Investigations into the potential for growing willow as a short rotation coppice (SRC) biomass crop in the uplands of mid-Wales began in the early 1990’s. Since then three PhD theses have been produced. The principal investigators have been R.W. Hodson (RWH, 91-95), R.J. Heaton (RJH, 95-99) and S.C. Lowthe-Thomas (SLT, 99-03, “the Salix Project”) under the supervision of Dr F.M. Slater and Dr P.F. Randerson of Cardiff University.

Research initially concentrated on providing evidence that willow SRC could be established in typical upland conditions and the use of agricultural fertilisers to supplement the poor local soils for SRC growth. Land management techniques such as optimal spacing, differential planting date, mulching materials and pest control (all important for maximising yields) have been investigated in relation to a range of willow varieties. The development and testing of non-destructive biomass measurement protocols has enabled work on crop yield potentials. Economic models developed by RJH have outlined hypothetical comparisons with sheep production. More recently, the ongoing development of “root camera” technologies provide insights into subterranean processes involved in biomass production and bio-engineering willow applications.

Fertilisation and Yields

At a time when many people doubted the potential for upland SRC willow as a viable crop, RWH demonstrated a >90% survival rate for four willow varieties at an altitude of 260m on a previously grazed clay loam site. The application of lime and artificial fertilisers produced a three-fold yield increase and at a later date digested sewage-sludge was shown to double yields.

In 1995, RJH planted SRC willow at an altitude of 365m at ADAS Pwllpeiran near Cwmystwyth in Dyfed. This site was limed and fertilised with cattle slurry which was found to double the yield of the untreated controls, producing yields of around 2.25 oven dry tonnes ha yr-1.

Crop Management

Research at Llysdinam has shown that the best establishment results are achieved in the uplands if the willow planting date is between January and mid-March (earlier than in the lowlands). Planting densities have been assessed to produce best yields at densities greater than 20,000 stems ha-1. Lime applications were found to be important in acidic soils, typical of the Welsh uplands, as willow requires a pH of at least 5.5.

Ground Cover Management

Mulching for yield improvements was initially suggested by Dr Sarah Lynn’s woodland trials using digested sewage sludge at Llysdinam in the late 1980’s. The efficiency of cattle slurry was investigated by RJH and the benefits of mulches for weed suppression, retaining and regulating soil moisture and temperature have been studied by SLT. Her studies have identified bracken as the most suitable mulch for use in upland Wales compared with polyethylene, flax, spruce woodchip and SRC woodchip. Bracken as mulch material is also recommended as it is readily available in the uplands and is easy to apply.

Insect pests and disease damage have been recorded for all stages of willow development in the upland sites. No severely damaging outbreaks have occurred to date and biomass yields have not been affected. The research has demonstrated that pesticides are not currently required for SRC willow grown in upland Wales.

Sowing white clover as a ground cover crop was also shown to encourage a greater diversity of flora and ground dwelling invertebrates in the coppice. SLT demonstrated that the maintenance of good soil structure and control of insect pests by natural predators can clearly be encouraged by an informed choice of ground cover.