RATE OF RELEASE OF NON-EXCHANGEABLE POTASSIUM BY ONTARIO SOILS IN RELATION TO NATURAL SOIL CHARACTERISTICS AND MANAGEMENT PRACTICES

Abstract

The rate of release of non-exchangeable potassium, i.e. potassium-supplying power, of 41 Ontario soils was measured by a continuous percolation procedure. It was found that clay content of the soil was the predominant factor affecting potassium-supplying power (r = 0.978). Potassium fertilization or intensive cropping of the soil caused no change in the potassium-supplying power of the soil. As potassium-supplying power was found to be a constant characteristic of soil and not a function of previous management, potassium-supplying power measurements should not be necessary in routine soil testing. Knowledge of potassium-supplying power can be deduced from particle size distribution. Because soils of different texture have different potassium-supplying power, the interpretation of measured exchangeable potassium in terms of fertilizer requirement will be different for soils of different textural class.