Recent Advance in Understanding the Role of Edaphic Factors in Regulating Soil N Cycling in New Zealand: Policy Drivers and Practical Solutions.

Land strongly underpins New Zealand's economy and plays an integral part in supporting New Zealand's top export earners: tourism and primary production. Government policy requires that land-use intensification, land-use change, and subdivision of land, and the discharge of contaminants avoids further degradation of freshwater resources. Furthermore, New Zealand is also required to report, annually, on greenhouse gas emissions under both the United Nations Framework Convention on Climate Change and the Kyoto Protocol. As a result of these policies and regulatory demands there are a number of relatively new government and industry funded research initiatives to understand the extent of the losses and to develop and deploy effective mitigation practices. Soil nitrogen (N) cycling forms a key component of the research funded within these new programmes since nitrate concentrations are increasing at many groundwater and river monitoring sites, and New Zealand's emissions of nitrous oxide (N2O) continue to increase. This is a consequence of the agricultural intensification of livestock-based farming systems, dominated by ruminant grazing. At a national scale ruminant urine is the most significant source of leached nitrogen and agricultural N2O emissions. As a consequence considerable soil and farm system research in New Zealand has focussed on enhancing N use efficiency by improving our understanding of the edaphic factors, (physical, chemical and biological) that regulate nitrate leaching and N2O emissions and using this knowledge to develop mitigation practices. A synthesis of the soil N cycling research performed in New Zealand over the last decade will be discussed, with practical management solutions highlighted.