Where most on-farm composting schemes tend to start with traditional green-waste and then progress to include other materials, Cambs grower Stuart Bedford has started with onion waste.

The waste crop comes from local processor Gs Growers in Ramsey, which has a stringent selection process to ensure supermarkets get the quality and grade of onions they require.

For Mr Bedford, it means there”s a consistent supply of waste material from the pack-house that is good enough to make a nutrient-rich soil conditioner.

“We”re currently operating under a restricted licence, which limits what we can do with the finished product,” says Mr Bedford.

“We are currently in the process of seeking a full planning application to ensure we can continue to develop our organic waste recycling business and expand more into green-waste composting,” he adds.

RESTRICTIONS

That restricted licence currently means the finished compost can only be spread on Mr Bedford”s land and cannot yet be sold off-farm.

Regular analysis of the onion-based compost mix has, he says, revealed a source rich in nitrogen.

“We can only apply about 800kg/ha,” he says. “Though every batch does vary, there”s plenty of goodness in the finished compost.”

Getting to that final stage takes around eight weeks from start to finish, if a quality product is the order of the day.

“We blend the onion waste with straw – at about 3t of straw to every tonne of onions – to ensure there”s plenty of fibre in the mix,” he says.

“The straw is also useful to absorb the onion liquor, as 200t of onions can produce up to 9000 gallons of juice.”

The waste is shredded by a Zago Eurogreen machine.

It looks not unlike a diet feeder and uses four horizontal, slow-speed augers that twist, rip and distort fibrous materials.

Mr Bedford”s 15cu m trailed machine takes around 20-30 minutes to chop and blend the mix of onions and straw, producing about 4.5t of material that is discharged directly into a windrow using the shredder”s conveyor.

According to rates of decomposition, the windrow is turned periodically using an excavator and the final product is passed over a screen to pull out the larger particles that can then be reprocessed.

Composting is more thorough and faster than traditional shredding techniques, says Zago importer King Feeders, as the slow speed rotors blend material within the shredder”s body, rather than layer the material in a heap like conventional shredding machines.

Such a blending action is claimed to result in the material requiring less frequent turning than traditionally shred wood and green-waste materials.

“Being tractor-powered also means the Eurogreen models are very quiet in operation, which helps us when working in close proximity to local residents,” says Mr Bedford.

Pleased that the firm has not been lured into making extravagant purchases on unnecessary processing equipment, Mr Bedford remains optimistic about the future of on-farm composting at Bury Lane Farm.

“Since we started composting onions five years ago, the workload has been steadily increasing,” he says. “We collect all Gs onion waste using a tractor and 14t trailer, which is kept busy almost all day, shuttling back and forth to the farm.”

“As one batch is processed through the shredder, we”re lining up the next load,” he adds. “We could almost do with a second shredding machine, or replace our current one with a much larger model.”

fwmachinery@rbi.co.uk