Lower dose of controlled/slow release fertilizer with higher rice yield and N utilization in paddies: Evidence from a meta-analysis

Context or problem: Improving the nitrogen (N) utilization together with obtaining an optimal crop yield is a worth exploring practice, especially in the smallholder farming regions. Objective or research question: Application of slow/controlled release fertilizer (SCRF) in paddies is an efficient strategy to ensure rice yield and to improve N utilization. Notably, the effects of SCRF often vary with the types and dosages of SCRF, rice variety, and soil properties. However, individual trials span a variety of practices and vary in their experimental designs and results that, in turn, make it difficult to determine its overall response. Methods: A meta-analysis using 184 studies in China was performed to analyze the effects of SCRF on rice yield and N utilization in relation to the environmental conditions. To do so, the SCRF type (slow-release fertilizer, SRF; controlled-release fertilizer, CRF; and bulk blend fertilizer, BBF), SCRF rate (the ratio of N dose in SCRF plots to CF control), the addition ratio of SCRF (the N dose ratio of SCRF to total), soil properties (pH, SOM, and TN), and rice varieties (japonica rice, indica rice, etc.) were taken into consideration. Results: The results showed that compared with CF, the yield and N uptake (NU) under SCRF increased by 6.0 % and 11.1 % respectively. N use efficiency (NUE) increased from 35.7 % (CF) to 44.9 % (SCRF). The SCRF rate and rice variety were the important factors affecting rice yield. The effect size increased linearly with the SCRF rate (P < 0.001). Herein, SCRF showed a negative effect when the rate was lower than similar to 80 %. Furthermore, the results of categorizing analysis showed that the higher relative rate (>90 %) could significantly increase the rice yield. Different from the other rice varieties, SCRF decreased the yield of three-line japonica hybrid rice. Also, the SCRF type along with its relative rate were crucial for NU and NUE. Unsurprisingly, the NUE increased with lower SCRF dose. Importantly, the treatment effect of BBF was better than those of CRF and SRF. Conclusions: The results suggest that SCRF, especially BBF is the suitable alternative fertilizer in paddies, which can achieve higher rice yield and N utilization with lower dosage. However, the response of rice variety to SCRF merits further attention in future studies.