Effect of potassium on uptake and incorporation of ammonium-nitrogen of rice plants

1. Rice was grown for 5 months in a sand solution culture at two different

1. K levels. The higher K supply resulted in a reduced uptake of Na +, Mg ++, and Ca++ by shoots. The uptake of NH4+-N of the shoots, however, was increased by the higher K supply.
2. In short term experiments, ill which the NH4+-N of the uptake solution was labelled by N 15, increasing K concentrations in the uptake solution did not depress the NH4 + uptake of young rice plants. Higher K concentrations in the uptake solution favoured the translocation of labelled N from the roots to the shoots. In some cases the higher K levels resulted also in an enhanced transfer rate of labelled N from the soluble to the insoluble N fraction.
3. Increasing levels of Mg++ in the uptake solution did not affect the uptake of labelled NH4-N.
4. I t is concluded that K + and NH4 + do not compete for common binding sites of the uptake mechanism in rice roots. This lacking competition suggests the speculation that NH4+-N is absorbed mainly in form of NH8 by plant cells.