Fertiliser timing and use of inhibitors to reduce N2O emissions of rainfed wheat in a semi-arid environment

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50kgN/ha) at sowing with and without nitrification inhibitor (3,4-dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N2O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160g N2O-N/ha, while the 0N control emitted 28gN(2)O-N/ha (over 201days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49gN(2)O-N/ha where N was applied at sowing, with background emissions of around 0gN(2)O-N/ha (over 177days). Inhibitors showed limited scope for reducing N2O emissions in this environment, however deferring N application until the end of tillering reduced N2O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11-31% and NUE was generally high (recovery efficiency>68%). However, deferring N application until the end of tillering in 2014 reduced yield (-19%) and recovery of applied N (-74%).