The dynamics of ammonia bi-directional exchange above agricultural crops

Significant uncertainties exist in ammonia (NH3) emissions from crop fields, which is relevant for the environmental impact of fertilizers.

To better understand NH3 bi-directional exchange in agricultural ecosystems, we measured NH3 fluxes above a corn field over two growing seasons. We found that NH3 volatilization following fertilization was significantly lower than reported in previous studies, revealing our still limited understanding of NH3 exchange processes. During fully developed corn canopy periods, NH3 emission and deposition were of similar flux magnitudes than after fertilization, which highlights the importance of the canopy for regulating net NH3 exchange and its impact on atmospheric reactive nitrogen.

A major source of NH3 to the atmosphere are emissions from synthetic fertilizer applications on agricultural fields, while their quantification is critical to propose effective NH3 control and mitigation strategies. However, to date large uncertainties in their magnitude exist. This is in part due to challenges in measuring NH3 fluxes and systematic differences between emission factor quantification methods. Consequently, our understanding of processes that control the exchange of ammonia within the soil-canopy-atmosphere interface is still limited.