Summary
This laboratory study evaluated the relative efficacy of two biological nitrification inhibitors—linoleic acid and linolenic acid—against the synthetic inhibitor dicyandiamide in a highly nitrifying soil. Whilst linoleic acid and linolenic acid significantly reduced nitrate concentrations, the mechanism differed from dicyandiamide: the biological compounds appeared to suppress nitrification indirectly through enhanced microbial immobilisation of ammonium and nitrate, rather than through direct nitrifier inhibition. However, application at high concentrations increased N₂O and CO₂ emissions, and the biological compounds exhibited substantially higher mineralisation rates, suggesting limited persistence in soil compared with dicyandiamide.
UK applicability
The findings are relevant to UK agriculture, where soil nitrification and associated nitrogen losses pose significant environmental challenges. The results suggest caution in adopting linoleic and linolenic acids as practical nitrification inhibitors at field scale, given their rapid mineralisation and potential to increase greenhouse gas emissions, though the study was conducted under controlled laboratory conditions and would require field validation under UK soil and climatic conditions.
Key measures
Soil NH₄⁺ and NO₃⁻ concentrations; cumulative N₂O and CO₂ emissions; 14C-labelled mineralisation rates of linoleic acid, linolenic acid, and dicyandiamide (measured as percentage mineralisation after 38 days)
Outcomes reported
The study compared the efficacy of biological nitrification inhibitors (linoleic acid and linolenic acid) against the synthetic inhibitor dicyandiamide on soil nitrate concentrations, ammonium dynamics, and nitrous oxide and carbon dioxide emissions in a highly nitrifying soil. Mineralisation rates of the inhibitors were also determined using 14C-labelled compounds.
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