Executive Summary

Soil Organic Carbon (SOC) refers to the carbon in soils associated with the products of living organisms. It is a heterogenous mixture of simple and complex organic carbon compounds which can be divided into different pools which serve different functions to soil ecosystems.

SOC is of fundamental importance to soil health/fertility and therefore to sustainable agriculture as it affects all three aspects of soil fertility, namely chemical, physical and biological fertility.

SOC is part of the global C cycle and the global SOC pool (1580 Gt) is twice as large as that in the atmosphere and nearly three times that of the vegetation biomass carbon pool. Soil organic carbon sequestration refers to the storage of carbon in soil and is being considered as a strategy for mitigating climate change. Globally as well as for some individual countries, it has been estimated that SOC sequestration has the potential to mitigate 5-14% of total annual greenhouse gas emissions for the next 50-100 years.  However, whether this potential is achieved depends on economic, social and political factors.

Based on limited local data and overseas experience, considerable SOC sequestration potential exists in NSW agricultural land.  The highest potential exists in pasture land in the higher rainfall regions (>450 mm), both as permanent pastures or as ley pasture in the cropping zone. Considerable increases can be achieved by pasture improvement and improved management practices. 

Significant SOC potential also exists in the low rainfall rangelands which comprises nearly 50% of NSW. Much of the rangelands are in degraded state and considerable total SOC sequestration can be achieved for a small rate of sequestration per hectare. Promotion of conservation tillage practices (particularly no-tillage) is important to halt further carbon losses from cropping soils (emission avoidance). Currently, there is only a 35% adoption rate of conservation tillage techniques in NSW. In addition, SOC can be sequestered by adopting new land conversion and soil amelioration options such as bioenergy crops from perennial vegetation, recycling organics including biochars, and by ameliorating sodic and acid soils. As a rough estimate, total SOC sequestration potential from pasture land, cropping land and rangelands amounts to 4.9 Mt C/yr (18 Mt CO2e/yr), which is equivalent to 11% of the total GHG emission from NSW in 2005.

Many of the management practices that are effective in increasing SOC in agricultural soils also improve productivity and profitability, conserve the resource base and protect the environment.  

In order to support a role for soil organic carbon in emissions trading, there is an urgent need to resolve several key research issues, namely developing low cost methods of accounting for soil carbon; quantifying net carbon sequestration under different management practices for different soil types, climates and agricultural systems by supporting existing long term cropping rotation trial sites and the establishment of new ones where appropriate; quantifying interactions of SOC sequestration with soil emissions of other GHG, namely N2O and CH4 and developing soil carbon models that can account for locally relevant agricultural management practices.

It is important to resolve outstanding research questions as a matter of urgency, to remove this barrier to inclusion of soil carbon in emissions trading.