Abstract
An experiment of rice cultivation with circulated irrigation of treated municipal wastewater in a closed system simulating paddy field was conducted as a feasibility study of resorce-saving cultivation with reduced amounts of irrigation water and fertilizer. In this system, surface water always infiltrate paddy soil, is drained from culvert at the bottom and then return to the surface. Rice growth, yield and its quality such as taste and metal contents were compared between two runs, (1) circulating treated wastewater diluted by the same volume of river water and (2) circulating only river water. In Run 2, chemical fertilizers containing nitrogen, phosphorus and potassium were applied to the system according to the costumary practice. In Run 1, treated wastewater could supply the required amount of nitrogen, while deficiencies of phosphorus and potassium were covered by chemical fertilzers. The result of experiment demonstrated that there were no significant differences in rice growth, yield and its quality between two runs, indicating negligible effect of circulated irrigation of treated wastewater on rice cultivation. However, in both runs, overgrowth of rice and low score of its taste were found probably because nitrogen was not lost by runoff in the closed system.
