10 September 1999

SRC expansion may prove good for contractors

New opportunities for

contractors may be provided

by the promised expansion

in the area of short rotation

coppice grown as an energy

crop. Mike Williams reports

IN the power station linked schemes, which appear to be establishing the pattern for much of the short rotation coppice (SRC) production in the UK, farmers provide only the land and prepare the soil for planting.

Contractors then take over with the specialised equipment needed for the rest of the production cycle.

Choosing equipment for planting and harvesting crops of coppiced willow and poplar is difficult because at this stage nobody appears to know which machines are best for UK conditions, but there are clearer guidelines about the cultivations needed before planting.

Soil is prepared during the autumn ready for cuttings to be planted in the October to March period, and cultivations usually start with deep ploughing – the deeper the better say the experts.

Cultivations after the plough should create a deep, fine tilth to allow close contact between the soil and the 18cm (7in) to 25cm (10in) long cuttings.

Getting the conditions right is important because SRC is an expensive crop to establish, with cuttings costing about 10 to 12p each and typical planting rates of 10,000 to 12,500 cuttings a hectare. Skimping on seed-bed preparation can easily be a false economy in a long-lasting crop, which could still be producing a harvest after 25 years or more.

This is still an early stage in the commercial development of SRC production, and some of the machinery used for planting and harvesting is borrowed from other crops. Machines for planting cuttings include the Super Prefer UT semi-automatic planter developed for field-scale vegetable crops, plus the Austoft designed in Australia for planting sugar cane.

The Austoft and the Super Prefer both handle cuttings which are previously cut to the correct length, but some planters are fed full length sticks or rods and include a cutting mechanism which trims them to size.

The Super Prefer and the Austoft were included when the Forestry Commissions Research Division carried out an SRC planter trial.

The trial also included a Salix Maskiner Step planter which handles full length sticks, plus a Catkin planter using previously prepared cuttings. There was also a brief evaluation of the prototype Turton planter, another planter using full-length sticks.

Machine prices quoted in the trial report published in 1996 (Report 5/95) varied from £2620 for the two-row Super Prefer to £25,000 for the four-row Salix Maskiner Step planter, and it was the Step planter which gave the best results with a 0.89ha/hour (1.3-acre) work rate and a £41/ha (£28/acre) operating cost.

The standard establishment technique is to plant each cutting vertically with no more than 2cm (0.8in) showing above the soil surface, but the Austoft planter places cuttings horizontally in the bottom of a 10cm (4in) deep furrow.

Horizontal planting could have important advantages says Damian Culshaw, the energy crop development manager for Roxburghshire-based Border Biofuels. His firm is directly involved in the production of SRC and is also looking at other crops with potential for generating electricity. Different planters have been evaluated on 40ha (59 acres) of SRC crops.

The machines include a planter developed by Border Biofuels and their Danish associate company to plant complete 2m (6.5ft) to 2.5m (8ft) long sticks horizontally under the soil, and the preliminary test results are excellent, says Mr Culshaw. "This should be less expensive than using the Step planter, and the growth we get from the horizontal stems is very good," he says. "Shoots develop along the length of the stem and grow like a hedge. It is too early to talk about yields, but at this stage it looks very promising."

Once the SRC crop is fully established, harvesting is the only regular attention it needs. Harvesting is normally a late autumn or winter job, and one approach is to use a self-propelled forage harvester.

The forager, with a special saw action cutting head, harvests the crop and reduces the sticks to chippings which are blown into a trailer.

Freshly harvested material has a 50% to 60% moisture content, which is acceptable in Sweden, where freshly harvested SRC is used mainly for winter heating. Most of the UK crop will be used to generate electricity and the power stations need a year-round supply, which means on-farm storage.

Although the forage harvesters cut-chip-load technique is efficient, there are also some disadvantages. A heavy self-propelled forager is not the ideal machine to work in muddy midwinter conditions, and it also leaves the grower with a large quantity of fresh chippings which need drying and special storage capacity.

This problem is avoided if the crop is harvested and stored as whole sticks, which dry naturally and can be stored in the open.

Various tractor powered stick harvesters are available, plus the self-propelled Seggerslaat Empire 2000 model, but the problem with all of them is the cost of handling the loose sticks plus the extra cost of chipping as a separate operation either on the farm or at the power station.

One answer to the stick handling problem could be to use a baler, yet another machine developed for other crops. The Scottish Agricultural Colleges (SAC) has made both round and square bales from SRC sticks using Claas Rollant and Quadrant balers. Both were successful, and the bales were easy to handle with a spike attachment on a loader. &#42