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Stubble
- Managing
the Resource
By Rohan Wardle
Research and
Extension Agronomist,
Southern Farming
Systems,
Ph. 0438 343 079 or
rwardle@sfs.org.au
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figures, photos and diagrams you will need to
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gschumacher@sfs.org.au
Rohan Wardle - National Landcare Research Project, initiated February 2005.
“Why Stubble Retention?”
·
h
soil water infiltration & PAW holding capacities.
·
i
surface (slaking) & subsoil (sodic) hostilities.
·
h
Organic Carbon %.
·
i
soil erosion potentials.
·
h
land stewardship by
not burning.
·
i
soil bulk densities.
·
h
energy supply to grazing animals.
·
i
off-site leakage/loss of nutrients & pesticides.
Credible benefits, but how do we make them work?
“Some
common approaches
to Stubble Retention”
Incorporation /
Destructive
High energy demands, with low
Summer rainfall events tending to limit the rate of stubble decomposition
“Surface
Retention of Stubble”
Time consuming, but effective!
“How about Grazing the energy reserves?”
Photo 1: Approx 8.5t/ha of
Residue
Photo 2: Approx 4.5t/ha of
Residue
Grazed with supplements:
•
Only a drop of
half a condition score.
•
Residue knocked
into furrows, requiring future management.
“Farmers out having a GO!”
“Why NOT Stubble Retention”
•Blockages
at seeding
– toolbar design
•Toxins
released from stubbles with rainfall
•h
biodiversity…slugs, snails, mice, other pests?
•Change
in micro-climate
–cooler,
wetter conditions slowing germination
•i
N availability / immobilization – C:N
•i
efficacy of some residual herbicides
•h
severity of foliar diseases – YLS, Scald…
“Common Problems
associated with Stubble Retention”
“Phytotoxic
Liberation”
Canola following Wheat
Research
(Bruce et.al; 2005) suggests that:
·
Stubble
retention can have a negative effect on plant establishment (up to 33%);
o
with
varietal influence (based on the vinegar effect) being highly
significant.
·
Shoot biomass
can be reduced by up to 30%.
·
Overall
grain yield can be reduced (up to 23%) with wheat stubble loads > 5-6t/Ha.
“Residue Managers
can offer hope”
Inter-row suppression of common weeds
Photos: Current results at Lake Bolac and Mt Pollock
“Micro-Climatic
Effects”
Canola following Wheat
Additional
Research from Bruce (et.al; 2005) suggests that:
·
Stubble
retention
↓
surface soil temperatures by up to 3.8ºC, resulting in seedling deaths.
o
This effect may be
worse in colder environments (especially the WD of Victoria), if crops are sown
late.
“Nitrogen Tie-Up”
·
As stubbles
decompose, soil N is tied-up by soil organisms that use it to
break down the residue, thereby limiting N available to the crop:
·
More a
problem (for cereals & canola) with dry Summers, followed by wet Autumns.
·
Consider
extra N at sowing, or grow grain legumes after cereals.
“Cellulose
Digesters”
Anecdotal
evidence suggests that:
·
Urea +
molasses + fulvic/humic acids + commercially available
bacteria and biological products can significantly reduce stubble residue
loads remaining on the surface.
·
Just
incorporation can ferment the stubble, killing any soil microbes:
o
The addition
of N & K can remedy this dilemma.
o
Current trial
work with caustic soda shows promise.
“Machinery
Requirements”
·
Deep toolbar
– vertical & horizontal clearance:
·
Minimise any
blockage / pinch points.
·
Residue
managers / disc openers, tine & press wheel assemblies:
·
Capable of
placing all seed & fertilizer in one pass with adjustable pressure for
optimal seed-soil contact;
·
Depth control
system dependant on press wheels.
·
Banding of N to
prevent toxicities.
“Toolbar designs
to maximise trash flow”
Photo: 2005 SFS Prototype
Photo: “Toolbar designs to
maximise trash flow”
Photo: the StubbleStar
more information ->
http://www.weeds.crc.org.au/projects/project_2_1_2_1.html
“Desired
Outcomes”
No “ONE”
solution
·
Everyone has a
combination of differing strategies
o
Variety selection
(short strawed)
o
N timing (canopy
management)
o
Harvest
distribution of residues
o
Stubble cut (200mm
– 300mm) vs left standing
o
Post harvest
incorporation vs seeding trafficability
o
Bale & remove vs
microbial digestion
o
Inter-row skip
seeding
o
Rotational
Management
•h
Harvest Index
Grain yield ÷ total biomass
“Burning is the
Current Non-Preferred Stubble Management Approach”
Proactive research will allow for its use as a strategic tool
into the future!
“Increasing
Incidence Of Glyphosate Resistance In Australia”
Graph: Number of resistant
populations – year.
“Ryegrass Control
With Burning”
Control is
more effective if stubble is in windrows
Emergence of ryegrass after
burning - % of untreated – windrow/standing
“Nutrients in
Wheat Stubble”
|
|
kg/t of stubble |
$/ha for 4t/ha of grain (HI=0.42) |
|
Nitrogen |
6 |
$33 |
|
Sulphur |
0.8 |
$1 |
|
Potassium |
44 |
$35 |
|
Phosphorus |
0.8 |
$1 |
|
Carbon |
400 |
????? |
“Current
Scenarios”
•
First field
visit – post sowing to review physical performances:
•
Field
establishment
•
Slugs, RLEM,
European earwigs, Lucerne Flea.
•
Economic
feasibilities of individual approaches.
•
Long-term
site benefits.
What works
for you???
“Managing the
Resource”
2005 Lake Bolac Trial Plan
“Stubble – the
Future”
•
If managed
correctly, stubble retention can be a useful weed management tool.
•
Every season
will present an alternative approaches.
•
Burning is
not the only tool available to manage crop stubbles.
Good
Luck!!
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