摘要:

Computer simulations of the effects of Langmuir and Freundlich-type competition, in binary systems under equilibrium and dynamic (time-dependent) conditions, have been presented and discussed.These simulations indicate that during competitive adsorption (for both Langmuir and Freundlich-type competition), the presence of a competing species can have a marked effect in depressing (lowering) the equilibrium isotherm of an adsorbing species to an extent determined by the relative solution concentrations, distribution and selectivity coefficients, etc.In Langmuir-type competitive dynamic (time-dependent) adsorption, the amount of adsorption can exceed the equilibrium value during some periods. In binary competition, the experimental conditions, such as solution-to-solid ratio, can have significant influence on the shape of the isotherm and thus on the isotherm parameters estimated.Freundlich and Langmuir-type competitive adsorption isotherms in binary systems may resemble the isotherms in single-species systems. Thus, with limited experimental data, one may easily overlook the presence of competitive adsorption, even when it has significant influence on the equilibrium adsorption isotherms, and the adsorption parameters may change from one set of experimental conditions to another. Accounting for competition should allow the estimation of correct parameters.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We studied the potassium-calcium and potassium-sodium exchange equilibria on three soil samples differing in their organic carbon content (OC) and cation exchange capacity (CEC). Homoionic (Ca or Na saturated) soils were equilibrated, with the solutions having a large range of potassium adsorption ratios (PARs) at 50 meq L-1total electrolyte concentration. We analyzed the data on exchange equilibria, using a thermodynamic approach and various selectivity coefficients.The normalized exchange isotherms for K+-Ca2+systems suggested higher specificity for K+to Ca2+in the first 50 to 75 percent of K+saturation. In the K+-Na+system the specificity for K+to Na+was, however, higher for the whole range of exchange isotherms. The soil high in OC (Soil 1) had higher preference for K+than the soils low in OC (Soils 2 and 3). The values of standard free energy change of the exchange reactions (ΔGr°) for K+-Ca2+and K+-Na+systems were negative for all the three soils tested. These values were, however, more negative for K+-Na+than for K+-Ca2+systems, suggesting higher preference for K+in the former. A comparison of ΔGr° values suggested that the effect of CEC on the K+specificity of these soil samples was only marginal, though that of OC was quite spectacular.The values of the Gapon selectivity coefficient (KG) decreased first sharply and then gradually with the increase in exchangeable potassium percentage (EPP). On the basis of (KG), the exchange isotherms were divided into three zones, representing exchange sites with high, medium, and low specificities for K+. The arbitrary limits for the three zones were < 5, 5 to 38, and >38; > 4, 4 to 15, and >15; and > 5, 5 to 15, and > 15 for Soils 1, 2, and 3, respectively. The exchange selectivity coefficient (KN) and AGr° for K+-Na+systems were different only marginally for Soils 1 and 2. However, for K+-Ca2+systems, the values of different selectivity coefficients (viz.,KG, Vanselow selectivity coefficient, and Krishnamoorthy-Davis-Overstreet selectivity coefficient) and AGr° for Soils 1 were considerably different from those for Soil 2. This suggested a differential role of OC on changing the selectivity of soil for K+in K+-Ca2+and K+-Na+systems.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We examined interactions of lime and phosphate and subsequent adsorption of phosphate, sulfate, and molybdate by a Spodosol, using incubation and isotherm studies.Incubation of the soil with lime decreased the quantity of added phosphate that could be extracted with sodium bicarbonate or anion exchange resin. When lime and phosphate were added simultaneously, liming increased phosphate adsorption. When the soil was incubated with lime and the moist soil then equilibrated (1:10 soil-solution ratio) with 5-üg/ml solutions of Mo, P, or S, liming increased subsequent adsorption of phosphate, had no effect on that of sulfate, but decreased that of molybdate. It is suggested that liming resulted in the formation of new, highly active, adsorbing surfaces in the soil through the precipitation of exchangeable aluminum as amorphous polymeric hydroxy-Al cations. The formation of these new surfaces had the greatest effect on phosphate adsorption and the least on that of molybdate, because in general, the magnitude of the decrease in specific adsorption of anions by soil surfaces as pH increases follows the order phosphate > sulfate > molybdate.Incubation of the soil with lime, phosphate, or both followed by air-drying, increased the net negative soil charge and clearly decreased subsequent adsorption of phosphate, sulfate, and molybdate by the soil. Evidently, air-drying significantly altered the surface charge characteristics of the limed soil, for liming increased phosphate adsorption by moist soils, but decreased that by air-dried soil. Crystallization of the amorphous hydroxy-Al surfaces, during air-drying, may explain the different adsorption characteristics of moist and air-dried limed soil with respect to phosphate and to a lesser extent sulfate.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We examined the sorption of nickel and zinc in three soils that were unamended, freshly amended, or preconditioned with gamma-irradiated sewage sludge. Metal sorption was also studied in the same soils treated with a 0.01NCaCl2-extract of the sludge. Adsorption of both metals was greatest in the unamended soils, less in soils preconditioned with sludge, and least in the freshly amended soils and sludge-extract-treated soils. We attempted to explain treatment effects on the basis of (1) reduced metal activity as a result of increased soil solution ionic strength, (2) reduced metal activity as a result of inorganic-metal complexes, (3) increased competition for sorbing sites, and (4) reduced metal activity as a result of organic-metal complexation. None of the hypotheses completely explained the observed treatment effects, although the data suggested that organic-metal complexes play a significant role in reduced free metal activity, particularly for Ni. Despite the reduction in metal retention effected by various sludge treatments, little Ni or Zn leaching is expected in these sludge-amended soils, for sorption of both metals is very high.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

I grew several warm-season forage grasses and a cool-season pasture mix of oats plus clover in a greenhouse on mixtures of soil profile horizon materials from an unmined lignite site in east-central Texas and then evaluated the suitability of the various soil materials for selective placement over regraded lignite mine spoil during land recla@@ mation. Mixtures of the clayey subsoil horizon materials with the sandy loam topsoil (A horizon) produced soils that had sandy clay loam textures. Whereas the topsoil had a pH of 6.3 and an electrical conductivity of 0.2 millimhos per centimeter, the pH of the soil mixtures ranged from 5.1 to 6.0, and the conductivities from 0.3 to 1.7 mmho/cm. Dry matter production was greater on the topsoil during early stages of plant growth, especially where no fertilizer was added. Differences among soils declined with fertilizer application and degree of plant establishment through successive harvests. Chemical analysis of plant tissue showed adequate uptake of added nitrogen and phosphorus plus indigenous iron, manganese, and zinc from all soils. There were no indications of physical or chemical properties that would adversely affect forage growth on any of the soils. I concluded that, given an adequate regime of water and nutrient supply, the various mixtures of soil profile horizon materials evaluated had the same potential for forage grass production as the genetic topsoil that occurred on the mine site. Any one or a combination of them could probably be used successfully in selective placement over mine spoil for revegetation. Because short-term greenhouse studies may not account for agronomic problems that might arise due to weathering of previously unexposed subsurface soil profile materials, these conclusions are currently being tested more extensively in field plot trials.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Numerical simulations of the dynamics of soil water in the root zone of a vegetated field show that the matric suction profile can eventually acquire the same shape as the relative root density profile. The suction at any depth is proportional to the correspond@@ ing root density raised to a power that depends on soil texture. This behavior is found only for fully grown root systems when the soil water distribution is controlled primarily by the water absorption by the roots; this becomes more likely as the soil dries out. That this power law is a solution of the continuity equation will also be demonstrated analytically.This functional relationship is used to show that, under these restrictive conditions, root zone soil moisture storage is a linear function of volumetric moisture at a particular depth, with the slope changing with depth but fixed in time. This hypothesis is supported by both laboratory and field soil moisture profile measurements, which were taken in fields with fully grown plants. No other model parameters need to be estimated, and the good agreement found constitutes an independent validation of the soil water extraction model under the plant and soil conditions described.Potential applications of these results include estimating soil moisture storage in the root zone from remotely sensed surface soil moisture and estimating the root profile from matric potential profile measurements.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID