Review
Establishing perennial grass energy crops in the UK: A review of current propagation options for Miscanthus

https://doi.org/10.1016/j.biombioe.2009.01.005Get rights and content

Abstract

A key UK government strategy is to expand the supply of home grown biomass and facilitate the development and competitiveness of a sustainable supply chain, while promoting low-carbon technology. Analysis of the potential supply chain suggests that this can, in part, be achieved by growing energy crops. Meeting expectations is, however, reliant on developing an economically viable biomass sector which incorporates efficient, sustainable and regional supply chains to increase biomass use.

This review aims to present the knowledge by which plant propagules, for the biomass supply chain, can be produced at minimum cost. It specifically addresses the potential of biomass production from the perennial grass Miscanthus. This review is part of a project to identify the causes for the apparent limitations in the establishment of UK perennial energy crops. The work reported here focuses on the knowledge available regarding the potential routes by which Miscanthus material could be mass produced.

The review concludes that high density plantings must be established to maximise yields. Vegetative clonal plant propagation is required to deliver uniform crops of selected germplasm. Commercial seed production in the UK is not possible and potentially undesirable for selected germplasm. Rhizome production and division is slow, but currently does not limit increases in production because the UK industry uptake is currently small. Uptake of new germplasm will be dependent on the use of rapid and cost effective plant propagation systems, particularly vegetative systems. The germplasm collection established provides an opportunity for genotypes to be propagated by a range of techniques to determine ease of propagation in terms of cost and multiplication rates. At present the establishment rate of Miscanthus is slow and this appears limited by economics; evidence suggests that the cost of plant propagules is one factor that constrains widespread planting. New techniques are required that simultaneously reduce unit costs of propagules and increase the speed of their availability to aid this developing industry.

Introduction

The UK is committed to producing an increasing proportion of its energy requirements (electricity, heat and transport fuels) from renewables, i.e. 10% electricity generation by 2010 with an aspiration for reaching 20% by 2020 if sustainable. At present about 1% of the heat supply in the UK is from renewable sources. However, the market potential for renewable and waste heat by 2020 has been estimated to be between 5% and 12% of the current UK heat requirement [1]. Bioenergy, as a primary energy source, contributes around 14% world-wide [2]. Generating energy from biomass, including that grown on agricultural land is now central to Department of Environment & Rural Affairs (Defra) and UK Government (UK Biomass Strategy) [3] and UK Energy White Paper along with EU (Biomass Action Plan; European Environment Agency, 2007) [4] strategic objectives and other international efforts to implement sustainable energy generation options. Renewable biomass crops have the dual benefit of providing a relatively low CO2 emission source, at least for growing, of energy and alternative non-food uses for land, with corresponding potential environmental and socio-economic benefits on a local and national scale [5]. Carbon neutrality, even for a biomass crop, is difficult to achieve, if all energy inputs are considered, i.e. those associated with harvesting and transport [6]. The total carbon mitigation calculated over 15 years of a Miscanthus crop averaged around 6 tonnes of carbon per year [7]. The relevance and likely implementation of bioenergy cropping depends much on energy costs and recent dramatic increases in oil prices will promote higher rates of emissions offsets delivered by PRG [6].

There are also possible negative impacts from extensive biomass plantings due to environmental pressure on farmland, forest biodiversity and soil and water resources [4], [6], [8]. Defra anticipate 125,000 hectares of energy cropping by 2010. More recent suggestions include the expansion of perennial energy crops to around 350,000 hectares by 2020 [9]. This would yield a total of land available for energy production, including biofuels with biomass crops, of around a million hectares of (17% of available UK arable land). This hectarage would provide approximately 96 TWh (8.3 Mtoe = tonnes of oil equivalents). The total UK energy requirement is currently 165 Mtoe. The UK currently generates only 3% of its electricity needs from renewables and many biomass schemes have been slow to develop relative to expectations. Meeting expectations is, however, reliant on developing an economically viable biomass sector which incorporates efficient, sustainable and regional supply chains to increase biomass use. With agricultural commodities recently reaching record high prices, the immediate outlook for increasing biomass grown for energy on UK agricultural land is challenging.

Section snippets

Perennial grass energy crops

The species which are known to have rapid growth rates (high biomass accumulation) are being utilised and exploited using knowledge of physiology and genetics of woody plants, such as willow and poplar, or perennial rhizomatous grasses (PRG). The woody species are used in short rotation coppicing systems (SRC), while the PRGs, such as Miscanthus, reed canary grass and switchgrass are cropped over an annual cycle. Both SRC and PRG systems have their strengths and weakness but the focus of this

The problem

The potential to grow Miscanthus commercially as an energy crop is now well documented [37]. Once established, crops will reach their maximum production rates in around 4 years and be viable for up to 15 years. However, to realise this potential requires the development of a commercial supply chain that must achieve a number of key objectives. To establish sufficient size plantations requires an ability to produce large numbers of plants. UK Government figures suggest a requirement for at least

Seed production systems

Miscanthus species generally do not flower in the UK due either to environmental limitations (they have a SD requirement) or some hybrids are sterile. The self-sterile (male sterile) habit of M. × giganteus precludes its establishment from seed. However, that is not the case with M. sinensis which does flower in the UK, albeit of variable seed viability [39]. Crop establishment with M. sinensis, from seed, is possible if drilled with pelleted seed [40]. Work with M. sinensis clones suggested to

In vitro propagation systems

Experimental in vitro Miscanthus propagation from axillary buds has been examined [22], with the induction of callus from shoot apices, leaf sections and immature inflorescences to generate polyploidy genotypes. As with many in vitro propagation technologies, protocols use axillary buds on shoot inducing media (modified Murashige and Skoog) with benzyladenine (BA) [N-(phenylmethyl)-1H-purin-6-amine] followed by indol-3-butyric acid (IBA) supplementation to induce root formation.

There is

Rhizome production systems

Miscanthus rhizome (modified swollen underground stem) is composed of a number of nodes at which meristem activity produces both roots and nodal bud initials, as well as, terminal buds (new shoots) by which the rhizome grows. Both the nodal and terminal buds can subsequently develop into aerial shoots. The rhizomatous habit facilitates below ground exploitation of soil resources and the development of a closed leaf canopy with a high LAI. The active development of rhizome terminal buds

Stem cutting production systems

Utilising nodal stem sections as a source of clonal material (i.e. ‘ratooning’, deriving new plants from rooting cut ‘nodal’ stem sections) is well practiced in agricultural species, i.e. sugarcane; a close relative of Miscanthus [63]. Sugarcane, is also a member of the Poaceae Family, within the genus Saccharum, with species of the two genera intercrossing. Vegetative production of various bamboos, also members of the Poaceae, can be achieved via ‘culm (vertical stem of foliage and flowers)

Conclusions

High density plantings of Miscanthus are required to maximise yields as establishment rates vary considerably depending on site selection and preparation, quality and age of rhizomes, length of storage, planting technique, and aftercare. The fact that UK commercial crops may not achieve planting densities which are optimal with respect to yield may be due to various factors including high propagation costs, poor establishment or improved practical knowledge in achieving the required density of

Acknowledgements

This work was financially supported by the UK Department of Environment, Food and Rural Affairs, through project NF 0439.

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