Stubble height and irrigation significantly influenced the carbon footprint of ratoon rice cropping system in South China

Context

Ratoon rice (RR) has witnessed a rapid expansion in China primarily driven by its superior profitability, cost-effectiveness and lower labor requirements compared to double-season rice (DR). Identifying proper management of irrigation and stubble height cutting is essential for balancing crop production, greenhouse gases (GHG) emissions of CO₂, CH₄ and N₂O, and economic benefits in RR cropping systems. Although the grain yield of RR is significantly affected by agronomic management, little is known about how agronomic practices influence the crop production, carbon footprint (CF), and net ecosystem economic benefits (NEEB) in RR cropping systems.

Methods

Field experiments were conducted to investigate the impacts of stubble height and water management on grain yield, GHG emissions, CF and of NEEB of RR during the cropping seasons of 2019–2021. The treatments included DR under farmers’ conventional fertilization and irrigation management, high-stubble ratoon rice under farmers’ conventional field water management (FWP), low-stubble ratoon rice under FWP, high-stubble ratoon rice under safe alternative wetting and drying irrigation management (AWD), and low-stubble ratoon rice under AWD.

Results

The major CF contributor was the direct GHG emissions (GHG_direct) from crop fields in different treatments. Relative to DR, the annual CF and yield-scaled CF (CF_y) of RR were reduced by 30.2–37.0 % and 6.21–23.7 %, respectively. The decrease in CF and CF_y of RR mainly resulted from the lower cumulative emissions of CO₂ and CH₄ as well as its shorter growth duration and lower crop biomass relative to DR. Low-stubble treatment led to a significant increase in GHG_direct compared to high-stubble treatment. However, the CF of low-stubble RR did not differ significantly from that of high-stubble RR due to a substantial enhancement in the net primary production. Low-stubble management reduced the CF_y of RR by 9.4–12.1 %, due to the higher grain yield. Relative to FWP, AWD had negligible impact on crop biomass and grain yield of RR, while significantly decreased the CF and CF_y by 17.6–33.2 % and 6.21–23.7 %, respectively. Relative to FWP, the adoption of AWD resulted in a notable increase in the NEEB of RR by 6.8–20.5 %, due to the substantial mitigation in CH₄ emissions and lower agricultural inputs of electricity and labor. Relative to high-stubble management, low-stubble management enhanced crop N recovery and reduced potential N loss to the environment.

Conclusion

In RR cropping system, low-stubble management coupled with safe AWD irrigation could be a promising strategy in reducing CF while maintaining higher yield and economic benefits without increasing the environmental cost in subtropical paddy field.