GCTV Ep#10 Grazing Stubbles (Water Use Efficiency Initiative)
Narrator: When GRDC supports research the expectation
is the outcomes will result in change on-farm.
Change such as the adoption of a new variety or new technology.
In this story the surprise result is a recommendation not to change as long as everyone keeps to
the rules, and it�s surprising for a number of reasons.
But first let go back to the experiment, which took place here at Temora and was replicated
at Condobolin.
James Hunt: Research Scientist CSIRO Sustainable Agriculture Flagship
We set up this experiment with Farmlink Research where we were comparing three strategies if
you like.
So complete stubble retention so no sheep going in there at all.
then grazing the stubble after harvest, the sheep would go in and we�d graze the stubbles
down to the level we thought was reasonable, and then also grazing the crop through winter
and the stubble as well.
Narrator: The experiment was to scientifically measure
the impact sheep have on stubble paddocks.
This region is very productive and often results in heavy stubble loads after harvest.
Grazing off those stubbles has been common practice.
The straw is a good source of carbohydrates and protein and the sheep had other uses.
Michael Sinclair: Grain Grower �Caithness� Temora NSW
Historically I guess we thought they were a good weed control over the summer time.
Any rainfall events that did occur the sheep were there to control the weeds when they
were young and also it was a great feed value for the sheep over that time, we gave the
pastures a break over the summer time so the land was there we used it, utilised it for
the livestock.
Narrator: However the move to farming systems that reduced
soil compaction by controlling paddock traffic and retained stubble to improve soil health
and moisture retention, had the mixed business farmers asking questions about the level of
impact their sheep were having and how that affected the next season�s crop.
Farmers like Michael Sinclair started to keep sheep off the stubble especially after the
run of dry years from 2000 on.
Michael Sinclair: We realised then that the sheep weren�t
actually controlling the weeds they were still there, the roots were still active dragging
moisture out so that was the reason for pulling the sheep off well not letting the sheep on
the stubbles over the summer time and turning to chemical control of the weeds to get a
definite kill.
Narrator: However when the rains returned so did the
heavy crop residues and the sheep were put back into the stubbles.
Around the same time GRDC�s Water Use Efficiency Initiative got underway and as part of that
program James Hunt and his research colleagues at Farmlink and NSW DPI established their
experiments.
Now as the trials are being finalised the various questions are being answered.
James Hunt: The thing about sheep compaction as opposed
to machinery compaction, machinery compaction is very deep because of the weight and width
of the footprint of a tyre whereas sheep compaction because the hooves are quite small it�s
only ever very shallow and so just the act of sowing with our knife points and press
wheels basically breaks-up that compaction so we never see a negative impact on the crop
and we also measure the crop very closely to see how its growing in response to that
compaction.
Narrator: As well as compaction the experiment measured
soil moisture levels.
These drink cans cover tubes that drop a metre 80 beneath the surface.
Within the tubes neutron moisture meters were placed to determine whether grazed plots had
a greater moisture loss due to runoff or evaporation compared to nil grazed plots.
Also moisture probes were used at 7.5 and 15 cm depths to get a good understanding of
water infiltration.
Early trial photos show an over-grazed plot from 2009.
It was grazed in winter and again after harvest.
In comparison this is the no graze plot from the same season.
The soil water content looked like this.
James Hunt: As you can see the lines are right on top
of each other in the surface of the soil and what that really tells us is that the differences
that we had between those two treatments weren�t due to evaporation and yeah what it demonstrated
was that the extra water we had wasn�t due to evaporation, the stubble preventing evaporation,
it was due to the stubble cover increasing the infiltration and so the difference in
water we do have at the bottom of the profile so more water had run in, in those plots.
Narrator: Stubble and retained crop residues tie up
nitrogen and one of the most interesting outcomes of the experiment was the contribution sheep
make to soil nitrogen levels.
James Hunt: When you have sheep grazing stubble you get
a much more rapid nitrogen cycling and the yield and protein advantages that we have
seen from having sheep in the system probably come from that.
Narrator: At Temora in 2011, at the time of sowing the
different plot treatments produced these levels of available soil nitrogen.
In 2012, again the three different treatments produced three different results.
Also measured were yield and grain protein levels.
James Hunt: Yields have been as good or higher in our
plots with sheep in them and our proteins the same compared to the stubble retention
treatments so this is indicating biophysically having sheep in your system doesn�t compromise
crop yield.
Narrator: While the Temora experiment was conducted
on small plots the trail at Condobolin was on a paddock scale and the similar Grain and
Graze program run by the Birchip Cropping Group also produced results that are consistent
with the Temora outcomes.
And given that nitrogen levels are running down across the southern cropping zone and
becoming more of a limiting factor on crop yields if sheep can positively contribute
to a cropping system the No Need to Change outcome should give growers confidence and
the knowledge they can get the positive benefits controlled traffic and stubble retention bring
to a farming system.
With this proviso.
James Hunt: As long as you obey those rules � which
are that you always control summer weeds and you always keep 70% of cover on paddocks at
all times you�ll still get good fallow efficiency so 70% is enough to prevent wind erosion,
water erosion and maximise infiltration so as long as you do that you can graze sheep
on stubbles but once you start breaking those rules you will compromise yields.
Ends