The grass is greener

Retired biology teacher Lesley-Jane Powell explains how she is helping to fight climate change – and earning a living – growing the environmentally friendly bioenergy crop Miscanthus

The Biologist 66(2) p28-29

When rumours in our village said a small power station was being built to fuel the local industrial park, my husband and I were intrigued. It was to be fuelled by biomass grown in the area and needed local farmers to commit land to growing a new crop, Miscanthus. As a retired biology teacher (and entomologist manqué) and a retired engineer, looking for a suitable investment for our pension pots, we investigated the possibilities.

Miscanthus is a perennial Asian grass that grows three to four metres high from rhizomes each year for 20 to 30 years. It does not need very fertile soil and does not yet have any serious pests. Once established, it only requires fertiliser on very poor land.

As we have no access to machinery, we were relieved to find we could use a contractor to cut and bale the crop once a year. Although it will flower in hot summers, being triploid it does not set seed, so it cannot spread and take over surrounding fields. We needed at least 10 hectares and initially we rented this to project organisers to grow Miscanthus rhizomes. That gave us the chance to see the cycle through.

The crop starts growing from the rhizomes in April and with rain and sun at the height of summer, it can grow several centimetres in a day. It provides cover for birds within a few days, and the decaying leaves between the plants feed insects and slugs, which support shrews, frogs, toads and hedgehogs.Miscanthus tallcane

In autumn decaying leaves feed worms and soil organisms thereby enriching and remediating the soil. The minerals from the leaves are stored in the rhizomes for the next year’s growth so little or no fertiliser is needed – Miscanthus can be grown in nitrate-vulnerable zones, which means it can be produced on land unsuitable for food crops. The canes remain until spring providing shelter for deer and other animals.

It grows quickly, so hedges can be left to get tall for caterpillars and leaf eaters; thicken up for nesting birds; allowed to flower for bees, butterflies and moths; and produce fruit and nuts in the autumn for voles, mice and squirrels. Ivy and climbers such as honeysuckle can be encouraged to grow up trees and tree stumps to produce overwintering seclusion for insects and other invertebrates.

As no herbicides are needed once the crop is established, wild flowers grow in the field margins. We have found a patch of southern marsh orchids flourishing near the ditch. Raspberries, blackberries, hogweed and willowherbs grow enthusiastically, and we also have smaller native plants including hedge woundwort, cow parsley and nettles. In the ‘holes’ among the crop are scarlet pimpernel, ragwort, field pansies and bindweed, which attract insects in summer and so the dragonflies hunting from the local ponds.

As the ragwort is too small to shed its seeds outside the surrounding canes, it supports cinnabar moths, which increase in number year by year until they eat it all without leaving any flowers to set seed and have to migrate elsewhere when they emerge from their pupae – an interesting example of biological control.

Miscanthus is a C4 plant and therefore has better water control than our local C3 crop types and can put more of the available energy into growth: it can reach four metres in height in a good position. Only the part of our field near the ditch is able to supply both the water and the sunlight to accomplish that, but everywhere else it can reach at least two metres and mostly three. Walking into the crop quickly gets you lost and in spite of ‘knowing’ that we were just walking straight across the field to look at the cattle trough one summer day, we ended up separated and at opposite ends of the field. We now stick to the margins when the crop is high.

After harvest, the soil is bare and as we are near the field where the Staffordshire Hoard was found, we have assiduous metal detectorists active. A Roman coin, possibly from the reign of the first black emperor, Septimius Severus, has turned up and, to everyone’s surprise, an 800,000-year-old ironstone hand axe. These finds have elicited considerable interest in local archaeological circles.

Even the erratic planting and large bare patches left when we inherited the crop from the renters gives us more than 100 Hesston bales each spring, enough to power about 20 homes for a year. Emissions from transport and processing often mean bioenergy crops that could be carbon-neutral are not. At the moment we send them to Brigg power station to be burnt for electricity generation.

If more local 40MW power stations could be built near suitable conurbations, better use could be made of the waste heat and less spent in fuel for transport. If more Miscanthus biofuel power stations could be built across the Midlands, we could even use the canals (and shire horses to pull the boats) to minimise fuel cost and emissions. Ideally, it would be grown on marginal land to reduce problems associated with biofuels and changing land use. As Miscanthus can be grown on land not suitable for producing food, perhaps food waste can be used more often to feed people rather than to generate electricity.

Miscanthus can be grown on contaminated land for phytomining, with any valuable metals recovered from the ash. Phytoremediation by Miscanthus can clear spoil heaps of metal residues and water from ponds of industrial effluent, although the safe management of the resulting crop must be considered. It can also grow on meadows liable to flooding or needed for flood control, or areas where sewage or grey water needs to be cleaned before being released into rivers. Promising research suggests that lignases can be used to clear lignin from the canes, and further chemical processing can provide liquid fuel from the remaining cellulose, although this is not yet commercially viable.

Food packaging is already being made from Miscanthus and as it is entirely compostable recycling is simplified and landfill reduced. Pellets or briquettes from the canes can be used for burning at home, as fillers for plastic or cement, or hot-pressed into plant pots that decay harmlessly after use. The bales can be used to build well-insulated houses. Miscanthus is also in demand for animal bedding.

Miscanthus mainAs well as a bioenergy crop, Miscanthus is being used in construction, packaging and animal bedding

Research has progressed from the sterile triploid variety grown at the moment to specialised types that could replace grass in upland areas, perhaps an option for farmers looking to diversify as meat consumption falls. These new varieties can be grown from seed making them cheaper and more convenient to sow, but they are still sterile at this latitude. The harvests are of the order of 10 to 15 tonnes per hectare, which gives a good return and is wildlife friendly, which means farming families would be able to replace their livestock with and still make a reasonable living.

Miscanthus is a fast-growing, high-energy crop that grows well in the UK. Here are the seeds to grow a low-carbon economy in the foreseeable future in time to cope with the changes required to limit global warming to 1.5°C.

Leslie-Jane Powell MRSB read zoology and entomology at Imperial College before teaching biology after training at Keele. She is now retired.

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