Assessment of nitrogen footprint and economic profit under different ratooning rice cultivation modes in central China

Significant progress has been made in studying greenhouse gas emissions, carbon footprints, and yield changes in ratooned rice fields across diverse cultivation practices. However, the nitrogen footprints of different ratooning rice cultivation methods remain unclear. Therefore, this field experiment used the life cycle assessment to study the effects of different ratooning rice cultivation modes conventional cultivation mode (CM) and two optimized cultivation modes (OM1 and OM2) on rice yield, nitrogen footprint, and economic outcomes. Among the three modes, the CM mode adopted traditional ratooning rice cultivation techniques, such as artificial transplanting, conventional fertilization, shallow flooding irrigation, stubble height of 20 cm, and excluding straw returning practices. The OM1 mode adopted mechanical transplanting, one-time application of slow-release fertilizer, dry-wet irrigation altenation, stubble height of 20 cm, and straw returning. The OM2 mode adopted mechanical transplanting, deep application of nitrogen fertilizer, dry-wet irrigation alternation, stubble height of 40 cm, and straw returning along with a decomposing agent. The results showed that OM2 had the highest yield in the ratooning season and the total yield in the rice season, which increased the yield in the ratooning season by 37.1% (P<0.05) and 28.1% (P<0.05) and the total yield by 21.7% and 12.5% (P<0.05), respectively, in comparison to CM and OM1. OM2 had the highest indirect active nitrogen emissions. In the context of direct active nitrogen emissions, there were no significant differences in the N₂O emissions among the three modes. However, OM2 significantly reduced NH₃ volatilization by 14.4% (P<0.05) in comparison to CM for main crop. Therefore, OM2 had the lowest annual active nitrogen emissions, which were significantly lower than CM and OM1 by 10.9% (P<0.05) and 2.2% (P<0.05), respectively. The nitrogen footprint of OM2 was significantly lower than that of CM and OM1 by 26.9% (P<0.05) and 13.1% (P<0.05), respectively. OM2 had the highest economic benefit, which was 20.9% and 29.2% higher than OM1 and CM, respectively. This study showed that the OM2 is a sustainable ratooning rice cultivation mode that effectively reduces nitrogen footprint while enhancing economic benefits. The potential for promoting this mode is substantial in the ratooning rice area of southern China.