Using 15N Isotope to Evaluate the Effect of Brown Coal Application on the Nitrogen Fate in the Soil-Plant System

The problems of high nitrogen (N) fertilizer application rate and low N utilization efficiency are common worldwide in vegetable plantations. Application of brown coal (BC, also known as lignite) can increase crop yield and fertilizer N recovery efficiency (NRE). However, the effect of BC application on the utilization and distribution of exogenous N in the soil-plant system under different fertilization strategies is unclear. The pot experiment was set up in three factors of randomized design, including N-15-labeled urea fertilizer, BC, and organic manure, and pakchoi was used as the test crop. There were five rates of N-15-labeled urea, including 0, 100, 200, 300, and 400 kg N ha(-1), two rates of BC with 5 and 0 t ha(-1), and the organic manure with 0 t ha(-1) which constitutes ten treatments. The other four treatments were the combination of one N-15-labeled urea rate of 100 kg N ha(-1), two rates of BC with 5 and 0 t ha(-1), and two rates of organic manure with 100 and 0 kg N ha(-1). In conclusion, the interaction of all N fertilizer rates combined with BC improved soil N-15 retention efficiency by 10.14% compared without BC amendment. Between 200 and 300 kg N ha(-1), the average potential loss rate of N-15 decreased by 10.41%. The application of BC could reduce N loss by enhancing plant N uptake and increasing soil retention. The combined use of 200 kg N ha(-1) fertilizer and 5 t ha(-1) of BC would maintain a high fertilizer NRE and ensure pakchoi yield.