The long-term nitrogen fertilizer management strategy based on straw return can improve the productivity of wheat-maize rotation system and reduce carbon emissions by increasing soil carbon and nitrogen sequestration

Problem

Facing the multiple objectives of increasing production, carbon sequestration, and nitrogen reduction in farmland, optimizing straw and nitrogen fertilizer management to achieve a balance between grain production and ecological safety in the wheat-maize rotation system has become increasingly critical and urgent.

Methods

This study conducted a five-year field experiment in the Guanzhong Plain of China from 2017 to 2021 to investigate the effects and synergistic regulatory mechanisms of straw disposal methods (straw return, no-straw return) and nitrogen application rates (0, 150, 225, 300 kg ha⁻¹) during the maize season on soil greenhouse gas (GHG) emissions, crop yield, and soil organic carbon (SOC) and soil toatl nitrogen (STN) content.

Results

The results showed that under the scenario of no-straw return, fertilization increased soil nitrous oxide (N₂O) emissions by 35.9–64.0 %, and annual total crop yield by 16.4–22.8 %; however, under the straw return scenario, the increase in soil N₂O emissions due to fertilization decreased to 26.7–62.0 %, while the yield increase rose to 19.5–25.9 %. The interaction effect between straw return and nitrogen application was significant, with straw return boosting the contribution rate of nitrogen application to yield (2.2–4.4 %) and simultaneously reducing the contribution rate of nitrogen application to N₂O emissions (3.0–27.5 %). The study also indicated that the yield-increasing effect of straw return continued to increase with the duration of straw return, with the contribution rate to yield reaching 9.9 % after three years of continuous straw return, while the contribution rate of nitrogen application to yield increased by an average of 3.0 % per year. This suggests that there is significant potential for coupling straw return with reduced nitrogen application. Straw return combined with nitrogen fertilizer increased SOC content by 7.9–40.1 % and 3.7–12.5 %, STN content by 1.0–22.8 % and 6.1–13.9 %, respectively, compared to sole nitrogen application and sole straw return. Pathway analysis indicated that straw return combined with nitrogen fertilizer mainly enhanced soil carbon-nitrogen sequestration, improved fertilizer utilization efficiency and crop nutrition levels, reduced net global warming potential (GWP) and greenhouse gas intensity (GHGI), and synergistically regulated to increase yield while reducing GHG emissions.

Conclusion

The study highlights that straw return lowers the threshold for nitrogen application levels, suggesting that regulating nitrogen application levels between 224 and 256 kg ha⁻¹ during the maize season, and maintaining a nitrogen application level of 195 kg ha⁻¹ during the wheat season, is beneficial for long-term stable production and emission reduction in the wheat-maize rotation system farmland.