Evaluation of environment on rice production for the rice terraces in Hoshino Village

Variables characterizing ambient environmental conditions (such as barometric pressure, solar radiation, rainfall, temperature, relative humidity, and wind speed) were measured between June and October in 2006 at the rice terraces in Hoshino village, Fukuoka prefecture. Differences in the environmental conditions of the three paddy fields located at different elevations in the same water system were assessed. Also, environmental factors that affected rice quality were identified using data collected during the beginning of a ripening period (20 days after heading) by principal component analysis. The study results demonstrated that the paddy field midstream in the water system had the least solar radiation because it was surrounded by slightly elevated mountains and forest. Average temperatures at three paddy fields during the ripening stage were in the range of an optimal temperature while the temperature during the tillering stage was below the optimal range at the fields upstream and midstream. The field downstream was the only case that the diurnal range of temperature was larger than that in the plain area. As the results of principal component analysis, average temperature, average relative humidity, and solar radiation during the beginning of a ripening season were shown as major environmental factors that affected rice quality. Average temperature had a positive effect on rice quality, and this effect could be explained by the negative correlation between temperature and amylose content. Relative humidity had positive effect, and solar radiation had positive effect.