Home' Grower : October 2010 Contents The South Australian Grower -- October 2010
yAS Mike Harrison plunged the pen-
etrometer into the soil directly below a
Murcott mandarin tree, a gasp rose
from gathered onlookers as it sank to the han-
dle. A penetrometer measures the resistance,
and to an extent the compaction, of soil.
The dramatic test showed just how accessi-
ble the soil of this particular section of the
citrus plantation was.
The gasp from the tour crowd made up of
mostly farmers and company reps came
from knowing the highly fertile soil is the
result of naturally introduced biology, not
The demonstration summed up the early
positive results Monduran Citrus has experi-
enced using compost, compost extractions
and compost teas to improve its growing
environment and, most importantly, to save
money. The farm which boasts 150 hectares
of orchards on the banks of the Kolan River,
was one of the stops as part of a Reef Rescue
Farm Tour put on by Queensland horticul-
ture group, Growcom, highlighting projects
which received Federal Government Reef
Rescue funding in the Bundaberg region.
Monduran Citrus was granted funding for
machinery and infrastructure to assist in nutri-
ent management by replacing some chemical
fertiliser and fungicides with compost prod-
ucts. About 50 horticulture stakeholders from
as far as Gayndah attended the tour.
Former organic farmer and now farm man-
ager Mike Harrison was bluntly up front
about his reasons for trialling compost as
"Mostly it has to do with your hip pocket.
It's got to be sustainable for all parties for it
to be beneficial," Mr Harrison said.
Having said that, however, Mr Harrison
explained the multiple environmental gains
the switch has given.
For almost a year now, Monduran Citrus
has been producing its own compost for trial
use within an orchard, just west of Gin Gin.
Some careful research, along with a touch
of trial and error, has gone into getting the
compost production process just right on
metres or so lines of mounded soil and
Green waste is secured from the local
Bundaberg Regional Council waste tip.
Moisture is applied to the material before
some gyprock paper (gypsum) is skimmed
across the top, followed by feedlot manure.
A critical part to getting the process going
is bringing it to the right moisture level.
The pile is inoculated with a compost tea,
taken from a special 'mother pile' which is
carefully reared, fed and maintained at a sep-
arate location. The compost pile is then aer-
ated and mixed with a turner, something
which will be repeated on a regular basis to
speed up the process. The pile is brought up
to 65 degrees Celsius (a natural occurrence)
then turned. This is done five times.
"That effectively kills all seeds and any
pathogens that might be in there. And
because we are dealing with dump material,
we have no idea what's in there," Mr
Like the moisture level, the temperature is
also carefully obser ved. Mr Harrison said
should it get to 70 degrees C, it results in a
While each compost is different depending
on weather conditions, it is normally ready
in about five weeks.
Mr Harrison said the aim is to establish a
wide variety of 'critters' such as fungi, bac-
teria, amoebae and beneficial nematodes.
It is anticipated that 5 tonnes per hectare
of pure compost will be initially applied, fol-
lowed by a reduced application the follow-
ing year of about 3t/ha.
A conventional fertiliser spreader is used to
distribute the compost directly under the
trees. Mr Harrison said any time of year is
suitable, however, he has been told winter
application is preferable.
Back in the shed, a 1000 litre container
equipped with two aeration pumps brews a
compost tea. Oxygen levels are closely mon-
itored to ensure the mix does not become
anaerobic, therefore killing living organisms.
Mr Harrison said brewing takes about 14
hours but climatic temperatures could vary this.
When applied, the compost biology makes
its way into the soil and sets about making
nutrients more available and interact with the
roots. In the case of the citrus orchard, the
equivalent of one application of pure compost
at 5t/ha has broken down a 150 millimetre
deep soil compaction layer under the trees.
Mr Harrison said the soil now had
improved moisture retention and drainage.
Changing the biology in the ground has
also seen a reduction in grass weeds,
replaced with more broadleaf weeds, requir-
ing only softer herbicides if needed.
So far, fertiliser use has been cut down by
Mr Harrison said flow-on benefits should
eventually include better fruit shelf life,
improved taste and better disease resistance.
He cautioned that it is not a miracle cure
by any means, and disease vigilance needs to
The ledger balance, though, was Mr
Harrison's initial spur to consider a new
"It's difficult to quantify exactly what your
cost savings are but my cost savings, just in
chemical fertilisers alone, would be around
50 per cent if not better without jeopardis-
ing the health of the trees, and in fact they
end up with a much better environment for
them to grow in," he said.
Investment and scale of this size is a long
way from tipping a few scraps and grass clip-
pings into the green tumbler in the back-
yard. Mr Harrison said that on a commercial
front, compost needs to be done correctly
from the start.
"Making a compost is not simple -- you
have to watch it, you have to monitor it, you
have to look at it under a microscope, all
those things," he said.
"Once you've got the compost on the
ground, you don't go and kill it with some-
thing else. It's very easy to head out there
with a few tonnes of something and then
what you've just done, you've undone."
Mr Harrison said conventional fertilisers
can still be used in conjunction with the
compost, but in small amounts.
Since Monduran Citrus's own compost
pursuits there has been considerable interest
from other growers. Mr Harrison advised
smaller scale producers without the capital
and knowledge to produce their own, to
look at buying in compost.
But the advice came with a warning.
"There are composts and there are com-
posts out there," he said.
"It's best to have someone look at them to
see that they are what they say they are.
"There's a lot of stuff out there that really
shouldn't be put on the ground."
The compost is turned after it reaches 65deg C to inject air into the pile and avoid it overheating.
Compost checks costs
Mike Harrison, farm manager, Monduran Citrus,
Gin Gin explaining penetrometer results which
show deep soil penetration because of active
biology in the soil from compost applications.
Improved soil biology has resulted grass weeds
being replaced with softer broadleaf weeds.
One of the piles of compost made from green
Some careful research, along with a
touch of trial and error, has gone into
getting the compost production process
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