FARMERS need to start managing soil carbon levels, but equally must find a balance between building carbon and profitability according to a CSIRO expert.
Jeff Baldock, of CSIRO Agriculture and Food, told the Grains Research and Development Corporation (GRDC) update in Bendigo recently that soil carbon levels were limited and that there was a trendline for lower levels across Australia's cropping zones, which in turn has impact on available nitrogen levels.
Overall, he said farmers needed to keep an eye on the future.
"It is important to consider whether future long term productivity and potential profit is not being eroded to maximise short term, annual values."
However, while he said farmers overall had to look to the long-term future and potentially sacrific short-term gains for longer term sustainability there would be times they would have to make a judgement call on profitability versus building organic carbon.
"Perhaps it is best to think about it like a bank, you try and build up your reserves whenever you can, but you know that sometimes you might have to take some out," Dr Baldock said.
"While overall the focus should be on making sure carbon levels are sustainable, on occasions where you have the potential for that big season then it may be a case of focusing on generating the best profits you can, then return to building carbon in following years."
In terms of generating soil carbon, critical in creating nitrogen in a plant available form, Dr Baldock said green manure was still one of the best options.
"Including a legume phase that can be incorporated into the soil as either green or brown manure is very beneficial," he said.
"There is the hit on the profit for that particular year, but the long-term benefits show a rotation with a green or brown manure phase is one of the most profitable."
He also said a grain legume crop, while not as efficient as a green or brown manure was also beneficial.
"Without a phase to build up carbon and mineralised nitrogen you become increasingly reliant on fertiliser N applications."
Dr Baldock said in terms of a narrow window focusing only on boosting soil carbon, incorporating organic matter, such as crop residue, via cultivation was one of the most efficient, however, he said from an overall farming systems point of view this had limitations.
"Leaving no cover on the paddock means an increased risk of erosion, whether that be wind or water erosion."
He said farmers would have to accept that altering management practices to maintain soil organic matter and nitrogen are likely to increase costs but said taking a long term view on the economics of current management was important.