Keywords: Potassium, Exchangeable potassium, Lattice potassium, Potash, Potassium buffer capacity.
The behaviour of potassium in soils is usually dependent on both surface and inter-lattice phenomena; patterns of behaviour in well-mixed soil-potassium systems are perhaps most simply determined by a combination of adsorption and desorption isotherms obtained in soil-dilute solution systems. Such isotherms can apportion added potassium between labile and fixed forms at any time following potassium addition to the soil. The shapes of desorption isotherms indicate that labile potassium can be associated with at least two types of adsorption sites commonly referred to as non-specific and specific; some of the latter are probably located at the rough edges of stacks of mica-like (illitic) and vermiculitic lattices. The inherent difficulties in assessing potassium buffer capacities are mentioned, chief among them being the slow release of initially non-labile potassium. Methods for measuring potassium release are discussed. Aspects of the nature of illite are considered and some caution is suggested in drawing too close an analogy between slow natural and accelerated artificial weathering of micaceous materials. Most practical problems of potash usage must be studied under field conditions, but the soils used in field trials should be properly characterised if full and extensive use is to be made of field-data.
Prof. P W Arnold, MA, BSc, PhD, ARIC. University of Newcastle upon Tyne, UK.
30 Pages, 2 Figures, 55 References.