Abstract
SummaryResponse to potassium fertilization was tested, over a two-year period, in 24 experimental fields, predominantly in coarse-textured soils. Only two fields showed significant yield increases. Potassium availability was estimated on the basis of (a) the free energy (ΔF) of potassium exchange for calcium and magnesium, (b) the proportion of potassium in total exchangeable cations, and (c) soluble potassium extraction in correlation with the potassium content of the plants. Woodruff's method (ΔF) yielded the best agreement (correlation coefficient r = 0·77). ΔF values showed a sufficient supply of available potassium, which may have accounted for the lack of response to fertilization.
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