An evaluation of methods used to cover bunker silos with oxygen barrier plastic to maintain the nutritive value of silage

Three experiments were performed in order to test the effect of different plastic coverings, and covering systems for use in sealing bunker silos. The objective of the first experiment was to evaluate the use of three plastic coverings using laboratory silos. Silos were filled with 14 kg of whole-plant corn forage (37% DM) to a packing density of approximately 223 kg of DM/m3, and were covered with a) 6 mil black/white polyethylene (P0), b) a 1.10 mil thick oxygen barrier plastic (P1), or c) a 1.77 mil thick oxygen barrier plastic (P2). Buckets were sealed and stored at between 20 and 32°C. Buckets were opened at 181 d after ensiling. Laboratory silos covered with P0 tended to have more silage spoiled at the surface compared to P1 and P2. Total DM recovery from the silos tended to be lower in P0 than P1. In addition, P2 tended to have a lower concentration of acetic acid than P0. All other fermentation and chemical contents were similar among treatments. In a second experiment, two different plastic covering systems were assessed as coverings for farm-scale bunker silos. Three silos were filled with about 550 t of whole-plant corn forage. One half of each silo was sealed with one of two covering systems. The traditional system was comprised of covering the silo surface with a 6 mil polyethylene plastic that was weighted down with split tires. A modified system was comprised of a single layer of 1.77 mil oxygen barrier plastic used as sidewall plastic and as a covering on top of the silo. A protective tarpaulin was also placed over the surface plastic, and was weighted down with gravel bags along the length of the sidewall and at the seams. Corn silage was sampled at 5 months post-ensiling. In silos covered with the traditional system, water from rain and melting snow was able to infiltrate into the silage mass closest to wall resulting in poor quality silage. Silage sampled further from the wall was generally of better quality than silage nearer the wall. Silage quality was maintained and not affected by water in silos covered with the modified system. Silage sampled furthest from the wall (not affected by water) had some indices of nutritive value and fermentation end products that were better than silage stored under the traditional plastic. In a third experiment, the same three bunker silos were used to evaluate the use of a thicker 5 mil oxygen barrier plastic (weighted down with gravel bags but not requiring the use of a protective tarp) to normal 6 mil plastic (weighted down with split tires). Side wall plastic was used in both treatments. After 6 months of ensiling, samples were taken at the midpoint of each treatment. In general there was no major advantage in using oxygen barrier plastic in this experiment perhaps because the use of gravel bags as a weighting method was not effective in keeping the plastic flush against the silo surface. This allowed for air to penetrate the plastic through points where animals had caused some damage, resulting in the plastic to balloon in certain sections of the silo. The thicker oxygen barrier plastic did not appear to cling as tightly to the surface of the silage as the thinner oxygen barrier plastic did in the first field experiment, making it necessary to implement a better weighting method for this type of plastic in future experiments.