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

Abstract

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.