Deep fertilization with controlled-release fertilizer for higher cereal yield and N utilization in paddies: The optimal fertilization depth

Belowground fertilization is a prevalent strategy for considerable grain yield and N utilization. However, the optimal fertilization depth remains uncertain in paddies, especially for slow/controlled release fertilizers. This study aimed to clarify the effect of deep "controlled-release blended fertilizer" (CRBF) fertilization on rice (Oryza sativa L.) yield and N utilization. Two N-fertilizer types were selected (a) urea and (b) CRBF, both combined at three fertilization depths (a) 0 cm, (b) 5 cm, and (c) 10 cm. The results showed that the grain yield was significantly affected by fertilizer type and fertilization depth. The yield achieved from CRBF was 7.8% higher than that from the urea application. Deep fertilization could also increase the rice yield with the optimum achieved from the 5-cm depth fertilization (yield increased by 15.1% compared to that from the manual surface fertilization). Overall, the 5-cm depth CRBF fertilization achieved the highest yield among all treatments with 12.21 and 11.84 t ha(-1) for 2018 and 2019, respectively. The larger sink was the main reason for this performance. Additionally, the higher photosynthetic efficient population after earing was another principal driver to the higher yield from CRBF. Due to the higher N uptake, CRBF application increased both N partial factor productivity (PFP) and recovery efficiency (RE) (P < .05); fertilization depth also had a striking effect on PFP and RE (P < .05 or .01). The 5-cm depth fertilization of CRBF achieved the highest N utilization for both years. The results suggest that 5-cm depth fertilization combined with controlled-release fertilizer is a suitable strategy for higher rice yield and N utilization.