Nutrients loss and their recovery during flooding periods in paddy fields

【Objective】 Flooding in paddy fields facilitates weed control, improves phosphorus availability, and aids in pest management. This paper experimentally studies leaching and recovery of nutrients during flooding period in paddy fields in the Tai Lake Basin. 【Method】 The experiment was conducted in a paddy field with well-established field and main drainage ditches. During the experiment, we measured the quantity and quality of water in each irrigation-drainage unit in both field and main drainage ditches. The significance of each nutrient was calculated using the entropy weight method to identify key water quality factors in each irrigation-drainage unit. The data measured in both field and main drainage ditches were used to calculate the recovery of the leached nutrients and their reuse. 【Result】 After the inception of the flooding, the concentrations of all nutrients measured in the ditches increased initially followed by a decline. In the main drainage ditches, it took one to two days for changes in the nutrient concentrations to emerge. At the end of the flooding, the concentrations of nutrients in all ditches were higher than those before the flooding; they decreased as water flow increased. The analysis of the entropy weight method showed that nitrogen was the key water quality factor in the field ditches, while COD was the key water quality factor in the main ditches. Our results showed that 45.56% of drained water was reused for irrigation, and the recovery rates of TN, NH4+-N, TP and COD were 51.96%, 33.68%, 57.61% and 42.65%, respectively. 【Conclusion】 The large irrigation volume used during the flooding period in the paddy fields increased the risk of nutrients leaching. Reusing the drained water is an effective strategy to minimize nutrients losses and reduce environmental pollution. Improving water conservation and reducing greenhouse emissions in each irrigation-drainage unit are crucial for developing sustainable agriculture in the Taihu Lake Basin.