A study of the effects of potassium fertilizer with special reference to wheat on boulder-clay soils

Abstract

SummaryA long-term rotation experiment testing the effects of applying K fertilizer in combination with N fertilizer and cropping treatments, and two experiments comparing the effects of residual and freshly-applied K together with N treatments over 3 years, all on boulder-clay soils, together with two detailed studies of the effect of K on the growth of wheat on a chalk soil very deficient in K, are described and the results discussed.Restricting the K supply had little effect on the growth of wheat until stem elongation began, but from then the growth of almost all organs was affected. It is concluded that there is no one mechanism by which lack of K in the soil restricts yield. It can decrease the area of the upper leaves, the dry matter produced in the upper internodes and ears, reduce the number of grains per unit area and the size of grain, but which of these is most important in a particular crop will depend on other cultural and environmental conditions.It is argued that boulder-clay soils should not be considered as a single class when giving advice on K manuring; more experiments are required to make practical recommendations more precise.