Reactive nitrogen (N) is increasingly added to the New Zealand environment because of increased sales of N fertilizer and increased human population. The Greenhouse Gas Inventory now reports in detail on changes for N losses from grazing animals from 1990 to 2010. Using animal numbers, we made assessments of N inputs and outputs for the 16 regions of New Zealand for 1990, 2001 and 2010 to assess temporal trends. Fertilizer sales have increased from 46 Gg N in 1990 to 329 Gg N in 2010, which leads to reduced biological N fixation by pastures. The import of oil-palm kernel has increased from zero to about 28 Gg N in 2010. Total N inputs are estimated to have increased from 689 Gg to 951 Gg N. The outputs of produce, leachate, gasses and sediment have increased from 771 to 866 Gg N; outputs to rivers may increase further if increases in outputs lag behind increases in inputs. Many of the inputs and outputs are well constrained because animal numbers have been used rather than land area, but uncertainties do exist for specific land-use classes. For example, the area of lifestyle blocks is approaching 800,000 ha and there is uncertainty regarding N inputs and outputs in this land use. There are also uncertainties in the amount of N fixation, the N loss by leaching in any one year, the amounts and fate of dissolved organic N, and the N content of eroded sediment. These uncertainties need to be resolved so that the amount of N stored in soils can be assessed. It seems likely that the N concentration of soils under dairying is increasing relative to the carbon concentration (i.e. soil C/N ratios are declining) but there is conflicting evidence as to whether the total N (and C) in these soils is increasing or decreasing.
