Agribusiness Crop Updates 2005
The art of burning
Peter Newman1 and Michael Walsh2
1
Department of Agriculture, Geraldton; 2WAHRI, University of WA
Key Messages

Removal of weed seeds at harvest will be the key to maintaining intensive cropping in
Western Australia as the frequency of herbicide resistance increases.

Burning of narrow windrows is an effective, and hopefully temporary means of
removing weed seeds in the short term, until an alternative mechanical innovation is
developed.
Background and aim
Wild radish and annual ryegrass are annual weeds that, because of their ability to produce
large quantities of seed, can establish a long-term viable seedbank after only one growing
season. The key to the successful management of these weeds is to deplete their seed
banks. As these weeds become resistant to more herbicides, seed bank management will
need to rely on control measures other than through the use of herbicides. Removing or
destroying weed seeds at harvest is likely to be a key, non-herbicide weed management
strategy to minimise inputs into weed seed banks.
The aim of this research was to evaluate the burning of header windrows for the destruction of
annual ryegrass and wild radish seeds.
Results
Burning temperatures
Previous research (Chitty and Walsh, 2003) demonstrated that 400oC for 10 seconds is
adequate to destroy ryegrass seeds. Similar studies have also determined that wild radish
pods will be destroyed by 400oC for 20 to 30 seconds or 500oC for 10 seconds (Walsh et al.
2004). This research was conducted by placing annual ryegrass and wild radish seeds in a
kiln at a range of temperatures for
varying amounts of time. The seeds were then tested for viability.
The temperature data in the graph below were recorded during burning of a lupin windrow
near Mullewa (Walsh et al. 2004). This data demonstrates that it is possible to achieve
temperatures above 500oC for as long as three minutes where there was 33 t/ha dry matter
in the windrow.
Burning temperatures through time (seconds) in a Lupin
stubble windrow
1000
Middle windrow
1cm below surface
soil surface
Temperature (o C)
900
800
700
600
500
400
300
200
100
0
1
75
149 223 297 371 445 519 593 667 741 815 889 963 1037 1111
Time (seconds)
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Agribusiness Crop Updates 2005
Weed germination after burning windrows
Research conducted at the Messina’s property at Eradu in 2003 revealed that 98% control of
annual ryegrass was achieved by burning narrow windrows. The trash removed – unburnt
treatment was used as the benchmark because ryegrass germination is impeded under unburnt windrow treatments.
Wild radish density in crop year after harvest / burning treatments Messina June 2004
Ryegrass densityin May'03 after windrow
burning treatments imposed in March '03
250
windrow
2
140
200
Wild Radish / m
Ryegrass denstiy / m
2
160
150
100
50
0
between
120
100
80
60
40
20
0
Trash removed unburnt
Normal trash burnt
Concentrated
windrow burnt
Double trash burnt
concentrated
windrow
unburnt
collect
everything
plastic sheet
unburnt
grain tank
collection +
windrow burnt
straw
spreaders
unburnt
In another trial at Messina’s in 2003/2004, there is evidence of wild radish seed
destruction/removal after a range of harvest and burning treatments of the 2003 lupin crop.
There are clear differences in wild radish emergence from the windrow between the
concentrated windrow burnt and un-burnt treatments, indicating that the burning was
effective at destroying wild radish seeds. The collect everything plastic sheet treatment
simulates the use of a baler where all residue from the header is removed. Wild radish that
emerged from within this treatment represents the residual seed bank. The grain tank
collection treatment refers to setting the header to catch as much wild radish pod in the grain
tank as possible. This was a very effective treatment at removing wild radish seeds at
harvest. The burning of windrows appears to have destroyed some wild radish seed at or
near the soil surface from the residual seedbank. Hence there being less wild radish
emerging from the windrow where windrows were burnt compared to the collect everything
treatment. The straw spreader unburnt treatment represents standard harvest practice.
Computer simulation
The following graphs have been developed using Ryegrass and Radish RIM, simulation
models to estimate weed seed banks following various weed management strategies. The
nil treatment in the graphs below represent a situation where resistance has developed to
selective herbicides, and the grower is achieving 90% control of wild radish or annual
ryegrass in each season. This is the standard treatment to which a chaff cart that removes
50% of the total ryegrass or a baler that removes 75% of the total ryegrass/wild radish seed
can be compared. Note: Chaff carts are capable of removing 70% of ryegrass seed entering
the header and a baler is capable of removing 98% of ryegrass/wild radish seed that enters
the header during harvest. The figures used here (i.e. 50% and 75% respectively) represent
a conservative estimate of the removal of the total ryegrass/wild radish seed production.
Early indications from field research is that burning narrow windrows may be almost as
effective (i.e. within 5 to 10%) as towing a baler when conducted appropriately.
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Grains Research & Development Corporation
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Agribusiness Crop Updates 2005
RIM simulation of Radish seed bank
90% Radish control all herbicides
Lupin : Wheat rotation
RIM simulation of Ryegrass seedbank
Trifluralin every year 90% ryegrass control
lupin : wheat rotation
Ryegrass seeds /m2
2000
1500
nil
chaff cart 50%
baler 75%
1000
500
Wild Radish Seeds / m
2
160
140
120
100
80
baler 75%
ni
60
40
20
0
0
0
1
2
3
4
5
6
7
8
0
9 10
1
2
3
4
5
6
7
8
9 10
Year
Year
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Agribusiness Crop Updates 2005
The RIM simulation demonstrates that both ryegrass and wild radish seed banks can be
reduced by targeting seed at harvest with a chaff cart and/or a trailing baler. However, due
to the longevity of wild radish seed in the soil it takes many more years to reduce a wild
radish seed bank than a ryegrass seed bank. Later harvesting will reduce the efficacy of the
chaff cart and the baler due to the shedding of both annual ryegrass and wild radish.
Conclusions

Removal of weed seeds at harvest will be of paramount importance to the future
success of intensive cropping in Western Australia

Towing a baler behind a header to catch weed seeds may only be financially viable
if there is a reliable market for the bales. Should a reliable market such as ethanol
or pulp production become available, it may be possible for growers to increase
profit while managing resistant weeds. Towing chaff carts is currently out of favour
with many growers for a wide range of reasons. Burning narrow windrows,
however, is a cheaper option and when conducted appropriately may be as
effective as towing a baler.

Burning narrow windrows is an effective means of destroying weed seeds at harvest.
However, it is not without risk, and must be conducted with care to avoid burning
outside the windrow. For this reason, burning narrow windrows should be viewed as
an interim measure until an alternate innovation for destroying / removing weed seeds
at harvest is commercially available.
The art of burning
Large wind erosion events that result from broad scale burning of paddocks is
unacceptable. The art of burning is to burn only that fraction that contains weed seeds
and leave the majority of the paddock with residues retained. Hence the development of
the technique of burning narrow windrows.
The Messina’s of Mullewa burn anywhere between 15,000 and 20,000 acres of windrows
in wheat, canola and lupin stubbles successfully every year. The secret to their success
has been to concentrate crop residues into a 500 mm to 600 mm wide windrows using a
simple chute mounted to the rear of the header. Although not the first growers to use
this technique they have made this a successful one for them across large areas of their
property annually. There are a few simple rules that the Messina’s follow that have
allowed windrow burning to be successful for them:

Harvest low to minimise the risk of the fire spreading into adjacent stubble.

Graze lightly with sheep to remove some of the leafy material attached to
the stubble to minimise the fire carrying into adjacent stubble.

Narrow windrows have a high tonnage per ha of dry matter within the windrow.
Twenty to
40 t/ha dry matter is common in a narrow windrow. This amount of dry matter
produces a fire hot enough to destroy weed seeds.

Narrow windrows (i.e. 500 mm to 600 mm wide) represent approximately 5% of
the paddock. Aligning windrows perpendicular to the prevailing winds will
minimise the erosion risk in the windrow.

Burn diagonally into the wind. This reduces the speed of travel of the fire while
allowing for wind to fuel the fire from the side of the windrow, resulting in a hot slow,
fire that burns to the soil surface where weed seeds are present. Harvesting up and
back facilitates this.
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Grains Research & Development Corporation
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Agribusiness Crop Updates 2005

Choose specific conditions for burning, i.e. warm weather with a light wind.

Avoid barley stubbles, the extra leaf makes it difficult to contain the fire to the windrow.

When harvesting with the chute attached to the rear of the header, if stopping in
the crop it is necessary to reverse the header immediately to avoid blockages.
Key words
windrow, burning, annual ryegrass, wild radish
Acknowledgements
Many thanks to the Messina family and to the funding body GRDC, for their ongoing support
of this research.
Project No.:
DAW 672
Reviewed by:
Dr Michael Walsh, WAHRI
References
Chitty, D. and Walsh, M. (2003). The burning issues of annual ryegrass seed control. In
'Agribusiness Crop Updates'. Perth, Western Australia pp. 32-33 (Department of
Agriculture Western Australia).
Walsh, M.J., Newman, P. and Chitty, D. (2004). The burning issue of weeds. Australian
Grain
14, 5-7.
Crop Updates is a partnership between the Department of Agriculture, Western Australia and the
Grains Research & Development Corporation
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