Potential Contribution of Circulating Paddy Irrigation to Sustainable Water Management for Conserving Environments

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Recycle of drainage water from paddies, which is referred to as circulating irrigation, is important for environment conservation in terms of effective water use and reduction of loads. The effects of circulating irrigation on annual effluent loads from the paddies were evaluated in the circulating and non-circulating irrigation paddies along Lake Biwa. As a result, in the circulating irrigation paddies, the reduction of effluent loads during the irrigation periods except the flood events was expected to be increased with the ratio of the reused drainage to the total irrigation water. However, such loads reduction cannot necessarily contribute to the environmental conservation up to the full potential, since the temporal increase of effluent loads during the times of flooding was inevitable and the substances brought back to the paddies were released in the non-irrigation periods.