farmta k
Locally specific guidelines for grain growers in the Mallee
Soil carbon in Mallee farming systems
While Mallee soils are not able to store large reserves of carbon, growers can
maximise the benefits that soil carbon provides. This edition of Farm Talk presents
10 things to know about soil carbon.
1. What is the difference
between soil carbon and soil
carbon turnover?
structure gives micro-organisms easy
cancels out four years of good carbon
access to carbon, resulting in faster
management.
decomposition and carbon losses. In
addition, low rainfall reduces potential for
Soil carbon refers to the absolute level of
carbon in the soil. This may be as low as
0.1 percent for a sand-dune and up to
about 2 percent for well-structured clay
soils. Changes in soil carbon levels are very
slow to occur, with estimates that it may
take about 20 years to observe any
measurable change in Mallee soils.
carbon inputs, biological activity and
4. What’s the benefit of
storage. These factors mean Mallee soils
maximising soil carbon
have a poor capacity for increasing soil
turnover?
carbon. However, we know that
increasing soil carbon turnover for the
Soil carbon turnover is central for soil
benefit of soil biology and fertility is
microbes to perform important tasks such
possible and this is something that Mallee
as nutrient mineralisation, disease
farmers can achieve.
suppression and soil structure formation.
In Australian soils, insufficient carbon
limits soil microbial activity and biological
Soil carbon turnover is the cycling of
carbon through the soil biota, plant and
3. How do farming systems
functions. Nutrient mineralisation is an
organic matter. The process transfers
affect soil carbon turnover?
important part of the cycle that provides
carbon and nutrients through different
the plant with the nitrogen, phosphorus
pools of soil organic matter. Increasing soil Farming systems which retain crop
carbon turnover can deliver benefits in soil residues, such as reduced tillage, stubble
and sulphur needed to grow a crop or
pasture with an optimum yield. Long-term
biology and fertility which can be
retention and use of break crops to
adoption of management practices that
observed in one to two years.
improve overall crop production, will
improved soil carbon turnover coupled
improve soil carbon turnover and soil
with increased carbon inputs will increase
fertility, while retaining base levels of soil
disease suppression potential of soil and
2. Why is maintaining soil
carbon.
reduce crop losses.
carbon challenging in the
Stubbles are about 30-40 percent carbon.
Mallee?
Increasing soil carbon turnover without an
Practices like tillage, windrow-burning and increase in the amount of carbon going in
grazing that remove stubble will reduce
to the soil will lead to loss of soil organic
Many Mallee soils are very sandy and are
carbon inputs for biological turnover.
low in clay content while clay is key to a
Trials in the Mallee have found a single
soil’s ability to hold carbon. Sand’s coarse
year of burning stubble and cultivation
Published June 2015
www.msfp.org.au
carbon.
farmta k
Locally specific guidelines for grain
growers in the Mallee
Growers can monitor soil carbon levels
with regular soil tests from accredited
laboratories. If soil carbon is decreasing,
then growers may need to consider a
Any practice which returns organic matter
change in farm practice, such as reducing
7.
Can
absolute
soil
carbon
be
to the soil will improve soil carbon
tillage, burning or grazing and including
turnover. This includes retaining stubble
increased?
managed pastures in rotation.
and choosing rotations with crops that can
Monitoring can help with decisions on
Possibly,
but
it
takes
time.
Traditional
be brown or green manured. It should be
complex issues such as integrated weed
practices,
including
tillage
and
burning,
noted that intense cultivation will
management. If soil carbon levels are
were
gradually
reducing
soil
carbon
levels.
accelerate carbon loss and therefore may
declining, it may be prudent to consider
With
modern
conservation
farming
limit the soil carbon turnover benefit from
other options before choosing to burn
practices,
soil
carbon
levels
are
becoming
green manuring.
residues, which would further decrease
stable. It can take 20 years for levels to
Increased biomass growth will provide
carbon levels.
increase significantly but it is more likely
more organic matter to return to the soil
they will remain static under best practice
through stubble retention.
9. Where can I find more
management.
5. How can soil carbon
turnover be increased?
Crop rotation will diversify the quality of
organic matter entering the and
potentially increase microbial diversity
and activity. Incorporating stubble
accelerates its decomposition in the shortterm but reducing tillage and retaining
stubble will maintain a carbon supply to
biota over longer periods and can
sequester carbon.
6. Are fertilisers bad for soil
carbon levels?
Not necessarily. When fertilisers are used
to increase crop biomass that is then
returned to the soil through stubble
retention, soil carbon turnover is
improved.
information?
Farming systems that are poorly managed
A range of grain growing resources and
will likely see soil carbon continue to fall
until it reaches about 0.1 percent – similar guides can be found on the MSF website:
http://msfp.org.au/
to a sand-dune.
If working with a degraded soil, it is
possible to increase carbon levels over 1020 years, until they reach levels consistent
with soils that are well-managed.
Although only an option for some farms,
applying composts, manures or bio-solids
at high rates will boost soil carbon levels
quickly.
8. How should soil carbon be
monitored?
TABLE 1: Farm practices and their impact on soil carbon turnover
Practice
Increase
Decrease

Retain stubble
Cultivation

Burning (including windrow burning)

Grazing

Increase crop biomass

Clay incorporation

Green manuring

Managed pastures in rotation

Weed-seed collection (e.g. chaff cart)

GRDC Guide to Soil Organic Matter:
www.grdc.com.au/GRDC-GuideManagingSoilOrganicMatter
Find more information about soil quality
at: www.soilquality.org.au/
10. Useful contacts
Michael Moodie
03 5021 9108
[email protected]
Jen Bond
03 5021 9100
[email protected]
Acknowledgements
Therese McBeath, Nigel Wilhelm, Gupta
Vadakattu, Rick Llewellyn.
This fact sheet is based on research conducted
by SARDI, CSIRO and the University of Adelaide
in conjunction with Mallee Sustainable
Farming, through the GRDC project MSF00003
‘Maintaining profitable farming systems with
retained stubble in the Mallee’.
A full list of research cited in this Farm Talk is
available at www.msfp.org.au.
Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of MSF or the Grains Research and Development Corporation (GRDC).
No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. MSF, GRDC and contributors to these guidelines may identify
products by proprietary or trade names to help readers identify particular types of products. We do not endorse or recommend the products of any manufacturer referred to. Other products may
perform as well as or better than those specifically referred to. MSF and GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying
on the information in this publication.
Published June 2015
www.msfp.org.au