Effect of nitrification and urease inhibitors on nitrous oxide and methane emissions from an oat crop in a volcanic ash soil

Nitrous oxide (N₂O) emissions from the Chilean agricultural sector are primarily associated with the use of nitrogen (N) fertilizers, so that the use of nitrification and urease inhibitors may represent a potential mitigation option. However, their effectiveness in volcanic ash soils with high organic matter is still uncertain. In this study, the effect of Dicyandiamide (DCD) and <em>N</em>-(<em>n</em>-butyl) thiophosphoric triamide (NBPT) on soil N₂O and CH₄ emissions from an oat crop was determined using a fully automated greenhouse gas measuring system. Three urea treatments were evaluated: 120kg N ha^-1, 120kg N ha^-1 + DCD and 120 kg N ha^-1 + NBPT (n = 3). A zero treatment (-N) was also considered. Annual N₂O emissions ranged from 0.36 to 1.00 kg N₂O-N ha^-1 (P > 0.05) whereas the net uptake of CH₄ ranged from 6.72 to 7.00 kg CH₄-C ha^‐1 (P> 0.05). Increases in N₂O emissions were associated with rainfall events, as characteristic of Mediterranean rain fed ecosystems. Soil CH₄ uptake did not vary among treatments but had a significant role offsetting N₂O emissions, resulting in total emissions ranging from -17.1 to 239.0 kg CO_2eq ha^-1 (P<0.001). There was no significant effect of DCD or NBPT on average soil mineral N concentration, and total N₂O and CH₄ emissions. NBPT significantly increased crop yield and crop N uptake by 27% and 33% respectively (P<0.05), resulting in greater N use efficiency. The use of DCD did not increase productive parameters, but resulted in a 35% reduction of the N₂O-N emission intensity (P<0.05). The study shows that volcanic ash soils have a relatively low N₂O emission potential due to physic-chemical characteristics and that NBPT could be used to increase N use efficiency in crops, while DCD has a potential to reduce N₂O losses per unit yield