Proceedings World Bioenergy 2010

Figure 1: Amount of biomass and botanical composition
in August 2009 in small plots 50 x 50 cm.
3 RESULTS AND DISCUSSION
There were significant differences in legume biomass
between the species mixtures (Figure 1). Alsike clover
was the most productive sown legume, followed by red
clover. Goats rue was a slow starter and it formed a low
but healthy undergrowth.
The nitrogen fixation as determined by the difference
method varied very much between plots and differences
between legumes were not significant. However there
was significantly less N-fixation, 28 kg N/ha, with full Nfertilization
compared to half N-fertilization, 39 kg N/ha.
The low nitrogen fixation rate was probably due to strong
competition from the very dense reed canary grass crop.
It was not possible to use the 15 N natural abundance
method to determine the N-fixation since the difference
in 15 N natural abundance in reed canary grass and
legumes was too small.
The amount of reed canary grass was higher with the
higher N-fertilization level (Figure 1). However the
difference was not significant. There were no significant
differences between the treatment with sewage sludge
and the corresponding treatment without sludge.
Establishment of reed canary grass undersown in
barley did not work well. The harvest was less than half
of the other species mixtures. Also there were more
weeds in the barley treatment. The reason is probably that
the barley was harvested with a stubble height of only 7
cm in early September 2008 and the reed canary grass
probably was not able to grow enough rhizomes before
winter to get a good spring growth 2009.
Both in October 2009 and in May 2010, the harvest
of the larger plots showed the same pattern as the smaller
plots, but due to the smaller variation there was
significantly more biomass with full N-fertilization. The
biomass harvest in spring was 64 % of the biomass
harvest in autumn, and there were no significant
differences in winter losses between treatments.
Three similar experiments have also been established
96 world bioenergy 2010
in other parts of Sweden. In two of these, there have been
large problems with weeds: white clover in one site and
couch grass in the other site. More information is given in
a recent report [4].
4 ECONOMICS AND CONCLUSIONS
An economic calculation showed that the
establishment costs (the first two growing seasons) can
be lowered by intercropping with red clover (Table 1).
However it is also involves more risks, related to weeds,
and cannot be recommended on fallow soil with a large
seed bank of weeds. Weed management with glyphosate
(Roundup) the year before sowing and Basagran SG
when the legumes have three full leaves, is recommended
in order to decrease the total competition of weeds.
Table 1: Establishment costs for reed canary grass. To
calculate the cost per MWh the establishment cost were
spread over 10 harvesting years with 5000 kg biomass
harvest/ ha and year and 4,2 MWh/ton field dry material.
RCG + red clover RCG
Half fertilization Full fertilization
SEK/ha SEK/ha
Seeds 1105 825
Fertilizer 2000 4000
Herbicides 500 250
Other 300 300
Plowing 1000 1000
Harrowing 675 675
Seeding
Spreading
200 200
of fertilizer
Application
825 825
of herbicide 300 300
Sum 6905 8375
Cost/MWh 32.9 39.9