Rice production environment in the rice [Oryza sativa] terraces of Hoshino Village, Fukuoka [Japan] Prefecture

The objective of this study was to provide useful reference data on the effects of environmental factors on rice production in rice terraces. Environmental indicators, such as meteorology, soil properties, and water quality, were measured in the rice terraces of Hoshino Village, Fukuoka Prefecture. The results revealed that during the ripening period, the average temperatures in the terraces were approximately 3degC lower than those in the plain area. In almost 50% of the surveyed paddy fields, the daily range of temperature was larger than that in the plain area. The daily solar radiation during the ripening period varied in the surveyed region, and the solar radiation conditions were disadvantageous in some fields. The effective cation exchange capacity (ECEC) of the soil was low in the paddy fields located upstream and was lower than 10 cmolsub(c)/kg in many of the paddy fields. The water in the surveyed region was clean because the region was located in the upstream area of a water system. However, small water volumes of a stream in the region resulted in high NO3-N concentrations in the water systems that were surrounded by tea fields. On the basis of these results, the effects of the environment on rice production in the surveyed region were assessed as follows: The low average temperature during the ripening period is advantageous for preventing the rice quality from deteriorating due to high temperatures. The large daily range of temperature is favorable ripening environment, which appeared in the paddy fields located in basin, which is surrounded by slightly elevated mountains to a large extent, or mountainside around the lowlands in the downstream of a water system. The small solar radiation found in some paddy fields is considered a negative factor that potentially lowers the rice yield. The ability of the soil to retain nutrients tends to be poor. Water environments are easily affected by the manner in which the surrounding land is used; thus, water systems with a high NO3-N concentration may have a negative impact on rice production, for example, by increasing the protein content.