Are NZ pastures gaining or losing soil carbon and nitrogen, and why?
“Land degradation is the most important environmental problem affecting extensive areas of land in both developed and developing countries….Well planned, long-term national and regional land conservation and rehabilitation programmes, with strong political support and adequate funding, are now needed.”
Article 14.44, Agenda 21, United Nations Earth Summit, 1992.
In New Zealand, pastures originally converted from forest are now subject to more intensive stocking and increasing fertiliser use. We know very little about how this intensification of land use has altered the amountsof carbon and nitrogen stored in the soil. Associate Professor Louis Schipper (Earth and Ocean Sciences) and colleagues from Landcare Research and GNS Science have been measuring soil carbon and nitrogen at 65+ pastures sites around New Zealand, and comparing their information with data recorded from the same pastures around 20 years ago. The team found large average annual losses of around 1 tonne per hectare of soil carbon and annual nitrogen losses of about 90 kilogram per hectare from dairying on flat land, and large gains on North lsland hill country.
The reasons behind these changes aren’t clear and a number of hypotheses are now being tested. These losses and gains are nationally important with respect to carbon accounting and maintenance of soil quality for production. Dr Dave Campbell (Earth and Ocean Sciences) and Professor Schipper are leading research in techniques for determining real-time fluctuations of carbon dioxide at paddock level. Their long-term vision is to develop a balance sheet of carbon exchange related to farm management practices to inform farmers about the environmental and production consequences of their land management decisions. In time, mitigation strategies will need to be developed to reduce and reverse carbon and nitrogen losses from soil.
External funding gratefully acknowledged: Landcare Research, MAF, DairyNZ, and others.
EARTH AND OCEAN SCIENCES, FACULTY OF SCIENCE AND ENGINEERING