15 July 1995 Ploughing Up A Warmer Climate - A Timely Tale In This Chilly Season

The global warming hypothesis is behind a project at Lincoln University investigating nitrous oxide emissions from grazed and ploughed soils.

Nitrous oxide is a greenhouse gas estimated to rank close to carbon dioxide in its contribution to New Zealand's overall greenhouse gas budget.

Animal urine is its most readily identifiable source, with the gas being emitted from the soil in the weeks following its deposit on the pasture or when ploughing takes place in preparation for cropping.

Ploughing stimulates soil micro-organisms and causes changes in the cycling of nitrogen through the soil. In Britain, for example, it has been found to raise the levels of nitrate which subsequently leaches into ground water.

"At Lincoln we are looking at the parts of the nitrogen cycle affected by ploughing – the pathways of denitrification and nitrification," says Dr Rob Sherlock of the Department of Soil Science who is supervising the project.

"The gas is produced by both pathways and the task is to try to find out how much gas is produced by each. That will then be modelled mathematically in order to introduce a predictive element to our understanding of the process."

Working on this is Ph.D student Christop Muller from Germany, supervised by Dr Sherlock with Soil Science head Professor Ian Cornforth as associate supervisor.

Although nitrous oxide is generally regarded as a minor greenhouse gas, it is involved in the formation of nitric oxide in the stratosphere which in tum is involved in the catalytic removal of stratospheric ozone, so understanding more about its emission is important globally as part of piecing together the ozone layer jigsaw.

Dr Sherlock points out that in New Zealand the sources of nitrous oxide are believed to be almost exclusively grazed pastures and ploughed soil, and while it ranks third among the greenhouse gases produced here after methane and carbon dioxide it is much longer lived than either of these so it takes on added significance in the global warming scenario.

The Lincoln Project has external funding from the New Zealand Institute for Crop and Food Research and is an example of collaboration between the University and a Crown Research Institute.

The Community Diary. Produced by The Community Relations Centre, Lincoln University, Canterbury, New Zealand.