Laser Weeding Svend Christensen

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Laser WeedingSvend Christensen
DIAS Danish Institute of Agricultural Sciences
www.agrsci.org
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Weeding Areas
Inter-row
Intra-row
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Cutting weeds with a CO2 laser. T. Heisel, J.
Schou, S. Christensen, C. Andreasen 2001. Weed
Research 41, 19-30.
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Why CO2 laser to cut weeds?

• Lasers concentrate energy in a thin beam and can
  be directed precisely and quickly to cut weed
  stems
• Lasers do not till the soil and initiation of new
  weed seed germination is thus not taking place
• Dicotyledon weed species can be killed and
  monocots can be reduced in size and delayed in
  growth
• CO2 laser is so far the most energy efficient
  laser

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• Circles pulsed IR light at 1064 nm from the
  fundamental frequency of a Nd YAG laser
• Triangles pulsed UV light at 355 nm from a
  tripled Nd YAG laser
• Squares continuous wave (CW) far-infrared light
  (FIR) at 10.6 ?m from a CO2 laser

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4 W 20 W
scissors
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Conclusions Weed Research 41, 19-30

• The relationship between dry weight and laser
  energy was successfully described using a
  non-linear dose-response regression model
• The regression parameters differed significantly
  between the weed species
• When stems were cut below the meristems, 0.9 and
  2.3 J/mm of CO2 laser energy dose was sufficient
  to reduce by 90 the biomass of C. album and S.
  arvensis, respectively
• Generally, no significant difference in biomass
  reduction compared with plants cut by scissors

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Using laser to measure stem thickness and cut
weed stems. T. Heisel, J. Schou, C. Andreasen, S.
Christensen 2002. Weed Research 42, 242-249.

• Investigate the influence of stem thickness on
  the energy requirements to cut the stems of
  Solanum nigrum and Beta vulgaris with a CO2 laser

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Materials methods

• Solanum nigrum and Beta vulgaris
• Intensity
• 0, 1, 4, 10, or 20 W
• Speed
• 0, 1, 5 or 10 mm/s
• Thickness measurement of the plants at point of
  cutting

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Non-destructive thickness measure
Example
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Dose-response model

• DOSE Intensity / speed (J/mm)
• Dose-response model

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Black nightshade
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Beet
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Thickness stem/leaf vs. ED90
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Conclusion Weed Research 42, 242-249.

• It was possible to use a laser to measure
  thickness non-destructively
• A laser-cutting tool for in-row weed control in
  sugar beets is unlikely to be selective in
  practice since results from B. vulgaris and S.
  nigrum differ by growth stage
• The non-linear model incorporating stem thickness
  described the data best
• indicating that it would be possible to optimise
  laser cutting by measuring stem thickness before
  cutting

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The effect of laser irradiation of meristem on
plant growth. Solvejg K. Mathiassen Thomas Bak
Svend Christensen Per Kudsk. DIAS Flakkebjerg
Bygholm
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Materials methods

• Laser/Spot size
• 1. 5 W, 532 nm, spot size 0.9 mm
• 2. 5 W, 532 nm, spot size 1.8 mm
• 3. 90 W, 810 nm, spot size 1.2 mm
• 4. 90 W, 810 nm, spot size 2.4 mm
• Species
• Stellaria media (common chickweed)
• Triplerospermum inodorum (scentless mayweed)
• Brassica napus (rape)
• Exposure (ms)
• 1.1 1.3 1.2 1.4
• 70 250 160
  
• 130 500 320
• 250 1000 640
• 500 2000 1260
• 1000 3000 2500

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S. media treated with the 5 W, 532 nm laser.
(ms) 130 250 500
1000
(ms) 500 1000 2000 3000
S. media treated with the 90 W, 810 nm laser.
(ms) 130 250 500
1000

(ms) 320 640 1260
2500
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T inodorum treated with the 5 W, 532 nm laser.
(ms) 130 250 500
1000
(ms) 500 1000 2000 3000
T inodorum treated with the 90 W, 810 nm laser.
(ms) 130 250 500
1000
(ms) 320 640 1260
2500
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B. napus treated with the 5 W, 532 nm laser.
(ms) 250 500
1000
(ms) 1000 2000
3000
B. napus treated with the 90 W, 810 nm laser.
(ms) 250 500
1000
(ms) 640 1260
2500
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DIAS Danish Institute of Agricultural Sciences
www.agrsci.org
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Discussion - energy

• Approximately 150 J/mm is needed to cut one S.
  nigrum stem with two-true leaves
• If we consequently cut in all rows between all
  beets leaving a guard of 2 mm on each side of the
  beet, approximately 1970 mm/m2 have to be treated
  corresponding to 2955 MJ/ha
• If we can control the laser to cut only where
  there are weed stems, there will be a potential
  saving. Realistically we must include 2 mm
  cutting on each side of the weed to account for
  laser energy build up time and possible
  inaccuracies.
• With an overall density of 250 weed plants/m2 of
  S. nigrum approximately 225 MJ/ha is required

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Discussion

• The results of the experiment show that stem
  thickness is an important co-variable that could
  be integrated in a model based on the
  dose-response model
• Further research should include investigations of
  the actual depth of the laser cut for various
  levels of DOSE and plant material to
• verify the energy calculations
• enable a test of the hypothesis that stem-shape
  or morphological or anatomical characteristics do
  not affect the effect of laser cutting