摘要:

The diffusivity concept remains up to the present time rather poorly defined physically. Indeed, the dependency of the diffusion coefficient upon the fluid content of the unsaturated porous medium is not clearly established yet.This paper presents an experimental approach of this dependency. The diffusivity coefficientD(&thetas;) has been measured at different water content &thetas; in horizontal columns of glass beads. An analysis of the method of measurement ofD(&thetas;) shows that simple relationships betweenDand &thetas; can be obtained within well-defined water content ranges. The phenomena occurring in the dry range of water content seem basically different from those in the wet range. Hence, the study of unsaturated flow through porous media is somehow to be reexamined in the whole range of water contents.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effects of temperature on the urease activity in soils in the presence and absence of toluene, a bacteriostatic agent, were investigated. The activation energies of the soil urease in the presence of toluene were much higher than those in the absence of toluene; however, the free energies of activation were essentially similar in both cases. From the considerations of enthalpies and entropies of activation of the soil urease and the previous observations regarding the association of soil urease in these soils, it is suggested that the urease activity in the presence of toluene is due to the extracellular enzymes adsorbed on or complexed with soil colloids.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Evidence based on x-ray powder diffraction and differential thermal analysis shows that calcium can form complexes with catechol-type soil organic compounds.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Effects of sulfuric acid applied to irrigation water on pH, Ca++, HCO3-, and H2CO3status are evaluated based on known relations of carbonate equilibria. Theoretical results are compared with experimental results obtained for waters with salinity classes C2, C3, ad C4 and alkalinity classes S1 and S2 at acid application rates of up to 6 me/liter. Results indicate that the theoretical analysis presented may be useful for calculating the amount of acid needed to prevent calcium precipitation as well as for predicting changes in pH and the above ion species upon the addition of sulfuric acid within the tested range.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Physical, chemical, and mineralogical properties of a Mediterranean red soil and a white Rendzina soil from Lebanon were characterized and related to their genesis. The Mediterranean red soil was almost decalcified. As a consequence, it had a fairly well developed soil profile. Illuviation of clay and the formation of an argillic horizon, accumulation of organic matter, enrichment of sesquioxides, and kaolinization were the major processes in the development of this soil.The white soil derived from soft limestone contained large amounts of CaCO3. As a result, it had a weakly developed immature soil profile. Weathering and subsequent release of sesquioxides, horizon differentiation, and clay transformation were retarded. Accumulation of organic matter was an important process in the development of this soil as it was in the Mediterranean red soil.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Thirty-nine Andepts from Costa Rica, Nicaragua, El Salvador, and Guatemala were studied. The main purpose of this work was to characterize the morphological, physical, and chemical properties and their relationships to elucidate on the problems of soil genesis, classification and productivity.The soils studied exhibit a relatively uniform morphology and contain large amounts of amorphous materials derived from volcanic glass. They have dark color, loamy texture, fluffy structure, thixotropic consistence, low bulk density, high specific surface area and exchange capacity, and acid reaction. Most are Dystrandepts and a few are Vitrandepts, Eutrandepts, and Hydrandepts. They are low in N and P, with moderate contents of exchangeable bases.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The movement of air to the rhizosphere through the plant tissue of lowland rice was studied using a15N-tracer technique. Rice plants, grown under submerged soil conditions, at different growth stages were placed in a glass chamber where the atmosphere of the shoot and root compartments was separated, permitting the shoot compartment to be filled with15N-labeled nitrogen gas. The atmosphere in the root compartment was analyzed for15N-labeled nitrogen periodically after the plants had been transferred to a greenhouse or growth chamber. Nitrogen gas taken up by the aerial plant parts moved to the roots and diffused into the rhizosphere. At the tillering stage, atmospheric nitrogen appeared to move slowly through plant tissues. The rate of movement of the atmospheric nitrogen was much greater in the rice plant at the heading or flowering stage than at tillering.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

To delineate the soil-water content in layers as thin as 0.1 cm in the upper centimeter of a field soil, a simple, easily constructed soil sampler was used. Samples were taken every 20 min during one day of soil drying after sprinkling the soil with 0.6 cm of water. The soil in this top centimeter dried fairly uniformly, with the 0− to 0.1-cm layer drying from 0.202 to 0.036 cm3cm−3in 8 hr. The 0.8− to 1.0-cm layer dried from 0.238 to 0.152 cm3cm−3in the same period. With the techniques and tools described herein, no difficulty was encountered in distinguishing the soil-water content of one layer from another.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The mineral soils described and analyzed in Ingham County, Michigan, by the end of 1966 were compared with the 7th Approximation (October 1966 supplement), official series descriptions, and the proposed guidelines for naming of mapping units. The results were: 1) Ten series not in the county legend had been described; two series in the legend had not been found. 2) Names of the mapping units agreed with 55 percent of the series descriptions. 3) There was a place in the 7th Approximation for over 96 percent of the soil descriptions. That has now (1973) been adjusted to about 99 percent. 4) Thus, the application of the system in Ingham County left much room for improvement in the description and naming of the map units. However, not many of these inadequacies are inherent in the new soil classification system.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Lindane-C14degraded slowly (90 percent recovered) in a sandy loam soil, incubated for 6 weeks under flooded conditions. The degradation products were isolated and identified by gas chromatography and mass spectrometry. The major degradation product was γ-3,4,5,6-tetrachlorocyclohexane (>5%), followed by γ-2,3,4,5,6-pentachlorocyclohex-1-ene (<2 percent) and small amounts of 1,2,4-trichlorobenzene, 1,2,3,5− and/or 1,2,4,5-tetrachlorobenzene, and 1,2,3,4-tetrachlorobenzene. Chloro-phenolic metabolites of lindane, observed in plants, insects, and mammals, were not detected in the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID