Improving the Carbon Content of Soil
Soil organic carbon (SOC) is the main constituent of soil organic matter (SOM). SOM is formed by the biological, chemical and physical decay of organic materials on the soil surface and below the ground. On average, SOM is composed of 50% carbon, 40% oxygen, 3% nitrogen and smaller amounts of other elements as micronutrients.
SOM varies in its stability. Some is labile, relatively quickly biodegradable, and other components are more stable (non-labile). The ratio of labile to non-labile depends on microbial conditions.
As in nature, we can transform arid soils into healthy soils and biosystems by accelerating pedogenesis processes..
The carbon sequestration potential under conventional farming practices should not be seen as the maximum possible or be the drivers of policy, when there is evidence that numerous innovators have been achieving greater bio-sequestration outcomes by some order of magnitude.
It is possible to biosequester up to 10 tonnes of stable carbon per hectare per annum back into our soils. This would regenerate their structure, hydrology, nutrient dynamics, bio-productivity and resilience.
How to increase soil carbon levels
The easiest way to increase your soil carbon levels is to incorporate more organic matter into and onto your soils, such as by maximising ground cover and mulching.
Generating SOM was a primary step for many of our case study farmers to improve their soil health, and this took a range of different forms…
Colin Seis of Winona near Gulgong in the NSW Central Highlands has developed and implemented a completely new cropping technique - ‘pasture cropping’ - which has led to dramatic increases in soil and soil minerals, including SOC. Pasture cropping involves direct-drilling crops into dormant native perennial grasses. Colin has also integrated time-controlled planned grazing, with sheep grazing prior to sowing, during growth before seed-set, and after harvesting. This technique promotes ongoing groundcover and minimal soil disturbance, supporting high biological functioning and constant formation of fertile soil.
Extensive soil testing on Winona, including paired-site analyses by the University of Sydney through the Communities in Landscape project, has shown that this technique has increased SOC by 203% in ten years. SOC has been measured up to depths of 500mm. In total, this equates to around 45 tonnes of SOC a hectare, or per hectare storage of around 170 tonnes of CO2 (equivalent) over the ten years.
Importantly, 78% of the newly sequestered carbon on Winona is in the non-labile (humic) fraction of the soil. This is therefore much more stable and significantly less subject to degradation.
In a very different environment in the NSW North West, Graham and Cathy Finlayson of Bokhara Plains are restoring the soil structure to claypans in the rangelands. Through planned grazing practices, stock are being used to break up the surface of the claypan, which formerly comprised 50% of their land. (See the transition in the image above.)
High density stock levels trigger soil disturbance, exposing seed already present or carried in from manure, stock hooves and/or hide and enabling it to germinate. The stock density used by the Finlaysons also ensures nutrient deposit (from urine and manure) carried in from other areas of higher natural fertility.
By allowing water and seeds to penetrate and also leaving manure fertiliser deposits, the claypan and degraded areas of Bokhara Plains are becoming revegetated. Soil structure is continuing to improve and SOC levels are increasing from the greater plant biomass and root systems in soil.
By regenerating the soil and increasing groundcover, the Finlaysons have significantly increased productive land on their property and improved their sustainable carrying capacity. Through addressing the health of the soil, the Finlaysons are creating a viable business and are moving towards drought-proofing their property.
It’s amazing how fertile soils can be built, and the photos of the soil and pasture changes from Colin Seis and the Finlayson’s places are inspirational. What does your soil look like under the surface? What percentage of groundcover do you have on top?
What are you do to improve your soil carbon levels?
Click on 'Comments' below and let us know.
Get involved! Take a photo of your soil profile, including a ruler or measure – maybe from various parts of your property (or your back yard or veggie patch) - and post it on our Facebook page or send it to email@example.com and we’ll share it for you. Let’s see how deep our topsoils go! (This will also serve a good record for your own regeneration journey!)
Until next week, when we look at the wonderful world of soil biology,
The Soils for Life Team