Synergistic effects of returning organic materials on crop yield, water and nitrogen use efficiency: A global meta-analysis

Returning organic materials (ROM) is recognized as a potential measure to synergistically improve grain yield, water use efficiency (WUE), and nitrogen use efficiency (NUE), but its effects vary widely with climate, soil properties, and field management practices. Consequently, we conducted a meta-analysis by synthesizing 2479 observations from 467 peer-reviewed publications to quantify the impacts of ROM on the grain yield, WUE, and NUE, as well as clarify the responses to different climatic factors, soil properties, and field management practices. The results showed that ROM significantly increased the grain yield, WUE, and NUE by 19.84%, 17.82% and 17.94%, respectively. Random forest model analysis showed that initial soil pH was the most important factor affecting grain yield and NUE under ROM, while organic material addition rate was the most important factor influencing WUE (P < 0.01). By comprehensively considering these factors, we found that under fine soil texture, low nitrogen input level (<150 kg N ha−1), and low organic material application rate (< 10 t ha−1), ROM can maximize synergistic improvements in the grain yield, WUE, and NUE. Our results can provide a theoretical basis for the efficient utilization of organic materials and the formulation of return strategies, thereby promoting the sustainable development of agriculture and the effective utilization of resources.