Mitigating the global warming potential of rice paddy fields by straw and straw-derived biochar amendments

The effects of incorporating rice straw or additions of biochar to rice paddies on climate change are uncertain. Both practices may have multiple roles in regulating greenhouse gas (GHG) emissions, and carbon (C) and nitrogen (N) cycling may be re-coupled. A mesocosm experiment was conducted to evaluate the effects of rice straw and straw-derived biochar amendments to rice paddies on methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions. Applying urea with straw increased total CH4 emissions during the rice season by more than 20 times compared with urea alone and decreased total CO2 uptake by 27.1%, but decreased total N2O emissions by 49.1%. Applying urea with biochar increased total CH4 emissions by more than 10 times compared with urea alone, but increased total CO2 uptake by 43.5% and decreased total N2O emissions by 8.4%. On a 100-year time horizon, N2O emissions dominated the global warming potential (GWP) of the three GHGs for all the N treatments, resulting in a positive GWP over the observation period. Applying urea with straw decreased the GWP by 436.9 g CO2-eq m(-2) season(-1) relative to urea alone, as the decrease in N2O emissions exceeded the increase in CH4 emissions as well as the decrease in CO2 uptake. Biochar amendment decreased the GWP by 375.6 g CO2-eq m(-2) season(-1), primarily due to increased CO2 uptake. Based on our results, the climate change mitigation capacity of straw amendment may be further improved by decreasing N2O emissions during the basal fertilization period via changing plant residue species combined with improved N management. Another improvement was to control CO2 emissions after the second topdressing through changing residue species and co-application of straw and its biochar. However, these measures require further evaluated to develop specific practices of crop residue management to address climate change.

Automated summary

The effects of incorporating rice straw or biochar to rice paddies on greenhouse gas emissions and carbon cycling vary. Changing fertilization methods can help reduce the potential impact of climate change.