Soils and carbon for reduced emissions

Why is soil carbon important?

There is growing appreciation for the critical role played by the existing store of carbon in our agricultural soils. There has been considerable discussion around the possibility of increasing soil carbon levels for potential farmer income via future carbon credit markets. However, of greater importance is the story around the valuable role played by existing soil carbon stores that offer great benefit to both agricultural productivity and the wider environment.

Soil carbon and organic matter play a number of beneficial roles and biological functions GRDC Krull et al. (2006) in agricultural soils and supports productivity via:
• Providing a slow release supply of nutrients
• Improving cation exchange capacity and nutrient holding ability
• Assisting soil structure and aggregate stability
• Reducing erosion risk
• Assisting soil water holding capacity
• Buffering against soil acidity
• Increasing soil biota diversity & abundance.

Maintaining or building reserves of soil carbon offers many benefits. As a result, farmer interest in practices and approaches that enhance the fertility, productivity and resilience of their soil assets is growing. There are also some positive signs that improvements to our understanding of the functions and measurement of soil carbon will prove useful for fertiliser decision making in future.

Climate change and the role of soil carbon as a sink

Soil is the largest reservoir of carbon in the terrestrial biosphere and a slight variation in this pool could lead to substantial changes in the atmospheric carbon dioxide concentration, thus impacting significantly on the global climate Chan et al. (2008); Luo et al. (2010). With global soils containing more carbon than is found in the atmosphere and biomass combined, soil carbon stocks are a significant carbon sink. Over the coming decades there is likely to be an increasing focus on maintaining global soil carbon stocks and exploring pathways for enhancing soil carbon stores.

It is also important to consider that as global temperatures rise due to climate change, soil carbon stocks may also be at risk as soils warm and rainfall patterns change Davidson et al. (2006); Meyer et al. (2018), and Roxburgh et al. (2020). As a first principle, a core focus will be to ensure the existing asset of current soil carbon stocks are well understood and managed sustainably.

As a general rule, many of Australia’s agricultural soils have lost a significant portion of the original soil carbon that existed in their natural state. Luo et al. (2010) suggest that, for Australian agro-ecosystems, cultivation has led to declines with total carbon loss of approximately 51% in the surface 0.1 m of soil. While maintaining or increasing soil carbon levels is a popular objective for many Australian farmers, we should also be mindful that in many situations this task will not be easy or without some fundamental shifts in understanding and land management practices.

Published: 2022

Author(s):

Updated 2022 by: Graeme Anderson, Melissa Cann & Heather Field Agriculture Victoria
Original 2015 edition prepared by: Liz Hamilton & Graeme Anderson Victorian Department of Economic Development, Jobs, Transport and Resources
With contributions from: Dr Fiona Robertson, Victorian Department of Economic Development, Jobs, Transport and Resources, Jeff Kraak, Fertilizer Australia & Gerard Fullerton, Back Paddock Company

ISBN: 978-1-76090-516-3