FIXATION OF POTASSIUM ADDED TO SOILS AND ITS RECOVERY BY PLANTS

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Abstract
Soil samples which fixed most of the added K against extraction with 1 N NH4OAc were found to release appreciable amounts of the fixed fertilizer K to plants in pot tests. In one experiment, even after growing four crops of oats, five additional crops in four soils removed 48% more K from the K-treated samples than from the controls. In another experiment, fixed fertilizer K in surface and subsurface samples of three soils accounted for about 48% of the K-uptake by oats and alfalfa. In a field experiment, most of the K applied was fixed against extraction with 1 N NH4OAc. Although nonexchangeable or fixed K was an important source of K for the plants, three years of cropping were not sufficient to demonstrate that it was derived from the fertilizer K applied.Repeated extraction of the soils with 0.5 N NaCl or continued leaching with 0.01 N HCl gave additional evidence of the release of fixed K.It was concluded that appreciable amounts of fixed fertilizer K may be recovered by successive crops, and this should be considered in soil management practices.
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