Mechanically Deep-Placed Nitrogen Fertilizer Modulates Rice Yield and Nitrogen Recovery Efficiency in South China

Mechanical deep fertilization is an efficient fertilization method. However, the effects of different types of nitrogen fertilizer on rice grain yield and nitrogen use efficiency under deep-application conditions remain unclear. In this study, field experiments were carried out in 2021 and 2022. The experimental treatments consisted of three types of nitrogen fertilizer, i.e., urea (T1), slow/controlled-release fertilizer (T2), and super rice special fertilizer (T3), applied at a rate of 150 kg N ha−1 via mechanical deep placement using Meixiangzhan 2 (MX) and Y liangyou 1378 (YL) as experimental materials. No fertilizer application was used as a control (T0) to calculate nitrogen use efficiency. The T2 treatment produced 29.03% and 25.52% higher grain yield for MX and YL because of the increase in productive panicles per ha and spikelet number per panicle, 21.20% and 13.68% higher nitrogen recovery efficiency, and 24.57% and 23.29% higher nitrogen agronomy efficiency than T1, respectively. In addition, the T2 treatment significantly improved the leaf area index and total aboveground biomass at the panicle initiation and heading stages. We also found that the POD, CAT, NR, and GOGAT of T2 for MX and YL at the heading stage were significantly enhanced compared to other treatments. Significant interaction was also observed in spikelet per panicle and 1000-grain weight between rice variety and nitrogen fertilizer type. Therefore, slow/controlled-release fertilizer application at the rate of 150 kg N per ha is a more feasible nitrogen fertilizer management strategy under mechanical deep placement, with the merit of increasing grain yield and improving nitrogen use efficiency in South China.