Summary
This laboratory study evaluated the relative efficacy of two fatty acid-derived biological nitrification inhibitors (linoleic and linolenic acid) against the synthetic inhibitor dicyandiamide in a highly nitrifying soil. Whilst the biological compounds significantly reduced nitrate concentrations, the mechanisms differed markedly: dicyandiamide directly inhibited nitrification and increased ammonium retention, whereas the fatty acids appeared to suppress apparent nitrification through promoting microbial immobilization of nitrogen. The authors emphasise the importance of distinguishing direct and indirect inhibitory mechanisms when evaluating nitrification inhibitors for agricultural use.
UK applicability
The findings are relevant to UK agricultural nitrogen management and mitigation of nitrate leaching, a regulatory concern under the Nitrates Directive. However, the study was conducted in laboratory conditions on a single soil type; field validation across diverse UK soil conditions would be necessary before recommending biological inhibitors as alternatives to synthetic compounds in practice.
Key measures
Soil ammonium (NH₄⁺) and nitrate (NO₃⁻) concentrations; cumulative nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions; ¹⁴C-labelled mineralization rates of linoleic acid, linolenic acid, and dicyandiamide after 38 days incubation
Outcomes reported
The study compared the efficacy of biological nitrification inhibitors (linoleic and linolenic acid) against synthetic dicyandiamide in controlling soil nitrification, nitrous oxide and carbon dioxide emissions, and determined the mineralization rates of these compounds. Results indicated that biological inhibitors reduced nitrate concentrations but through indirect microbial immobilization rather than direct nitrification inhibition.
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