The technique is akin to putting grass in a zippered sandwich bag and then removing the air. About 160 tons of freshly cut alfalfa, fescue, clovers, puna chicory, ryegrass or other forage is laid in windrows on the bottom sheet of plastic, which is rolled like a scroll on two pieces of pvc pipe. As the sheet fills, the scroll unrolls, exposing fresh areas on the sheet. The cutter dumps loads until there is just enough plastic sheet remaining around the edges to be wrapped around the pvc pipes and sealed with c-clips, also cut from pvc pipe. Finally, a vacuum pump is connected to a perforated length of pipe that was placed among the windrows before the bag was sealed.
Air is removed until the bag is flattened against the silage.
The air must be removed daily until the silage is opened, a task that requires only minutes per day. The emergency tactic worked so well, that Wright made it part of his MIG program. It seems that no matter how well you manage grazing, in spring ryegrass, alfalfa and other grasses are growing so fast the cows can't eat it all. Later, when you are between seasons or the weather heats up, there are bare spots all over. Vacuum silage provides my cows with high quality forage to bridge that gap until a fresh paddock is ready.