loamy, mixed, thermic Haplic Durixderalfs) was used. In the first experiment, both A-PAM and C-G (first letter refers to the charge and the second to the polymer type) significantly (95% confidence level) increased the number of cotton seedling emergence as compared with the control. A-PAM provided for higher seedling emergence than C-G. The penetrometer resistance was in the order: control > C-G > A-PAM, whereas the aggregate stability was in the opposite order. In a second experiment on tomato seedling emergence, penetrometer resistances were in the general order: control > latex > A-G > others, which were about equal. The average tomato seedling emergence was considerably higher for the polymer-treated soil than for the control, but variability precluded the establishment of significant differences between the treatments. The third experiment investigated treatment effects on penetrometer resistance and aggregate stability without seedling emergence. The aggregate stability was in the order: N-PAM > A-G > A-PAM = C-G = N-G = latex > control. When latex was excluded, an inverse relationship (r2= 0.73) was found between aggregate stability and penetrometer resistance. Treatments did not affect evaporation from the soil in any of the tests.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Clayey Spodosols and Andisols showing a biosequential relation occur in the Shimokita Peninsula, northeastern Japan. The Spodosols appear only in association with the Hiba tree (Thujopsis dolabratavar.HondaiMakino), a strong podzolizer, at elevations of 150 to 300 m. They show remarkable eluviation and illuviation and chemical and mineralogical properties common to most Spodosols. We classified them as Haplorthods and Placorthods. Haplorthods do not satisfy the morphological spodic criteria, but the chemical spodic criteria are satisfied when (Fep + Alp)/% clay ≥ 0.1 is employed. Although Placorthods have an albic horizon and a placic horizon, they do not meet the chemical spodic horizon criteria.The Andisols do not have such thick, dark A horizons as those formed under Japanese pampas grass vegetation in northeastern Japan because they are formed under broad-leaved tree vegetation. However, they also show unique properties common to most Andisols in Japan and meet the andic soil properties. We classified them as alic and typic Andisols. The former contain a significant amount of KCl-extractable Al.The transition of Spodosols to Andisols was observed to be caused by the conversion of Hiba vegetation to broad-leaved tree vegetation. Changes in the morphological, chemical, and mineralogical properties are taking place accordingly.It is very important to examine both the morphological and chemical spodic criteria and the implications of the unique parent material of ash-derived Spodosols. The separation of ash-derived Spodosols and Andisols should also be critically studied.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We present a rapid numerical solution for vertical, transient flow of water in unsaturated soil. The model is labeled the moving mean slope model (MMS model), because it uses the slope of the natural log of the hydraulic conductivity (K) versus soil-water potential (ψ) curve as a dynamic parameter. The MMS model is developed from a model for flow in homogeneous, relatively wet soils presented by Wind and von Doorne (1975). The model can simulate transient flow in homogeneous and heterogeneous soils correctly for any rang e of soil-water content. This has been validated against semianalytical solutions and solutions obtained with traditional finite-difference and finite-element models. A Courant number analysis method is presented to make direct comparisons of criteria for avoiding numerical errors for the MMS model compared with traditional finite-difference models. For coarse-textured soils, the MMS model uses about the same computer time as the traditional finite-difference and finite-element models. For soils ranging from fine-textured to medium-textured, the MMS model is one to several orders of magnitude faster than the traditional numerical models.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Chlorsulfuron was applied conventionally in the fall and over snow-covered winter wheat in an aqueous suspension with graphite powder and urea ammonium nitrate in February and March to determine downslope herbicide movement in runoff. Plots were established in fields with slopes of 8 to 14%. Snow depth during winter application ranged from 20 to 60 cm. Soil samples collected in the spring 0.6, 0.9, 1.5, 2.4, 3.7, 5.2, 7, and 9.1 m downslope from each treated plot were analyzed using a lentil bioassay technique to determine the presence of herbicide. Chlorsulfuron residues were detected as far as 3.7 m down-slope from plots. Less downslope herbicide movement occurred when chlorsulfuron was applied with graphite over snow than when applied as a conventional fall treatment. If herbicide is applied over snow without graphite, significant amounts may be lost as a result of erosion.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID