Grain Yield, Milling Quality, and Seed Viability of Rice as Influenced by Time of Nitrogen Application and Time of Harvest1

Abstract

AbstractSince the development of high yielding tropical rice (Oryza sativa L.) cultivars like ‘IR8,’ attention has turned to the differences in grain quality among rice cultivars. In field experiments at the IRRI farm, we studied the optimum time for applying nitrogen to rice cultivars for maximum grain yield, highest milling yield, and maximum seed viability. We applied ammonium sulfate at 60 kg/ha N in the 1969 wet season and 150 kg/ha N in the 1970 dry season. We used the cultivars IR8, ‘IR20,’ ‘C4‐63,’ and ‘RD1’ in the 1969 wet season and IR8, IR20, ‘IR22,’ and RD1 in the 1970 dry season. Farmers in South and Southeast Asia grow these cultivars on millions of hectares.Split application of nitrogen increased grain yield over single basal application in some cultivars by minimizing lodging.Topdressing of nitrogen at heading increased the percentage of head rice (unbroken polished grains) which was associated with higher protein content under that treatment. IR22, whose percentage of head rice was higher than those of the other cultivars tested, showed no further increase in head rice with nitrogen topdressing.Based on maximum grain yield with highest milling recovery and seed viability, the best time for harvesting transplanted rice was between 30 and 42 days after heading in the wet season and between 28 and 34 days after heading in the dry season.