Good soil smells fertile, all musty and moist.
Good soil doesn’t thoroughly crumble or stick to your fingers like glue but leaves a healthy stain, just like when you have to peel the potatoes.
Good soil is teeming with active life from microbes to molluscs to mould, all interacting to transfer nutrients around and into plant roots.
Good soil has carbon in it.
No surprise then that after decades of ignoring most climate mitigation options, the Australian government has realised that soil might be a place to put some of the excess carbon that society has emitted.
Some time ago, CSIRO suggested that 35-90 million tCO2e could be stored annually into Australian soil via sound vegetation management and improved tillage practices.
No comment that the range is 55 million tCO2e from the country’s premier science organisation; perhaps soil is tricky.
A more recent report by AgriProve estimated there was potential for at least 103 million tonnes annually to be stored across the country. Excellent news.
However, here is what it says on the Agriprove website
AgriProve is Australia’s leading soil carbon project developer, taking farmers on the journey from building soil carbon in the field to selling carbon credits to governments and companies with carbon liabilities.
They are bound to be bullish.
Good soil contains carbon
Before we go on, the case for soil carbon is strong.
Land management depletes soil carbon in most agricultural soils to the point that biological activity, nutrient exchange and soil physical properties are compromised often to the point of soil degradation.
Actions that promote soil carbon retention — ground cover, minimum tillage, water retention — are essential to reverse these trends and promote soil health. Such actions are pivotal to future food even without a sequestration benefit.
Good soil has carbon in it.
Policy that promotes soil carbon gains as an offset for carbon liabilities sounds like a win win — sequestration and soil health benefits. Landholders win and so do companies with a need to buy offsets. Heck, even the government wins through facilitating a market for offsets.
But there are a few problems.
Soil carbon will not be enough to offset agricultural emissions, let alone the coal industry. The idea we can bail out the coal industry with soil carbon is just fanciful.Richard Eckhard, Professor of Sustainable Agriculture, University of Melbourne.
Prof Eckhard also reminds us that soil carbon in Australia is 90% dependent on rainfall. This is true. Soil biology is moisture driven, and it’s the biology responsible for moving and storing carbon.
The snag is that rainfall is expected to decline due to climate change in many areas.
“Why would we hedge our future climate change strategy on something that climate change itself is going to challenge?”
Learn to love variability
Nothing in nature is ever what it seems because nature varies in place and time.
No two fields are the same ecologically, no matter how hard we try to homogenise them for what we think is efficient production. No two patches, even teaspoons of soil, are the same.
Start to think about variance rather than focusing on averages or the seduction of multiplication (that always ends up with a large number).
Ask questions about variability, how much of it we understand, and what we can do to work with it.
Be comfortable that precision may not be possible, especially when it comes to soil.
Accept variation so long as the general is in the right direction.
Sometimes soil carbon sequestration might be temporary, but that is ok if it is positive on an ecological time frame.
What sustainably FED suggests
We are not surprised that CSIRO hedged their bets with a wide range in their sequestration estimation. But it is risky to generalise because the real challenge is knowing what to do where.
So should we hedge on soil carbon?
Yes, and even though it will never be enough, we should do it nonetheless. Soil carbon should always be a core focus of land management because it helps plants grow.
It is also worth remembering that ecological time matters, and patience is a virtue in anything to do with food production.