Losses of native mineral-associated organic nitrogen through microbial mineralization and gaseous emissions induced by ammonium and nitrate addition

Summary

This 2024 laboratory study examines how exogenous ammonium and nitrate inputs trigger accelerated microbial decomposition of native soil organic nitrogen and increase gaseous nitrogen losses. The findings suggest that fertiliser nitrogen addition may stimulate mineralisation of existing soil organic matter pools beyond the added nitrogen itself, potentially reducing long-term soil nitrogen storage capacity whilst increasing atmospheric emissions. The work contributes to understanding nitrogen cycling dynamics in amended soils and has implications for optimising nitrogen use efficiency and mitigating greenhouse gas losses in agricultural practice.

UK applicability

The mechanisms demonstrated are relevant to UK arable and grassland soils, where mineral nitrogen fertilisers are widely applied. However, field applicability depends on soil type, climate, and management context; laboratory conditions may not fully replicate UK field moisture, temperature, and biological regimes. The findings support the case for more precise fertiliser timing and rate management to reduce both environmental loss and organic matter depletion.

Key measures

Rates of native organic nitrogen mineralisation; gaseous nitrogen emissions (composition and magnitude); soil mineral nitrogen pools; microbial activity or biomass; potentially ¹⁵N or ¹³C isotopic tracing to distinguish native from added nitrogen

Outcomes reported

The study measured microbial mineralisation of native soil organic nitrogen and quantified gaseous nitrogen losses (likely N₂O, NO, N₂) following ammonium and nitrate addition to soil incubations. Outcomes included changes in soil organic nitrogen pools and emission rates relative to unfertilised controls.

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