Ammonia emissions from nitrogen fertilised agricultural soils: Controlling factors and solutions for emission reduction

Environmental context: Ammonia emissions from inorganic nitrogen fertilisers used in agriculture can impact air quality, human health and ecology. This study quantifies such emissions and their controlling factors from UK and Ireland agricultural soils. Emissions are variable and, from non-urea fertilisers, substantially exceed maximum emission factors used by the UK Department for Environment, Food and Rural Affairs. This suggests that UK emission factors need to be refined further, with consideration of inter alia land-use, fertiliser type, soil pH and chemical inhibitors.

Rationale: Ammonia (NH₃) emissions from inorganic nitrogen (N) fertilisers applied to agricultural soils have negative implications for environmental quality and human health. Despite this, efforts to reduce NH₃ emissions in the UK have achieved limited success. This study aims to provide an overview of NH₃ emissions from UK and Ireland agricultural soils receiving N fertilisers, their regulating factors and the potential role of inhibitors in reducing current NH₃ losses.

Methodology: A systematic literature search was performed to identify relevant experimental data and studies, and the extracted data (total of 298 field fertilisation events) were categorised and analysed systematically.

Results: NH₃ emissions ranged from -4.00 to 77.00% of applied fertiliser-N lost as NH₃. In addition to fertiliser type, NH₃ losses were also significantly affected by land-use type and soil pH. Urease and combined urease and nitrification inhibitors significantly reduced emissions by 74.50 and 70.00% compared to uninhibited-urea respectively.

Discussion: In addition to fertiliser types, land-use and soil pH were found as factors for consideration as modifiers to the maximum NH₃ emission factor (EFmax) values currently used in the UK, in order to improve estimations of NH₃ emissions, particularly from non-urea fertilisers. This is imperative as NH₃ losses exceeded current EF_max limits, particularly in the case of non-urea fertilisers, by 34%, implying that NH₃ emissions estimated from UK synthetic fertiliser require further refinements. NH₃ losses are not completely inhibited, inhibitors cannot be solely relied upon for tackling NH₃ emissions from UK and Ireland fertiliser usage and further research is needed into alternative mitigation methods to further reduce NH₃ losses.