Sunday, February 11, 2007

What is the potential value of soil carbon to farmers?

Soil carbon credits represent a big additional re venue opportunity for some farmers, according to this exerpt from
Dr Christine Jones' paper "Aggregate or aggravate? Creating soil carbon" (YLAD Living Soils Seminars: Eurongilly - 14 February, Young - 15 February 2006)


Soil carbon content is usually expressed as either a concentration (%) or a stock (t/ha). Unless the depth of measurement and soil bulk density parameters are known, it is not possible to accurately convert from one unit of measurement to the other.

For the sake of illustration however, some simple assumptions can be made. Changes in the stock of soil carbon (t/ha) for each 1% change in measured organic carbon (OC) status for a range of soil bulk densities and measurement depths are shown in Table 1. Numbers in brackets represent tCO2 equivalent. An explanation of these terms follows.

Soil bulk density (g/cm3) is the dry weight (g) of one cubic centimetre (cm3) of soil. The higher the bulk density the more compact the soil. Generally, soils of low bulk density are well structured and have ‘more space than stuff’. The lower the bulk density the more room for air and water and the better the conditions for soil life and nutrient cycling. Bulk density usually increases with soil depth. To simplify the table it was assumed that soil bulk density did not change with depth

CO2 equivalent. Every tonne of carbon lost from soil adds 3.67 tonnes of carbon dioxide (CO2) gas to the atmosphere. Conversely, every 1 t/ha increase in soil organic carbon represents 3.67 tonnes of CO2 sequestered from the atmosphere and removed from the greenhouse gas equation.

For example, from TABLE 1 we can see that a 1% increase in organic carbon in the top 20 cm of soil with a bulk density of 1.2 g/cm3 represents a 24 t/ha increase in soil OC which equates to 88 t/ha of CO2 sequestered.

TABLE 1. Changes in the stock of soil carbon (tC/ha) for each 1% change in measured organic carbon (OC) status for a range of soil bulk densities and measurement depths. Numbers in brackets represent tCO2 equivalent.

Value of soil carbon. Sequestered carbon is a tradeable commodity. It has different values in different markets and the price is subject to market fluctuation. If the CO2 equivalent in the above example was worth $15/t, the value of sequestered soil carbon in ‘carbon credits’ would be $1,056/ha. If the soil carbon concentration was increased by 1% to a depth of 30cm rather than to 20 cm, this would represent 132 t/ha sequestered CO2 at a value of $1,980/ha.

If organic carbon concentrations were increased by 2% to a depth of 30 cm in the same example, this would represent $3,960/ha, that is, almost $400,000 in ‘carbon credits’ per 100 ha of regenerated land. These levels of increase in soil carbon are achievable, and have already been achieved, by landholders practicing regenerative cropping and grazing practices.

Even if organic carbon levels were only increased by 0.5% in the top 10 cm of soil this would represent 22 t/ha sequestered CO2 valued at $33,000 per 100 ha regenerated land (assuming a soil bulk density of 1.2 g/cm3 and a price of $15/t CO2 equivalent).

Carbon credits for sequestered carbon are not an annual payment. In order to receive further credits, the level of soil carbon would need to be further increased. It is also important that the OC level for which payment was received is maintained.

This is not difficult with regenerative regimes in which new topsoil is being formed. Biological activity is concentrated in the top 10cm of most agricultural soils, but regenerative practices rapidly expand this activity zone to 30 cm and deeper. Many benefits in addition to potential carbon credits accrue to increased root biomass and increased levels of biological activity in soil.

The majority of Australian soils have lost enormous quantities of organic carbon and this process needs to be reversed. What has gone up must come down. Soils, plants, animals and people will benefit when we take ‘recycle and re-use’ to the next logical step and recycle the excess carbon currently in the atmosphere.


Unknown said...

Stateline on Friday night had a spectacular breakthrough interview with John Williams - NSW Commissioner for Natural Resources - on the sequestration of carbon and its use as an income stream for farmers. He is beating your drum. A transcript can be found at the ABC website. Worth a read.

Michael Kiely said...


Thank you. I was outa town and at conferences til now - this is great news.