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Guide 20
Guide 2017
preservation with minimal DM losses. The result is well-
preserved silage with minimal waste, better feed value and
good intakes. Good preservation keeps the development of
spoilage organisms like clostridia, moulds and yeasts at bay.
The preservation process cannot begin while there is any air
left in the pit. So lack of attention to detail in sealing the pit will
delay the preservation process and increase losses. Silage pits
must be air-tight.
Keeping the air out
The amount of air in the pit before sealing depends a lot on
the grass DM. Below 24 per cent DM, there is very little space
for air as these spaces are filled with e uent. Less rolling of
this type of material is being recommended. For material over
30 per cent DM, air can find its way deep into the pit unless it
is very well rolled and consolidated. Leafy, wet, short chopped
grass will compact a lot better than dry, long chopped, stemmy
grass. Nowadays, pits are filled very fast so there isn't much
time for rolling and consolidating. There isn't enough room in
pits for two machines to safely operate. The loader is heavy
but usually has wide tyres. Compacting the grass poses a
challenge. The best that can be achieved is to spread out loads
as evenly and thinly as possible leaving no lumps and humps
or hollows. The sides of clamps pose a particular problem. We
make them relatively steep which means they can't be rolled on
for consolidation. It is important that the sides are well built with
a uniform slope, without humps or hollows.
This will ensure that the silage covers will lie right up against the
ensiled material leaving no air pockets once weighted down.
Another problem becoming increasingly evident is that pits are
being overfilled. I get the impression that some farmers feel they
can expand numbers and still manage with their existing silage
pits. The height at filling and even at feed out is dangerously
high. Pits are getting narrower and narrower as they rise,
increasing the danger of the loader toppling. The e ect of
consolidation is lessened also. At feed out stripping back the
cover and tyres becomes a lot more dangerous and di cult.
Covering the pit to maintain an air-tight seal is most important.
The surface of the grass before covering should be smooth,
without humps and hollows to eliminate air pockets and ensure
any rainwater falling on the covers will flow o fully. Water
lodged continuously in depressions causes surface damage
underneath and if it leaks through, will leave a column of bad
silage at that point. The covers must be weighted down well
using a combination of tyres, mats, gravel bags and nets. Nets
are great for keeping the covers in close contact with the
ensiled material. Nets should be non­slip to make them safe to
walk on.
Bags should be filled with pea gravel for drainage so they will
last. Tyres should be placed edge to edge and heavy lorry tyres
used along the sides. Gravel bags are very good because they
exert much more pressure for their size than tyres. Therefore
they should be used along in a line to seal clamps at ground
level. This seal should ideally be right in close to the ensiled
material, inside any channel in order to prevent any air getting
back up the pipe in the channel during storage. Overlaps of
the covers should be 1.2m to 1.8m long. Overlaps should be
weighed down with gravel bags as well as tyres to make them
air-tight. All too often, I see polythene on the sides of clamps
flapping in the wind or damaged from dogs, cattle, etc., or
because after the initial covering it was never retightened once
the clamp has settled. This causes massive surface waste and
poor preservation in layers below this surface waste.
Top and side waste seems to be worse on the windy side of
clamps. Wind blowing over silage creates all sorts of pressures
that will force or suck air if there are any deficiencies in the
covering. Regularly inspect and repair silage covers. Catching a
damaged cover early can help minimise spoilage from oxygen
Walled pits are better and safer as silage storage structures
than clamps. They are generally easier to cover e ectively also.
However, I have often seen waste along the top and in by the
walls. Waste at the walls is often triangular shaped, widening
towards the floor, indicating that air and/or water got in where
the covers meet the wall. Gravel bags are needed here also
and any water flowing o the cover towards the wall should
be channelled away in a depression before the wall. The wall
should be lined with polythene as well.
The polythene cover should extend from past the channel in the
floor to out over the wall or up and over a guide rail, if present.
When the pit is being covered this sheet should be folded
back first and overlapped with the top covers. It still needs to
be sealed with the gravel bags and rainwater deflected. Some
complain that it is too di cult to manage this extra sheet lining
the wall. It really boils down to the fact that they don't want to
put in the extra e ort to cover the pit properly. Grass can get
caught up in this sheet, especially if the guide rail is present.
This makes it di cult to fold back smoothly over the surface.
The other benefit of this sheet lining the wall is that it protects
the wall surface, wall floor joint and channel from wear from
e uent with unwilted crops.
Overfilling of walled pits is also common and is not a good
practice. This makes e ective sealing of the edges more
di cult. To prevent surcharging the walls with extra weight over
their design weight, grass piled above the walls should slope in
at 45 degrees. This makes e ective rolling at the walls di cult.
Rolling at the walls should be done before the grass raises
much above the top of the walls.
Silage covers
There is a wide range of silage covers available. These can be
used with tyres, mats, nets and gravel bags. There is evidence
that some of the newer covers may have some advantages
over the normal practice of using two black polythene sheets.
There are covers with cling film properties (clear or slightly
coloured) which cling better to the ensiled material preventing
air pockets forming, so reducing the amount of air taken in
throughout the storage period. Other products are described