摘要:

Similar Na-Ca exchange constants were obtained for the soil-NaCl-CaCl2and soil-Na2SO4-CaSO4systems when the ion association model was imposed upon the latter sulfate system. The exchange constants for both systems were also comparable to the constants computed on the basis of the mean activity coefficient principle. The interrelation between the associated and nonassociated models for solute composition and their advantages and disadvantages are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A quantitative analysis of a mass transfer problem of chemicals in porous media is presented. The specific problem considered is that where the inflow boundary has an initial zero concentration, receives an inflow of chemical concentration U0for a period of finite duration T1, after which the inflow continues with water of zero chemical concentration. Free and sorbed phase chemical concentration distribution equations are first obtained for dispersion during the time period 0 < t < T1, during which the chemical enters the soil. The solutions are presented in the form of single convolution integral expressions obtained by Laplace transform techniques. This resulting distribution becomes the initial concentration distribution for the subsequent leaching process during the time period T1< t < T2. Equations are developed which describe the free and sorbed phase chemical distributions resulting from the leaching process. Solutions to both sets of equations are obtained by numerical quadrature techniques. A typical example is displayed.The scheme that is presented is easily adaptable to a repeating or “pulsed” system. Periodic application of a fertilizer, followed by irrigation, is an example of such a system.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A greenhouse experiment was conducted on three soils with differing cropping and fertilization histories to determine whether unenriched fertilizer N can be used in the same manner as15N-enriched fertilizer to estimate the amount of plant N derived from fertilizer. Estimates using unenriched fertilizer N were compared with estimates using two15N enrichment levels. Use of unenriched fertilizer N led to underestimation of the amount of fertilizer N in the plant material in four of six cases when compared to15N-enriched fertilizer. Standard deviations of the estimates of fertilizer-derived N in plant material were considerably greater when unenriched fertilizer was used.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Polyvinyl alcohol (PVA) was added to surface cores of the Urrbrae fine sandy loam (1) to study the effect of plant growth on PVA adsorption when the soil was in various cultural phases, (2) to measure the long-term effects of PVA on soil stabilization when the soil was incubated for 2.5 years, and (3) to calculate the terminal energy of rain required to disperse the surface of treated cores.Both wheat and pasture roots reduced the effective stabilization of surface soils by PVA. After 2.5 years' incubation, the PVA or components of its breakdown in soils were still successfully stabilizing the surface of the cores. Terminal energies required to disperse a PVA-treated surface were low (0.14 joules cm−2) and this energy could be obtained by 6 hr of 1.5 cm hr−1of natural rain.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Clay mineralogy of soils derived from volcanic ash under tropical conditions was studied by differential dissolution, x-ray diffraction, DTA, infrared analysis, and scanning electron microscopy. Andepts and oxisols of the mountains and lowlands of Indonesia and Costa Rica were used. The results showed the presence of substantial amounts of amorphous material mixed with crystalline clay. The amorphous fraction in andepts, with SiO2/Al2O3ratios of 0.6, contained allophane as was indicated by scanning electron micrographs. Although the oxisols had amorphous substances with SiO2/Al2O3ratios of 1.0, which were in the range of allophane, scanning electron microscopy showed the presence of a dispersed and fine-grained compound different from allophane. The crystalline clay in the andepts and oxisols was identified by DTA and scanning electron analysis as kaolinite. X-ray diffraction did not reveal 1:1 lattice type of clay in andepts and exhibited only very weak peaks at 7.10–7.24 A in oxisols for halloysite and kaolinite. Data indicated that in Indonesia and Costa Rica gibbsite formation was greater in mountain than in lowland soils.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Experiments were conducted under greenhouse and field conditions to determine the effects of Mo and S applications on the Mo and Cu concentrations of timothy, alfalfa, and red clover. Applications of S decreased the Mo concentrations of tissues of all crops. A significant interaction between Mo and S was observed, whereby the decreases in Mo concentration of tissue with applied S were more marked when Mo was added than in the absence of applied Mo. Without applied Mo, the Mo concentration of tissues was higher under field than under greenhouse conditions. The total S concentration of timothy and red clover tissues ranged from 0.15 to 0.21 percent and was not affected by the applications of S or Mo. Copper concentrations in crop tissues of greater than 5.7 ppm, associated with 0.15 to 0.21 percent S in tissues, with less than 0.5 ppm Mo applied to the soil, as reported in this paper are considered to be safe from the animal nutrition standpoint. Levels of tissue Mo resulting from application of 0.5 to 1.0 ppm Mo, which were reported as toxic from an animal nutrition standpoint, were corrected by applications of 50 to 200 ppm S. In the second and subsequent cuts, 50 ppm applied S was adequate in alleviating Mo toxicity at all levels of applied Mo. Under greenhouse conditions, yield response to added Mo as obtained on red clover was related to tissue Mo concentrations of 0.22 ppm.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Measurements of the widths of the annual rings to indicate the amount of soil moisture available to trees may not be reliable. Other means of measuring growth are suggested.The growth of apricot, almond, and peach trees were not adversely affected by variations in the amount of readily available soil moisture.The results show that high soil moisture does not result in greater growth than when it is at a lower level, but duration and the time the trees are supplied with readily available soil moisture and the time at which its deficiency occurs may be critical.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Plant growth possibly is reduced in soils which contract sufficiently with drying to compress or deform the roots. Small holes, which simulated root holes, were made in moist clods with a tapered awl. The hole diameter decreased as the moist clods dried. The amount the diameter decreased was significantly related to clay content and the difference between the dry- and moist-clod bulk densities but not to the sand content.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The Green and Ampt model is compared to a more exact delta-function model. It is shown that the position of the wetting front is predicted by the Green and Ampt equation with, at most, a 20 percent error and that the error decreases even further when a pressure head is present at the soil surface.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID