Organic Fertilizers Application: Impacts on VOCs and Air Quality Implications

Organic fertilization has been gaining increasing attention in recent years due to its significant soil health benefits and its alignment with European environmental and agricultural strategies. A considerable percentage (10.4% in 2022) of agricultural fields across Europe currently incorporate organic fertilizers into their management practices one or two times/year, and this proportion is projected to increase by 25% by 2030. Consequently, the environmental impacts associated with organic fertilization, particularly volatile organic compounds (VOCs) emissions, which tightly connected with air quality and health risk through their contribution to secondary pollutants, have become a critical area of study but remain poorly understood. To address these concerns, the SOFORA project was established to quantify agricultural gas emissions, including VOCs, nitrogen oxides (NO_x), ammonia (NH₃), ozone (O₃) and particle matters through laboratory measurements and field campaigns. The project also aims to develop robust models to estimate emission levels resulting from the application of various types of organic fertilizers under different agricultural conditions.

During the laboratory measurements conducted as part of the SOFORA project, the dominant VOC profiles and their magnitudes were found to be highly dependent on the specific type of organic fertilizer applied. To investigate these emissions under real-world conditions, eddy covariance techniques and proton transfer reaction mass spectrometry (PTR-MS) were utilized. Field experiments were carried out in the spring and autumn of 2023 at two agricultural sites in France: a wheat field and a white mustard cover crop field. Both experiments ensured consistent crop field footprints within the measurement zones, enabling reliable data collection and an accurate representation of emission dynamics in agricultural environments.

Field measurements confirmed the short-term but significant release of gases and their potential impact on air quality following organic fertilization. VOC emissions were observed to persist for over seven days post-application for both fertilization types. Approximately 2% of the total applied carbon was estimated to be emitted as VOCs from green waste and digestates, respectively. Peak emission fluxes were approximately 85,000 μg m⁻² h⁻¹ and 53,000 μg m⁻² h⁻¹ for total VOC emissions at noon on the first day after application of green waste and digestates, respectively. VOC emissions were dominated by acetic acid, methanol, and acetaldehyde for green waste applications, and by methanol, isoprene, and acetone for digestates. These compounds are estimated to have a high potential contribution to ground-level ozone and/or aerosol formation.

Volatilisation of organic fertilizers may contribute much more significantly than expected to atmospheric burden, leading to broader environmental impacts such as air quality deterioration and nitrogen deposition. Further high-resolution measurements are needed to refine our understanding of these processes and develop strategies to mitigate potential trade-offs between sustainable soil management and environmental protection.