At the Wagga Wagga Grains Research
Update, Colin McMaster shared
the latest research on summer cover
crops, specific to central and
southern New South Wales in winter
dominated rainfall areas.
We looked at what are the key
drivers for retaining summer fallow
moisture, and it does that always
lead to increases in grain yield.
He started with some key advice for
local growers - before
you make any cover crop decisions,
understand the pros and cons.
So some of the benefits are you've
got to have reduced wind erosion,
you're going to have cooler
temperatures. You're going to have a
more consistent soil temperature.
You've also got less herbicide
applications over the summer fallow
period. There's actually going to be
forage value from those grazing
crops.
You're potentially going to be
increasing your total carbon
percentage and therefore you're
going to be improving your
microbial activity as well within
that. The cons of summer cover crops
are you've got reduced mineral
nitrogen availability, you've got
reduced grain yield,
you've got higher risk
of soil water deficit in low
rainfall years, so you're increasing
your risk profile.
You could have patchy crop
establishment and
you're also increasing potentially
your disease risk for the following
winter cash crop.
Since November 2018, Colin's
managed a range of research trials
at Parks and Canowindra
to better understand how summer
cover crops can benefit and
integrate with the broader farming
system.
The primary aim of this particular
trial is to determine
what's the net water cost to grow a
cover crop.
What's the net water gain for the
following winter cash crop?
And then what's going to be the
impact on the following grain yield
from that winter cash crop.
So so that's the primary purpose.
The secondary purpose
is to observe how does it fit within
the farming system.
So how is it going to impact
nitrogen levels, total carbon
levels? What's the grazing value
of those cover crops?
What's going to be the disease
implications of those cover crops?
So there's a lot of other secondary
questions that we're also trying to
address.
It's all part of a wider GRDC
investment on summer cover crops in
the northern region with similar
trials set up across New South Wales
and Queensland growing areas.
As Colin explains, his
central New South Wales trials have
delivered some surprising insight on
cover crop performance.
It was quite surprising from these
trial results that
the soil water recharge following a
cover crop was was really quite
high. So if you get
a really wet year or you get
rainfall post cover crop
termination, the recharge is going
to be really quick, which is
fantastic.
But if you don't get any rainfall
after you terminate the cover crop,
you're obviously going to be in a
soil water deficit.
So there's a benefit, but
there's also a risk associated
with that.
Even if you do get a really wet
year, the soil
water can catch up, but you're going
to leave a nitrogen deficit behind
that's probably going to need
correcting for your following winter
cash crop. So you really need to be
aware of, you know, really aware
of those those factors.
For grain only operations, the
trials highlight the risks
associated with growing cover crops
in a short fallow.
Both of the trial sites showed that
grain yield reduction was reduced
by growing a cover crop.
So really, you're better off
to try and just conserve stubble by
using current techniques, retaining
stubble. There's all sorts of things
disc machines, stripper front,
there's a lot of technology out
there to try and retain your
stubbles and control your subtle
weeds are probably the best
best management still. The
main reason for that is you're not
having to grow any biomass that
using water to grow that biomass,
you're just growing the grain.
But if your
goal posts is that you've got a
bare, bare ground and you need
ground cover from an erosion
perspective, it makes a lot of
sense. Though from a mixed farming
perspective, it's a different story
as there are more options to utilise
that cover crop biomass.
So if you've
got livestock within the system,
livestock are worth a lot of money
and you can convert that biomass to
dollars.
You just need to keep in mind that
if you are going to be grazing it
and trying to grow a cash crop
the following season, you
really need to make sure it's a high
output system.
So your nutrition needs to also be
well-suited to that and not have
your nutrients limited.
Coming to the end of his
presentation, Colin offered some
good cover crop advice for all
growers to consider.
The key thing to take out of this
research is be very
clear of what your goals are if
you're interested in cover cropping,
there's many pros and cons.
Be aware of all the pros, be aware
of all the cons, understand
the mechanics of it so you can see
whether it's actually going to
achieve your your particular goal
posts.
So just be aware of the risks
and the rewards.
Colin McMaster from the New
South Wales Department of Primary
Industries.
And this video is one in a series
of update videos recorded at
the 2020 GRDC Grains
Research Updates.