I was having a discussion recently with my mother about carbon. She asked if there was a difference between soil carbon and tree carbon, and then suggested I could write a column about it - thanks Mum!
Soil carbon and tree carbon are very different things, both from an ecological aspect as well as in the carbon trading world.
Tree carbon is an estimate or measurement of the amount of carbon stored in vegetation above ground. It is the carbon in the timber.
Soil carbon is a measurement of the carbon stored within the soil. This is directly linked to the level of soil organic matter. As the organic matter portion of a soil profile increases (e.g. humus or the dark colour of soil) so does the organic carbon content. Organic carbon is about 58 per cent of organic matter.
Soils are made up of mineral matter (clay, sand, silt), pore space (for air and water/water vapour) and organic material.
The organic material can be broken down into living organisms, fresh residue (recently died roots), decomposing organic matter (old roots breaking down and dead microbes) and stabilised organic material (carbon/humus). Hard, cloddy soils are low in organic matter with shallow root systems and low levels of plant growth. You can have hard cloddy soils (low soil carbon) in areas that have plenty of trees (tree carbon).
Soils with more carbon usually feel 'spongy' underfoot. More soil carbon increases water infiltration, retention and nutrient availability to the plant, meaning we have better plant health, better animal health and then better human health. It really is central to all that we do in agriculture.
The key to soil health is green leaf and living root systems at depth that interact with the soil bugs. We can influence all these with our grazing management decisions.
Nature has fine-tuned a symbiotic relationship over 375 million years whereby the plants feed the soil bugs (the bugs receive around 40pc of the sugars produced from photosynthesis) and the bugs feed the plants (by bringing nutrients to the root systems). They also increase the amount of soil carbon you have.
So, which one is better? They are both important. Soil carbon is directly linked to soil health and your productivity levels. The right balance of trees on your land increases diversity, shade, nutrient cycling, water retention and thus also contributes to soil health. Nothing in nature can be looked at in isolation.
- David is chief of delivery for agricultural consulting and education company, RCS Australia. www.rcsaustralia.com.au 1800 356 004
