Acid soils – pHCa below the targets of 5.5 at the surface and 4.8 in the subsoil – limit the potential for plant growth and biomass production. This in turn limits the buildup of soil organic carbon. Soil organic carbon levels are higher in areas of higher rainfall and higher biomass production, on soils that are unconstrained by water availability. See the soil acidity page for more information.
Liming is a cost-effective way of removing an acid-soil constraint to plant growth, resulting in greater biomass production, and increased soil organic carbon.
Benefits from liming for carbon sequestration
Co-benefits of liming acid soils are improved production and a lower cost of production because of the reduced soil acidity.
Opportunities for liming:
- Soils are too acid on 80% of the grainbelt and reducing this effect would improve yields over a large area.
- Improved soil quality increases soil organic carbon so liming is considered a benefit regardless of whether sequestered carbon is traded.
Risks from liming for carbon sequestration
Risks from liming specifically for carbon benefits:
- Carbon credits from liming do not exist because it is not considered as additional to normal production practices.
- The potential carbon benefit detracts from the primary message of managing soil acidity to reduce the loss of production potential from poor performing, low pH soils.
- A better understanding of the optimum limits and ability to maintain the increase in soil organic carbon is required.
- Leakage (carbon dioxide emissions) can occur by carbonate lime dissolving and releasing bicarbonate which evolves into carbon dioxide and water.
- The voluntary market price for soil organic carbon is uncertain.