Carbon farming: claying to increase soil carbon content

Page last updated: Thursday, 8 November 2018 - 9:24am

Spreading clay on light, sandy soils helps to increase soil water holding capacity, retain nutrients and overcome water repellence. Adding clay to non-wetting sands also increases potential to store soil organic carbon.

We provide this information to support land manager decisions about investing in carbon farming.

Benefits of claying to increase soil carbon content

Claying is used on light-textured, sandy surfaced soils (mainly coastal or inland sandplain landscapes) to overcome soil water repellence. Water repellence in soil is caused by dry coatings of hydrophobic (water-hating) material on soil particles or aggregates, as well as hydrophobic organic matter, such as fungal strands and particles of decomposing plant material.

Claying water repellent sands increases potential soil organic carbon storage, mostly due to an increase in plant biomass production, and partly due to clays physically protecting soil organic carbon from microbial breakdown. The positive effects of claying last for many years.

Carbon benefits using an approved methodology do not exist for claying.

Co-benefits of claying:

  • improved ability of the soil to capture and store water and retain nutrients
  • increased capacity of low clay soils to stabilise organic carbon
  • increased crop production
  • even weed germination allowing a better weed kill.

Opportunities for claying exist for sandy soils with less than 5% clay, which in total cover 5 million hectares in Western Australia. Claying can lead to increased soil carbon in the top 30cm by 2–3 tonnes per hectare.

Risks of claying to increase soil carbon content

  • Not all clays are suitable for this activity.
  • Claying for carbon sequestration would probably not qualify as additional to normal practice.
  • High clay rates at the surface can result in surface sealing and can reduce root development into the subsoil.
  • Crops on clayed paddocks produce a large biomass but are prone to haying off and poor yields in dry seasons.
  • Clay spreading works on most soil types but may have low returns for warm, shorter season environments.
  • Claying at recommended rates is expensive.
  • Increasing and maintaining organic carbon in coarse-textured sandy soils can be difficult.

Contact information

Rob Sudmeyer
+61 (0)8 9083 1129