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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18053)
Authors:   M. Kim, M. Kim, M. Seo, N. Lee, K. Roh, and M. Koh
Keywords:   Paddy fields, Nutrient load, Irrigation water, Drainage water, Nitrogen, Phosphorous

The aim of this study is to evaluate the load of nitrogen and phosphorous in irrigation and drainage water from paddy fields. Water management practices that can reduce eutrophication and meet water quality requirements will also be addressed. Continuous monitoring from May to September 2002 and 2003 was conducted for quantification and qualification of irrigation and drainage water at paddy fields (15 ha) in Korea. Water balance and concentration variation of TN and T-P were independently compared for water assessment at each rice cultivation period. Rice land preparation and transplanting periods usually marked the highest water demands when compared to other periods of cultivation. Overall, there was a significantly greater net irrigation rate observed during the transplanting period in 2002 (92.3%) and 2003 (87.2%). A small difference in T-N concentration between irrigation and drainage water was observed. However, there was a dramatic change in T-P concentration during the rainy season. It indicates that drainage water management during rainy season is significantly important due to the increase of adsorbed phosphorous caused by soil loss from paddy soil. Generally, daily nutrient load follows the pattern of surface drainage water, but this pattern is changed by rainfall events. The nutrient load in drainage water depends on rainfall and surface drainage water amount from the paddy fields. Interestingly, the load of T-N and T-P outflow is vastly smaller than the inflow load due to the natural filtration that occurs during the cultivation period. It is concluded that the paddy fields have a beneficial effect on the ecosystem and decrease eutrophication in the water. Agricultural practices with good water management are strongly suggested to further reduce daily load of nutrients in the water. This will reduce the net volume outflow of nitrogen and phosphorous from paddy fields during the transplanting period and the rainy season.

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