Home' Grower : March 2012 Contents The South Australian Grower – March 2012
Measure carbon to
build healthy soils
❏ By KAYLEE MAITLAND
SOIL organic carbon? You see it
on your soil tests and you
probably know a higher number
is better, but do you know why?
It is used an indicator of organic
matter levels in soils.
There are no tests available to
measure the exact amount of
organic matter in soils but soil
organic carbon, the carbon
associated with organic matter in
soils, can be accurately measured.
Those measurements are then
used to estimate levels of soil
organic matter, so a higher level
of soil organic carbon means a
higher level of soil organic matter.
So why is organic matter
important for soils?
Soil organic matter plays
multiple roles in maintaining
healthy and productive soils.
• Provides an energy source for
beneficial soil organisms like
bacteria, fungi and earthworms
• Is a source of nutrients
• Improves soil structure
• Increases soil moisture holding
• Buffers soil against
• Contributes to cation exchange
Soils with more organic matter
can support a greater diversity
and number of the soil organisms
that can assist in nutrient turnover
and improvement of soil structure.
Soil organisms help create the
‘glue’ that sticks soil particles
together, creating the variety of
soil crumbs and pore spaces that
make up good soil structure.
SOC level is an important indicator
of soil organic matter levels, but
knowing the type of organic carbon
is equally important as it can
greatly impact on soil productivity.
Four different ‘pools’ of organic
carbon have been identified by
CSIRO* that range from those that
breakdown quickly (within days)
and to those that take hundreds
of years to breakdown and are
The four ‘pools’ are:
• Crop residues include shoot
and root residues on and in the
soil which normally have a
particle size greater than 2
millimetres and are readily
available to provide energy to
soil organisms and be broken
down to improve soil
conditions. This is the most
labile and most available pool.
• Particulate organic matter is
smaller plant debris, particle
size 0.05-2mm and is readily
broken down in suitable
conditions but more slowly
than crop residues. This pool is
important for soil structure and
also as an energy source for
• Humus is decomposed organic
material made up of molecules
stuck to soil minerals and the
particle size is generally less
than 0.05mm. Humus is
particularly important in nutrient
retention and provision – the
majority of the available nitrogen
in organic matter is in the humus
pool. It breaks down less readily
than POM or crop residues.
• Recalcitrant organic matter has
a variable particle size and is
decomposes very slowly. If
enough of it is present it can
contribute to cation exchange
capacity and soil temperature
buffering. This organic matter is
usually in the form of charcoal
and is the least labile pool.
A high proportion of labile
organic carbon i.e . crop residue
and particulate organic matter,
means higher soil fertility
because the organic carbon is
more readily decomposed to
provide the energy for the soil
organisms that cycle nutrients.
Most soil organic matter breaks
down and so needs to be
replaced by fresh organic matter.
Compost can add soil organic
matter to your soil and replenish
soil carbon stock.
Soils with organic matter less
than 3.5pc for clays, and 2.5pc for
lighter soils, are likely to benefit
from the addition of compost. So
what are the options for
increasing organic matter levels?
In the past, vegetable growers
have used cover crops or green
manure crops in between crops to
boost organic matter levels, but
increasing pressures on production
often leave no time for those crops.
That is where compost can play
an important role as it boosts
organic matter levels whilst a
crop is being grown and provides
organic carbon in a form that can
be readily decomposed and used
by soil organisms.
Details: Kaylee Maitland, Compost for
Soils 08 7329 0422, 0408 818 436 or
■ Increase moisture-holding
■ Buffer against tempera-
■ Organisms broken down
to improve soil conditions
☛ FACT SHEET
Vegetable growers have often
used cover crops or green
manure crops in between
crops to boost organic matter
levels, but increasing
pressures on production often
leave no time for those crops.
08 8380 8554
Old Port Wakefield Rd
Ph 08 8556 5295
ABN 99 098 515 283
NATURES FERTILISER has all the attributes of a great all round organic
fertiliser. It provides a well balanced slow release nutrition for all types of
crops. It has a good percentage of Organic Carbon which most Australian soils
are lacking. Organic Carbon is essential for holding nutrients in the soil.
FOR MORE INFORMATION AND ORDERS
PHONE CHRIS WATTS MOBILE 0408 826 932
• HACCP APPROVED UNDER CERTAIN CONDITIONS
• BETTER SPREADABILITY
• REDUCED ODOUR
• SAFER TO HANDLE
• IMPROVED MICROBIAL ACTIVITY
Supplying the man on the
land since 1989
Straw Based Chicken Manure
plus many trace elements
Farmers, if you are considering using chicken manure this
coming season, you need to order now!
Suppliers of Nature’s Fertiliser Composted Chicken Manure,
Cow Manure also available
COMPARE THE ANALYSIS COMPARE THE COST PER ACRE COMPARE THE SOIL
BENEFITS WITH YOUR CURRENT FERTILISER
COMPOSTED FOWL MANURE
23% 3.8% 2.2% 1.8% 3 .4% 61% 208* 493* 1315* 142*
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