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Fenland maize set to fuel biogas operation

Sunday 17 March 2013 06:00

One of the UK's largest salad and vegetable producers is set to grow 800ha of maize on the Fens this year to generate 2.4MW of electricity to serve 4,500 houses and fuel a major new mushroom operation.

Based on two year's experience - including a 320ha crop in 2012 - the company is backing specialist, high yielding energy maize types and will be looking for the spring sown crop to help ease soil management issues.

G's part of the Shropshire Group expects their 2.4MW plant at May Farm, Littleport - which will be managed by Shropshire Energy Company - to come on stream in May.

The key driver behind their decision to build the plant is to supply power and heat to their mushroom operation which now delivers 100-130t a week for Tesco as part of the supermarket's drive to stock fresh, UK produced mushrooms in its stores on a daily basis. However, the plant will also supply electricity to local homes.

Will Forbes, director of Riverfen Farms, the Shropshire Group's business responsible for the 2,220ha of arable land around the plant, which features largely wheat and sugar beet, is now charged with producing 40,000t of maize every year for Shropshire Energy UK Ltd.

The operation will also benefit from 20,000t of vegetable trimmings - mostly from onions, beetroot and lettuce - grown on land that Riverfen Farms rents out to other farms in the Shropshire Group.

"Sugar beet and wheat are effectively seen as a break crop within the vegetable and salads business at the core of the G's operation on soils that range from light, black peats to heavy clay," explains Mr Forbes.

"We see maize not only as the best means of supplying the bulk and high DM crops for the maximum methane yields we need for the biogas plant, but also as a chance to improve soil management across the rotation. Slotting in after wheat and beet in the rotation, it will give us time to repair soil structure."

With 15,500t of maize from 2012 now clamped in readiness for the plant, the key will be to get the right mix of maize and vegetable trimmings within the digester. "We'll have to be careful in order to get the right balance of onion trimmings as these could affect the bacteria in the digester," says Mr Forbes.

"At the end of the process we will also be using heat to kill off any bugs in the biodigestate, effectively pasteurising it for one hour at 70C. This way, we can be sure of no issues with contamination. It will all be stored in AgBags for around six months before it is used as a valuable fertiliser across the farm."

In 2012, Riverfen Farms opted to grow 350ha of specialist biogas varieties Fabregas, Ronaldinio and Kontender from KWS. Eastern Counties contractor Oliver Arnold drilled and harvested the crop, which was managed by Riverfen Farms' farm manager, Ed Cross.

"The maize effectively provides us with another break crop and is particularly useful on ground where we would ordinarily try and muddle in a late planted wheat," says Mr Cross. "So, instead of drilling wheat right through to January or February, we will gain time to properly restructure the soil prior to drilling the maize."

In 2012, poor weather meant there would have been a clash with the farm's potato lifting operation, but in a more normal year, Mr Cross expects the maize to follow on from this crop.

"We have had a lot of issues with weed beet in the beet crop," says Mr Cross. "It is a case of one year seeding, nine year's weeding. While tractor hoeing and weed wiping helps to an extent, we have had to take some fields out of production, but this will be less of a problem now because maize herbicides will take out the weed beet."

The key to wheat production on the operation's fertile ground is good standing power. The breadmaker Solstice is a key variety and helps make use of the high fertility left after a salad crop. "Salads are 98% water, so take very little out," he says. Alongside Solstice, short, stiff, feed wheats Grafton and Humber provide a high yielding alternative.

The farm's wheats are drilled from mid-September, and, as the requirement for a larger maize area kicks in, fields that aren't drilled by early November will become maize.

"We always follow potatoes with sugar beet using Dow Shield to take out the volunteers, finding that Roundup is not effective," says Mr Cross.

"Now maize gives us another opportunity to control volunteer potatoes by letting the frost get to them over winter and so clean up the ground prior to salad crops. We face increasing potato cyst nematode issues, so removing the volunteers also helps reduce any build up of this pest."

This year's maize followed on from a trial of 55ha in 2011 to look at the best varieties, row spacings and management approaches. Early-drilled, the 2011 crop grew away well and the farm used irrigation to even it up.

In 2011, maize after wheat did 52t/ha, but in contrast crops grown after late lifted potatoes on ground that was heavily mauled did 35-40t/ha.

On the back of this, the farm selected Fabregas, Ronaldinio and Kontender for their 2012 crop. All three are from a different maturity class and were grown in blocks to potentially provide a sequential harvest.

The specialist biogas varieties Ronaldinio and Fabregas were the earliest drilled and expected to be the last to come to harvest, while the very early hybrid, Kontender, was later drilled and expected to provide a start to the harvest.

"The first crop - across 35ha - was drilled on 23-24 April 2012 and while it was up within three to four days, struggled in the cold, wet weather that followed. The plants soon used up any remaining energy from the kernel and we were a bit worried," says Mr Cross.

The rest of the crop was drilled between the 11 and 14 May after a break in the wet weather and in contrast this crop never looked back.

"We work on 42m tramlines so have difficulty spreading a prill that distance. The dribble bar helped avoid scorch from the nitrogen, which can be a problem in the maize crop," adds Mr Cross.

Weed control was taken care of using Starane followed by Sampson Extra. "Because of the potential risks with residues left in the tank on our salad crops, Calaris is not an option," he adds.

"Harvest wasn't easy given the wet season, but we averaged 45t/ha with the best fields doing 51-52t/ha. There was a clear week to 10 days' difference in maturities along the lines we'd have expected, but a couple of degree's frost in late October brought them all forward.

"While we had a planned harvest sequence, notice of an imminent road closure meant we had to rejig our plans and it was all a bit of a rush in the end. However, we are pleased to have clamped over 15,000t and that should see us through before the 2013 crop comes on stream."

This spring, Fabregas and Ronaldinio will both take 40% of the cropped area, but the early variety Kontender will be replaced with Severus.

While maize looks like being the ideal partner for vegetable waste in the AD plant, Riverfen Farms is also trialling specialist KWS high DM energy beet varieties Lissy KWS and Gerty KWS.

"Both looked well on our black fen land, doing 65-70t/ha, which is as good as most of our sugar beet varieties this year, and may provide a higher dry matter partner to maize," says Mr Cross. "They have been lifted and stored whole, covered by maize, in readiness within one of our new purpose-built clamps."

When digestate from the AD plant becomes available, most will go on to a growing crop of either wheat or maybe maize at an early stage of growth and this will bring further benefits in terms of fertiliser savings and improved soil condition.

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