INFLUENCE OF FORM AND MODE OF NITROGEN FERTILIZER APPLICATION ON THE AVAILABILITY OF SOIL AND FERTILIZER POTASSIUM

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Abstract
Ammonium applied alone or after addition of K depressed the uptake of K by oats grown in a sandy loam soil in the greenhouse. When NH4 was added first and K later at seeding, however, NH4 increased K-uptake. In the absence of K fertilizer, NH4 reduced the release of non-exchangeable K to the plants. When added prior to or at the same time as K at seeding, NH4 reduced K-fixation. This inhibitory effect of NH4 on fixation of added K was reflected in higher amounts of K in solution as shown by lower pK[long dash]1/2p (Ca+Mg) ratios. These results of chemical extraction of the soil indicated that the effects of NH4 on K-uptake by the oat crop arose from reactions in the soil.

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