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Effect of Time of Harvest and Nitrogen Level on Yield and Grain Breakage in Transplanted Rice¹

An application of up to 120 kg/ha of nitrogen fertilizer in the dry season huproved the milling quality of the chalky varieties ‘IR8,’ ‘IRS,’ and ‘Sigadis’ but not that of the nonchalky variety ‘C4-63.’ An application of up to 60 kg/ha of nitrogen increased the protein content of brown rice of the four varieties but increased the head rice yield of only Sigadis, the most chalky of the four varieties; the head rice yield of the other three varieties remained unchanged.

Irrespective of variety and nitrogen level, the optimum time of harvest of transplanted rice for obtaining maximum grain and head rice yields and highest germination percentage was between 28 and 34 days after heading in the dry season, and between 32 and 38 days in the wet season. These heading periods correspond to moisture contents of between 22 and 19% and between 21 and 18%, respectively.

Lodging increased grain yield losses in both seasons, with the losses being greater when harvested late; therefore, lodging-susceptible varieties should be harvested earlier than lodging-resistant varieties. Nitrogen fertilization in the dry season delayed by 2 to 4 days the optimum time of harvest of the improved varieties IR8, IR5 and C4-63.

Key Words: Chalky varieties • Head rice yield • Lodging • Heading date • Milling quality • Milk stage • Dough stage

² Former Rockefeller Foundation Scholar, University of the Philippines College of Agriculture; and Agronomist, The International Rice Research Institute.

Received for publication October 24, 1969.