Soil Organic Matter – What The Science Tells Us

GRDC - Lynne M Macdonald (CSIRO), Mark Farrell (CSIRO) and Jeff A. Baldock (CSIRO)

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

The authors of this paper note in the conclusion: "Scientific literature estimates Australian SOC accumulation rates in cropping and pasture systems to be approximately 0.1 to 0.3 t C/ha/yr, while higher rates (0.3 to 0.6 Mg t C/ha/yr) are estimated when converting from cropping to pasture. It is however acknowledged that there is a lack of data to inform SOC accumulation rates under a broader range of alternative management practices. Building SOM stocks at higher rates is possible through bold management changes that maximise carbon inputs and minimise loss pathways, but expenditure and opportunity costs need to be evaluated on an individual basis.  It can be useful to estimate SOM accumulation targets based on local knowledge of the potential changes to plant biomass production. Taking a long term (decadal) view on building and using SOM and the associated nutrient flows is critical to ensuring that future productivity will not be compromised to maximise short term (annual) profits." Please access the full paper via the link below if this research interests you.

The take home messages from this GRDC funded research are below. Please access the full paper via the link below for methodology, references, acknowledgements and discussion.

Take home messages from the paper include:

  • 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.

2020 - Australia - GRDC - Lynne M Macdonald (CSIRO), Mark Farrell (CSIRO) and Jeff A. Baldock (CSIRO)
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