I’m sure we have all been there – standing atop a silage clamp throwing tyres whilst covered in foul smelling “silage tyre juice” - and I’m sure many have had the thought “there must be a better way than this”. Well there are certainly lots of alternatives, but why do we still cover silage with old car tyres and what are the advantages and disadvantages of alternative solutions?

What do tyres do on the clamp?

So let’s start by considering what the tyres are doing, and it’s more than just holding the sheet down. Sure the tyres (or whatever other solution you might consider) need to hold the sheet down onto the clamp to stop it blowing away but to minimise waste, you need to make sure you get good silage to sheet contact. If there is not good surface contact then you get a gas pocket between the silage surface and the sheet and this is leads to spoilage of the silage. Unless you are using a cling film type of gas barrier, you need to get the sheet down onto the surface of the silage and keep it there.

The tyres provide the weight to hold the sheet in place but their shape also protects the sheet from damage. The lack of sharp edges prevents the damage during covering and uncovering whilst the tyres are in place. Tyres also shade the surface of the sheet and produce a boundary air layer. This helps to provide a more stable temperature under the sheet that can help with silage preservation. You also need to make sure the rainwater gets away from the sheet to avoid potential leakage or possible icicle punctures during cold weather.  

What would the ideal silage tyre do?

So there’s more to it than weight – now what exactly would the ideal silage anchor need to do.

1)    Hold the sheet down, as we have seen

2)    Protect the silage from excessive thermal variations.

3)    Not damage the sheet during placement, once in place or when being removed

4)    Be quick to place as you need to get the clamp covered and “airtight” really quickly to minimise in clamp losses at ensiling.

5)    Be robust since they are going to live outside and be exposed to the weather, silage and UV attack

6)    Protect the silage from bird attack and protect themselves from rodent attack

7)    Be cheap

8)    Be modular so that the clamp can be opened or uncovered in small increments, hopefully without using complex machinery.

9)    Should be environmentally sound

10) Ensure good sheet surface drainage

11) Be hygienic

That’s quite a list and used tyres seem to have most of this covered. Used tyres hold the sheet quite well and insulate as we have discussed but they also protect the sheet during handling and are modular so quick to place and remove. They are also cheap (or free) and are a good re-use of a product that’s has its primary use. So tyres are good but there is still room for improvement.

 What’s wrong with old car tyres?

Used car tyres only provide partial pressure on the sheet surface and this can lead to sagging or bagging of the sheet with resultant spoilage. This can also produce low spots that retain rainwater and produce potential leakage through the sheet.

Unused silage tyres also take up quite a bit of storage space and are quite difficult to store efficiently. So it’s usual to find a small mountain range of tyres somewhere out of view. Used tyres also need to be inspected and damaged ones rejected as any projecting steel bands will puncture the sheet and/or your hands, both of which are undesirable. And then there is the juice, the foul smelling dirty water that lurks inside the tyre cavity. Not only is it going to ruin your day and your overalls, it’s also going to ruin your silage. This liquor is a soup of micro life forms and toxins that will cause, at best, local wastage to the silage.  

Alternatives to used car tyres for securing silage sheets

So there are a few downsides to used tyres but what are the alternatives?

The very first silage clamps were protected by a layer of topsoil but that’s really not a viable option on today’s scale of silage clamp. Removing the soil inevitably sacrifices the sheet itself so farmers started putting the soil into sacks to hold down the sheets.

Rough wave netting

The most common alternative to a full set of tyres is a heavy-duty top sheet – a sort of nylon chain mail cover for silage.  The aerodynamic properties of these rough texture covers mean they are much less likely to be moved by the wind. The roughness induces vortices that mean the cover maintains its position in the same way the dimples on a golf ball make it fly straighter – apparently.  These heavy-duty covers also help to protect the gas membrane (sheet) from bird and storm damage. A net alone is not sufficient however and whilst the number of “tyres” required is reduced, you still need weights along the edges of each net and rows around 5m (or 15’) apart to hold the nets in place. So what can you use?

Gravel Bags

The cover suppliers offer all sorts of options but gravel bags are a very common economical option. Filling gravel bags with your own ballast makes this an affordable solution although it does make the first use a very time consuming job. However thereafter these do meet many of the requirements we are looking for such as easy stacking and storage. Gravel bags don’t hold “silage tyre juice” but they can suffer from rodent damage. This can quickly transform a gravel sack into just a gravel pile!

Bales

Straw bales, ideally rectangular rather than round, are possibly one of the best methods of securing the silage sheet in a silage barn. Barley straw bales placed “on the flat” provide really good sheet contact over the entire clamp and keep a constant compressive load. Outside you would need to sheet the straw on top of the clamp and this is all getting a bit high and complicated so it is not really an option for uncovered clamps. You also need to be careful with wheat straw and with the edges of a bale as the sharp ends can puncture the sheet. You also need to use the straw at the same rate as you use the silage or you will need to find somewhere else to store the straw as you want to uncover the silage.

Tiles

Plastic or rubber tiles or mats are good solutions that provide just about all the advantages of tyres without any of the downsides except one. They are really robust, provide good contact, are modular and are really good to store, but they do cost much more than free tyres.

Whilst the use of woven textiles as the sheet restraint can reduce the requirement for weights there are still some issues. They are particularly quick and labour efficient to place and they offer good bird attack prevention – one of the real downsides of tyres. But on the negative side they are difficult to handle once the clamp has been opened for a while as there is a lot of material to roll up and remove. There are also cost implications and it’s unlikely that are going to outlast an old car tyre. If you already have old car tyres, it’s hard not to use them but if you are clamping thousands of tonnes of silage each season the thought of manhandling all those tyres will almost certainly make the cost of a textile much easier to swallow than a mouth full of silage tyre juice.

If you want to discuss the options for covering your silage in more detail or any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremy@silageconsultant.co.uk

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