Performance of Miscanthus x giganteus (Greef et Deu) established with plastic mulch and grown from a range of rhizomes sizes and densities in a cool temperate climate

Abstract The effect of biodegradable plastic mulch, rhizome size and planting density on establishment, annual harvested biomass yield of miscanthus and nutrient content were studied at two sites in Northern Ireland. In a split plot experimental design plastic mulch treatment was applied randomly to main plots (covered or left uncovered) after planting rhizome fragments varying in size (by weight) and planting density which were assigned randomly to subplots in four replicated blocks, at each site. Mean shoot density over both sites was 7.8 and 12.6 m −2 for unmulched and mulched in October of the establishment year. Averaged over all sites and planting treatments, uncovered total biomass yields were 0.47, 4.79, 7.74 and 8.12 t DM ha −1 , for the first four annual spring harvests, respectively, mulch increasing these yields by 68, 49, 36 and 24%, respectively. Although there were significant effects of rhizome size and density, the effect of plastic declined at successive harvests for large and medium sized rhizomes and high and standard densities. The main effect of plastic mulch was to increase the shoot population density, and shoot number per plant, especially in plants from rhizomes planted at a low number per unit area. Although there were soil moisture deficits in some months, mulching was considered to have improved yields mainly by increasing shoot density due to higher soil temperatures during establishment followed by a mild winter. By the third year, plastic mulch had no significant effect on recommended planting density at all harvests. Plastic mulch had no marked effect on content of N, P or K in biomass. Covering miscanthus rhizomes with a biodegradable plastic mulch is an effective management tool to increase miscanthus biomass production in a cool temperate climate, at least in the first 3–4 years of production. This is mainly due to increase in soil temperature during establishment and the subsequent year. Mulching allows the optimum planting density of rhizomes to be reduced. Despite additional cost plastic mulch represents an economic benefit to the crop.