Soil Organic Carbon represents the largest terrestrial sink for carbon stocks and is directly linked to agricultural productivity – the higher the SOC level, the more productive the land.
Soil carbon projects offer a no-regrets pathway to scalable sequestration because they avoid the negative carbon/land use trade-offs of tree planting schemes.
Major soil disturbance results in the loss of SOC. This happens quickly under long fallow and conventional tillage but complete ground cover with green growing plants can reverse SOC loss.
Consequently, there is widespread interest in pasture cropping and zero, no-till and conservation farming practices. Improved grazing practices have the potential to sequester carbon in extensive native pastures, particularly deep-rooted perennial grasses and legumes.
Based on previous studies, a conservative estimate of the expected rates of sequestration applicable to Australia appears to be around 0.5 to 1 tonne carbon per hectare per year through improved grazing practices (such as rotational cell grazing, deep rooted perennial pasture species). However, sequestration may be higher or lower depending on soil type, climate and management practices. I can provide guidance here.
How to rebuild soil carbon
The Australian Government’s Emissions Reduction Fund (ERF) offers incentives for the establishment of eligible greenhouse gas (GHG) abatement projects through emissions avoidance or increased carbon sequestration. The Measurement of Soil Carbon Sequestration in Agricultural Systems Methodology creates the opportunity for all eligible farming enterprises, including appropriate grazing, cropping and horticulture, to increase soil sequestration and create carbon credits.
I believe with applied biology, increase/changes to deep rooted perennial legumes, and forages in rotation, we will be able to increase soil carbon considerably in cultivation country and extensive grazing areas.
These changes would be applicable under “material change of practice” and eligible as a soil carbon project. The activities will need to be implemented following project registration and include:
- Applying nutrients, lime or gypsum to improve soil health.
- Installing new irrigation with water sourced from privately-funded farm water efficiency savings.
- Re-establishing or rejuvenating a pasture by seeding.
- Establishing and maintaining a pasture where there was previously no pasture (cropland or bare fallow).
- Altering stocking rate, duration or intensity of grazing.
- Retaining stubble after crop is harvested.
- Converting from intensive tilling to reduced or no tilling practices.
- Modifying landscape features to remediate soils.
- Using mechanical means to add or redistribute soil through the soil profile.
However, this is just the ‘icing on the cake’. The more tangible and direct benefits from increased soil carbon include yield gains in crop or pasture through increased moisture holding capacity and ability to hold nutrient through better cation exchange capacity. Certain types of soil organic matter can hold up to 20 times their weight in water. Research has shown that for each 1 per cent increase in soil organic matter, the available water holding capacity in the soil increases by 3.7pc.
Calculate your gains
For every tonne of soil organic carbon sequestered, we multiply it by 3.67 to get tonnes carbon dioxide (CO2) equivalent sequestered. The latest spot price for ACCU’s is $16.50/tonne CO2.
If, for example, we start with a soil weight of 1.4 grams per cubic centimetre and convert this across 1 hectare to 0.2 metres deep, that equates to 2,800 tonnes of soil per hectare. If we get a change in soil carbon from say 1pc to 1.1pc, that is an extra 2.8 T/ha carbon in that soil or 10.276 tonnes/ha of CO2 equivalent. That is ambitious. It also depends on sequestration rates and change of practice. Being more conservative, let’s say 1T/ha of carbon sequestered per year x 3.67 x $16.50/tonne = $60.55 /ha/yr.
Baselining is the first significant step in a soil carbon project and involves quantifying soil carbon stocks on the proposed project area. The initial carbon stocks are used to determine any prospective soil carbon sequestration, so the earlier baselining occurs, the more soil carbon, potentially, will be available to trade.
The cost of baselining depends on the size of the property. As a guide, around 200ha would cost about $5,000 (ex GST), whereas around 400-500ha costs around $10,000 (ex GST).
Thomas Elder Consulting’s (TEC) baselining will not limit soil sampling to 300 millimetres. There is often more soil carbon below 300mm than above and this carbon is likely to be very stable. Furthermore, properly managed land is expected to promote deeper soil carbon.
We also undertake detailed soil mapping, with Peter specialised in this area.
Many other providers only estimate the total amount of soil carbon and don’t provide any information about how soil carbon varies across paddocks. TEC, however, will locate the better spots for carbon sequestration, and the connections between management practice and the carbon level. Your TEC consultant will precisely assess soil variation to a depth of 1 to 2m, which significantly improves the accuracy of the soil carbon measurement. The more accurate the measurement, the more carbon is saleable, thanks to less variation in the projected carbon yield.
Peter Spies is an approved adviser under the Land Restoration Fund – Carbon Farming Advice Rebate program in Queensland. This is to assist eligible applicants with the cost of accessing eligible advice about undertaking a carbon farming project on their land through the Land Restoration Fund. The Carbon Farming Advice Rebate Program provides landholders with rebates of up to $10,000 to offset the cost of obtaining relevant advice related to carbon farming projects.