One-time application of controlled-release bulk blending fertilizer enhanced yield, quality and photosynthetic efficiency of late japonica rice

Controlled-release urea (CRU) releases nitrogen (N) at the same pace as rice uptakes N, which can effectively improve N use efficiency, increase rice yield and improve rice quality. However, few studies have described the effects of the application of CRU on the photosynthetic rate and endogenous enzyme activity of rice. Accordingly, a two-year field trial was conducted with a total of seven treatments (CK, no N fertilizer; BBF, regular blended fertilizer; RBBF, 20% N-reduced regular blended fertilizer; CRF1, 70% CRU+30% regular urea one-time base application; CRF2, 60% CRU+40% regular urea one-time base application; RCRF1, CRF1 treatment with 20% N reduction; RCRF2, CRF2 treatment with 20% N reduction). Each treatment was conducted in triplicate. The results showed that the N recovery efficiency (NRE) of the controlled-release bulk blending fertilizer (CRBBF) treatments was significantly increased over the two years. There were significant yield increases of 4.1–5.9% under the CRF1 treatment and 5.6–7.6% under the CRF2 treatment compared to the BBF treatment, but the differences between the reduced N treatments RBBF and RCRF2 were not significant. The photosynthetic rates under the CRF1 and CRF2 treatments were significantly higher than under the other treatments, as well as significantly increased RuBPCase, RuBisCO, GOGAT and GS enzyme activity. Additionally, the soil NH4+-N and NO3−-N content under the CRBBF treatments was significantly higher at the late growth stage of rice, which was more in line with the fertilizer requirements of rice throughout the reproductive period. The CRBBF also led to some improvement in rice quality. Compared with the BBF and RBBF treatments, the protein content under the CRBBF treatments was reduced but the milling, appearance, eating and cooking quality of the rice were improved. These results showed that the application of CRBBF could improve the NRE, photosynthetic rate and endogenous enzyme activity of rice, ensuring sufficient N nutrition and photosynthetic material production during rice growth and thereby achieving improved rice yield and quality.