Emission factors for estimating fertiliser-induced nitrous oxide emissions from clay soils in Australia’s irrigated cotton industry

As a significant user of nitrogen (N) fertilisers, the Australian cotton industry is a major source of soil-derived nitrous oxide (N2O) emissions. A country-specific (Tier 2) fertiliser-induced emission factor (EF) can be used in national greenhouse gas inventories or in the development of N2O emissions offset methodologies provided the EFs are evidence based. A meta-analysis was performed using eight individual N2O emission studies from Australian cotton studies to estimate EFs. Annual N2O emissions from cotton grown on Vertosols ranged from 0.59 kg N ha–1 in a 0N control to 1.94 kg N ha–1 in a treatment receiving 270 kg N ha–1. Seasonal N2O estimates ranged from 0.51 kg N ha–1 in a 0N control to 10.64 kg N ha–1 in response to the addition of 320 kg N ha–1. A two-component (linear + exponential) statistical model, namely EF (%) = 0.29 + 0.007(e0.037N – 1)/N, capped at 300 kg N ha–1 describes the N2O emissions from lower N rates better than an exponential model and aligns with an EF of 0.55% using a traditional linear regression model.