Influence of Ammonium Concentration on Uptake and Content of P, K, Ca and Mg in Rice Grown in Solution Culture

Abstract

Summary The rates of total ion uptake per 5 plants and the rates of ion uptake per gram of root dry weight were first stimulated by the increasing NH4+ concentration to a certain extent, this stimulation then disappeared as the NH4+ concentration continued to rise, which then suppressed these uptake rates. Rates of P and Mg uptake per plant were stimulated until about 1500 µ M. N and declined beyond; whereas rate of P uptake per unit of root was stimulated until 2200 µ M. P and that of Mg up to 1500 µ M. N. For K absorption, both these rates were stimulated to about 1100 µ M. N and then decreased. Rates of P, K and Mg uptake per unit of root continued to decrease with advancing plant age, like those of NH4+ (DOGAR and TANG VAN HAI, 1977) whereas the rates of total uptake continue to increase with increasing plant age. P uptake reached its maximum at 100 days, whereas Mg uptake continued into the repening stage, attaining its maximum at flowering. The total P, K, Ca and Mg content in the plant, follows approximately the same pattern as that of their uptake from the solution. The content of P, K and Mg increases under the increasing NH4+ concentration in the nutrient solution, stabilizes for a while, and then decreases. Ca content decreases immediately with increases in NH4+ concentration. Total ion content in young plants is higher than in the older ones, probably due to dilution effect of growth. Content of total P, K, Ca and Mg was markedly suppressed at higher NH4+ concentrations, indicating disturbed nutrient balance.