Article
Grass harvesting key to add plant efficiency
Cropping at 1,652ha Savock Farms in Aberdeenshire has changed significantly in recent years to provide feedstocks for a 2.5MW anaerobic digester that came online in 2018. Rye, triticale and specialised grassland leys have come into the rotation, for the primary purpose of fuelling the AD plant. These now make up around 60% of the farmed area, with the remaining 40% continuing in conventional arable production. Harvesting the rye and triticale has required investment in a selfpropelled forage harvester with a dedicated header, whilst the biggest changes in the machinery fleet have been necessary for making grass silage from the 400ha of grassland. “We had no grass machinery at all before we had the AD plant,” explains business owner Andrew Booth, “but its important that we have full control over the process of silage making and hence we’ve bought all the equipment we need. “Running the AD plant is all about maximising the efficiency of gas production, and that’s dependent on the quality of the feedstocks. In the case of the grass silage, we want the best quality material possible, so cutting at a time of day – usually between 10am and 4pm – when the sugars are at their highest is important.” 18
With grass leys potentially cut three or four times in a growing season, the aim is to be able to operate at a capacity of around 100ha/day, thereby cutting grass as close as possible to optimum maturity and ensiling the crop quickly at the target dry matter of around 30%. In order to fine-tune cutting and harvesting timing, Andrew uses his own in-field moisture level tester to obtain an instant analysis of crop condition. Taking 10g samples of fresh grass for analysis in this way provides the all-important indication of what’s happening in the field. Andrew’s strategy has been to buy machinery, as far as possible, from a single specialist manufacturer, and through a local dealership that can provide any necessary backup and prompt supplies of parts. Ravenhill Tractors, with a main depot based at Dyce, Aberdeen, and longstanding Kuhn dealers, offer the ideal solution. “One of the challenges we face when buying machinery is the amount of change there is in the industry, with companies regularly being bought-out or amalgamated,” says Andrew. “That can bring some uncertainty, with things like the continuity of models and the availability of spare parts, so we thought long and hard before deciding on our grassland machinery.
“We’ve gone with Kuhn because they are a primary manufacturer with a good reputation for strength and reliability, and with a long history in hay and forage equipment. Ravenhill Tractors is a company we know well, who have been Kuhn dealers for a very long time, so this was the right option for us.” To create enough mowing capacity, the Savock Farms fleet includes both triple-gang and frontand-rear mounted disc mower conditioner units, these providing 9 metre and 6 metre cutting widths respectively. Including Kuhn’s patented OptiDisc cutter bar and Protectadrive gear train safety system, the units offer the important combination of mowing efficiency, manoeuvrability and reliability, whilst the steel flail conditioning units have widely adjustable intensity to allow for a range of field conditions. “We have some older grassland and as well as newer leys that are comprised of varieties selected specifically for AD,” says Andrew, “and the weight of crop and conditions can also vary, so it’s important to have the potential to adjust the conditioning intensity.” With optimum crop conditioning, tedding out is rarely required, so – after a period of wilting – the mowers are usually followed by the grass rake. Again, choice of machine has been critical in helping to maintain
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overall operational efficiency, with Andrew opting for a Kuhn GA 15131 Gyrorake. This four rotor hydraulic drive machine has a variable operating width, from 9.5m up to 14.7m, and can produce a swath width from 1.4 to 2.5m, with full control through the ISOBUS on the tractor. This ability to adjust the machine according to conditions is another key point in maintaining field efficiencies. “We want to provide a constant feed into the chopper, so a consistent presentation is important to minimise the passes across the field and maximise field efficiency,” adds Andrew. “The four rotor rake has the capacity and flexibility that we need to optimise performance.” The grass is picked up by an 850hp Fendt forage harvester, operating as close to a 6mm chop length as possible to maximise performance in the AD plant. With high quality ensiled grass used alongside rye, triticale and farmyard manure from the farm’s intensive beef finishing enterprise, feedstocks are entirely home produced and – when used in the correct ratios – ensure the best possible gas outputs from the AD plant. It’s the details in the production and use of feedstocks that can make all the difference to plant performance, and that’s critical when payments are based on a fixed price contract for gas output.
