Mechanical deep placement of slow/controlled-release fertilizer increases grain yield and nitrogen use efficiency by improving the carbon and nitrogen metabolism abilities of rice

Background and Aims Slow controlled release fertilizer has been paid more attention because of its slow release and long fertilizer cycle, the mechanized deep slow/controlled-release fertilizer (SRF) is desirable owing to its high nitrogen use efficiency. In this study, we elucidated the effects of mechanized deep SRF on the characteristics of carbon and nitrogen metabolism, grain yield and nitrogen use efficiency (NUE) of rice. Methods A two-year field experiment was conducted. Two rice cultivars, i.e., Meixiangzhan 2 (MX) and Y Liangyou 1378 (YL), were used and three kinds of fertilization modes, i.e., mechanized deep placement of conventional urea (CU), slow/controlled-release fertilizer (SRF) and compound fertilizer (CF), at 150 kg N ha ^− 1 , were designed, respectively. Results The results showed that the grain yields of MX and YL for SRF were 29.04% and 25.52% greater than those of CU, respectively, owing to the greater number of productive panicles, spikelets per panicle, and 1000-grain-weight. The nitrogen recovery efficiency of MX and YL under SRF were 42.31% and 33.65% higher than those under CU. The SRF treatment produced higher nitrogen agronomic efficiency (21.17 kg kg ^− 1 and 23.75 kg kg ^− 1 ) for MX and YL, which were 82.19% and 68.20% higher than those under CU, respectively. Moreover, the SRF treatment significantly improved the leaf area index and total aboveground biomass at the panicle initiation and heading stages, and nitrate reductase, glutamate synthase and glutamine oxoglutarate aminotransferase activities. The results of structural equation model (SEM) showed that yield components and nitrogen metabolism enzymes had significantly positive and direct regulatory effects on rice yield. Nitrogen use efficiency was significantly positively regulated by the activity of nitrogen-metabolizing enzymes and the accumulation of nitrogen. Conclusion Mechanical deep placement of slow/controlled-release fertilizer at a rate of 150 kg N per hectare increases grain yield and nitrogen use efficiency, which can be an efficient nitrogen fertilizer management practice in South China.