# Feasibility of Utilizing Biodegradable Plastic Film to Cover Corn Silage under Farm Conditions
## 4 Discussion
After 85 days of conservation, the MB film began to biodegrade, and this led to a depletion of the fermentative products, an increase in the yeast and mold counts and a decrease in aerobic stability. These results indicate that the use of MB is not useful to avoid the aerobic deterioration of corn silage after about 3 months. [PERSON] et al. [21] and [PERSON] [22] reported, in plastic bag experiments, that a biodegradable film could be a promising alternative to a PE film for indoor conservation periods as long as 4 months. However, the considered biodegradable plastic films were less effective when utilized to cover silage under outdoor conditions [23], which are comparable with the conditions of the present experiment. Plastic films play a fundamental role in the upper part of horizontal silos, which are difficult to seal properly [40] and are prone to spoilage [8]. The mechanical and physical properties (i.e., film integrity and oxygen impermeability) of a plastic film and their maintenance over the conservation period are key factors in the preservation of forage quality in the upper part of horizontal silos [4]. A characteristic that separated the MB films from the PE and OB films is their water vapor transmission rate (WVTR), which was 10-fold greater in the MB films than in the PE and OB ones. A greater WVTR has been reported to cause wilting in the upper part of silages covered with MB films [22]. The drawback of this characteristic is that as moisture is lost, the porosity of silage increases, and this could allow a more rapid movement of oxygen, thereby increasing the aerobic deterioration of silages. However, the three films that were tested in this experiment had very different oxygen permeability degrees, with OB showing the lowest value, that is, 1000-fold lower than in PE, and halfway between the two MB film. Before the biodegradation of MB, its low oxygen permeability determined a reduction in the yeast count in the upper part of silages, resulting in yeast count that was close to that of the central part (MB-FF). Interestingly, these values were close to those found in OB films, thus indicating a similar effect of the two plastic films in the first three month of conservation. The reduction in the yeast count led to higher aerobic stabilities of OB and MB than PE at 85 days of conservation. Several experiments [9; 11; 36] reported that corn silage in the upper layer under an OB film had a lower yeast count and greater aerobic stability than silage stored under a conventional PE film. The increased aerobic stability and lower yeast count in the upper layer of the silage, stored under an OB film, have been attributed to reduced oxygen permeation through the silo seal during conservation. Further research is needed to find a biodegradable plastic film to cover silage that will be stable for periods of up to 8 months under outdoor conditions [9; 16] to combine the needs of farmers to have stable silages for long conservation periods and to reduce plastic consumption and waste production. The length of conservation represents a critical point for the quality and stability of silage. A long conservation period in complete anaerbiosis determines a decrease in the yeast and mold counts and improves the aerobic stability of silages [41]. Aerobic stability has been found to be positively correlated with the length of conservation in laboratory-scale experiments [42]. However, it could be difficult to ensure complete anaerbiosis during a long conservation period under farm conditions. Plastic films can be punctured by a wide variety of sources (e.g. birds or rats) and this allows oxygen to penetrate. External heat sources (e.g., solar radiation) can increase the temperature of stored silage, thereby creating areas with conditions predisposed to silage deterioration [43]. Furthermore, the oxygen permeability of a plastic film is higher for high temperatures. In the present experiment, the yeast count increased slightly after 185 to 230 days of conservation.