HARRY and his wife Sally are collectively breathing a sigh of relief because Midge and Ted have taken a detour on the way home and with luck will be back after scanning.

The prospect of having to deal with Ted chipping in while everything else is going on is almost too much. The scanning will be difficult enough because during meal breaks, even with the shelving of the Emissions Trading Scheme, Norm will use every chance he has to talk to Harry about why he should start selling carbon credits, known as off-sets, through soil carbon. Over dinner with Harry, Sally agreed to do some research.

Sally found the claims about the amount of soil carbon that can be sequestered varied tremendously. CSIRO estimates that in Australia, about 25-40 million tonnes of CO2 equivalents could be sequestered annually through soil sequestration. This amount is much smaller than many groups claim.

Australian research shows that cultivation leads to a loss of soil carbon - and although farm strategies can be developed to increase it - these strategies will yield different results with different soil types and rainfall patterns. Sally identified a real cost in building up soil carbon because of the stable relationship between nitrogen, phosphorous and sulphur which are all required to build soil carbon.

It costs about $430/ha for pasture establishment, then 100kg single super/ha every year at $400/t. Spread over a 10-year period, the cost is about $80/ha/yr. At the suggested starting price of $10/ tonne for carbon, it is uneconomic.

Sally realised there are two distinct messages she needed for the inevitable debate with Norm. First, that soil carbon is good and helps ensure healthier soils and plants.

Second, that under current rules and prices, the cost of sequestering soil carbon makes it uneconomic as an off-set. The value of pasture for the production of meat, wool or dairy products is greater than the value of the same pasture left to decompose to produce soil carbon.

Sally also discovered some of the claims about large amounts of possible soil sequestration are based on inadequate testing regimes. For testing to be meaningful, a minimum number of samples taken over the whole farm are needed to provide baseline data. Then testing will be required every five years to quantify any "leakage". Stocking rate cannot increase because that would inhibit soil carbon build up. The promoters of payment for soil sequestration ignore these basic rules.

The McNabb family holds the full gambit of opinion on climate change and carbon pollution. Sally is thoughtful and concerned for her children. Midge agrees. Ted reckons it is all rubbish and Norm wants everyone to get into the carbon credit market because he can see a buck in it. Harry is too busy to spend much time on it but is inclined to agree with Sally that "we should be doing something".

  • Mike Stephens is a consultant with Mike Stephens and Associates.