Integrating agronomic practices to reduce greenhouse gas emissions while increasing the economic return in a rice-based cropping system

The effective mitigation of greenhouse gas (GHG) emissions from crop cultivation requires an overall consideration, due to the trade-off relationship between GHGs and the mitigation measures sometimes undermining grain yields and economic returns. To explore the maximum potential of GHG mitigation without sacrificing economic returns, we investigated the GHG emissions, crop yields and economic returns over two years in three rice-cropping systems (rice-wheat, RW; rice-fava bean, RB; and rice-fallow, RF). Different N fertilization levels and straw incorporation methods were employed in each of the rice-cropping systems at the study site, in the Taihu Lake region (TLR) of China. Bean straw produced in the RB system was fermented aerobically before incorporation, while straws produced in the RW and RF systems were directly incorporated into the soils. Relative to the traditional RW system, methane emissions during the rice seasons were significantly reduced by 29-44% in the RB system; annual N inputs were reduced by 43%; annual nitrous oxide emissions for N fertilization treatments were decreased by 56-69%; and the average rice yield was increased by 5.2%. As a result, the GHG intensity (GHGI) was significantly reduced by 11-41%, and the annual net economic benefit (NEB) was increased by 22-94%. Compared with the RW system, the GHGI in the RF system was increased by 8-30% and the NEB was decreased by 3-33%. Considering the current rice/wheat production practices employed in the TLR, the GHGI could be reduced by 26% while the NEB could be improved by 23%, with an annual reduction in the N application rate (currently 525 kg N ha−1) by 20% and the conversion of the RW systems into RB systems that use straw fermentation. The results of this study suggest that high economic return and GHG mitigation could be simultaneously achieved by the integrated adoption of reasonable reduction in N application rates, the use of appropriate rice-cropping systems and by employing eco-friendly straw management.