摘要:

The hydrodynamics of a sphere moving through a viscous liquid inside a slit is discussed. The effects of the walls are approximated by an image method. The correction of the diffusion coefficient of the sphere depends on the ratio of the slit width and the radius of the sphere. The theory is applied to the self-diffusion of water in swollen clays. Using the Stokes radius of a water molecule, the wall effects partially explain the reported decrease of the self-diffusion in thin interlamellar water layers. The residual decrease corresponds to the immobilization of a small amount of water, of the order of half a monolayer at the clay-water interface. This is about equal to the commonly assumed hydration of the exchangeable cations. The present interpretation of available data implies that there is no significant increase of the viscosity of the remaining interlamellar water and that there is no significant viscoelectric effect near charged clay surfaces.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Equations representing the relationship between water content and suction were derived theoretically on porous bodies having developed structure, using a previously published model.The resulting equations showed the curves on which the minimum fraction of the total apparent water volume, which is retained in dimensionless suction rangeHtoH+ ΔHor logHto logH+ Δ logH, appeared at a certain suction by the effect of the pore structure factor.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

The occurrence of blue-green algae in cultivated and noncultivated soils in Whitman County, Washington, was studied over a 12-month period.NostocandAnabaenawere found in the soils,Nostocbeing ubiquitous. Microbial enumeration was by the most-probable-number method. Moisture and temperature were recorded on each sampling date, while climatic and agronomic events were noted and chemical properties estimated for four soil series. The infrequent occurrence and low densities of blue-green algae in the soils make improbable any assumption that nitrogen input by blue-green algae is significant in this region. Rapid loss of surface soil moisture, seasonal climatic fluctuations, slightly acid soils, and agricultural practices were probably the major reasons why greater numbers and diversity of blue-green algae were not observed on cultivated soils, while uncultivated soils supported more kinds and numbers.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

In the greenhouse at Haryana Agricultural University, we studied the effect of various sources and levels of zinc with sulfur on the yield, uptake, and utilization of sulfur. Sulfur was applied at 0, 40, 80, and 120 ppm as K2SO4, and zinc was applied at 0, 5, and 10 ppm as ZnCl2, Zn-EDTA, and Zn-Rayplex. Application of S up to 80 ppm increased dry matter and grain yield significantly. Zn-EDTA was found superior to ZnCl2and Zn-Rayplex in increasing dry matter and grain yield of soybeans. Zinc application at 5 ppm gave the highest dry matter and grain yield. Application of 120 ppm S significantly increased total S and fertilizer S concentration in all plant parts. There was no effect of Zn sources on concentration and uptake of S. The uptake of total and fertilizer S generally increased up to 80 ppm S and 5 ppm applied Zn. The effects of S $ Zn levels and S ± Zn sources on total S uptake revealed that 80 ppm S + 5 ppm Zn and 80 ppm S with Zn-EDTA gave higher S uptake over other treatments at 45 and 110 days. Percentage of utilization of fertilizer S and S removed from soil decreased with increasing levels of S and increased with increasing levels of Zn at 45 and 110 days. More than 50 percent S had been absorbed at 45 days by the crop. At maturity (110. days) the amounts of fertilizer S retained at the 80-ppm-S level were 26.97, 17.82, 15.38, and 40.82 percent in leaves, stems, pod husks, and grain, respectively.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Investigations to find out the effect of sulfur (S), phosphorus (P), and molybdenum (Mo) application on the concentration and uptake of P by soybean, cv. Bragg, were conducted at Haryana Agricultural University. In greenhouse experiments on soil deficient in S and P, S was applied at 0, 40, 80, and 120 ppm as K2SO4, and P was applied at 0, 40, and 80 ppm, as Ca(H2PO4)2. The application of S showed a synergistic effect on the concentration of P to a certain level of applied S in different plant parts of soybean. The application of P up to 80 ppm increased the P concentration significantly, but Mo application produced an antagonistic effect and significantly depressed P concentration in leaves, stems, pod husks, and grains of soybean. Total uptake of P at both sampling stages increased significantly with 40 and 80 ppm applied S and P, but application of Mo decreased P uptake at maturity. The application of S, P, and Mo affected the concentration of P in various plant parts at both stages of crop growth. The concentration of P in 45− and 110 day-old leaves gave significant positive correlation with P uptake and grain yield.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

A greenhouse experiment was conducted with an acid soil, with and without lime, pretreated with cadmium at rates up to 10.0 micrograms per gram of soil in factorial combination with low to high amounts of copper, nickel, and zinc. The treated soils were placed in sealed pots, flooded, and cropped to rice under flooded management to have a measure of Cd availability at low addition rates, as influenced by low to high addition rates of Cu, Ni, and Zn under unlimed and limed conditions. Yield of rice grain was related to metal treatments and soil pH through multiple regression analysis. The most significant equation revealed the parameters influencing grain yields to be only soil pH and the Cu addition rate (combining the unlimed and limed soil experiments). Disregarding the high Ni treatment, we found the Cd content of rice grain to be dependent upon the Cd addition rate and soil pH only; additions of Cu, Ni, and Zn had no significant effect on Cd uptake and accumulation in rice grain. The maximum permissible Cd addition rate was found to be strongly pH dependent.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We studied the physical properties of some eroded soils of the rain forest and savanna zones of southeastern Nigeria. These soils were on slopes of 4 to 22 percent, and the degree of erosion varied from very slight to catastrophic. Texturally, the top soils were sand and loamy sand, and most profiles were uniform to considerable depths. Their total porosities ranged from 40 to 61 percent, macropores constituting 35 to 60 percent of these. Infiltration rates ranged from 10.1 to 357.1 centimeters per hour, and saturated hydraulic conductivities of the top layers ranged from 7.1 to 33.1 centimeters per hour. Water release curves showed considerable loss of water (41 to 67 percent) between 0 and 80 centimeters of water tension, in conformity with the textural and organic matter status of the soils. An erodibility rating curve showed the Onicha-Mbaise and Agulu soils to be most erodible and the Nsukka soils to be most stable. The implications of these findings for soil management practices and cropping systems are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Scanning electron micrographs (SEM) of crusts of loessial soils are presented. SEM observations were performed on crusts formed by raindrop impact at various stages of their formation. The crust structure was compared to the natural undisturbed soil. During the crust formation, a middle-term stage developed at which coarse particles, stripped of the fine ones, composed the surface layer of the soil. At the final stage of the crust formation, the coarse particles were washed away, and a thin seal skin, about 0.1 millimeter thick, formed the uppermost layer of the soil. A depositional crust, which was formed mainly by the translocation of fine particles, was marked by the presence of a thin skin also about 0.1 millimeter thick, suggesting involvement of similar secondary mechanisms of formation. This work illustrates the use of SEM for the study of soil crust formation and structure.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID