Fertiliser nitrogen source and the use of nitrification inhibitors are tools to reduce nitrous oxide emissions and improve agronomic performance in temperate grassland

The application of nitrogen (N) fertilisers to agricultural soils is a common practice that can result in significant nitrous oxide (N 2 O) emissions. Nitrogen source and the use of nitrification inhibitors (NIs) have shown potential to reduce N 2 O emissions from agricultural soils. However, to date most studies conducted in temperate grassland have tested one or two NIs in isolation, often with one N source such as urea. Hence, the present study tests the effect of four NIs: 3, 4-dimethylpyrazole phosphate (DMPP), dicyandiamide (DCD), nitrapyrin (NP) and a novel new NI 5-methoxy-3-methyl-1H-pyrazole (MMP) with both urea and urea ammonium nitrate (UAN) applied in autumn and spring seasons. Calcium ammonium nitrate (CAN) was included as a common N fertiliser used in Europe and also an acidified liquid amide-N (Flex-N) that is also in use but limited trial work has been published. This is the first study to report on N 2 O emissions and agronomic performance of the NI MMP, doing so with both solid and liquid fertiliser, and the acidified liquid amide N product (Flex-N). The urea, Flex-N and UAN fertilisers lowered the N 2 O-N emission factor (EF) by 84, 78 and 68 %, respectively compared to CAN across seasons. In autumn, urea and UAN treated with NIs reduced the N 2 O-N EF by up to 64 % and by up to 60 % compared to untreated urea and UAN, respectively. In spring, urea and UAN treated with NIs reduced N 2 O-N EF by up to 88 % and by up to 37 % compared to untreated urea and UAN, respectively. Inclusion of NIs increased pasture yield and N uptake in both seasons. These study results suggest that fertiliser N source and the use of NIs are effective tools for reducing N 2 O emissions while improving yields and N utilisation. • On average, the use of urea, Flex-N and UAN lowered the N 2 O-N emission factor by 84, 78 and 68 %, respectively compared to CAN fertiliser. • Urea and UAN treated with nitrification inhibitors (NIs) mitigated the N 2 O-N emission factor by up to 88 % and 60 % compared to untreated urea and UAN, respectively. • Urea or UAN treated with NIs showed a trend of improved pasture yield, N uptake and apparent fertiliser N recovery compared to untreated urea or UAN. • The use of NIs with urea had a stronger effect in spring than in autumn, whereas NIs with UAN had a stronger effect in autumn than in spring in the current study.