Absorption, Translocation and Assimilation of Ammoniumand Nitrate-Nitrogen in Rice Plants as Affected by the Supply of Potassium, Calcium and Magnesium

Rice plants (Oryzn sativa L., var. Asominori) were treated with complete, minus K (-K), Ca-limited (-Ca) and minus Mg(-Mg) nutrient solutions for 10 days. Absorption, translocation and assimilation of ^<15>NH_4-N and ^<15>NO_3-N fed for 2 days to the treated plants were investigated, and in vivo nitrate reductase activity (NRA) was intermittently determined after the initiation of the treatment. 1) Absorption of ^<15>NH_4-N was not significantly different among treatment, while lower absorption of ^<15>NO_3-N was observed in -K and -Ca treatment. 2) Translocation of ^<15>NH_4-N from root to upper parts was not affected by treatment, but translocation of ^<15>NO_3-N was inhibited by -K and -Ca treatment. 3) NRA of rice plants was decreased by -K and -Ca treatment, and repressed when NO,-N was replaced with NH,-N ‘alone and in combination with NO,-N. 4) Assimilation of ^<15>NH_4-N into amino acids and protein was increased by -K treatment, but assimilation of ^<15>NO_3-N was inhibited by -K and -Ca treatment. These results indicate that nitrogen metabolism was disturbed by -K and -Ca treatment when rice plant was fed with NO,-N but not when plant fed with NH,-N.