Abstract
The cyclic irrigation system has been practiced in Japan for reducing pollutant outflow loadings from paddy fields. The cyclic irrigation is an irrigation method to reuse water by pumping drainage water and re-distributing it to the farmland. Quantification and assessment of the effects of the cyclic irrigation are needed to identify management options for maximizing the benefits of cyclic irrigation. The study was aimed at assessing loading characteristics from paddy field area under the cyclic irrigation and developing a model for simulating water and material flow in paddy field area that can be used as a management tool. The study was carried out in a paddy field in the Asagoi District, Oumihatiman city in Shiga Prefecture, Japan. Using the results of water quality analysis, the average net loadings of T-N and T-P were estimated for both cyclic and non-cyclic irrigation sites. The result indicates a higher nutrient absorption rate in the cyclic irrigation site than that in the non-cyclic irrigation site. The developed cyclic irrigation model showed good agreements between observed and simulated drainage volumes and nitrogen loadings. The scenario analysis by application of the model showed a potential of reducing the loading amount by increasing the cyclic irrigation ratio and reducing the amount of fertilizer application without affecting the rice yield.
Highlights
The average net loadings of total nitrogen (T-N) and total phosphorus (T-P) in the cyclic irrigation site were negative, while they were positive in the control site
Negative net loadings suggest that nutrients are accumulated or absorbed in the cyclic irrigation site
The effects of the cyclic irrigation on the discharge of nutrients from paddy field were analyzed by using the field observed data and developing
Summary
Biwa Lake is the biggest lake in Japan and an important water source for 14 mil-. In the late 1960s, water pollution and eutrophication have progressed in Biwa Lake and became a serious environmental problem. Shiga Prefecture acted against this problem by enacting the Eutrophication Prevention Ordinance. The eutrophication has been controlled to some extent, but occasionally water bloom has been observed, and further improvement of Biwa Lake water quality is needed [1]. Shiga Prefecture enacted the ordinance for promoting Environment Friendly Farming (EFF) and the direct payment system was introduced to encourage farmers to adopt EFF. In EFF, more than 50% of chemical application compared to ordinary farming should be reduced
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
