Autumn 2017 EN

English Issue
Biogas Journal
| Autumn_2017
Table 1: Base data for a cost comparison between maize silage and maize stover silage
Removed
fresh weight
Removed dry
matter yield
Dry matter
percentage
Silage
loss
Organic
dry matter
percentage
Organic dry
matter yield
after silaging
Methane yield
Methane
yield
per ha
Electricity yield
per ha 6)
t fresh weight
per ha
t dry matter
per ha %
% dry
matter %
t organic dry
matter per ha
Nm 3 (t organic dry
matter per ha)
Nm 3 per
ha
kWh el
per ha
Maize silage
(whole plant)
Maize stover
silage
51 1) 17.0 33 6 95 15.2 337 4) 5,116 20,423
9.7 2) 4.9 51 8 3) 93 2) 4.2 295 5) 1,237 4,937
1)
Average yield of silo maize from 2009 though 2014 (Bavarian State Office for Statistics).
2)
Two-year results of the practical harvest technology trial, which are also realistic in practice.
3)
Silage loss based on expert estimates.
4)
Methane yield of silo maize according to the biogas calculator of the LfL (http://www.lfl.bayern.de/iba/energie/049711).
5)
Methane yield of maize stover in reference to organic dry matter: 87.5 percent of silo maize (according to the results of the batch trials).
6)
Assuming a 40 percent rate of utilisation for electricity of the methane used in combined heat and power generation.
the dry matter contents of the plant residues
(= maize stover) were in the range of
silo maize (30 to 35 percent).
In contrast to the visual appearance, the dry
matter contents were not high even for very
ripe residual plant parts. Nevertheless, depending
on weather conditions during the
harvest, the crop can still dry significantly.
For this reason it is advisable to recover
the maize stover immediately following the
grain harvest. With average crude ash contents
of 7.9 percent (2014) and 6.2 percent
(2015), contamination can be classified
as unproblematic. The “natural” crude
ash content of the plant residue is about 4
percent; the increase in crude ash contents
by 2 to 4 percentage points is due to contamination
during the harvest.
If the stover yields that were actually removed
and the crude ash content that was
measured were used to calculate the methane
yield per hectare, the yield would
be about 1,500 Nm 3 CH 4
per hectare,
i.e. about 20 to 25 percent of that of silo
maize.
Suitability of grain maize
stover as silage
To use maize stover all year round, it must
be suitable for silage. Its designation as
“straw” leads to the assumption that this
substrate performs very poorly as silage.
However, standardized silage trials have
shown that maize stover generally performs
very well as silage and that dry matter loss
is low if oxygen exclusion is guaranteed.
Even the aerobic stability was, for the
most part, high after the silo was opened.
This was also confirmed in the trials, even
with higher dry matter contents and poorer
maize stover quality (e.g. remained in the
field for a long period), although in such
cases, loss could have already occurred due
to processes in the field.
One challenge is certainly the ability to
compress the maize stover in the silo. In
an initial silage trial in the silage tunnel,
the densities measured were about half that
of silo maize. This has consequences with
regard to the required space for the silage
and brings with it the risk of spoilage if air
should enter. The extent to which the silage
tunnel results can also be applied to silage
in clamp silos must be clarified in further
trials. In practice, silaging maize stover
seems to work well. Often professionals
work with mixed silage or a “cover layer”
of wetter substrates (e.g. grass or a catch
crop) is applied to the silage.
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