"Soils can be a net sink": Senior Soil Scientist

'The long term trial results highlight the fact that, by using the right management practices, we can turn a farm from a C source to a C sink," says Dr K Yin Chan, Principal Research Scientist (Soils), NSW Department of Primary Industries. Dr Chan was delivering a presentation to a group of landholders at Junee Reef, a four hour roadtrip we took on 21 June, 2007 to see if we could make contact with this legendary soil carbon expert. The Junee Reef Hall was full to capacity to hear the great man and have an update on an extraordinary program of soil tests involving hundreds of landholders across the Murrumbidgee Catchment.
Dr Chan has a research project which has stretched over 20 years, the only one of its kind. He has some startling conclusions. In the soils studied, he found that there was on average 70 tonnes of soil carbon per hectare under undisturbed native vegetation. This fell dramatically to 40 T/ha under conventional tillage by the 1940s. It rose 5T/ha under Reduced Tillage, to 45T/ha. Dr Chan believes we can recover the balance. He calls it the "Soil C Sequestration Potential".


How can we do it? Dr Chan provided some clues. There is a strong correlation between conservation tillage and higher soil carbon scores with traditional tillage/stubble burnt SOC scoring 1.5% vs no tillage/stubble retained 2.5%. In the bottom chart we have the results of 20 years' research. It measures the movement in soil carbon in kg/ha/year. From left to right, we have Wheat and Lupin rotation under Conventional Cultivation/Stubble Retained at 200kg/ha/yr lost vs No Till at only 5kg lost. When the stubble was burned in these cases the loss for Conventional Cultivation blows out to 280 kg/ha/yr and 150kg/ha/yr for No Tillage stubble burned. For Continuous Wheat under Conventional Cultivation losing the maximum amount recorded 419kg/ha/yr. The same combination but with added Nitrogen reduced the damage to 305kg/ha/yr. Best performing combination was Wheat/Clover rotation which shows that the introduction of a grazing phase turns the process around, with a 200kg/ha/yr increase in soil carbon where No Till/Stubble Retained is practiced. That's more than 0.6T/ha.yr. Where the land management strategy is Conventional Cultivation/Stubble Retained the loss is 80kg/ha/yr.

The amounts are small, but none of the techniques studied is as effective at creating carbon in soils as 'carbon farming' techniques. In these studies - them most advanced to date - there is no controlled grazing, no pasture cropping, no biological ameliorants to kick start the process, etc

But the lessons are important as the basics of soil carbon losses.

At the same meeting we met up with DPI Soil Physics Technical Officer, Albert Oates. He has been selected to lead the team for a study into the role of pastures in locking up carbon under a range of management practices. "Soils under permanent pasture might have the greatest potential to lock-up carbon dioxide as soil organic matter," he says. He is looking for farmers in central and southern NSW with paddocks with a known history. "Of particular interest would be paired paddocks, which allow comparisons to be made. Examples include cropped versus old perennial pasture, annual pasture vversus perennial and set-stocked versus rotationally grazed. If a farmer has a paddock likely to be of very high organic carbon status, that would also be of interest." The three-year project will be led by Dr Yin Chan with input from Soil Chemist Dr Mark Conyers, Modeller Dr Deli Liu, Research Agronomist Dr Guangdi Li, Soil Scientist Dr Brian Murphy of DNR and Mr Oates. A number of district NSW DPI agronomists and a technical officer, Ros Prangnell, are working on the project.
Contact: Dr Chan on (02) 4588 2108 and Mr Oates on (02) 6938 1874.