Abstract
The chemical properties of creek waters derived from Chikugo and Yabe rivers in southern Fukuoka Prefecture were examined from 1992 to 2001. The waters were sampled at 11 places several times during the period from puddling of paddy fields to the ripening of rice plants and during the non-irrigating period. The waters on average showed a higher value than the standard for agricultural water in T-N and COD. The values except DO, SS and T-P were higher in the irrigating period than in the non-irrigating period. In the last ten years, neither major deterioration nor improvement were found judging from the values of chemical properties measured. However, the yearly fluctuation in NH4-N and NO3-N contents were large, especially in the non-irrigating period. The ratio of NO3-N to total nitrogen was high in the tillering stage of rice in both creeks from Chikugo and Yabe rivers. It is estimated that 40% of the nitrogen fertilizer for the second topdressing at the ear formation staged can be reduced, judging from the amount of nitrogen in irrigating waters.
