Interaction between Plant Nutrients: III. Antagonism between Potassium, Magnesium and Calcium

Abstract

Abstract In well buffered soils calcium ions occupy the majority of exchangeable sites in the soil colloids. Also, the fraction of exchangeable magnesium is considerable, while the monovalent cations only occupy a few percent of sites. Among the monovalent ions potassium is withheld more strongly than sodium. Therefore, potassium ions only leak out by drainage in small amounts until the soil is overfertilized by potassium. The first year's result of applying potassium chloride may lead to a higher yield even when the soil is not deficient in potassium, because chloride may increase the amount of dissolved cations in the soil solution. If a larger amount of potassium is applied than removed by the crop, potassium is accumulated in the soil and this leads to an antagonistic effect on the uptake of magnesium and calcium. The antagonistic effect of potassium was found to be considerable when the activity ratio between potassium and calcium in a soil extract (1 part soil to 2 parts water) during the period of growth and after harvest was higher than 10 (μmol kg-1 soil)1/2.