Can reduced-input direct seeding improve resource use efficiencies and profitability of hybrid rice in China?

The mechanization of rice production in China has been accompanied by a rapid reduction in agricultural labor forces and increase in machinery purchase subsidies; however, the comprehensive performance of several major mechanized production modes regarding output, environmental protection, and profit remains uncertain to the Chinese government and farmers alike. Here, a five-year (2015-2019) field experiment was conducted to analyze the performance of farmers' mechanized seedling transplanting (FMST), farmers' mechanized direct seeding (FMDS), and reduced-input direct seeding (RIDS) concerning grain yield, energy use, greenhouse gas emissions, and economic benefits. RIDS used an unmanned aerial vehicle for sowing, fertilizing, and spraying, while adopting no-tillage, bed-furrow irrigation technology. The quantity and stability of RIDS-produced grain were similar to those of FMST and higher than those of FMDS. Furthermore, RIDS yields required significantly less machinery, human labor, fuel, and water, with 34.72% and 24.03% decreases in total energy input compared to that for FMST and FMDS, corresponding to 1.45- and 1.34-fold increases in energy productivity, respectively. The resulting CO2-eq emissions from agricultural inputs for RIDS were 71.26% and 71.32% of those for FMST and FMDS, while CH4 emissions were 32.60% and 29.24% of those for FMST and FMDS, respectively. Despite the high N2O emissions and decomposing trend of soil organic carbon in RIDS, the net global warming potential still decreased by 48.84-58.36%, and the carbon sustainability index and carbon efficiency ratio increased by 87.67-142.14% and 105.32-188.22%, respectively, compared with those of FMST and FMDS. RIDS had the lowest cost, its net return was USD 298.81 ha-1 higher than that of FMDS (similar to FMST), and its benefit-cost ratio was 10-36.19% higher than that of FMST and FMDS. Generally, RIDS offered a higher-yielding, cleaner, more sustainable rice production technology for meeting the needs of the Chinese government and farmers.