Cyclic irrigation supplements irrigation and reduces flood, which has the potential to reduce the harm of drought-flood abrupt alternation and agricultural non-point pollution, but there is no effective method to simulate water cycle in paddy field under cyclic irrigation of drainage water. Thus a water balance model was built to describe the inflow of drainage and outflow of irrigation water requirement for a pond under cyclic irrigation of drainage water. Drainage amount was calculated with the improved SCS (soil conservation service) model. Rice irrigation water requirement amount was estimated from crop water requirement, leaching water amount and effective precipitation. Crop water requirement amount was calculated with the Penman-Monteith equation and crop coefficient method, and the effective precipitation was calculated with the USDA (United States Department of Agriculture) SCS method. The model application showed that there was plenty of drainage water for reuse in paddy area of Zhanghe irrigation district, and the drainage amount contributed 18.1%, 41.2% and 16.9% of irrigation water requirements for dry year, normal year and wet year, respectively. The actual reuse amount of drainage water was affected by irrigation-drainage area ratio, pond capacity ratio and pond initial storage ratio. Supplement irrigation ratio was defined as the ratio of cyclic irrigation amount of drainage to total irrigation amount, and drainage reuse ratio was defined as the ratio of cyclic irrigation amount of drainage to total drainage amount. Supplement irrigation ratio and drainage reuse ratio increased with the increase in irrigation-drainage area ratio and then stabilized at the maximum for different hydrological years. The maximum supplement irrigation ratio of about 20% and the maximum drainage reuse ratio of about 60% were observed at the irrigation-drainage area ratio of 0.15 and 0.5, respectively, for the dry year and normal year. For the wet year, the maximum supplement irrigation ratio of about 20% and the maximum drainage reuse ratio of about 100% were observed at the irrigation-drainage area ratio of 0.4 and 0.15, respectively. Supplement irrigation ratio and drainage reuse ratio increased with the increase in pond capacity ratio and then stabilized at the maximum for different hydrological years. As the pond capacity ratio increased to 1 000, 2 000 and 700 m3/hm2, the drainage reuse ratio reached the maximum of 100%, respectively, for dry year, normal year and wet year. The maximum supplement irrigation ratio of about 20% were observed at the pond capacity ratio of 1 500 m3/hm2, and the higher increase period of supplement irrigation ratio occurred at the pond capacity of below 700 m3/hm2 for dry year and 300 m3/hm2 for normal year and wet year. As the pond initial storage ratio increased to 0.7, 0.9 and 0.9, the drainage reuse ratio started to decrease from the stable maximum of about 60%, 40% and 100%, respectively. Supplement irrigation ratio increased with the increase in pond initial storage ratio and then stabilized at the maximum of about 20% with pond initial storage ratio of 0.7 for dry year, and 0.9 for normal year and wet year. The water cycle model in paddy district under cyclic irrigation of drainage water can be an effective method for matching pond size or drainage-irrigation area, and be used for different weather and soil conditions. However, the weather and crop condition variations of different districts should be considered because the pond and drainage-irrigation area are obviously affected by local conditions.%排水循环灌溉可补充灌溉和减少涝水排放，具有缓解南方稻区旱涝急转和农业面源污染危害的潜力，但仍无有效的模型来模拟排水循环灌溉驱动下的水文过程。为此采用penman-monteith公式和作物系数法并考虑稻田渗漏与降雨有效性条件下应用水量平衡估算水稻灌溉需水量，改进SCS（soil conservation service）模型估算排水量，再以塘堰为对象建立调蓄排水和灌溉需水的水平衡演算模型。在漳河水库灌区应用该模型发现，水稻种植区存在大量的排水可供灌溉利用，而排水循环灌溉利用量受灌排面积比、塘堰容积率和塘堰初始蓄水率的影响；提高灌排面积比和塘堰容积率能明显提高补充灌溉率和排水再利用率，当两者达到一定值时补充灌溉率和排水再利用率便稳定在最高值，补充灌溉率高达20%；补充灌溉率随塘堰初始蓄水率的增加而缓慢增至20%，排水再利用率先随初始蓄水率的增加而稳定不变，随后逐渐降低。排水循环灌溉驱动的水循环模型为合理匹配排水循环灌溉的塘堰或排灌规模提供有效方法。
展开▼
