EXCHANGEABLE CALCIUM AND POTASSIUM IN SOILS AS AFFECTED BY CROPPING AND FERTILIZATION

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Abstract
Six soils of 3 soil series were analyzed for exchangeable Ca and K by means of electrodialysis after they were cropped to a 4-yr. rotation for 15 yr. in iron cylinders, and exposed to natural weather conditions. Each soil type was represented by a series of cylinders. The soils were treated with limestone or mineral fertilizers, or both, and some were untreated. Limestone increased the exchangeable Ca in some of the soils but not in others; an explanation for this difference is offered. A relation-ship was not found between the quantity of limestone applied to the soils and the quantity of exchangeable Ca which they contained as a result of the treatment. The exchangeable Ca of the untreated soils was related to their pH, but such a relationship did not hold for limestone-treated soils. Fertilizers in the soils with or without limestone had little or no effect on the quantity of exchangeable Ca. In no case did an application of muriate of potash with other minerals enhance the exchangeable K. At the end of the expt. the soils contained few exchangeable cations other than Ca. No relationship was found between the colloidal content of the soils and the exchangeable Ca present at the beginning or at the end of the expt. During the expt. the exchangeable K and, with one exception, the exchangeable Ca of the untreated soils were reduced, while in one of the latter Ca remained unchanged. The results suggest that the quantity of exchangeable Ca held in the colloidal complex of humid soils, resulting from an application of CaCO3, depends more on the ability of the soils to adsorb Ca than on the quantity of Ca applied in the form of lime. In that event, the pH of a soil that contains native CaCO3 or one to which lime has been applied would not necessarily be a relative measure of its content of exchangeable Ca.
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