Step 5. Clamping

How to achieve the correct silage clamp density and why effective sealing is so important.

Good consolidation to squeeze out as much air as possible is key. For grass at 30% DM, aim for a target silage density of 250 kg of DM/m3 (750 kg fresh weight/m3).

If you trap too much air in the clamp when you ensile the grass, you reduce fermentation quality and increase aerobic instability problems at feedout.

Often, silage isn’t consolidated enough simply because trailers are arriving at the clamp too quickly and grass is not spread properly.

Independant Silage Expert, David Davies explains the key things to think about when filling and sealing your silage clamp.

You can only really efficiently consolidate the top 15cm. So layers should be even and no greater than this depth, before being compacted and the process repeated with the next layer. For effective consolidation, consider using a compacter that equals the full width of the tractor, so that you’re not just consolidating beneath the tractor wheels.

Pay particular attention to the edges which are more difficult to consolidate.

Also, avoid over-filling the clamp. Once clamps are filled above the walls, density drops.

TOP TIP: To prevent air spoiling the silage, seal the clamp with
high-quality, overlapping sheets, weighed down well especially at the edges.


Once consolidated, sealing the clamp will stop air / oxygen ingress, which is essential for fermentation and aerobic stability.

Use side sheets, and leave a good overlap with the top sheet of 1, preferably 1.5 metres . Once the clamp is filled, the side sheet should be folded in, an oxygen barrier film placed on top and then a top sheet.

Always put as much weight on top of the clamp as possible. That top weight maintains better density in the weakest part of the clamp, which is the top.

Remember also to pay attention to the ramp. If carbon dioxide is allowed to seep out of the bottom of the clamp (because it is heavier than air), it creates a vacuum, which sucks oxygen in. So, as well as sheeting the rest of the clamp correctly, ensure there is at least half a metre of extra silage sheet at the front of the clamp, and weight it down well all around the edge.

Multi-cut hints and tips

A useful benefit from cutting grass while it's younger and contains less stem materials is that it's easier to consolidate in the clamp.

However, that's no excuse for cutting corners. The same rule applies about filling in layers a maximum of 15cm deep.

Machinery-wise, a good piece of equipment for loading the clamp is a push-off buckrake. This helps maintain an even layer as you drive up the clamp, making it easier to consistently achieve the correct 15cm layer depth.

Volac and Germinal have developed a 10-point multi-cut grass silage checklist, designed to help you get the most from your grass silage making process.

We not consolidating clamps enough, we really should focus much more attention on the consolidation.
— Dr David Davies, Independent Silage Consultant

Want to learn more? Take a look at the next step.