Soil organic matter – what the science tells us

Take home messages

• Stocks of soil organic matter (SOM) and the associated carbon and nutrient flows are key to healthy, sustainable, and resilient agricultural systems
• Declining SOM impacts the soil’s ability to support key soil functions, including the capacity to deliver N
• Estimates of soil organic carbon (SOC) accumulation rates following relatively modest management changes in Australian cropping and pasture systems typically range from 0.1 to 0.3 tonnes C/ha/yr (also expressed as Mg or Megagram C/ha/yr)
• Building SOM stocks at higher rates is possible through bold management changes that maximise carbon inputs and minimise loss pathways
• Expenditure and opportunity costs need to be evaluated on an individual basis
• A long term (decadal) cyclical approach to management of SOM and nitrogen budgeting will ensure that future productivity is not compromised by short term (annual) approaches that don’t capture the value of banking SOM for use in subsequent seasons
• SOM and SOC mean different things and are explained in this paper.