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by Alison Martin
Brian Herbert, an agronomist and Technical Director of Singleton Agriculture woke at 4:30am, got in his car and drove for 6 hours. A customer with a large herd of cattle to feed wasn't pleased with his silage. There were holes in the plastic wrap on the bales and the farmer wanted some answers and he wanted them soon.
Finally arriving on a beautiful estate with elegant trees and rolling pastures Brian found the silage bales had indeed got holes in them and further inspection showed white patches caused by fungal growth due to air and water entering the bale.
The plastic covering had been damaged, but Brian found punctures, not an inherent failure in the plastic. He looked around for the cause of damage and saw that the field next door had about 60 pheasants on it. The customer was indignant “They never perch on these bales!”
When he told me this story, Brian did an impressive impersonation of a cock pheasant strutting about, flapping its wings and digging its claws into the bales. “There was no netting to keep the birds off the plastic,” he said loudly in his Yorkshire accent thumping his fist down on the table in frustration, “Penny-pinching! Not enough layers of plastic either, this crop demanded at least six layers.”
I laughed, but then the penny dropped. How much did that spoiled silage really cost? The costs of production would include equipment, fuel, time, fertilizer etc, but right at the end of the process, skimping on the ensiling of fodder can lead to spoilage and losses in nutrition of up to 12%. This is a loss equivalent to wasting one in every eight acres.
“Losing it at the end like this, after you've incurred all the cost of production is sinful,” says Brian, a veteran of the agricultural plastics industry. “Inefficacies earlier in the production chain have a much lesser effect that ones right at the end, so it is the ones at the tail that need to be tackled as a priority.”
Brian's premise is basic. Making silage is an anaerobic fermentation process, which simply means that in a sealed container with no extra air, grass ferments generating carbon dioxide, which you can see when the bale balloons up after wrapping.
But if additional air somehow gets in through the plastic, it sets off a secondary fermentation fouling the silage. If soil or dock leaves are present, they create conditions, which favour the growth of fungus resulting in a 'sloppy sad heap of mess that cattle won't eat.
Air can get into silage any number of ways, from errant pheasants pricking holes in the covering to someone putting their heel through a silage sheet, using the wrong colour of wrap because it's a bit cheaper or insufficient layers of film to save on cost.
In the late 80s when wrap was initially used on bales it was thought that four layers were optimal. Now, a better understanding of what happens inside the bale has proved, kilo for kilo, that six layers are cheaper than four when it comes to feed value. Despite improvements in plastic polymers, wrap is no thinner than it used to be as it is the gas permeability rather than the puncture resistance that is the main issue, so using a minimum of six layers to wrap and seal a bale properly is currently recommended.
All plastic wrap is permeable to some degree, but on a hot day silage wrap expands, like anything else, making it more permeable. Black plastic wrap absorbs more heat than white or pale green plastic and so expands more, making it more gas permeable and letting in oxygen, whereas paler coloured plastic heats up less providing a better barrier.
Skimping on plastic in not recommended for clamps either, the correct film combinations will produce a better product on pit silage because it reduces heat damage and gives the most effective seal. Black plastic coverings on silage pits can get so hot that you can't put your hand on it, literally frying the silage underneath costing up to £6 or £7 per square metre in nutritional value losses in the top 18 inches. The cost of this is nearly £3000 on a 16 x 30m silage pit.
To avoid such losses Brian recommends using a thin clear 40- micron under sheet to stop air getting back in immediately, and cover with a thick 125 or 150-micron sheet, rather than 100 microns. A white sheet is better than a black sheet to reflect heat. (Don't be tempted to save £2 on a thin silage sheet.) Then cover with a net and bag the sides down so air can't get in. Oh, and use sandbags instead of tyres.
“Tyres are a total menace, I've seen one farmer lose three cows in 18 months due to the wire lining in tyres getting down through their stomachs causing tearing, infection, blood poisoning and eventually death. Also rain water sitting in tyres for too long turns bad and can cause problems if it gets into the silage.”
Once during his crusade to persuade farmers to be penny wise when making silage, Brian visited a customer whose silage wrap was splitting. “He was wrapping bales at barely 14 revolutions on his single arm wrapper, giving him just 3.5 layers on average, the average meant that some parts had four and other parts had only a single layer – guess which bit split?”
So he got a couple of trial rolls out of the boot, gave them to the farmer and persuaded him to kick the machine up to 25 revolutions giving six layers to a bale. “Those are the best bales I've made, those are,” smiled the man. But as he went to leave Brian noticed him click the machine back to 14 revs. Brian turned and asked him why. He replied, “Oh it's too expensive to do it your way!”