Dynamic interactions of nitrogen fertilizer and straw application on greenhouse gas emissions and sequestration of soil carbon and nitrogen: A 13-year field study

The application of nitrogen (N) fertilizer and straw (S) is a common practice in rice cultivation. However, the dynamic changes in the long-term effects on methane (CH₄) and nitrous oxide (N₂O) emissions and soil organic carbon (SOC) and total nitrogen (STN) sequestration rates are poorly documented. A field experiment was performed in the years of 1-2, 6-7 and 12-13 in China with three treatments: no N or S (-N-S), 300 kg N ha^-1 without S (+N-S), and 300 kg N ha^-1 combined with 4.8 t ha^-1 S (+N+S). Compared with -N-S, CH₄ emissions in +N-S varied from a negative effect in years 1-2 (-11.3%) to a positive effect in years 12-13 (7.6%). However, a constant increase was found in +N+S by 3.7, 15.8 and 7.6 times in years 1-2, 6-7 and 12-13, respectively. For N₂O emissions, +N-S relative to -N-S increased by 5.4-8.9 times, and +N+S increased the emissions by from 3.0 to 5.2, and to 17.3 times, respectively. Therefore, the global warming potential (GWP) of CH₄ and N₂O emissions in +N+S was 3.3-3.7, 7.7-14.3 and 5.8-7.8 times higher than that in +N-S and -N-S, respectively. The grain yield of +N+S ranged from 5.6 to 10.0 t ha^-1, 30-56% and 42-71% higher than that in +N-S and -N-S. Moreover, the SOC sequestration rates of +N+S decreased from the values of 2.7 to1.6 and to 0.4 t C ha^-1 yr^-1, respectively, which were 15-80% and 17-73% higher than those of +N-S and -N-S. Compared to -N-S, the +N-S and +N+S increased STN sequestration rates by 0.01-0.06 and 0.03-0.05 t N ha^-1 yr^-1, respectively. The findings suggest that the positive effects of N and S on the GWP and STN sequestration showed an upward and then downward trend, while the SOC sequestration exhibited a continuous decline.