Soil drivers of NH3 emissions in a fertilized sunflower agroecosystem

Tóth, Eszter and Balogh, János and Bozóki, Zoltán and Horváth, László and Nagy, Zoltán and Oltvári, Zsófia and Takács, Tünde Mária and Pintér, Krisztina (2026) Soil drivers of NH3 emissions in a fertilized sunflower agroecosystem. ATMOSPHERIC POLLUTION RESEARCH, 17 (11). No. 103202. ISSN 1309-1042

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Abstract

Ammonia (NH3) volatilization represents a major pathway of reactive nitrogen loss in agroecosystems, yet the soil controls governing its variability remain insufficiently understood. In this study, we quantified soil-atmosphere NH3 fluxes in a fertilized sunflower field in Hungary using multi-point field measurements (20 locations, 18 campaigns), combined with detailed soil, canopy, and microclimatic observations. To identify the dominant drivers of NH3 flux variability, we applied a Random Forest modeling approach complemented by SHAP-based interpretation. The RF and SHAP analyses indicated non-linear, modelled associations of NH3 flux with soil temperature, moisture, humus content, and the [NH4+]/[H+] proxy (Γ). Notably, properties measured in deeper soil layers (20–30 cm) contributed to the model predictions, indicating associations between NH3 flux variability and vertically structured soil processes rather than surface conditions alone. NO3− emerged as a conditional, state-dependent model-associated indicator, potentially reflecting broader N-transformation dynamics and covariance with soil moisture and temperature rather than a direct causal effect on NH3 volatilization. These findings emphasize that NH3 fluxes arise from complex interactions among soil chemical status, microclimate, and nitrogen transformation processes within the soil profile. The results demonstrate that data-driven approaches can provide new insights into nitrogen cycling processes in agroecosystems.

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