Interaction Between Potassium and Calcium in Their Absorption by Intact Barley Plants. II. Effects of Calcium and Potassium Concentration on Potassium Absorption.

Rates of K absorption by young barley plants grown for 20 days in flowing nutrient solutions have been studied at 3 solution K concentrations (20, 200, and 2000 mum) and at 2 Ca concentrations (250 and 2500 mum). Increasing solution K increased plant K content, concentration, and rate of absorption: solution Ca concentrations had no effect at any K level.Rates of K absorption were only one-half to one-fifth of those reported for excised barley roots at similar K concentrations in solution. If the reported rates of K absorption by the high-affinity mechanism in excised barley roots were maintained in growing plants they would have given, within 3 days, the equilibrium concentrations of K in plants of the present experiment. Thereafter the rates of K absorption by the high-affinity mechanism would have been more than adequate to maintain plant K and would need to have been compensated by K efflux.It is suggested that, for all concentrations of K in solution, the high-affinity mechanism dominates the absorption of K by barley plants grown for more than a few days.