FARMER’S WATER MANAGEMENT PRACTICES AND EFFECTIVE RAINFALL AND RUNOFF RATIO OF PADDY FIELDS

摘要

Effective rainfall, which was used in paddy fi eld under current farmer’s water managementpractice were monitored during 2008 - 2012 period in South Korea. Two studied paddy fi elds(HY and JS) have area of 13.69 and 8.06 ha and it was composed of several paddy plotsseparated by irrigation and drainage canals. Rain gauges and sets of water level gaugeswere installed at irrigation and drainage canal. A water level gauge was set up at the outlet ofthe drainage canal to measure discharge from the paddy fi elds. The effective rainfall ranged388.8-798.8 mm and average was 555.8 mm for HY site. Those ranged 345.3~535.0mm andaverage was 436.2 mm for JS site. About 65% and 45% of rainfall for HY and JS was usedin paddy fi eld. Runoff ratios of paddy fi elds for rainfall class 0~10mm, 10~30mm, 30~50mmand above 50 mm were also examined to evaluate farmer’s water management practice. Theobserved runoff ratios were 0.13, 0.19, 0.27, and 0.38 for HY site, respectively. On the otherhand, the runoff ratios were 0.20, 0.28, 0.49, and 0.57 for JS site, respectively. Since height oflevee for each paddy plot is about 100~300mm, a plot has enough room for hold rainfall, butfi eld data showed that some rainfall was not used effi ciently. It confi rmed that farmers havelittle incentive to effectively use rainfall for rice paddy culture because they can use irrigationat no charge. One of the reasons for poor water management at farm level was inadequatefunctionality of the drainage system. Drainage pipes, which are widely used in Korea wasconsidered to be modifi ed or replaced to reduce uncontrolled drainage from paddy fi eld.