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Stracathro Estates – AD Plant

THE ESTATE

Stracathro Estate 4,220 acres include 500 acres of commercial and amenity woodlands, six tenanted farms and 2,270 acres of intensive arable cropping.

The Estate has embraced renewable energy through various developments – wind power, solar power, biofuel boilers and now a large Anaerobic Digester Plant. Having the AD Plant has completely changed how they farm at Stracathro.

To feed the AD Plant a move from conventional arable cropping and growing specialist energy crops was necessary. The first energy crops were sown in summer 2016, with the biggest change being the establishment of grass leys.

It is my belief that by reverting to a crop rotation including short term grass we will greatly improve our soil structure and fertility and halt the slow decline in major nutrients through crop offtake and erosion. In effect, we are proposing a return to traditional livestock farming where nutrients are returned to the soil rather than being exported through crops leaving the farm. A closed nutrient cycle.

THE CHALLENGE

The challenge for Alex Eggo was to come up with an appropriate mixture to help deliver the quantity and quality of grass silage required for the AD Plant. After careful consideration a mixture was first sown in 2016. Its performance more than exceeded expectation and a further 300 acres was established in 2018.

To meet the challenge of providing feed stock for a medium sized gas to grid AD Plant and still retain a healthy crop rotation rather focuses the mind. With maize not an option this far north and adhering to the simple adage of stick to what you know best we settled on a mix of short-term grass, whole crop rye and fodder beet. The aim is to maximise DM yield per acre. Our first two seasons 2017 and 2018 have been very different. 2017 giving exceptional grass and rye yields – grass averaging 6T DM from a fresh weight yield of 19.5T per acre and Whole Crop rye 5.6T DM from 16T per acre and with beet at 30T fresh weight and 7T DM per acre. With the very late cold spring followed by drought conditions, 2018 has been a very different beast and yields across the board down 15% with grass yielding 16 tonnes, Rye 14 tonnes and the early beet lifting is correspondingly lower at around 28 tonnes. Although this was slightly disappointing it has demonstrated the resilience of the three crops. Over two very different years we have achieved an average DM yield of 6T per acre. To put this in to perspective it would take an exceptional 7T per acre crop of wheat to match this on a DM basis. The challenge now is taking this forward and adapting what we have learned in the last two seasons into a more productive system. I personally think that reducing from 4 to 3 grass cuts per year may result in higher dry matter bulkier crops. The next stage will be discussing this option with Alex Eggo who has been extremely helpful and very patient in guiding me through the intricacies of grass varieties.

Production in full swing with 120 tonnes of feedstock per day supplying the Stracathro AD Plant in August.

At Stracathro AD Plant, some of the figures take time to get your head around. Work started on the site in early August 2016 with a target of delivering gas to grid by 30th September, being the first of many hurdles to clear. The plant has a build cost around £11,000,000 and production capacity of 3,750,000 m3 biomethane annually, this is a rather meaningless figure which roughly equates to the annual power demand for 3000 medium-sized homes. The plant started full time production in October 2018 and requires 120T of feedstock per day, and produces the equivalent amount of digestate, which needs to be stored and returned to the land.
Annual feedstock requirements of around 42,000T need three acres of silage clamps and take the produce from just over 2000 acres of arable ground to fill them.

THE ADVANTAGE

The big advantage to the estate is we have changed from producing commodity crops for a fluctuating market to having an index linked contract to supply energy crops to a willing customer right on our doorstep. From a purely farming perspective the advantages are potentially greater, with the introduction of better rotations resulting in more productive, healthier soils, reduced use of chemical fertiliser and less exposure to the grain markets.

Gordon Cairns, Stracathro Estates.