Biofuel potential of Rushes
Scope
• Potential of rush as a biofuel
• Determine calorific value
• Compare with available alternatives
Juncus effusus
• Juncus family - Approx. 300 spp worldwide • J effusus habitats are diverse
– moist areas at forest margins,– wet grasslands,– wetland margins– lake shores– river banks– wet meadows – Some bog
Soft Rush
• Moderate amount of research on Juncus spp in Ireland
• Slightly surprising given label as agricultural weed
• Might suggest that issues concerning soft rushes are minimal or have been solved
In Ireland
• Broad distribution in Ireland
• In many areas, with poorer soils, some fields almost completely covered
• Some work to reclaim peat soils for agricultural use in Mayo in 2001 – but soft rush invaded and became dominant
Biology
• Hab prefs previously covered
• Rhizome permits vegetative growth producing new shoots and also reproduces by flowering
www.irishwildflowers.ie
Biology
• Rhizome grows at about 2cm per year
• Can send adventitious roots up to 50cm below surface, commonly 20cm
• Growth of roots and shoots accelerates from March onwards – flowers June/July/August
Growth
Growth reaches a maximum in the summer and is generally positivelycorrelated with seasonal climatic factors, and negatively correlated with standing - dead biomass parameters
Growth
• Produces very high numbers of seeds - estimated at 4 milion per square metre
• But seeds represent tiny fraction of biomass produced annually (0.27%)
• Soil seedbank remains viable and provides for events such as flooding
‘Control’• Undesirable aspects of soft rush growth not a recent
problem.
• Classified as a weed as it is unpalatable to stock and low feed value It is well known as an agricultural
• Soft rush is quite resilient, not normally eaten by stock, but they will at high densities
• Soft rush resistant to grazing pressure, trampling and annual cutting
Control
• Hydrologic conditions that favour the development of rush stands will not change with control methods such as:– Cutting– Herbicides– Grazing
• Common to drain and cut or cut and spray
Effects of cutting• Research in 1939 - two cuts in two consecutive years produced an
80% reduction in shoot numbers
• This work also stated that it was important to have first cut in July – before and after was less effective at control
• Work in 1936 suggested that rushes seemed to be most susceptible to weakening if cut shortly after mid - summer.
• Others noted that some rush species do not flourish at sites where hay is cut annually fields cut for hay year after year.
• Trials in 1964 found that mowing repeatedly 4–6 times per year was required to control the rushes but would not eliminate them.
Effects of cutting
• 1995 work suggested that cutting to half their height had no effect
• Cutting to ground level twice a year over two years effective at controlling them
• Most control methods in use in Ireland involve herbicides in combination with cutting or drainage – depending on land use
Energy Content
• Determined moisture content– 5 size classes of rush
20 – 30 cm 30 – 40 cm 40 – 50 cm 50 – 60 cm >60cm
Moisture content
Length class Number of rushes Mean length Wet mass(g) Dry Mass % Moisture
20-30cm 12 25.46 4.35 3.01 30.72
30-40cm 16 33.93 10.73 7.48 30.32
40-50cm 34 45.1 28.89 20.23 29.99
50-60cm 23 53.26 26.79 18.83 29.72
60-70cm 15 64.1 21.67 14.79 31.75
Rushes had approx 30% moisture content when harvested
Moisture content
• Also looked at some commercial products
MACE wood briquettes approx 25% NCF wood logs approx 15% Turf 16 - 35%Peat briquettes 10%Kiln dried wood 9% Miscanthus 9 - 20%Strogs 12%
Energy content
• Used bomb calorimeter
• Calibrated with standard material
• Determines energy content by ability to heat known mass of distilled water when substance is combusted in presence of oxygen
Energy ContentFuel MJ/Kg
Coal 27.1 - 33
Straw Briquettes 16
Miscanthus 18
Turf 14-18
briquettes 17
>60cm rush 17
50-60cm rush 18.7
NCF wood logs 19
Mace wood briquettes 19
Summary to date
• High moisture content but relatively easy to dry
• Obviously don’t have to get moisture to zero• Very low ash content on combustion• Very low density when dry• Energy content comparable to currently
available products• Perhaps consider them as an addition
Main source
• Forest Ecosystem Research Group Report Number 69