Building up soil organic carbon on-farm is a slow
process, can be expensive
and the benfits are
hard to quantify.
But researcher and grower groups
in Western Australia
say it has the potential to
boost crop yields, grain quality
and the health of sandy
soils. DAFWA
Development Officer Liam Ryan
explains the soil carbon
challenge facing growers.
"It's quite tricky trying to build soil carbon
levels in WA, primarily because we operate
in quite marginal systems, so
soil type and climate
are typically the main restrictions
on what soil carbon levels we can attain.
Then when you couple that with the fact that
our net primary productivity, basically
how much biomass we grow,
isn't that great,
and you're in a warm climate with sandy
soils, there's typically not a whole lot of opportunity
to store carbon, for most areas of WA."
Long-term GRDC
and federal government funded soil biology
trials in WA
are led by
DAFWA Research Officer Dr. Francis Hoyle.
These are investigating changes in
soil organic carbon.
"So now that the Liebe Group long-term soil biology trials
have been running for 13 years,
there's a lot of great data to pull out of that
and some of the key outcomes we're interested in
is the increase in soil organic carbon.
There's been about an 8 tonne increase in
carbon storcks through
the 0-30cm layer
through the application of 80 tonnes
of chaff. There's also
been a lot of other positive flow-on
benefits. Nutrition
in particular is seeing about an
extra 20kg
of nitrogen cycled through that
organic matter pool just through
the addition of organic matter.
Also, massive increases in K
and P as well.
The cation exchange capacity
is increased by about 48%
and water holding capacity by about 6%
It really affirms all the benfits from
increasing soil organic carbon.
The challenge for us now is to move from
what's probably an unrealistic scenario,
the application of 80 tonnes of chaff,
to increase carbon stocks to those sort of levels
through practices that
could be ordinary within a farming
systems context."
On-farm application of
the findings is being investigated by
local Grower Groups looking
at benefits and pitfalls of a range
of strategies to boost
soil carbon levels.
"At the moment going forward, it's looking at
things like soil amelioration
which is quite a hot topic and
understanding that if we do go through and Mouldboard
plough a soil profile or spade it
and we have a redistribution of carbon stocks at
depth, is that then going
to act as a bit of a buffer to help us out
later in the season where you have that
band per se of cation
exchange capacity and
water retention? So even though we have that loss of carbon
in that top 10cm when we do go through and
ameliorate through
some forming of ploughing or significant ploughing
hopefully we can then build up
that carbon stock and hopefully
through time, have a greater soil organic carbon level
than we did previously."
Buntine grower and Liebe Group member Stuart McApline
has been working for
many years to increase his own soil carbon level.
"What excites me most
about building a healthy soil that is
healthy chemically, physically and biologically
and building carbon is trying to work out how
efficient we can get with our inputs because if we can
lower our inputs
considerably, and I've done this myself on the farm
with what I've been doing with soil biology
and soil health, then we reduce our risk quite
considerably and I beleive that we can farm
in these dry areas if we can get our input costs right down."
Stuart has been using a range of strategies to
improve soil health and nutrient use efficiency.
"We're trying to move as much to a controlled traffic system
to maintain those compaction levels.
Close attention to pH and incorporation of lime ameliorants.
As your soil has the ability to function at a higher level and be
more efficient, once you start dropping your fertiliser rates
then some of that biological activity has to kick into gear and start
working. Then through the photosynthesis process
the plants are pumping carbon into the soil
to feed the biology to help find that
nutrition and lift that efficiency in the soil
so the whole soil starts going to another level again.
It's a continual
fine-tuning of that system."
Stuart says although the long term soil
biology trial at the Liebe Group
site is using uneconomic levels of organic matter,
it is providing an indication of the potential benefits to growers
when soil carbon levels are elevated.
"We're seeing some quite significant differences in yield
in particular seasons
and a lot more nutrient holding capacity
Today digging up the plants, there were a lot better root structures
pH was better at depth because
of that soil structure as well.