Stacking silage above the walls - a good idea?

When you think silage clamp, do you imagine a huge three sided box, because I’m guessing most people do. For me a silage clamp or silage pit has walls on two or three sides, but for some walls are an unnecessary expense, or an unaffordable luxury. And while it’s true walls are expensive there is a benefit from having something to hold the silage tight and there are hidden costs from deciding to make silage on a simple flat pad. The biggest of those costs is hidden because its made up from increased losses caused by not having walls - and don’t think you have automatically dodged those losses by building walls - because it’s all to do with how you fill your clamp.

How much silage do you lose?

If you have read pretty much any of the other pieces in this series, you will know that losses are a major focus - and that’s because the losses can be horrendous. If you were to store your wheat in good conditions for four or five months, you might expect to load out 98-99% of the grain you stored. Those missing 1-2% will not have been stolen by the rodents (hopefully) but each and every grain will have respired gently during its hibernation and will have burned a tiny amount of energy in doing so. This respiration adds up to those limited losses that you can expect. Do the same with silage, store it in perfect conditions, and you might expect to lose 5.0%-7.5% of the nutritional value. While that’s not as great as grain it’s only half the story because unfortunately there are only a handful of farmers that limit losses to these sorts of levels.

Obviously the losses vary widely across the profile of each silage clamp because the best place to protect the silage is right there in the centre of the heap. The closer you get to the edges, the more likely it is that the losses are more than optimal, and most of us will expect to see the biggest losses on the “shoulders” of the clamps.

Wastage you can see and and losses you can’t

Seeing wastage on the shoulders of a silage clamp is only part of the story though. When you see spoiled or wasted silage, the material you’re looking at has probably lost most or all of its feed value. I say probably because it depends what you are doing with it; it’s highly likely no livestock will actually eat it but you could still “feed” it to an anaerobic digester. But even if you do get it into the tank, this stuff has little or no nutritional value left in it as the energy and proteins have all gone.

So what about the invisible losses, because, as I have said many times, it’s the invisible losses that are the biggest enemy to everyone making and storing silage. Well if you imagine there is pure great silage in the middle of the clamp and inedible sludge on the shoulder, then there must be a range of quality and losses between the two extremes. And it’s this transitional zone that I want to explore here because the walls, or lack of them, play a big role in minimising the size of the zone.

The slope is the big problem here because its much much more difficult to compact silage on a slope than it is on a level surface. I’m sure we have all seen lots of techniques being used to try and get a good tight silage surface on the side slopes of a silage clamp. But unfortunately however much patting down that the loader does with the fork or however may passes the compactor wings do, these areas are never compacted as well as the nice flat areas of the clamp. And it’s this lack of compaction that is the biggest factor leading to the increased losses.

What do silage losses cost?

To get an idea of how much this is costing you need to put some figures to this. There are a number of different ways of counting the costs of lost silage nutrients but perhaps the easiest concept is to think of how many mega joules of energy have been lost. Once you have that figure you can convert it into potentially lost milk, meat or gas yield. You can also calculate what you would have to buy in as supplementary feed to replace the lost energy.

This is the technique I use to “value” losses during a site investigation but before we can put a cost to the loss, you have to decide how much energy has actually been lost. I have a formula for this evaluation that takes into consideration the angle of the slope, the type and weight of the compaction together with the chop length and dry matter of the forage amongst other things.

Working out if walls are worth the cost

Using this system I recently did some payback calculations for a farmer who was storing a huge quantity of silage. The numbers I came up with were quite large even after I applied my “correction value” so I wasn’t too surprised when the manager expressed his surprise at my calculations (that’s putting it mildly). A couple of days later we discussed my findings and the  manager said that because he didn’t believe my figures, he had gone out and done his own study of the areas in question including some sample analysis. And he was astonished to find that we were both wrong, because the actual losses were about twice what I had concluded. I didn’t have the heart to tell him the my “correction value” had halved my initial numbers because even I thought they were unbelievable.

Now this is all very well and good, but surely this only applies if you don’t have any walls? Well I don’t think so because if you stack the silage up above the walls then it’s just like having a “wall-less” clamp on top of a walled clamp. I would argue that you should calculate the silage losses on the whole clamp in two sections to accurately represent the whole clamp. The area below the top of the walls as one section and then adding the “heap” stacked above the walls.

Is stacking silage above the walls a bad idea?

Under some circumstances the practice of heaping silage up can make good sense. I need to be really clear with this, because the walls must to be designed and built for these loads. You also need to make sure the stack of forage is stable and safe too, but in the right situations, stacking silage above the walls can make sense. The really critical aspect is the angle of the silage slope; stack it as steep as it will go and sure, you will get a lot in the clamp, but you will also lose loads of feed value. By being a little less ambitious and making a much more shallow slope angle and then the chances are that you will get far far lower losses.

What I would really stress though, is please don’t underestimate the cost of losses on a slope. If you are really honest with the calculations then you will have the correct information to make a proper costed and calculated decision about the benefit (or otherwise) of clamp walls. You can then decide exactly how much space you need store your silage. Having some accurate numbers at hand and making quantified decisions is always a much better strategy than relying on gut feel and hope.

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