Invited Talk for Centre for Atmospheric Science Seminars

Title

Modelling and Assessing the Impacts of Intercropping, as a Sustainable Farming Practice, on Food Security, Air Quality, and Public Health

Abstract

Agriculture is the major emitter of atmospheric ammonia (NH$_3$) in Europe, China, and the US (85$–$95%). This NH$_3$ is also attributable to approximately 20% of the fine particulate matter (PM$_{2.5}$) formed, which harms human health in the neighbourhood areas. The fast-growing food production, due to the rising world population and their more meat-inclined dietary habits, could thus worsen the pollution problem. Previous field studies have shown that soybean intercropping can exploit the mutualistic interactions between crops to promote legume nitrogen fixation for enhancing crop yield, reducing fertiliser use, and thus diminishing NH$_3$ emission. In this study, we aim to investigate the potential benefit of large-scale intercropping on crop productivity, air quality, and public health. To quantify crop yield and NH$_3$ emission under intercropping, we implement into a soil biogeochemical model, DeNitrification-DeComposition (DNDC), a new scheme to parametrize the belowground interactions of intercropped crops. With the DNDC -simulated NH$_3$ emission, we predict the formation of downwind PM$_{2.5}$ using a global 3-D chemical transport model, GEOS-Chem. We find that, if all Chinese farms are adopting maize-soybean intercropping, the same croplands which were initially for only maize or soybean can now produce both crops with comparable yields (90-100%) as their monoculture counterparts. The fertiliser use for intercropping is 42% lower, leading to a reduction in NH$_3$ emission by 45% and a drop in PM$_{2.5}$ concentration by up to 2.3% (equivalent to 1.5 μg m$^{-3}$). This improvement can spare the Chinese government USD13 billion per year in air pollution-related health damage costs. Toward a better understanding on how regional conversion to sustainable farming alternatives may affect global climate and air quality, we are developing a process-based NH$_3$ volatilisation scheme and the parametrisation of crop-crop belowground interactions into the Community Earth System Model (CESM). We hope that our study can help policymakers to evaluate the costs and benefits of adopting sustainable alternatives and derive a science-based long-term strategy for food security and air pollution mitigation.