Recovery efficiency and loss of 15N-labelled urea in a rice-soil system under water saving irrigation in the Songnen Plain of Northeast China

From 1980 to 2016, the increase in grain production in the Songnen Plain of Northeast China was significant, which was caused by a continuous increase in the use of nitrogen fertilizer; however, the partial fertilizer productivity (PFP) is gradually decreasing, and a large amount of nitrogen fertilizer is lost to the environment, leading to a series of environment problems. This test combining a field plot test with an in-situ micro-zone test, six treatments were set: two irrigation regimens (controlled irrigation and flooded irrigation) and three N rates (85, 110 and 135 kg ha(-1)). the recovery and loss of nitrogen fertilizer in a rice-soil system under controlled irrigation regimen were studied. Also, the basal, tillering, and panicle fertilizers were marked, and the absorption and accumulation of different periods N-15-labeled urea under different water and nitrogen control regimens as well as the residual rate of N-15-labeled urea in the soil layer of paddy soil in each period were quantitatively analyzed. Each period nitrogen fertilizer recovery and loss in the rice-soil system were quantitative analyzed. The results showed that the loss rate of the rice-soil system of controlled irrigation was reduced by 15.42-28.64% under the three nitrogen application levels compared to conventional flooded irrigation in the black soil region of the Songnen Plain. The system also maintained the original rice yield and greatly reduced the threat of nitrogen fertilizer loss to the environment in the black soil region. The total nitrogen recovery rate in the rice-soil system ranged from 69.18% to 74.19% with controlled irrigation regimen under the different nitrogen application levels, and the nitrogen recovery rate of the basal fertilizer was 41.46%-48.85%. The nitrogen recovery rate of the tillering fertilizer was 84.20-95.85%, whereas the nitrogen recovery rate of the particle fertilizer was 89.57-93.80%. The total nitrogen recovery rate of the rice plant was 32.05-38.83%, the recovery rate of the basal fertilizer was 11.78-16.44%, and the recovery rate of the tillering fertilizer was 37.49-39.02%. The recovery rate of panicle fertilizer was 54.15-68.38%. Rice-planting under controlled irrigation can effectively reduce N fertilizer losses and also increase the dry matter accumulation of rice plants, which was found to be 13.27-27.52% more than that of the conventional flooded irrigation regimen. The controlled irrigation regimen not only meets the current requirements for grain yield, but also plays a role in saving water, increases production, and reduces environmental pollution.