Relative efficacy and stability of biological and synthetic nitrification inhibitors in a highly nitrifying soil: Evidence of apparent nitrification inhibition by linoleic acid and linolenic acid

Summary

This laboratory study compared the efficacy and fate of two biological nitrification inhibitors (linoleic and linolenic acids) with the synthetic inhibitor dicyandiamide in a highly nitrifying soil. Whilst linoleic and linolenic acids suppressed nitrate accumulation, they did so through indirect mechanisms promoting microbial immobilisation of nitrogen rather than direct inhibition of nitrifiers, and their rapid mineralisation (37–61%) at high concentrations increased gaseous emissions. The findings suggest that future research must distinguish between direct nitrification inhibition and indirect nitrogen cycling effects when evaluating candidate inhibitors.

UK applicability

These findings are relevant to UK agricultural practice, where synthetic nitrification inhibitors are used to mitigate nitrogen losses in intensive systems. The demonstration that plant-derived fatty acids may promote nitrogen immobilisation rather than nitrifier suppression could inform the development of biological alternatives, though field validation under UK climatic and soil conditions would be required before practical recommendation.

Key measures

Soil NH₄⁺ and NO₃⁻ concentrations; cumulative N₂O and CO₂ emissions; ¹⁴C mineralization rates of linoleic acid (47–56%), linolenic acid (37–61%), and dicyandiamide (2.7–5.5%) over 38 days incubation

Outcomes reported

The study measured the effects of linoleic acid, linolenic acid, and dicyandiamide on soil nitrogen dynamics, nitrous oxide and carbon dioxide emissions, and the mineralization rates of these inhibitors in a highly nitrifying soil. Linoleic and linolenic acids decreased nitrate concentrations but increased N₂O and CO₂ emissions at high application rates, whilst dicyandiamide reduced nitrate and increased ammonium.

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