Silage Advisory Centre

Forming densely packed, well chopped bales is important for producing quality silage. Densely-packed forage will mean less air within the bale, and chopping forage during baling results in a rapid release of sugars. These two factors will result in the rapid growth of desirable bacteria that are essential for good silage preservation.

But just as important, as well as being densely-packed, bales must be well formed. For bale-wrap to work to its best potential, bales should remain ‘round’ and square edged, otherwise leakage can occur, leading to air penetrating the bale and resulting in spoilage.

At IBERS, Aberystwyth University (previously IGER) our extensive studies over the years have evaluated what effects bale shape and different bale-wrap treatments have on the quality of the seal on silage bales. During winter, we evaluate individual experimental bales by pumping the air out to create a vacuum, then measuring the time taken for that vacuum to be lost as air re-enters the bale through the bale-wrap.  A long time period before the vacuum is lost indicates a good seal and good quality silage.

Our research has shown that with low dry matter silage, the shrinkage of the forage within the bale can cause corrugations to form in the bale-wrap. In a study funded by bpi.agri and Dow Europe where 1^stcut grass was ensiled after either a one or two day wilt, the silage wilted for one day had a dry matter (DM) of 28% and the bale-wrap offered a seal of 47 seconds before the vacuum was lost, whereas the silage wilted for 2 days had a DM of 38% and a seal of 92 seconds. Therefore, the corrugations formed on the lower DM bales allowed easier passage of air in and out of the bale, leading to moulding and lower quality silage.

So could we not use thicker, stonger bale wrap than standard 25 micron (µm) bale-wrap? As well as being more expensive, our studies have shown that using thicker film is not beneficial. A thicker film may be less plyable, which does not move with the silage as it sinks, leading to air movement into the bale.

The switch from using baler twine to net-wrap on bales led to an improvement in bale shape. Twine formed air channels around the bale, which could result in deterioration in silage quality. But using net-wrap does not always overcome the problem of uneven bale edges. These uneven edges, caused when the net-wrap does not reach the edge of the bale, can result in the formation of ‘shoulders’ along the edge of the bale. Shoulders can create air pockets under the balewrap, as well as cause undesirable over-stretching and under-stretching of balewrap. Quite often, when wrapping stemmy material, loose leafs of forage from these uneven edges can end up wrapped between bale-wrap layers, creating air pathways that could result in mouldy silage. Using a full width net-wrap that is as wide as the bale, or a net-wrap that comes over the bale edge can improve bale shape.

Always ensure that you ensile well made, densely-packed bales that remain ‘round’ and square edged. These factors as well as using 6 layers of film will give you the best performance from your bale-wrap.