Reducing the Environmental Impact of Silage Bales

Baling silage is generally a more expensive way of making silage compared to clamp storage and silage quality tends not to be quite as good.  As baler technology develops, the quality and quantity of silage in a bale is increasing.  However, the environmental issue of plastic use and disposal remains a big concern with baled silage.  Relatively high dry matter silage should be the goal to maximise the nutritional value and dry matter in each bale, potentially reducing the number of bales required and amount of plastic used.  At the same time, care must be taken so that nutritional value is not compromised when aiming for high dry matter silage, as illustrated in a small experiment involving SRUC farms.

On each of the four farms, two bales from the same stack were weighed, along with the wrap and net.  Forage samples from each bale were analysed for nutritional quality and the amount of dry matter, protein, and energy per bale and per kg of plastic were calculated.  The results are presented in the following tables:

Table 1. Average silage bale analysis per farm

Farm	Average bale weight (kg)	Plastic (net + wrap) per bale (kg)	Silage dry matter (g/kg DM)	Silage ME (MJ/kg DM)	Silage protein (g/kg DM)
1	832	0.75	242	11.15	104
2	765	1.29	323	10.45	118
3	720	2.15	431	9.5	114
4	331	2.25	845	7.69	72.9

There was a big difference in bale weight as well as plastic use, which ranged from 0.75 kg to 2.25 kg per bale, varying with manufacturer and the number of wraps applied.  The highest dry matter forage (hay) was the poorest in nutritional value, which was to be expected.

Table 2. Nutritional value per bale

Farm	Dry matter per bale (kg)	ME per bale (MJ)	Protein dry matter per bale (kg)
1	201	2,241	20.9
2	247	2,581	29.1
3	310	2,945	35.3
4	280	2,153	20.4

The highest dry matter bales (farm 4) had the lowest amount of ME and protein per bale on the back of the poorest analysis, indicating that there is a trade-off between dry matter and silage quality.  The ME and protein content per bale increased as the dry matter of the bales increased from 242 to 431 g/kg DM, regardless of analysis.  The range in ME per bale was 792MJ, equivalent to 149 litres of milk (worth £40.23 at a milk price of 27p/litre) or an additional 13 kg growth on a 400 kg steer, worth £29.90 at £2.30/kg liveweight.

Table 3. Nutritional value per kg of plastic (wrap and net)

Farm	Dry matter per kg of plastic (kg)	ME per kg of plastic (MJ)	Protein dry matter per kg of plastic (kg)
1	268	2,988	27.9
2	191	2,001	22.6
3	144	1,370	16.4
4	124	957	9.1

There was great variation in nutritional value per kg of plastic, with three times as much energy and protein per kg of plastic in bales from farm 1 (wettest bales) compared to farm 4 (driest bales).  This is because the wettest bales used the least amount of plastic.

The farms with the higher dry matter forage used more plastic wrap.  This is not unexpected due to the physical nature of very dry forage and the need to protect these bales from damage and air ingress through punctured plastic.  This results in higher costs when making high dry matter silage; more wrap is required and hence the greater the environmental impact.

There are many manufacturers of plastic bale wrap, which is available in a vast array of colours.  While the wrap must perform well, by being tough and resistant to damage, protect forage from UV light and provide an airtight seal, consider its disposal and what that costs.  Black or coloured plastic has an environmental levy charge added to each roll to help with disposal costs due to its lack of demand for recycling.

There is now clear plastic wrap available, with the used wrap being in much higher demand than black or coloured wrap, as it can be recycled into a wider range of products.  This could save farmers money in the long run, as it has significantly lower disposal costs and some recycling companies will take delivery of it free of charge.  Clear plastic also allows you to monitor keeping quality of the silage before feeding out and it is thought to deter birds as they see their reflection in it.

There are many factors to consider when making baled silage. These include:

• The target nutritional quality of the silage, which will depend on the class of livestock it is fed to.
• The target dry matter and hence how much silage needs to be made.
• Plastic use, which will depend on the number of bales and the dry matter.
• Type of plastic used and ease of recycling and cost.

All the above factors will influence the overall production costs to the farm.  Aiming for a higher dry matter content means less bales are required to meet the farm’s forage demand, and this in theory could help balance out the increased amount of plastic required per bale.  However, dry matter should not be maximised at the expense of nutritional quality, especially if that leads to increased feed costs (and increased carbon footprint) over the winter.  Consider all these factors and what can be done to reduce the environmental impact of your silage making practices, without incurring increased costs at the farm level.

Lorna MacPherson, lorna.macpherson@sac.co.uk