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Oct 20, 2021

Don’t confuse vapour barrier film with oxygen barrier film when sealing silage

Oct 20, 2021

Much thought, planning, labour and effort goes into planting, harvesting and storing silage to optimise its nutritional quality and dry matter content. These decisions can have a major impact on livestock health and performance – and ultimately, the profitability of your enterprise.

In this context, the importance of silage film selection cannot be overstated. Farmers are faced with a wide range of options when it comes to plastic film to preserve silage, including conventional black-on-white polyethylene film, oxygen barrier film, cling film and underlays.

There is confusion between ‘vapor barrier’, cling film, underlay and ‘oxygen barrier’ film. While they appear physically similar, there are a number of important differences in their design, composition and manufacturing technique that can have a major impact on the outcome.

Vapor barrier films and others are made of polyethylene and are widely used in the construction industry to prevent the migration of water between the external and internal walls of buildings. Used in agriculture, they serve an important role in preventing rain or humidity from entering the silage stack or pile.

However, they are not designed to retard the migration of air. Viewed under a microscope, polyethylene contains microscopic holes that allow oxygen to infiltrate silage, often causing significant spoilage in the top 60 to 90 cm of the stack or pile.

Polyethylene film is sometimes used as an underlay to eliminate air pockets between the forage and the top cover film. Whilst this serves a useful purpose, again, it will not prevent the infiltration of oxygen into the stack or pit.

Limiting oxygen infiltration is the single most important factor in maintaining forage quality and reducing wastage, particularly in long-term storage. Oxygen is one of the main reasons why crops are harvested at specific crop moistures and why pits and stacks must be filled quickly, packed well and sealed immediately.

Optimal fermentation and storage of silage must occur under anerobic conditions and this is best achieved using oxygen barrier film. Oxygen barrier film comprise several layers of film, typically an ethylene vinyl alcohol (EVOH) core surrounded by additional layers of polyethylene. In between these sheets are additional layers of polymers that ‘glue’ the sheets together. This creates a multi-layer oxygen barrier film.

All true oxygen barriers used in agriculture have a minimum of five, or more commonly, seven to nine layers, for optimal resistance to the passage of oxygen and long-life flexibility. Properly placed, sealed and protected, they will help to produce to a top-layer forage quality that is nearly identical in quality to the interior of the silage mass.

Whilst the primary role of oxygen barrier films is to prevent oxygen from entering the silage pile or bunker, they also prevent the outward flow of gases produced during fermentation within the forage mass and serve as a vapour barrier.

The Oxygen Transmission Rate (OTR) is an industry standard test that should be available with any quality film. An OTR of less than 15 means the film is effective in blocking the infiltration of oxygen. By comparison, polyethylene films can have an OTR of 900.

Lallemand Animal Nutrition is a leading supplier of strain-specific forage inoculants and sealing systems specially selected for use in Australian conditions, They include strain-specific MAGNIVA forage inoculants, Silostop oxygen barrier film, SilageKeeper UV covers and SealKeeper gravel sealing bags.