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Follow up on colourful haylage bales

Follow up on colourful haylage bales

We got some questions on how much the different colours of the plastic film for haylage/silage bales affect the feed quality. Trioplast have performed measurements of sunlight reflectance on the different colours and here they answer how their own colours reflects sunlight.

Background:
Today it’s common to see wrapped bales in several different colours and the different colours support different foundations, which is great! But the colour of the plastic film can actually affect the temperature of the silage/haylage bale. The sun warms up the bale and white film reflects the sunlight and thereby keeps the temperature down. Darker film on the other hand absorbs sunlight and gives a higher temperature inside the bale. Black film absorbs the most sunlight.

When the temperature increases the permeability of the film also increases and more oxygen enters the bale. Six times more oxygen permeates the film at 50°C compared to at 15°C. Higher oxygen supply and temperature in the bale implies increased activity of the butyric acid producing bacteria, which leads to reduced quality and feed losses. It is therefore important to keep a low temperature in the bales to have the best quality and economy in the production. Therefore choose as light coloured film as possible for wrapping of forage.
(Reference: ©Trioplast. 2012. Balhandboken ISBN 978-91-637-1823-6 (in Swedish))

Answers from Trioplast:

What are the differences between plastic films with different colours? Reflectance, permeability
The lighter the colour the less heat impact. Higher temperature in the bale promotes growth of unwanted bacteria. Higher temperature also increases the permeability of the plastic and oxygen can then more easily enter the bale. Both these factors have negative effects on silage quality.
White colour has the highest sunlight reflectance, thereafter pink, yellow, blue, light green, dark green and black. Black has the absolute lowest reflectance and therefore cause much larger heat impact than for example white, pink, yellow and blue.
If one is still going to use darker colour (for different reasons) it is better later during the year as sun impact is lower then.

Are there numbers on reflectance from plastic with different colours?
Yes we have our own measurements performed by SP (RISE) but this only applies our own colours. It cannot be used as some sort of universal values for the industry.
For the Trioplast colours: White, pink and yellow are within SP’s (RISE) demands according to the certification for silage stretch film (SPCR 063) regarding reflectance. Blue is just outside and then comes light green, dark green and as previously stated far from demands comes black.

Sara Muhonen, AgrD

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