Effects of air temperature, nitrogen concentration in irrigation water, and cultivation practices on rice production in the rice terrace region

Rice production in the rice terrace region was investigated, using three paddy fields located at different altitudes in different water systems in Hoshino village, Fukuoka prefecture, Japan. The effects of air temperature, nitrogen concentration in irrigation water, and cultivation practices of individual farmers were assessed, based on the growth indicators, yield components, and physicochemical properties of brown rice. It was found that abundant amounts of nitrogen-comparable to the standard nitrogen fertilization for the Yumetsukushi cultivar-were supplied from the irrigation water of field 1. Initial growth was restricted in field 2, due to early transplantation and early basal fertilization, resulting in a large percentage of ripened grains (PRG) and low protein content. The early transplantation resulted in a higher air temperature during the early ripening period and led to low amylose content. The 1000-GW was small in field 3; this was because the accumulation of starch in each grain was insufficient, due to the small production of dry matter per tiller. The underlying reasons were thought to be increased respiration and reduced efficiency of photosynthesis, both caused by excessive growth. Based on these results, the following recommendations for improving rice production in the region are indicated: an earlier transplantation date, to increase air temperature during the early ripening period and restrict initial growth; a reduction of basal nitrogen fertilization, to preclude excessive growth; and avoiding nitrogen-fertilizer applications on fields where abundant nitrogen is supplied from irrigation water.