Carbon footprint of maize production in tropical/subtropical region: a case study of Southwest China.

Maize production is critical in tropical/subtropical regions, especially in developing countries where maize is a staple food. However, its environmental costs remain unclear. Southwest China is a tropical/subtropical region with large-scale maize production in each of its sub-regions. In the present study, we used Southwest China as a case study to evaluate the greenhouse gas (GHG) emissions and carbon footprint (CF) of maize production during 1996-2015 using life cycle assessment to identify the driving factors behind the GHG emissions and CF and to propose potential mitigation strategies. The mean GHG emissions of maize production per year during 1996-2015 was 4132 kg CO-eq·ha, and the CF during this period was 961 kg CO-eq·Mg. The GHG emissions and CF in Southwest China were 2-4 times higher than those of other major maize-producing regions worldwide. The GHG emissions and CF were both significantly correlated with the N surplus. The N surplus was also linearly correlated with annual precipitation, annual temperature and growing degree days, but not significantly related with soil pH. Scenario testing showed that the CF of maize production in Southwest China could be reduced by 41%, i.e. to 437 kg CO-eq·Mg, by farmers adopting a comprehensive strategy including recommended fertiliser application rates, innovative fertilisers, and crop management to decrease GHG emissions and achieve the yield potential in the region. Integrated soil and crop management is essential for sustainable maize production in tropical/subtropical regions with complex and changeable ecological conditions, especially in developing countries where maize is a staple food.