Nitrogen reduction with green manure roots return maintains spring wheat yield and alleviates soil N2O emission in saline-alkali agroecosystem

Abstract

The growing global demand for grain drives a greater need for nitrogen (N) input. Yet, it contributes to nitrous oxide ($N_2$O) emissions, aggravating global climate change. To tackle this dual challenge of fulfilling crop demands while maintaining or reducing $N_2$O emissions, a field study was performed in wheat-green manure cropping system to assess the effects of varying fertilizer application (N100, N90 and N80: N fertilizer reduced by 0%, 10% and 20%) combined with green manure return strategy (GMR: green manure roots return, GMRS: green manure roots and shoots return), and wheat fallow after harvest (CK) on wheat yield and yield stability from 2020 to 2024, $N_2$O emissions, as well as $N_2$O emission intensity from 2022 to 2024. Results showed that, although N fertilizer combined with green manure return strategy increased spring wheat yield by 8%–22% by increasing soil mineral N contents, it decreased yield stability compared with CK. Soil $N_2$O emissions were mainly negatively and positively regulated by pH and NO${}_3^{-}$-N content in saline-alkali soil, respectively. N80 decreased cumulative soil $N_2$O emission and $N_2$O intensity by 20% and 10% compared with N100, respectively. Irrespective of the variations in N fertilizer levels, GMR decreased cumulative $N_2$O emission and $N_2$O intensity by 20%–34% and 22%–38% compared with GMRS, respectively. Overall, the findings highlighted N fertilizer reduced by 20% (160 kg N ha ⁻¹) with green manure roots returned in relative to normal rate (200 kg N ha ⁻¹) is a viable option to ensure spring wheat yield and alleviate soil $N_2$O emission in saline-alkali agroecosystem.