Is it worth sheeting silage?

There are few jobs that are universally hated. A good friend of mine is adamant that he actually enjoys decorating, and I have met people who claim to love washing up, but I can’t recall ever meeting someone who loves sheeting a silage clamp. And on the basis of what goes up must come down, who in the world loves unsheeting silage? If you are that person please stand up and tell the world ‘cos no one I know has ever met you.

So if we all hate it so much, why do we still labour away to sheet silage only to uncover it again as the feed face demands? Previously I have looked at automation of the whole process but isn’t it just worth exploring the true cost of sheeting? What does it really cost you to sheet the silage clamp, and what are the downsides of not covering the silage at all?

Why do we bother sheeting silage?

If you are a regular reader of these articles I don’t think you need the read this next bit because you are already keen to maximise your silage quality. For everyone else then this next bit is just a brief summary of why you might want to sheet silage.

Silage is a method of preserving forage via fermentation. The fermentation process needs to be anaerobic or the silage will spoil so the sheet is there to “seal” the forage from oxygen rich air. It’s also there to keep the rain off but if that was its only purpose, then a roof would do the job just as well. The gas sealing function is the reason why it’s just as common to sheet a silage clamp in a barn as it is to cover an outdoor clamp.

By compacting the silage well you should be driving as much air out of the fresh forage as possible. If the chop length is correct and the clamp well filled, then the silage will be dense and tightly packed and this makes it much, much less permeable to gases. And this is where the “no sheet” movement has come from. Because if you get it really tightly packed, does it matter if the top few millimetres gets spoilt because this will only just help to seal and protect the rest of the silage won’t it??

Can you seal silage with a wet layer?

A wetter layer of forage is definitely more dense and will certainly knit together more easily to form a less permeable layer, but is this enough? Well these ideas started a team of people thinking about sheeting silage so they decided to do some trial experiments and actually measure the losses from the silage at different depths with the clamp. Finally we would have some decent data to make a value judgement from rather than hearsay and prejudice.

Now before we get into the numbers, there is a small but important thing to note. In all cases there were increased losses from the top layers and this “wasted” silage was particularly unpalatable to livestock. In diets with as little as 10% of this “exposed” silage mixed in, the intakes from cattle were significantly reduced. The fussy eaters were leaving perfectly good silage maybe because it was just tainted with the spoilt stuff off the top of the clamp.

Is uncovered silage OK for AD plants?

Luckily the bacteria inside an AD plant are not so fussy because there are no taste buds inside the intake system. So if you know that the spoilt silage is going to get used, maybe it’s worth accepting a degree of losses to save the costs of sheeting silage. That was my thought on setting out to research this project, so lets get into the numbers.

The losses were, unsurprisingly, greatest on the surface and declined as you progress through the silage profile. The bald figures make for some scary reading, but you need to remember that there are still losses under a plastic sheet so it’s the additional losses that you need to consider. Once we filter that out, it looks like around 70-75% of the dry matter silage is lost in the top 250mm. This declines to around 30-35% at 500mm and around 5% at 750mm. From there on the losses “normalise” so at a depth of around 1m from the surface of the silage there is no significant difference. It’s also important to remember that these losses were recorded in dry conditions so there are no influences from rainfall effects,

Deeper is better if your not going to cover it.

So if you are storing a large quantity of silage, say 10,000 tonnes, and heaping it up to 5m or more, then maybe these losses aren’t a problem because they are only in the top layer. Or are they, because silage isn’t cheap; the solution to this question is in the maths.

Assuming 10,000t at around 750kg per cubic metre density, you would need to store just over 13,300 cubic metres. At 5m high this would give you a surface area of around 2,665 square metres. Working these losses through that area and depth and assuming a cost per tonne of £45 per tonne, you will get a total loss of just over £19,800. That’s quite a big number but it is only 4.4% of the actual silage total cost, so maybe that sheet is not worth bothering with?

Is it worth sheeting silage to save 4.5% of losses?

Irrespective of how much you might hate hauling sheets around on silage, you should really know how much it might be worth. So let’s assume you push the boat out and use an oxygen barrier and a multi layer sheet. That little lot will cost you around £4,000 per year to cover this 10,000t clamp. Now add some protection nets and gravel bags to hold it all down and because you’re too busy in the office, you buy ready filled bags and replace them and the net every 4 years. That’s will add another £1,275 to the bill.

Materials are one thing, but it is the labour cost that usually kills the benefits of this sort of work. So let’s assume your contractor is “too busy” to help sheet the clamp. I have assumed you might need 6 unlucky guys for 2 hours plus one telehandler / loader to cover the clamp. And to uncover the silage I have worked on a couple of hours for a two person team for every ?? per week including a loader again. At £20 per hour and £57 an hour for the man and loader, this comes to a total yearly labour and machinery cost of £6,700. Total it all up and it’s around £11,975.

It might be a lot of work and money, but sheeting the silage is actually saving you over £7,800 per year! Now you might argue that my assumed cost of silage is too high, or that you should just store it deeper to minimise the losses. But for comparison, if your silage is only £35 per tonnes you still save almost £3,500 a year. And if you store the silage deeper the amount it costs you remains the same, it is just a lower percentage of the total sum.

So however I look at it, I can’t really find an argument that makes it financially sensible to leave the silage uncovered. You might read these figures and still decide that you are prepared to accept the costs because of operational or environmental reasons, and that’s fine as long as you understand the real cost to the bottom line. Otherwise, order the sheets, get everyone else in the yard and make sure you have some urgent business elsewhere when the contractors is tipping the last load, because sheeting silage really does pay.

If you want to discuss covering your silage or would like to discuss any other aspects covered in this series, contact me at jeremy@silageconsultant.co.uk

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