Co-benefits of sustainable farming methods to safeguard food security and environmental health in China: a modelling study

Abstract

Background: Modernised farming has contributed significantly to the increased global food supply over the past half-century, albeit while creating severe threats to the environment. Excessive application of chemical fertiliser has in particular led to massive release of reactive nitrogen compounds into the atmosphere, where they become major components of fine particulate matter (PM2·5) pollution, with detrimental effects on human health. Various sustainable farming methods with lower environmental impacts have been experimented with and practised in many countries, but their wider benefits beyond the farm scale have rarely been examined. One such method is intercropping with soybeans, which takes advantage of the nitrogen fixing ability of soybeans to improve nutrient use efficiency and reduce fertiliser use. Methods: We developed a computational modelling framework using the GEOS-Chem and DNDC models, revising the representation for soil nitrogen processes and crop-crop interaction. We did model experiments to quantify the benefits of nationwide adoption of maize-soybean intercropping systems in China in terms of gains in crop production, decreases in fertiliser consumption, and reductions in ammonia (NH3) emissions. We further examined how the decline in NH3 emissions could reduce the downwind formation of PM2·5 and the associated public health costs. Findings: Annual mean PM2·5 concentrations can be reduced by up to 1·5 μg/m3 with the nationwide adoption of maize-soybean intercropping, with a corresponding annual net economic benefit of US$67 billion, of which $13 billion arises from saved health costs from reduced air pollution. Interpretation: Our study shows the wider economic and environmental value of intercropping systems for promoting both food security and public health, serving as a basis for policy consideration by governments and stakeholders. The same modelling framework can likewise be used to investigate the large-scale impacts of other sustainable farming methods. Funding: General Research Fund the Hong Kong Research Grants Council, the Area of Excellence Scheme, and the CUHK Vice- Chancellor Discretionary Fund.