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1.
Soil- and stream water elemental concentrations from a subcatchment in the Lake Gårdsjön area have been used to evaluate the importance of ion exchange processes on the transport of cations to aquatic ecosystems. The importance of cation exchange processes in the upper organic and upper B soil horizons was demonstrated using lysimeter water data from a recharge area and soil water flow simulated with SOIL model during winter rain events with high sea-salt concentration. The importance of the hydrological conditions, such as water flow and water pathway, silicate weathering and the ion exchange of Al with H+ on the streambed materials in controlling cation concentrations in soil and stream waters are also discussed. With the SAFE model, the contribution of cations from ion exchange by depletion of base cations from the exchange matrixes compared to from weathering was also assessed. SAFE calculations indicate that the release rate of base cation by ion exchange to runoff water has decreased since 1945 and is very low, approx. 0.1 keq/ha per year, at present time as a result of soil acidification due to S and N inputs. 相似文献
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A one-dimensional equilibrium model for the movement of ionic species through a saturated soil is presented. Physical processes considered include mass flow, ion exchange, precipitation and dissolution. Precipitation involves the cationic species which is desorbed upon ion exchange and the anionic species in the leaching solution. In the presence of a precipitate, ion exchange takes place at two separate interfaces, moving at different velocities through the soil. At the first interface, precipitation takes place in conjunction with ion exchange, and at the second interface the precipitate dissolves and ion exchange proceeds. The conposition of the transition zone between the two interfaces is calculated from the conditions of mass conservation and electroneutrality, a linear ion-exchange equation and a solubility product. 相似文献
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A one-dimensional equilibrium model for the movement of ionic species in a saturated soil is presented. Physical processes considered include mass flow, ion exchange, dissolution and precipitation. It is assumed that ionic concentrations in the soil can be described with step functions.The model assumes that a precipitate initially present in the soil dissolves upon leaching the soil with a solution not containing the ionic species that make up the precipitate. Unlike the situation in the absence of a precipitate, ion exchange would take place at two separate interfaces, moving at different velocities through the soil. At the faster penetrating interface, the precipitation would take place in conjunction with ion-exchange. At the slower penetrating interface, the precipitate initially present plus the secondarily formed precipitate would dissolve and ion exchange proceed.The composition of the transition zone between the two interfaces is calculated for step functions, from the conditions of mass conservation and electroneutrality, a linear ionexchange equation and a solubility product. 相似文献
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《Communications in Soil Science and Plant Analysis》2012,43(20):2673-2679
A hypothesis is tested that allows study of not only the quantity but also the quality of ion exchange in soils, composts, peats, and its mixtures, which is common in natural and synthetic ion exchangers, on the basis of the ion-exchange process and its selectivity. For practical application of ion exchange in the soil not only the quantity of base cations and hydroxon ions bound by the solid soil phase is significant but also their readiness to ion exchange or ion exchange elasticity. Selectivity of ion exchange, expressed by selectivity coefficient, reflects the readiness of ion exchange while ion-exchange thermodynamics show the degree of spontaneity of the ion-exchange process. The results document that soil humus is the highest-quality ion exchanger in soil and that its quality may be assessed by the proposed method. The effort to replace humus by any synthetic ion exchangers cannot be successful: Although they have a high value of cation exchange capacity, they also show high selectivity for ions of higher valence and low ion-exchange elasticity, and their desorption of calcium and magnesium is poor. 相似文献
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Cation exchange is often studied with disturbed and dried soils, but the applicability of the results to undisturbed soils is not straightforward. We investigated the value of exchange coefficients obtained from standard procedures for predicting cation exchange in soil. Columns of undisturbed and disturbed subsoil of a Luvisol (SBt horizon) were leached under saturated conditions with 0.4, 4, 20, 41, 102 and 205 mm BaCl2 at a Darcy velocity of 1400 mm day?1. The model PHREEQC was used to calculate one‐dimensional transport, inorganic complexation and multiple cation exchange. Two model variants were tested: m1 (exchangeable cations obtained by percolation with NH4Cl) and m2 (exchangeable cations obtained by shaking the soil with BaCl2). The exchange coefficients (Gaines–Thomas formalism) were calculated from the ion activities in solution and exchangeable cations obtained by NH4Cl percolation (m1) or shaking with BaCl2 (m2). Variant m1 predicted cation exchange of the disturbed (homogenized) soil for the entire BaCl2 concentration range, whereas variant m2 resulted in a two‐fold overestimation of desorbed K for all experiments, which was related to large amounts of K released from the soil by shaking with BaCl2. In experiments with undisturbed soil, variant m1 predicted the concentrations of Mg, Ca, K, and Na in the solution phase and the sum of cations released from exchange sites. However, variant m2 predicted changes in ion concentrations and exchangeable cations somewhat less well. This study suggests that the amounts of exchangeable cations and exchange coefficients obtained from experiments with homogenized soil by percolation are useful to predict cation concentrations in column experiments with undisturbed soils. 相似文献
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概述了在农业领域中应用离子交换树脂获取土壤养分含量的研究进展,探讨了树脂的预处理方法、使用形式以及提取土壤养分的基本操作和影响因素,同时提出该技术在提取土壤养分中的应用前景及需要解决的问题。 相似文献
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D. R. BOULDIN 《European Journal of Soil Science》1989,40(2):309-319
A model is developed which describes uptake of Ca, Mg, K, NO3 , Cl, and SO4 . The electrical neutrality of plant and soil are maintained through exchange of H or OH at the root-soil interface, constant partial pressure of CO2 and non-exchangeable H reaction with the soil cation exchange complex.
An important innovation in this model is the inclusion of electrical neutrality as a condition for plant, soil and soil solution. The uptake of cations is a function of both concentration of anions in solution and the suite of exchangeable cations. The model emphasizes an important role for CO2 in soil chemistry and plant nutrition. Presently, the model is most useful for generating research hypotheses. Perhaps the most important hypothesis is that something about as complicated as the present model will be required to model multiple ion uptake and crop yields. 相似文献
An important innovation in this model is the inclusion of electrical neutrality as a condition for plant, soil and soil solution. The uptake of cations is a function of both concentration of anions in solution and the suite of exchangeable cations. The model emphasizes an important role for CO
10.
Influence of soil solution Ca concentration on short-term K release and fixation of a loamy soil 总被引:1,自引:0,他引:1
A. SCHNEIDER 《European Journal of Soil Science》1997,48(3):513-522
The Ca concentration of the soil solution influences K plant nutrition by its influence on K concentration of the soil solution and on soil buffer power through ion exchange and K release or fixation. The effects of the imposed solution Ca concentration on the estimates of these parameters and on these two phenomena were studied on a loamy soil. Potassium sorption and desorption experiments were conducted for 16 h at five initial Ca concentrations (from 0 to 10?1 M) and followed by the measurement of soil exchangeable K (ammonium acetate extraction). Soil K-Ca exchange properties and the contributions of exchangeable K and non-exchangeable K to K dynamics of the soil-solution system were estimated. The‘Ratio Law’ applied for the medium range of Ca concentrations, i.e. 10?1 M to 10?3 M. But, it failed for some experiments at small initial Ca concentrations (0 M and 10?4 M). This failure went with a decrease of the number of sites of great affinity for K in K-Ca ion exchange and/or a decrease of the amount of K not in exchange equilibrium with Ca but extracted by M ammonium acetate. Release of K increased and fixation of K decreased when Ca concentration increased. The relation between the change in the amount of non-exchangeable K during the experiment and the initial constraint (ø) was curvilinear on the large range of ø investigated. But, this relation was independent of Ca concentration. The K concentration of the solution for which neither sorption of K by the soil nor desorption of K from the soil occurred decreased and the slope of the sorption-desorption curve at this K concentration increased when the solution Ca concentration decreased. These two parameters can be considered the K concentration of the soil solution of the soil and the buffer power of the soil, respectively, only if the initial Ca concentration imposed during the sorption-desorption experiments is close to the Ca concentration of the soil solution of the soil. A predictive model of the soil buffer power based on ion exchange and release-fixation properties is proposed. Despite some discrepancies at very low Ca concentrations (<0·5 mM Ca) when‘Ratio Law’did not apply the agreement between calculated and observed values was good. The model permits the correction of the experimentally obtained buffer power for the bias related to the great solution volume: soil weight ratio commonly used during the sorption-desorption experiments. 相似文献