Release of potassium from soils with different base exchange capacities

The purpose of this study is to determine the effect of the base exchange capacity of the soil and of different complementary exchangeable ions present in the soil on the availability of exchangeable potassium as determined by chemical quick test methods.

Exchangeable potassium may be defined as that potassium which is held by the soil colloidal material and which can be replaced by another cation under suitable conditions. Many authors believe the exchangeable potassium represents the bulk of the potassium used by plants. It has been known for a long time that plants get nutrients from the soil solution. As potassium is lost from the soil solution through plant feeding and leaching, it may be replenished from the exchangeable supply. Recently Jenny and Overstreet (5, 6)¹ concluded that roots may obtain exchangeable potassium directly from colloidal particles by contact exchange. When they placed excised roots in water and electrolyte solutions, the roots did not lose any potassium, but when excised roots were placed in clay suspensions, the amount of potassium in the roots greatly affected. If the clay was saturated with some ion other than potassium, the roots lost potassium. If the clay was partially or wholly saturated with potassium, the roots gained potassium. These experiments show that exchangeable potassium may be used directly for plant growth.