Improving Yield and Nutrient Uptake Potentials of Japonica and Indica Rice Varieties with Nitrogen Fertilization

The most important problem in achieving high yields in rice is how to increase the nitrogen (N) absorption at each growth stage without reducing the percentage of ripened grains. Proper amount and timing of application could reduce N losses and increase fertilizer use efficiency while cost of production is also reduced and yield is increased. In order to avoid losses and to use soil-and fertilizer-nitrogen efficiently, it is necessary to develop better ways of predicting the optimum amount of N needed by the rice plants. A field experiment was conducted to determine the effect of different levels of N on N uptake, yield components and dry matter yield of japonica (Hatsuboshi) and indica (IR-13) rice varieties. Results showed an increasing trend in the N uptake, rice yield, panicle number, tiller number and dry matter production, with increased amount of applied N fertilizer. The yield (brown rice) of the two varieties (Hatsuboshi, 3.2-6.5 tons ha ; IR-13, 1 2.6-6.4 tons ha ) did not differ significantly (p=0.05). However, the agronomic efficiency (AEN) of IR-13 was 1 significantly higher than Hatsuboshi. There was a 30 kg ha increase in the yield of brown rice and about 1.4% 1 increase in the total N uptake for every additional kilogram of applied N ha . Higher correlations (p=0.001) 1 were found between the yield (r = 0.96; r = 0.99), number of panicles (r = 0.98; r = 0.96) and number of tillers (r = 0.96; r = 0.97) and N uptake (r = 0.97; r = 0.95) of japonica and indica rice varieties and applied N, respectively. The increase in yield (ton ha ) of japonica (y = 1.07x + 2.5) and indica (y = 1.24x + 1.5) could be 1 attributed to the increase in N uptake with increased application of N and mineralized soil N after flooding. However, best timing and amount of N application should be determined to reduce N losses and increase soil and fertilizer N efficiency while cost of production is also reduced but yield is increased.