Nitrogen inputs and outputs for New Zealand at national and regional scales: Past, present and future scenarios

The Nanjing Declaration on Nitrogen Management calls for national governments to optimise N management by several strategies including assessment of N cycles. In New Zealand, reactive N continues to be added to the environment mainly by biological N fixation, and increasingly from N fertiliser additions. Here, we extend our work on N budgets in 2001/02 for New Zealand (267 000 km²), at both national and regional scales, to 1861, 2020 and 2050. We first attempt to estimate the N cycle for 1861, the year of the first census and when European settlers were beginning to clear large areas of forest for agriculture in some regions. For the future, we adopt two scenarios: agricultural production increasing at 3% p.a., and a “cap and trade” scheme for N. These scenarios provide instructive results by projecting two very different potential policy directions into the future; they do not represent predictions. The 3% growth scenario warns of ever‐increasing N loads on the environment. The cap and trade scenario (such as may be introduced by regional councils) supports the development of a mechanism by which farmers might constrain N losses without regulations being introduced. These scenarios seek to provide farmers, industry and regulators with an understanding of the large range of future possibilities. This paper highlights the urgency with which primary industry must move away from increased production per se to systems where value is added to products

Managing pollutant inputs from pastoral dairy farming to maintain water quality of a lake in a high-rainfall catchment

A study (2004–11) of a dairy catchment stream entering an oligotrophic lake in an area of very high rainfall (~5 m year–1) yielded median concentrations of total nitrogen (TN), total phosphorus (TP), suspended sediment (SS) and Escherichia coli (E. coli) of 0.584, 0.074 and 3.7 g m–3, and 405/100 mL (most probable number method), respectively. Trend analysis indicated significant (P < 0.01) decreases for TN (–0.08 ± 0.02 g m–3 year–1), TP (–0.01 ± 0.005 g m–3 year–1) and SS (–0.45 ± 0.14 g m–3 year–1) and were partly attributable to improved exclusion of cattle from the stream. Water balance calculations indicated that approximately one-half the rainfall left as deep drainage that by-passed catchment outlet flow recorders. Estimates of catchment yields for TN were improved by taking into account groundwater hydrology and concentrations from well samples. Storm-flow monitoring inflows exceeding the 97.5th percentile contributed ~40% of total loads leaving the catchment so that specific yields for SS, TN and TP augmented by groundwater inputs and storm flows were ~960, 45 and 7 kg ha–1 year–1, respectively. These compared well with modelled results for losses from dairy farms in the catchment of 40–60 kg N ha–1 year–1 and 5–6 kg P ha–1 year–1 and indicated that attenuation losses were relatively small. © CSIRO, 2013