Ammonium and Nitrate Uptake and Utilization Efficiency of Rice Varieties as Affected by Different N-Concentrations

To find out the optimum mixture ratio of ammonium and nitrate on rice plant, 4 rice varieties were examined during 14days after transplanting in hydroponics with the different ratio of ammonium to nitrate(100:0, 75:25, 50:50, 25:75 and 0:100). The highest N uptake from solution and the maximum plant dry weight were 60~70% ammonium and 30~40% nitrate mixture treatment both in Japonica and Tongil type rice plants. And with the same varieties N-uptake and N use-efficiency were compared between 10.0mM and 1.0mM nitrogen using 70% ammonium and 30% nitrate for 24days after transplanting. Rice plants absorbed more nitrogen(131~145%) in 10.0mM than 1.0mM treatment but accumulated N in rice plants were almost the same in both treatment. Among the tested rice cultivars, dry matter production and total accumulative nitrogen in rice plants were much high in Tongil type than japonica type rice cultivars. N-recovery ratios of rice plants from uptake N were 90.8-99.0% in low concentration N solution(1.0mM), but 69.4-81.7% were observed in high concentration N solution(10.0mM). It means that suppling low concentration N steadily will be better to prevent loss of N without reducing of growth in rice plants.