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Harvesting Willow Rings Around Prairie Marshes

Philippe Savoie, Research Scientist, AAFC

Frédéric Lavoie, Graduate Student

Luc D’Amours, Graduate Student

Bill Schroeder, Research Manager, AAFC-PFRA

John Kort, Research Scientist, AAFC-PFRA

Presented at the CSBE/SCGAB Annual Meeting

North Vancouver, BC, July 14-16, 2008

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Presentation Outline

1.Introduction: wetlands, natural vegetation, and co-existence with agriculture

2.Methodology: describe site and prototype for harvesting

3.Results: harvest rate, biomass recovery

4.Conclusions

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Introduction: (a) Agriculture and wetlands

North American Prairie farmland is often close to wetlands, marshes, sloughs and potholes

Many of these wetlands were drained in the XXth century to facilitate mechanized agriculture

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Introduction: (b) Management of wetlands

Current policy is to protect remaining wetland sites because they play an important ecological role for water control, plant diversity and wildlife habitat

Find peaceful co-existence between wetland protection and agriculture

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Introduction: (c) Vegetation around potholes

Typical sequence of vegetation between the pothole and the agricultural field: (a) Cattails and bulrushes; (d) Sedges: (c) Willow.

Risk of encroachment, so some form of vegetation control is required

(Source: Huel, 2000 – Managing Saskatchewan Wetlands.)

Pothole

Agricultural field

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Introduction (d) Prescribed burning or harvesting

One practice is to cut, pile and burn the woody crop on site: expensive and no value from the biomass

Another option is harvesting and chipping willow with a modified forage-harvester: machines are very expensive (> $500,000)

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Introduction (e) New bio-baler for woody crops

AAFC developed a bio-baler in 2006 to harvest willow plantations: moderate cost (≈ $70,000)

Modified in 2007 to work in rough terrain and fallow land

Other potential applications: harvesting brushes on pasture and under power lines, forest understory

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Objective & Methodology (a) Willow ring sites

ObjectiveObjective: assess harvesting willow rings with the bio-baler

Methodology: Two potholes in Indian Head, SK with natural willow (Salix bebbiana and S. petiolaris)

Ring #1: 5-m width, 690 m², average stem diameter 17 mm

Ring #2: 3-m width, 1280 m², average stem diameter 12 mm

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Methodology: (b) Bio-baler

Original bio-baler (2006): 4 saw blades (2.0 m cut width), 12 hammers for shredding, round baler with a single compression belt (1.2 m wide bales, up to 1.5 m Ø and 500 kg)

Modified header (2007): saw blades removed, replaced by 20 hammers for cutting (2.3 m width) & shredding; same size bales; 2007 version used in SK

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Shredder design parameters

Hammer: 1.7 kg, cutting width of 145 mmHinged on rotor turning at 2200 rpmCutting tip rotated along a 500 mm ØPeripheral speed of cutting edge: 58 m/s

Distance between hood and flail adjusted for moderate shredding, just enough to ply branches into the baling chamber (minimum chipping)

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Pushbar system

A double push bar system in front of the header pushed the upper part of stems forward to facilitate cutting and grasping by the shredder of the bottom part of the stem.

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Results: (a) Biomass harvested from willow rings

(Average 1.35 m Ø bales) Site #1 Site #2

Number of bales harvested 9 6

Mass per bale (kg) 347 251

Moisture content (%) 40.4 42.7

Bale density (kg/m³) 199 144

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Results: (b) Harvest capacity and yield

Site #1 Site #2

Time per bale (s) 189 256

Capacity (t wet/h) 6.61 3.53

Biomass harvested (kg DM) 1858 864

Harvested yield (t DM/ha) 26.9 6.7

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Results: (c) Loss and biomass recovery

Site #1 Site #2

Loss measured (kg wet/m²) 2.64 0.71

Loss estimate (t DM/ha) 15.7 4.3

Total yield (t DM/ha) 42.6 11.0

Percentage recovery (%); (average loss = 38%)

63.2 61.2

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Results: (d) Quality of cut

Bio-baler with shredder cutter-header (2007 version) left splintered stems after cutting; OK in natural stands

Previous bio-baler (2006 version) with saw blades left clean cut stems after harvest (preferred in plantations)

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Conclusions

The bio-baler successfully harvested willow rings around prairie potholes at rates of 3.5 t/h in low yield and 6.6 t/h in high yield

Actual harvest rates would be 2 to 4 t/h because of frequent machinery displacement to access potholes

At 40% moisture, the value of biomass (1.2 to 2.4 t DM/h) at about $50/t DM would not compensate the cost; some environmental benefit has to be added to justify mechanical harvest

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Future perspectives

Biomass recovery averaged 62% in willow rings; this can significantly reduce wild fire risk while leaving some residual biomass on the ground

Bio-baler could be used to clean alleys in tree plantations, natural forests and other brush covered areas that need to be managed

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Acknowledgements

Agriculture and Agri-Food Canada

Natural Resources Canada and CBIN (Canadian Biomass Innovation Network)

Natural Science and Engineering Research Council of Canada

Questions?