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

Abstract

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 15N-labeled urea fertilizer, BC, and organic manure, and pakchoi was used as the test crop. There were five rates of 15N-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 15N-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 15N retention efficiency by 10.14% compared without BC amendment. Between 200 and 300 kg N ha−1, the average potential loss rate of 15N 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.