Effects of straw returning and organic substitution on crop yield and field nitrogen loss under wheat-maize rotation system

Objectives The effects of different fertilization measures on crop yield, nitrogen use efficiency and field nitrogen loss in wheat-maize rotation model were studied, so as to provide a basis for practical application.

Methods We searched literatures on the CNKI and Web of Science, using key worlds wheat, corn or maize, wheat-maize or wheat-corn, manure, organic fertilizer, substitution or replace, straw incorporation or straw returning or straw mulching, yield and nitrogen, from January 2000 to December 2023 within the wheat-maize rotation area of China. A total of 64 articles were screened out for the extraction of data. A meta-analysis method was used to compared the effects of conventional chemical fertilizer, straw returning, organic substitution and straw returning + organic substitution on crop yield, nitrogen utilization rate and nitrogen loss.

Results The average yield of wheat and maize under conventional chemical fertilizer was 6.06 t/hm² and 7.79 t/hm², and the nitrogen utilization rate was 36.3% and 34.2%, respectively. The main nitrogen loss was leaching and NH₃ volatilization. Maize season was the main nitrogen loss, accounting for 57.7% of the annual nitrogen loss. Compared with conventional chemical fertilizer, straw return significantly increased wheat yield by 21.8% and maize yield by 6.1%, but brought a risk of increasing NH₃ volatilization and N₂O emission; organic substitution significantly reduced nitrate leaching by 39.6% in wheat season and 27.7% in maize season, and reduced N₂O emission in maize season by 21.2%, but led to fluctuated wheat yield greatly, and the yield increase rate was averaged 3.6% under the optimal substitution ratio of 20%−40%; straw return + organic substitution measure increased wheat yield by 16.4% on average and increased maize yield by 17.7%, and reduced NO₃⁻-N leaching by 24.1% during maize season. It was worth noting that compared with straw returning, straw returning + organic substitution significantly increased crop yield (wheat 5.7%, maize 13.4%), but increased maize season N₂O emission (61.9%).

Conclusions Both straw returning and organic substitution, individually and combined, exhibited notable impacts on crop yield in wheat-maize rotation systems. However, they also presented certain limitations. Organic substitution proved most effective in minimizing nitrogen loss from cropland, but only when implemented at an optimal substitution ratio, did it achieve optimal yield enhancement and emission reduction. When straw returning was integrated with organic substitution measures, it demonstrated the most pronounced effect on yield improvement. Nevertheless, the impact of this combination on reducing farmland nitrogen loss remains understudied and unclear, necessitating further investigation.