Carbon farming trials in the Hunter Valley have replicated those of other districts in showing there are many variables involved in successfully lifting soil carbon levels.
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Perhaps the biggest variable is rainfall. No rain results in diminishing carbon levels but that situation can quickly turn around should the season improve.
This was the main message at a soil carbon field day held at Mirannie near Singleton.
One of the speakers at the day was Susan Orgill, soils carbon research officer, Wagga Wagga Agricultural Institute, NSW DPI who said results of trials throughout the state showed there were so many variables that affected soil carbon.
“In an 18 year trial a 1 per cent increase in carbon had been achieved with no real difference between native or introduced pasture species – the big difference was rain,”Dr Orgill said.
“When it rained carbon levels increased and they diminished during drought. Grazing management, soil types and levels of nutrients, and presence of legumes all affect the soils capacity to hold and store carbon.”
Finding the best method to promote soil carbon will require more trials and research she suggested.
At the soil carbon trial conducted between October 2014 and June 2016 on two grazing properties at Mirannie and one at Vacy near Maitland the results showed the value of chicken litter, Organic Growth Medium (OMG), biosoils and food waste in promoting pasture production. Conversely tradition fertilisers such as single super, gypsum or lime appeared ineffective.
Commenting on the trail results which were conducted with the support of the Australian Government’s Action on the Ground initiative John Drinan said much more work would be required to understand what was needed to increase soil carbon levels consistently across a variety of farm environments.
One trial which clearly showed what worked on-farm in promoting tropical legume pastures, another important part of improving soil productivity, was conducted by the Dungog-Gresford Land & Beef Group with support from the MLA.
DPI, technical specialist pastures, Neil Griffiths said the trials conducted on five sites ranging from low to high fertility soils showed the need to knockdown pastures/grasses in the paddock before sowing the legumes.
“Unless the competition is knocked out the legumes won’t thrive – it’s that simple,” he said.
Mr Griffiths said a spray regime, mulching or grazing could be used to suppress existing pastures to ensure the best start for the legumes. The other message was Haifa white clover remained the most productive legume outperforming any of the new varieties.