What do you need to know about silage clamp compaction?

What do you need to know about silage clamp compaction?
The maize silage harvest is upon us in Europe and you may well be getting your clamps ready for a very important few weeks as you make the silage you will be relying on over winter to feed your cattle or biogas plant.

The way you fill and compact the clamp is integral to producing good maize silage, we have brought together some great advice from a range of sources below to identify some areas you might be able to improve your operation.

Why does compaction matter?

The key to good silage is the compaction in the clamp as this reduces the air (containing oxygen) between the silage particles. Removing air creates the anaerobic conditions which is crucial for good fermentation and creating the best possible preservation of your crops.

What does good compaction look like?

When maize silage is delivered to a clamp its density ‘loose’ is surprisingly hard to calculate as this will depend a lot on the Dry Matter (DM) and chop length of the crop. The closest measure we can find is that ‘loose silage’ delivered to the clamp prior to compaction will be roughly half the density of the final compacted crop (.4t/m3 loose compared to .8t/m3 compacted).

This puts into perspective the effort required to produce good silage, you are reducing a full trailer into half its size in the clamp.

How is compaction achieved?

There are several areas that must be considered to achieve the best compaction possible.

Machinery weight

Machinery weight is a simple measure to understand the compaction required on a clamp, its also the easiest to understand and a great starting point.

A rule of thumb is that for the best compaction you should have between a third - quarter of the weight of the silage entering the clamp in 1 hour in compacting machinery on the clamp. 100t an hour entering the clamp would need between 25 to 30t of compacting weight in machinery on the clamp or two to three tractors.


Machinery weight alone is not enough to achieve high levels of compaction, ensuring the clamp is filled in even layers to ensure the compaction is uniform throughout the clamp.

The size of these layers varies in research articles, but the general rule is between 10cm (4 inches) and 15 cm (6 inches), research suggests that doubling in layer thickness can more than halve the final silage density. Other machinery such as buck rakes and silage forks can be useful to achieve this effect to help to spread silage evenly.

Contact area

Weight on the clamps and spreading silage are both very important factors to achieve the best compaction, but how that weight is transferred to the silage is also important – usually a tractor is designed to minimise the ground pressure below the wheel to minimise soil damage but you are looking to achieve the opposite when working on a silage clamp.

This is the reason you may look at removing dual wheels and adding extra weight to farm machinery (this can be achieved through water filled tyres or steel weights added to tractors).

Another option would be to use train wheel type compactors which not only add weight to machinery but also apply that weight in a very uniform and direct way to the silage surface.


The only variable left once you have considered the above and you have defined the tractor type, weight and the intended silage layers is the time you spend on the clamp with your machinery.

Ideally the clamps would only be filled at the speed you can compact the silage effectively which may mean reducing the speed of the harvesting operation so you can meet a recommended one minute per tonne, per compaction vehicle (this could mean one tractor can only compact 60t of silage into the clamp per hour).

This ratio is very hard to keep, as the speed of the harvest crew often dictates the speed material arrives at the clamp – and you may not be able to control this, it will also vary with the size of the clamp but is interesting to consider as a base level.

As well as the amount of time on the clamp you may want to consider the speed of machinery on the clamp, 2-3 mph is the maximum and travelling any faster could reduce the effect of the machinery’s compaction on the clamp.