Fig. 1. Changes in NH₄⁺, NO₃⁻ and N₂O during incubation of soil microcosms for 24 days.

Microcosms were incubated after amendment with a slow-release, urea-based fertiliser that contained 15% free urea, or with water only (no fertiliser), in combination with 1-octyne, acetylene or no inhibitor. a–c present data in which NH₄⁺ was supplied at a low continuous rate, through slow mineralisation of native organic nitrogen (phases 1 and 2) or of polymethylene urea (phase 2). d–f present data in which NH₄⁺ was supplied at a single high concentration, through rapid mineralisation of free urea within the slow-release fertiliser (phase 1) or through addition of urea (phase 2). Phase 1 (days 0–10) is indicated by a grey background and phase 2 (days 10–24) by a white background. Inhibitor treatments were applied to fertiliser-amended microcosms by additional amendment with urea or water. NH₄⁺ and NO₃⁻ concentrations were determined in destructively sampled microcosms and cumulative N₂O production was determined following repeated sampling of headspace gas. Data represent mean values and standard errors of three replicate microcosms