Industry developments are looking at ways to make forage conservation more sustainable, but do not expect to see biodegradable wrap any time soon. Jane Carley reports.
With the drive to reduce single-use plastics currently a key focus for many industries, the spotlight is inevitably turning to agriculture. Plastics are widely used in crop production and preservation; research shows about 12.5 million tonnes were utilised in 2019. Yet, recycling rates are comparatively low and the viability of deploying recycled materials in its manufacture depends on the end use.
Extensive study into silage preservation has been carried out at IBERS in Aberystwyth. Agricultural researcher Rhun Fychan says: Silage plastics are designed to offer top quality preservation of silage and are made using high quality polymers. Considering ways to make it more sustainable is a complex issue bale wrap is a high-tech product made of 25 micron film and designed to be applied in five to seven layers, so it is a difficult product to develop from biodegradable materials.
Biodegradable films are subject to stringent controls and can currently only be used indoors they could potentially only last for a few months before silage quality is affected and many farms will want to keep them considerably longer than that.
Lloyd Dawson, Commercial Sales Director at Berry BPI Agriculture, points out that bale wrap has been developed to last for a defined period.
He says: If the wrap breaks down before that period, not only is the silage itself lost, but there is also the cost of the machinery involved in producing silage to consider.
Biodegradable films break down on contact with the soil, and it is not always easy to say how long silage bales will be stored for. In 2022, the dry summer meant that less bales were made, so farmers are likely to make more this time. Even maize covers will sometimes disappear too soon or sometimes not at all. The use of biodegradable wrap is not feasible or scalable at the moment.
In its current format, silage stretch film is 100 per cent recyclable and thus can be considered as a process rather than as packaging, he says.
Netwrap and twine are packaging; net, in particular, is difficult to recycle as it can be contaminated with fodder and is hard to shred into smaller pieces for processing.
Producing the film from recycled plastic does not offer an immediate solution either.
Using recycled content would make 25 micron film heavier and actually put more plastic into the market, Mr Dawson says.
Mr Dawson also points out that new product developments focus on making wrap longer, lighter and stronger than the original product.
With Silotite Pro1800, rolls that were1,500 metres long are now 1,800m, giving 20 per cent more per reel. We have reduced the weight of the plastic but not the strength. This cuts transport, handling and packaging by 20 per cent, so reducing the number of boxes, packets and cores needed per season. Operators can also be more productive as they are not having to change rolls as often.
Another update is to eliminate the cardboard box.
We use a plastic sleeve which is ten times lighter and can be recycled with the bale wrap, so for every 10 rolls we are getting rid of 45kg of packaging."
Baler developments have also made a contribution, he says, with film-on-film systems replacing netwrap with a wide width film, which can be recycled with the bale wrap and, moreover, improve silage quality.
Rhun Fychan says that used bale wrap is of high value for recycling, but needs to be kept clean and dry.
Recycling sites are available at a number of locations in the UK, but farmers have to pay for the service at the same rates as other waste in my view, there should be a financial incentive to recycle farm plastics.
Bale wrap recycling schemes in the UK have not been successful, agrees Lloyd Dawson.
Just 25 per cent of plastic used is returned by farmers. There have been three attempts at voluntary schemes, and while accreditation protocols such as Red Tractor require farmers to recycle, they will only do what is needed to comply.
Where wrap is recycled, it can be used as up to 30 per cent of the constituents of silage sheets, Mr Dawson says.
It could go higher up to 60 per cent to make a product that is not as strong but still functions. At the end of that life, the sheets can be recycled and made into products such as plastic furniture.
Farmers must take responsibility; Ireland has a legislated scheme where farmers pay 240 (211) per tonne, but this compares well with what supermarkets have to pay under extended producer responsibility. It is not something you can put a voluntary levy on as some distributors will not apply it, so any companies who do want to contribute to sustainability are at a commercial disadvantage.
He suggests that bring centres might be a workable alternative to farm collections, with smaller farms being able to put two years worth of plastic in a load.
Where covers for silage clamps are concerned, traditional silage films are constructed from a mix of raw materials of varying quality, explains Will Wilson of Silostop.
He says: The latest development is High Oxygen Barrier film, which is made from mainly virgin materials as a food grade stable product. It is designed to reduce dry matter (DM) losses in the upper layer of the silo, eliminate waste on the surface and shoulders, and increase aerobic stability at feed out.
Results using High Oxygen Barrier silage films show under 5 per cent surface silage losses Silostop Agri is looking into the use of more recycled material in manufacture, but only if the technical properties of the sheets can be retained.
In addition to the 80-micron 11-layer Silostop Max, the company offers 45-micron 9-layer Silostop Orange, which uses less plastic and is ideal for single-cut crops; achieving the same results.
Mr Wilson says: It is not UV-stable, so it needs an Anti-UV cover, which is reusable for up to 10 years and is 100 per cent recyclable, helping farmers cut plastic use by 60 per cent.
While it is possible to reuse plastic covers, and many farmers will redeploy last years sheets as an extra layer against the clamp walls, the practicalities of packing away and storing sheets, plus the risk of contamination of the following crop, make it difficult, he points out. The covers are, however, 100 per cent recyclable.
Just as with silage stretch film, the challenge with developing biodegradable covers is defining the period in which they will start to break down.
Concerns about plastic may be one factor which continues a move away from baled to clamped or large bagged silage that we are seeing. For many farms, the silage quality is key and it is a convenient way to feed out, Mr Wilson says.
Rhun Fychan suggests: Clamp coverings offer more immediate potential for using biodegradable materials, so I would expect developments to be seen first in that area.
IBERS is studying the use of plant material to produce plastic and has applied for funding to look at biodegradable wrap in the future.
Biodegradable plastic trials
Researchers at the University of Turin Ernesto Tabacco, Francesco Ferrero and Giorgio Borreani carried out a study into the feasibility of utilising biodegradable plastic film to cover corn silage under farm conditions in 2020.
The study evaluated the shelf life of Italian-made Mater-Bi biodegradable plastic film under outdoor conditions, analysing its effects on the fermentative characteristics, microbial counts and aerobic stability of corn (maize) silage. It was compared with commercially available polyethylene and high oxygen barrier films.
The maize was ensiled in 30 drive-over piles covered with either Mater-Bi, polyethylene or oxygen barrier films. Each pile was opened after 21, 85, 133, 195 and 230 days of conservation, and the effect of the film was assessed in silage samples that were both close to and far from the film.
The positive effect of the oxygen barrier film was found to last throughout the whole conservation period, while conventional polyethylene film showed a good conservation effect for 133 days. Mater-Bi, the first completely biodegradable and compostable bio-based polymer, showed similar characteristics to oxygen barrier film for three months of conservation, after which it began to biodegrade, demonstrating its limitations for long-term silage preservation.
https://www.mdpi.com/2076-3417/10/8/2803
