“Give it a good rolling son, squash it down well.”

Those words used to ring in my ears every time I took to the buckrake tractor. That was a long time ago now and the importance of rolling or compacting clamp silage has been well known for very many years. But what are you trying to achieve when rolling the silage?

There are several aims in compacting silage but most importantly you are trying to expel – or squash out – all of the air from the material. In addition, good consolidation squeezes a few more trailer loads into the clamp and increase the chances of a good fermentation. Maximising the tonnes in the clamp is obvious, but how does this increase the chances of a good fermentation?

 The fermentation process relies on micro life forms; predominantly bacteria and these are (unsurprisingly) very small. An inch gap between one colony of bacteria and another might as well be half a continent so making sure there is close contact is good practice. This basic geography is also one of the reasons why length of chop is so important (see elsewhere in this series for more information on this).

 Good consolidation also makes the heap more stable by binding layers together. It also makes traveling up and down the clamp easier, safer and quicker. So we all know consolidation important, now you just need to drive around on the clamp for a bit don’t you?

 Not quite. For grass, whole crop and all but a very few maize crops, layers need to be kept to about 150mm (6 inches) to ensure good consolidation. If you have layers half a metre thick, it doesn’t matter how heavy the rolling tractor is, you wont get good consolidation. The shovel or buckrake driver needs to evenly spread 150mm thick layers of material onto the rolled surface. This gets difficult when trailers are queuing up to tip but a silage spreader on the compacting tractor can be a very effective solution.

 Is heavy better when it comes to rolling silage?

Not always, in general the amount of consolidation will depend on the pressure generated under the tyres of the tractor. If the tyre pressures are too low, a heavy tractor or shovel will squish the tyres down, increasing the contact area and reduce the pressures underneath the tyre. Therefore you should aim to run the tyres at “road” pressures to maximise the effect of driving over the clamp.

 It’s vital to check the weight of the filling and compacting vehicles against the design of the clamp walls. The British Standard that governs the design of walls allows the designer to choose (historically 6T) 8T or 10T tractor loadings. Remember, this is the gross vehicle weight, including fuel, driver, ballast, dual wheels and the fork full of silage. It is easy to see how you can quickly overload the clamp.

 If vehicles are over the design weight limit, they can still work on the clamp as long as they keep away from the walls. How far? Well at least the height of the wall, so if the clamp is 3m high, then a heavy tractor can’t go closer than 3m from the wall. Make sure you have a tractor under the wall design load limit to roll close to the walls.

 So more rolling is better? No not always, it is possible to over roll a clamp. You will be familiar with the green sludge that accumulates on the apron on the clamp that’s constantly driven over by the tractor and trailers. This quickly loses most of the sugars as the cell walls get crushed and broken, allowing all the nutrients to escape as effluent. You also need to remember that whilst you are trying to remove oxygen rich air, you are also trying to build up carbon dioxide levels in the clamp to inhibit aerobic micro-organisms. Over rolling can squeeze out the CO2 and suck back in oxygen, so stop when enough is enough.

 What about train wheels?

Well they are heavy, they create high pressure underneath as they don’t have pneumatic tyres and they can cover a much larger area than the tyres of the tractor. The compaction pressures under a steel roller can be 40% higher under a tractor tyre. This means compactors can be a quick means to good consolidation on the clamp, just remember the design weight limit as “train wheels” will add 2.5t-6.0t to the tractor weight. As forager output increases, ensuring good clamp consolidation using just the tyres of a tractor or shovel is getting more difficult. So don’t overlook this part of the process, it’s vital to ensure a good fermentation and minimise in clamp losses.

 If you need further information or help on how consolidate your silage, or for any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com