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 1