Pasture mix key for soil carbon losses
A Matamata dairy farm has become ground zero for a team of Waikato scientists searching for ways to lower agriculture’s greenhouse gas emissions.
Soil carbon and nitrous oxide losses are being measured on the
200 hectare farm owned by Terry and Margaret Troughton and managed by their son Ben and wife Sarah.
Their findings so far in a project funded by the New Zealand Agricultural Greenhouse Gas Research Centre were outlined at a field day on the farm.
Better pasture management, genetics, feed and nutrition had been done well, but new strategies were needed to take the project the next step forward, Landcare Research’s Jack Pronger said.
New Zealand was coming under increasing pressure to lower its greenhouse gas emissions, of which 50 per cent came from biological agricultural emissions.
‘‘We need to find solutions that work for everyone. New Zealand farmers to date had made great advances over the last 20 years and it’s really about emissions intensity, so we are getting more product per unit emissions, but more needs to be done.’’
‘‘I think realistically to bring agricultural greenhouse gas emissions down, it will be the cumulative effect of a lot of small changes to management practices.’’
Scientists have been carrying out research on the farm since
2011. Their first task was calculating its carbon exchange in the pasture in order to obtain baseline data.
There was 100-300 tonnes of carbon a hectare within the top one metre of soil on a typical New Zealand dairy farm, Waikato University’s Aaron Wall said.
On the Troughton’s farm, there was about 160-260t of carbon per hectare within the top metre and
200t/ha is the average across the farm.
Wall said they were interested in how that changed.
‘‘The key number we are measuring with this equipment is
CO2 exchange - how much comes down and how much goes back up into the atmosphere.’’
A machine was used that took air samples and measured the carbon dioxide and nitrous oxide concentrations of that sample at a rate of 20 times a second. Samples were taken of feed to analyse its carbon content to determine how much carbon left the farm. On this farm, the inputs going on included home grown maize silage, and imported grass silage.
Wall also looked at the impact cultivation had on carbon losses. Cultivation for re-grassing, pasture renewal or crop establishment caused carbon losses because it killed photosynthesis, he said.
The loss rate was determined by the soil moisture content and the length of time the paddock was bare.