Improving yield and nitrogen use efficiency through alternative fertilization options for rice in China: A meta-analysis

Applying alternative fertilization practices instead of conventional fertilizers might improve rice yield and nutrient use efficiency in rice cropping systems. However, the results range widely among individual studies, making generalizations difficult. Here, we investigated five alternative fertilization options (slow-release nitrogen fertilizer, SRF; organic fertilizer, OF; straw return, SR; green manure, GM; secondary/micronutrient fertilizer, SMF) and performed a meta-analysis to quantify their effects on rice yield and nitrogen (N) use efficiency across different rice types in China. Yield responses were significantly positive under all alternative fertilization options relative to those obtained with conventional fertilization, and the magnitude of yield increase exhibited the following the order: OF (7.8%) > SRF (7.4%) > GM (6.7%) > SR (5.4%) > SMF (4.6%). Furthermore, the recovery efficiency (REN), agronomic efficiency (AEN), and the partial factor productivity of nitrogen (PFPN) were increased by 6.0-34.8%, 10.2-29.5%, and 4.7-6.9%, respectively under the alternative fertilization options relative to conventional fertilization. The application of SRF and SMF generated higher yield responses in single rice than in other rice types, whereas OF and SR application resulted in better performance in early and middle rice. The rice yield response was maximized when approximately 70% slow-release N was combined with approximately 30% conventional N according to the quadratic relationship between the percentage of slow-release N substituting conventional N and the yield response. It was estimated that the total N rate could be reduced by up to 32% without yield loss with the application of slow-release N fertilizer instead of conventional N fertilizer. When organic N fully or partially substituted inorganic N, yield response declined with increasing substitution level, and the substitution proportion needed to be controlled below 20% to maintain rice yield. The meta-analysis results clearly demonstrate that appropriate alternative fertilization options can increase both rice yield and nitrogen use efficiency, and that conventional chemical fertilizers can be partially replaced with alternative ones without negatively affecting rice productivity.