GCTV Ep#12 Subsoil Manuring
Narrator: When a high rain fall zone wheat crop that
should have been yielding five to six tonnes to the hectare was instead producing four,
this southern region grain grower began looking more closely at his soil.
John Sheehan: Yaloake Estate, Ballan VIC You know we were growing all this biomass
but not producing grain at the end and that’s when we started to look below the crop and
identified this almost wet plasticine, this impenetrable clay and that’s when we became
interested.
We decided to engage in some more research and figure how to manipulate this soil.
Whether it was a physical or chemical constraint, we were unsure in those early days.
Narrator: That research started 8 years ago and initially
involved soil scientists from La Trobe University, the Victorian Department of Primary Industries
and collaborating farmers.
Experimentation began using various soil conditioners, what researchers like to call amendments.
John Sheehan: We were looking at very coarse sands, gypsums
and then we started to progress into high end products like Lucerne pellets.
Started to see real benefits from any of these high nitrogen products such as dynamic lifters
and things like that and we started to really see these changes in that soil structure.
Narrator: The response was rapid with John Sheehan seeing
yield increases of up to 60% the following year.
The soil issue at Yaloake Estate wasn’t an isolated situation.
Across Victoria’s high rainfall zone heavy clay subsoils prevail.
Soils so tightly packed, very little pore space exists between the clay particles.
Renick Peries: Soil Scientist DEPI VIC For a good crop to grow we know there should
be at least 10% of macro porosity.
Macro porosity helps one drainage, second to provide air or aeration of the soil, and
also thirdly for the roots to penetrate into the subsoil.
Narrator: The collaborative research that Yaloake Estate
and La Trobe had been doing provided a base for Renick Peries.
His theory was that it should be possible to develop the technology to encourage biological
activity that could significantly change the subsoil’s structure and its water holding
capacity.
With support from GRDC and in collaboration with the farmer group Southern Farming Systems
he ran trials incorporating chicken manure into the clay subsoil using a modified deep
ripper.
Renick Peries: What we are seeing today is that it has worked
and that the soil is holding onto that increased porosity for five years plus.
And we’ve got yield results just delivered to GRDC showing that in those validation trials
that we started in 2009 up to the fourth year there’s incremental benefits and at the
fourth year itself there was one site in western Victoria that produced two and a half tonne
of extra canola which within itself was sufficient to cover the initial costs of the operation.
Narrator: Chicken manure was incorporated at two rates,
20 and 10 tonnes to the hectare.
These plots were compared to others where an equivalent rate of inorganic nutrients
was dropped into the rip lines.
Another plot had a mixed application, 10 tonnes of chicken manure and the balance in, inorganic
nutrients, to match the 20 tonne per hectare manure treatment.
There was also a control plot, which was deep ripped without manure or inorganic nutrient,
added.
The deep litter chicken manure produced the best results, and the 20 tonne per hectare
rate, the best overall.
Renick Peries: The yield differences across all sites and
seasons were anywhere between 40% and 90% across the different sites.
In terms of water, the water was measured through neutron moisture metres and we found
during Summer fallow period the soil was able to store more water almost three times the
amount of water that the control treatments were able to hold and that amount of water
was available to the crops during grain fill.
Narrator: The use of an organic manure compared to an
inorganic nutrient demonstrated there was more at work than NPK in these trial results.
The heightened microbial activity results in root exudates that affect the clay matrix.
Renick Peries: In the subsoiled manured plots we’d actually
made topsoil out of subsoil, compared to the control.
Narrator: While chicken manure delivered positive results
further research will be undertaken using other organic manures.
And before growers rip into their paddocks there’s a word of caution.
Have soil core samples taken to determine how shallow or deep the sodic clay layer is.
Renick Peries: We tend to go between 5 and 10 centimetres
into the clay layer because ripping has to be done with a lot of care because this sodic
soil you don’t want sodic soils to be brought to the surface.
Narrator: It’s the sodium cat ions in the sodic clays
that can cause dispersion of clay particles and clog soil pores inhibiting water infiltration.
And the timing of the subsoil manure application is another aspect to be considered and avoided
if the subsoil is too wet.
Renick Peries: We tend to recommend to people that they do
it in February - March but sometimes if you have a dry season you can extend that to say
April
Narrator: Yaloake Estate is so convinced by their own
results they’ve built this commercial sized applicator and used it on 100 hectares, applying
20 tonnes of chicken manure per hectare at 40 cm depth to make sure its in the clay layer.
What’s its costing is less exact.
John Sheehan: Look very challenging to get a gauge of that
but we’re spending in a range of about $1,000 a hectare of total costs to buy the product,
to transport the product and put it into the ground.
So we’re starting to get a better handle on that now as we’ve progressed down the
more commercial side of it.
Narrator: If the 60 hectares of canola and 40 of wheat
on those treated paddocks yield an additional 50 to 70% as expected, Yaloake’s capital
costs for subsoil manuring should be covered in the first year according to John Sheehan.
And in those early trial plots the ongoing residual benefit is a bonus.
John Sheehan: So we’re still seeing yield response five,
six years down the track.
Some of our earlier trials which we aren’t really evaluating now but we’re still seeing
canopy variation and obviously yield response.
Narrator: Not every grower might have close proximity
to commercial quantities of chicken manure but with other organic manures to be trialed
its research that has already delivered for grain growers in the high rainfall zone and
could deliver more yet.
Ends
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