| Summary: | Effective water and nitrogen (N) management strategies are critical for sustainable agricultural development. Lysimeter experiments with two deep percolation rates (low percolation and high percolation, i.e., LP and HP: 3 mm d<sup>−1</sup> and 5 mm d<sup>−1</sup>) and five N application levels (N0~N4: 0, 60, 135, 210 and 285 kg N ha<sup>−1</sup>) were conducted to investigate the effects of controlled drainage on water productivity (<i>WP</i>) and N use efficiency (<i>NUE</i>) in water-saving irrigated paddy fields. The results demonstrated that NH<sub>4</sub><sup>+</sup>-N and NO<sub>3</sub><sup>−</sup>-N were the major components of total nitrogen (TN) in ponded water and leachate, accounting for more than 77.1% and 83.6% of TN, respectively. The risk of N leaching loss increased significantly under treatment of high percolation rates or high N application levels. High percolation loss required greater irrigation input, thus reducing <i>WP</i>. In addition, N uptake increased with increasing N application, but fertilization applied in excess of crop demand had a negative effect on grain yield. <i>NUE</i> was affected by the amount of N applied and increased with decreasing N levels. Water and N application levels had a significant effect on N uptake of rice, but their interaction on N uptake or <i>NUE</i> was not significant. For the LP and HP regimes, the highest N uptake and <i>WP</i> were obtained with N application levels of 285 kg ha<sup>−1</sup> and 210 kg ha<sup>−1</sup>, respectively. Our overall results suggested that the combination of controlled drainage and water-saving irrigation was a feasible mitigation strategy to reduce N losses through subdrainage percolation and to provide more nutrients available for rice to improve <i>NUE</i>, thus reducing diffuse agricultural pollution. Long-term field trials are necessary to validate the lysimeter results.
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