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 positively
correlated 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
NCF wood logs approx
Turf
Peat briquettes
Kiln dried wood
Miscanthus
Strogs
25%
15%
16 - 35%
10%
9%
9 - 20%
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 Content
Fuel
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