Deep placement of nitrogen fertilizer increases rice yield and energy production efficiency under different mechanical rice production systems

Increasing energy output and improving energy production efficiency is essential to ensure the long-term sustainability of rice production systems in China. Present study assessed the energy input/output and its production efficiency for manual transplanted rice with manual broadcasting fertilizer (TR-MBF), mechanical pot-seedling transplanted rice synchronized with deep fertilization (MPST-DF), and mechanical hill direct-seeding rice synchronized with deep fertilization (MHDS-DF) in a three-year field experiment. Two rice cultivars i.e., Yuxiangyouzhan (YXYZ, inbred rice) and Wufengyou615 (WFY615, hybrid rice) were used to determine the energy input/output and production efficiency of each system. Results depicted that the MHDS-DF and MPST-DF treatment substantially improved the grain yield by 20.9% and 32.3% for WFY615 and YXYZ owing to enhanced total above-ground biomass (TAB) and leaf area index (LAI), respectively. Means across years and cultivars for energy input in the TR-MBF, MPST-DF, and MHDS-DF were remained 31918.0, 35267.1 and 36036.7 MJ ha−1, respectively. The energy consumed by diesel and fertilizer for energy inputs in the production system exceeds 70% of the total energy input. Moreover, the three rice production systems were highly dependent on non-renewable energy. The highest output energy and net energy were obtained for MHDS-DF and MPST-DF treatments with 221517.2 and 185670.0 MJ ha-1, respectively. Among the three rice production systems, the highest energy use efficiency, energy productivity efficiency, energy profitability efficiency was found in MPST-DF, which was slightly higher than MHDS-DF. However, the human energy profitability efficiency of MHDS-DF treatment was significantly higher than other treatments. Therefore, MHDS-DF and MPST-DF could be best alternative technologies than conventional rice production systems with improved energy input and energy production efficiency in South China. Furthermore, both MHDS-DF and MPST-DF would also be suitable in the regions with lack of labor force for rice production.