Effects of ear fertilizer application on yield and grain quality of rice cultivar 'Koshihikari' under high temperature

The quality in appearance of brown rice has significantly decreased due to high temperature during the ripening period. A major rice cultivar 'Koshihikari' was cultivated in Shiga, Japan in 2010 and 2011 when high temperatures continued during the ripening period. The transplantation period and the amounts of basal fertilization and additional fertilization were varied. For each test condition, a test section was provided with different dosage in the first application (seven days after ear formation: ear fertilization I) and the second application (14 days after ear formation: ear fertilization II). The total dosage of fertilization after ear formation was 4 gN/square m. The effect of the fertilization on the rice yield and the quality of the brown rice was then examined. As a result, the rice yield and quality of the brown rice fluctuated depending on changes in the transplantation period and the amounts of basal fertilization and additional fertilization. Meanwhile, a comparison among different dosages in ear fertilization I and ear fertilization II including 2-2, 1-3, and 0-4 gN/square m exhibited a trend of the weight of polished brown rice decreasing and appearance of the brown rice improving when the dosage was low in the first application and then high in the second application. The quality of the brown rice's appearance increased with the decreased amount of milky white kernel and base immature kernel. The protein content of the brown rice tended to increase when the amount of fertilization in the first application was decreased and then increased in the second application, though the rate of increase was small. When high temperatures continue during the ripening period, a standard fertilization of 2-2 gN/square m produces sufficient yield. Yet, changing to 1-3 gN/square m is effective to improve the quality of the brown rice if the brown rice's appearance becomes worse with the standard fertilization.