ASSESSMENT OF NITROGEN USE EFFICIENCY AND YIELD BASED ON NITROGEN RATE AND FERTILIZATION PRACTICES IN LOWLAND RICE (Oryza sativa L.) IN YEZIN, NAYPYITAW, MYANMAR

To ensure the achievable rice yield, adequate fertilization especially nitrogen (N) plays a crucial role in rice production. Nitrogen management for respective rice cultivars in specific paddy cultivating areas should be formulated to promote the sustainable and profitable rice production while improving N use efficiency and the environmental conservation. Field experiment were undertaken in dry season and wet season through using Yadanar Toe rice variety and Sin Thukha rice variety respectively to investigate the suitable N rate for optimal rice production and to determine N use efficiency of rice in the research farm of Yezin Agricultural University in 2017. Eight treatments including different rates and application methods of N fertilizer; T1 (No fertilization), T2 (0 kg N ha−1), T3 (30 kg N ha−1), T4 (77.6 kg N ha−1 as prilled urea, PU), T5 (100 kg N ha−1), T6 (130 kg N ha−1), T7 (160 kg N ha−1) and T8 (77.6 kg N ha−1 as urea super granule, USG) were laid out as randomized complete block design with three replications. The highest grain yield was achieved from the application of 100 kg N ha−1 in both seasons; 8.2 ton ha−1 in Yadanar Toe and 4.6 ton ha−1 in Sin Thukha. In both seasons, the optimum grain yield was observed from the application of 77.6 kg N ha−1 as either PU or USG. The plateau and the reduction of grain yield occurred at 130 kg N ha−1 and 160 kg N ha−1. The application of USG and the highest N rate provided higher N uptakes in both seasons irrespective of rice varieties. The efficiency of N use ranged from 4.5 to 13.5 in summer and from -0.3 to 13.4 in monsoon, and the highest N use efficiency (NUE) was obtained from the application of 100 kg N ha−1 in summer and the application of 30 kg N ha−1 in monsoon. The isotopic technique using 15N labeled urea revealed that the best NUE was obtained from USG (77.6 kg N ha−1) among different application rates and methods in summer