RUNOFF PATTERN OF PESTICIDES FROM PADDY FIELDS IN THE CATCHMENT-AREA OF RIKIMARU RESERVOIR, JAPAN

Patterns of runoff behaviours in concentration and loading of pesticid es from paddy fields have been intensively observed in the catchment a rea of Rikimaru Reservoir, mainly during the regular application perio d of fungicide during the summer. The runoff characteristics of three pesticides (pyroquilone, isoprothiolane and flutolanil) from paddy fie lds to the drainage river differed from one another due to their water solubilities. The linear correlation between the water solubilities a nd the amounts of pesticide runoff loadings from paddy fields to the d rainage river and reservoir during dry weather days was confirmed as g ood on log-log paper. To reduce the risk to raw water for drinking in the reservoir the method of irrigation water management for paddy fiel ds should be improved.