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Biomass crops

Learn about the biomass crops miscanthus, willow and poplar and their potential to capture carbon

Image source: Terravesta

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Miscanthus

Miscanthus, Miscanthus × giganteus, is a fast-growing, rhizomatous C4 grass species that is hardy in temperate climates. With a productive life of 15-20 years, miscanthus grows to 3-4m in height, achieving annual above-ground, dry-matter biomass yields in excess of 15 t/ha, which are typically higher than short-rotation coppice (willow or poplar). In addition to baling or pelleting for bioenergy production, miscanthus can be used in the manufacture of biocomposites or for animal bedding.

Miscanthus is suited to a wide range of soils, and it can be grown on marginal land where soil quality is lower or there is a risk of flooding. Most miscanthus is clonally-propagated, with commercial crops established from rhizomes, leading to relatively high uniformity. Post-planting crop input requirements are low, with few known pests or diseases and little response to nitrogen fertiliser. Its extensive rhizome and root system mean that miscanthus can help to stabilise soils and trap nutrients, reducing erosion risk and protecting water when grown in buffer zones. The crop cover also provides shelter for wildlife, especially over the winter.

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Willow

Willow, Salix spp., is the most common species grown within Short Rotation Coppice (SRC) for bioenergy production. With planting densities of up to 15,000 plants/ha, the crop can be harvested on a 2-5 year cycle and remain productive for up to 30 years. The crop grows vigorously, especially when young, and can reach 6-8m in height between harvests. The plant is then cut back, leaving the stool from which shoots regrow.

 

Willow is suited to a range of soils, including marginal or reclaimed land, but the crop has a high demand for water so may not perform well on sandy soils or in low rainfall areas. There are many willow varieties registered and available commercially in the UK, with northern temperate species best suited to the UK climate. The crop has a low input requirement but responds to nitrogen fertiliser. It is at risk from pests and diseases, the main mitigation for which is choice and mix of varieties, but supports biodiversity, in particular invertebrates and birds.

Poplar, Populus spp., is a group of fast-growing temperate tree species, making them well suited as a bioenergy crop. Poplar can be grown as Short Rotation Coppice (SRC), harvested every 2-5 years and remaining productive for more than 20 years, or as Short Rotation Forestry (SRF), with plants growing by up to 3-5m per year, depending on variety and location, and with a fully mature height of up to 30-50m.

 

Poplar suits most soil types, but grows best on well-drained, fertile loam soils. The crop can be grown on marginal land, and is useful as a windbreak, but waterlogging can be detrimental to some poplar types. For large areas, planting several varieties in separate blocks should be considered. As with willow, poplar can help to reduce erosion and support increased biodiversity, although fencing may be required to protect young trees from rabbits or deer. There are also several insect pests that can damage leaves.

Poplar

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Image source: Energy Crops Consultants

Carbon capture

Biomass crops have the potential to remove significant amounts of CO2 from the atmosphere. Combining the production of bioenergy, from biomass, with carbon capture and storage technologies (BECCS) could in turn achieve net reductions in emissions. For example, one study has shown the potential for miscanthus to absorb the equivalent of 26 tonnes of CO2 per hectare per year, with 3.05 tonnes of CO2 captured in the roots and rhizomes, or net 2.35 tonnes of CO2 per hectare per year after deducting emissions resulting from production and delivery of the biomass. Capturing and storing some of the carbon dioxide released when the biomass is burnt would further increase the net carbon capture.

More information

Miscanthus

Willow

Poplar

Carbon Capture

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