POTASSIUM-SUPPLYING POWER OF SOME CANADIAN SOILS

Abstract

The amounts of exchangeable potassium in surface samples of 11 Canadian soils were significantly correlated with uptake of potassium by plants in the greenhouse. Per cent K-saturation and water-soluble potassium were indicative of the percentage of K-uptake that was derived from soil potassium in exchangeable form at the time of seeding.Amounts of non-exchangeable potassium extracted from the soils by repeated boiling in 1 N HNO₃, by H-saturated exchange resin, and by continuous leaching with 0.01 N HCl were significantly correlated with each other and with the amounts of this form of potassium removed by plants.Following cropping, release of non-exchangeable potassium to exchangeable form during moist incubation of the samples for 112 days was slight. When samples containing different levels of exchangeable potassium were incubated moist for 13 months and then wetted and dried five times, potassium tended to be released to exchangeable form or converted to non-exchangeable form depending on initial level established. The degree of K-saturation at which potassium in six Ontario soils would be expected to be at equilibrium was estimated by regression to be 1.21 per cent. There was evidence that the degree of K-saturation for equilibrium in a Brown soil from Saskatchewan was at least 4.5 per cent.