An assessment of nitrification inhibitors to reduce nitrous oxide emissions from UK agriculture

A trial was conducted consisting of 14 experiments across sites in England of contrasting soil type and annual rainfall to assess the effectiveness of nitrification inhibitors (predominantly dicyandiamide (DCD) but limited assessment also of 3, 4-dimethylpyrazole phosphate (DMPP) and a commercial product containing two pyrazole derivatives) in reducing direct nitrous oxide (N2O) emissions from fertilizer nitrogen (N), cattle urine and cattle slurry applications to land. Measurements were also made of the impact on ammonia (NH3) volatilization, nitrate (NO3-) leaching, crop yield and crop N offtake. DCD proved to be very effective in reducing direct N2O emissions following fertilizer and cattle urine applications, with mean reduction efficiencies of 39, 69 and 70% for ammonium nitrate, urea and cattle urine, respectively. When included with cattle slurry a mean, non-significant reduction of 56% was observed. There were no N2O emission reductions observed from the limited assessments of the other nitrification inhibitors. Generally, there were no impacts of the nitrification inhibitors on NH3 volatilization, NO3 leaching, crop yield or crop N offtake. Use of DCD could give up to 20% reduction in N2O emissions from UK agriculture, but cost-effective delivery mechanisms are required to encourage adoption by the sector. Direct N2O emissions from the studied sources were substantially lower than IPCC default values and development of UK country- specific emission factors for use in inventory compilation is warranted.