Characteristics of nitrogen loss through lateral seepage in paddy fields under irrigation and drainage regulation

The aim of this paper is to investigate the effects of irrigation and drainage regulation on nitrogen (N) lateral seepage process in paddy fields, and four treatments were designed: controlled irrigation and controlled drainage (CICD), controlled irrigation and free drainage (CIFD), flooding irrigation and controlled drainage (FICD), and flooding irrigation and free drainage (FIFD). The dynamic changes of total nitrogen (TN), NH₄+-N and NO₃−-N concentrations in different soil at depths under different treatments were monitored, and the effects of lateral seepage driven by moisture on lateral seepage of N load and loss rate in bunds were analyzed. Results showed that the controlled irrigation treatment delayed the peak time of N concentration in the soil solution at all depths of the bund except for the 10–20 cm depth and reduced the peak TN and NO₃−-N concentrations within the soil solution from 0 to 40 cm of the bund compared to the flooding irrigation treatment. In addition, compared with FIFD, CICD reduced the N load from lateral seepage of bund by 73.3%, and decreased the N loss rate from paddy field bund by 2.3%. Therefore, controlled irrigation and drainage is an effective management practice.