Worldwide, agricultural soils produce over 40% of emissions of the third most important greenhouse gas, nitrous oxide (N2O) according to Denman et al. (2007). In the atmosphere, the lifetime of N2O is 100–150 years and it is the single most important precursor to compounds that deplete stratospheric ozone, adding to its significance as an environmental pollutant (Ravishankara et al., 2009). The strength of agricultural soil emissions as an N2O source can be estimated by compiling an inventory, as done annually by signatory nations in accordance with the United Nations Framework Convention on Climate Change (UNFCCC). Grassland occupies 41% of New Zealand's (NZ's) land area and pastoral agriculture is the country's main economic activity. In accordance with NZ's commitment to the UNFCCC, a pastoral agriculture soils inventory of N2O emissions is compiled and reported annually. Between 1990 and 2011, the most recently reported year of data, NZ's inventory increased by 29% from 25.4 to 32.8 Gg N2O y−1 (Ministry for the Environment, 2013). For UNFCCC inventories, a primary variable is the direct emission factor (EF), the proportion of the quantity of nitrogen (N) applied to soils emitted into the atmosphere as N2O.