Number of layers of plastic impact bale gas tightness

Number of layers of plastic film on the bale has an impact on the bale’s gas tightness. In this study the bale gas tightness, density, surface damages, total nutrient losses and losses caused by surface mould growth was investigated when wrapping bales with 6 or 8 layers of Horsewrap and regular standard bale wrap. 16 bales with each 6 and 8 layers of stretch film were wrapped with Horsewrap and standard bale wrap, in total 64 bales. The crop was 2 cocksfoot leys from the second cut. The two stretch films were 25 µm thick, 750 mm wide and pre stretched about 70%, and the overlap on the bale was 50% of the film width.

Surface damages (bird attacks) on the 6 layer standard bale wrap were markedly different from the three other treatments (Table 1). Besides birds there are quite a lot of problems with cats, but it can also be dogs and other animals, that scratches and makes holes in the bales. 6 layers of standard bale wrap resulted in large surface damages and losses, but adding 2 layers substantially decreased the problems. 6 layers of Horsewrap was comparable to 8 layers of standard bale wrap. There was no big difference between 6 and 8 layers of Horsewrap and 8 layers of standard bale wrap. However, for both stretch films the gas tightness was about twice as good with 8 layers than with 6, which indicates that both joint tightness and the leaking of air through the plastic was improved. Gas tightness is measured by inserting a one way valve (Ekolag) through the plastic, creating a small negative pressure and the time in seconds that it takes for the negative pressure to rise from -20 mm to -15 mm water column is measured.

In conclusion, bales should be protected against bird attacks; otherwise there is a risk for mould growth that can result in large nutrient losses. Number of layers of plastic film had an impact on surface damages and losses. In this study the difference in nutrient losses between 6 and 8 layers of plastic film was calculated to 56 g/kg DM, and with 330 kg DM per bale the economic loss was calculated to 2.5 Euros per bale.

Sara Muhonen, AgrD

Reference:
Jacobsson F. 2002. Paketensilering som belyser inverkan av sträckfilmens kvalitet vid inplastning med 6 och 8 lager sträckfilm. Examensarbete inom Lantmästarprogrammet. Institutionen för jordbrukets biosystem och teknologi, SLU, Alnarp. (in Swedish)