摘要:

The present article elaborates the idea of using natural or artificial slopes as contributors of water to lands under cultivation. The process of lateral flow in a sloped soil layer bordered by a soil surface and an impermeable membrane is considered.Solutions are presented in nondimensional form. An interesting phenomenon, which broadens our ideas about unsaturated filtration, was obtained.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The nature of the binding of divalent metal ions by humic acid was examined by a modified potentiometric titration procedure involving sequential additions of metal ion to solutions of the humic acid at constant pH. At pH values below the point of oxide hydrate formation, the drop in pH resulted from release of protons from participating reactive groups; at higher pH values and at highM2+/humic acid ratios, additional protons were released from hydration water of the metal held in 1:1 complexes. At least two major sites were involved in complex formation.Stability constants were in excellent agreement with those obtained by conventional titration and followed the order Cu>PbCd>Zn. LogK2values varied only slightly over a wide pH range and increased greatly with decreasing concentration of supporting electrolyte. Differences between humic acids in their ability to bind divalent metal ions were negligible.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Mixed, washed cell suspensions of denitrifying bacteria were unaffected with regard to the rate of denitrification by increased surface areas in the form of glass beads, clays, and oven-heated soils of different textures. Evolution of the soluble gases, nitrous oxide and carbon dioxide, was increased with increased surface area. Formation of gaseous nitrogen from cells incubated in an argon atmosphere always exhibited a characteristic lag period. This lag period was attributed to the solution not being saturated with nitrous oxide since the lag was abolished when cells were incubated in a nitrous oxide atmosphere.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Soils, litter, and plant communities were sampled at 11 locations along an elevation gradient from subalpine woodland to saline semidesert. All soils were derived from granite, and the transect represents decreasing intensity of leaching and increasing nutrient accumulation toward more arid climates. Concentrations of Na, K, Ca, and Mg in water-soluble, exchangeable, and acid-soluble surface and subsurface soil fractions increased toward lower elevations in the residual soils of mountain slopes, but not all concentrations were significantly correlated with elevation. Soil K concentrations were higher in communities with a tree stratum, presumably because tree uptake and foliage leaching keep a larger pool of K in circulation. The four elements, but especially Na, increased rapidly toward lower elevations in the bajada soils below the mountains. Nutrient concentrations tended to increase toward lower elevations in surface litter and in native plant foliage. Litter nutrient pools were maximal at upper-middle elevations in pine forest to pine-oak woodland, and decreased toward highest and toward lower elevations (but showed a secondary maximum in the saline semidesert of lowest elevations). Foliage nutrient concentrations were more strongly correlated with the acid-soluble than with the water-soluble or exchangeable soil fractions, and the acid-soluble fraction may better represent long-term availability in steady-state flow to the plant community than the other fractions. Tissue nutrient concentrations ofAvena fatuagrown in pots in surface and subsurface soils from the different sites were more consistent than the different nutrient concentrations of native species in the same soils. Most relationships observed were curvilinear; the measurements taken reflect complexly interrelated aspects of the nutrient designs of ecosystems as these change in response to difference in climate and soil-forming processes.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The K supplying and fixing capacity of A and B horizons in seven Latosols and seven Andosols from Costa Rica was determined by successive cropping in the greenhouse, using tomato (Lycopersicum sculentum) as indicator plant, and by successive soil extractions and incubations.The K supplying capacity of A and B horizons in Latosols and Andosols, measured by plant dry weight, K uptake, and exchangeable K in the soil, was high for the first two successive crops but dropped drastically for the succeeding crops. While some exchangeable K was fixed during the first two crops, some nonexchangeable K was released during the third crop to replenish the low levels of exchangeable K. Potassium fertilization increased the exchangeable K fixed and decreased the nonexchangeable K released during successive cropping in both soils and horizons.The K supplying capacity, measured by successive extractions with normal, boiling HNO3, was similar to that indicated by plant growth and K uptake. While soil incubation under continuously wet conditions favored fixation of exchangeable K, incubation under wet-dry cycles resulted in release of nonexchangeable K.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Seven chemical extractants for determining available soil phosphorus have been compared with respect to their effectiveness in extracting phosphorus and the precision of the extracted phosphorus in predicting the phosphorus fertility of the soils.Strong alkali extraction using 0.1Nsodium hydroxide extracted the most phosphorus but was the least precise in predicting yields (r= 0.58). Inclusion of organic phosphorus in the sodium hydroxide extract reduced the precision further (r= 0.56).Extraction with dilute acids and an anion exchange resin gave lowest values for available phosphorus but resin extraction was superior to dilute acid extraction in predicting percentage yields, with a correlation coefficient of 0.72 for resin extraction compared with 0.60 and 0.68, respectively, for 0.002Nsulfuric acid and 3 percent acetic acid.Extraction with 0.5Msodium bicarbonate and 0.03Nammonium fluoride plus 0.025Nhydrochloric acid were equally precise in predicting percentage yields with correlation coefficients of 0.67 and 0.68, respectively.The phosphorus extracted with 0.03Nammonium fluoride plus 0.1Nhydrochloric acid gave the highest correlation with percentage yield (r= 0.74). This method, being additionally simple, quick, and effective ir extracting phosphorus, has been recommended for the routine soil testing for phosphorus in the acid soils of southeastern Nigeria.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

A numerical model of soil water dynamics was devised to simulate infiltration, drainage, evaporation, and water storage in texturally layered profiles. The layers consisted of sandlike, loamlike, and claylike soil of known hydraulic properties. Data presented on the flow patterns of the variously stratified profiles illustrate the interactions between soil and weather variables which govern profile water storage. Fine-textured layers tend to impede infiltration but may in the long run promote drainage of overlying layers. Toplayers of coarse texture tend to inhibit evaporation. Since the relative hydraulic conductivities of layers of different textures vary as soil moisture suction changes in time, it seems extremely difficult to predict the dynamic behavior of composite profiles without the benefit of a comprehensive simulation model. Shortcomings of the present model are pointed out, however.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID