POTASSIUM-SUPPLYING POWER OF VIRGIN AND CROPPED SOILS

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Abstract
A study was made of the rate of change of K from nonexchangeable or fixed forms to the exchangeable form in cropped and virgin soils as measured by the amts. of K removed by 4 crops of oats and 6 cuttings of Ladino clover from these soils in pot cultures. Ladino clover removed 1.2 to 1.7 times as much nonexchangeable K as oats from 4 of the soils in which the original levels of exchangeable K were relatively high, whereas oats was either equal to or superior to the clover in this respect in the other 2 soils in which the contents of exchangeable K were relatively low. Liming of the acid soils tended to repress the total and nonexchangeable K removed by oats. Leaching the soils with a CaCl2-MgCl2 soln. to reduce the content of exchangeable K prior to cropping increased the amt. of nonexchangeable K removed by 4 crops of oats. That fixed K becomes available to a considerable degree for crop use is indicated by the recovery by 4 crops of oats of 24 - 47% of the amts. fixed.
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