Energy to burn

by Amanda Holder (a PhD student at Aberystwyth University working on the multi-centre MAGLUE research programme)

As I have spent a lot of time over the past two years crawling around a field not far from the offices at Pwllpeiran I thought it would be a good idea to explain that there was a purpose to it!  It was all in an effort to record soil emissions of the greenhouse gas nitrous oxide emitted during the period of land preparation and planting of a new crop of Miscanthus (of course, why else!).

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Field work selfie!

In order to combat climate change there is a need to reduce emissions of greenhouse gasses such as carbon dioxide, nitrous oxide and methane into the atmosphere. Producing energy from plants to reduce the use of traditional fuels such as coal and gas can help to do this.  Miscanthus is a tall perennial grass, similar in appearance to bamboo, which can grow up to 3 metres in one growing season. Harvested annually its rapid growth makes it good for use as a biofuel (being burned to produce electricity).

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Miscanthus growing in plots at Pwllpeiran

As with all plants Miscanthus absorbs carbon dioxide from the air during growth.  However, it is important that the full greenhouse gas implications of converting land to Miscanthus are understood. This is where I come in.

The period of land use change can be considered a ‘hotspot’ for release of greenhouse gasses from the soil due to the  disturbance involved.  To investigate the extent of soil nitrous oxide fluxes during the establishment of Miscanthus a set of 12 trial plots were set up at Pwllpeiran.  Two types of Miscanthus (the commercially available variety and a new hybrid) were planted using different reduced tillage methods, with some plots retained as sheep grazed pasture for comparison. Minimum tillage (soil cultivated to a shallow plough depth before planting) and no tillage (Miscanthus planted in slots cut into the ground) methods were used for the commercial variety, and the new hybrid was planted with minimum tillage under a film mulch layer.

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The new Miscanthus hybrid being planted.

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The plots set up and testing soil emissions when grazed grassland is converted to Miscanthus.

To record the soil nitrous oxide emissions the hard work started before planting began, with samples taken before any intervention, and then continuing until the plants were 18 months old. To do this, in each plot, a circular plastic ‘collar’ was inserted into ground and then every two weeks a lid was clamped to the collar creating an air tight chamber.

A few spare chamber lids were stored in the field and proved to be popular with local wildlife …

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Field vole nest, latrine, and escape hole made underneath a spare chamber lid that was stored in the field.

…but don’t worry the vole kept his home for the year as the spares lids weren’t needed!

Samples of air were taken from inside the chamber through a rubber seal using a syringe. These were taken at 15 minute intervals over the period of one hour. The samples were then taken to the Centre for Ecology & Hydrology at Lancaster (a partner in the project) where they were analysed for levels of nitrous oxide.

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Gas chromatography machine used to analyse the samples of air taken from inside the sealed chambers.

In the end the study was more than worth burning up some of my own energy!  The results obtained can be used to help balance the pros and cons of land use change to Miscanthus.  It was found that soil nitrous oxide emissions from the cultivated plots were higher than the uncultivated sheep pasture, but levels were similar to those for when a grass ley is reseeded. There was no difference between the cultivation methods tested, or the type of Miscanthus. Work with mature crops of Miscanthus had already shown that their fluxes are very similar to pasture.  When specific emissions related to the cultivation ‘hotspot’ are put into the context of the 15-20 year crop life time the impact is small and overall greenhouse gas balances for using Miscanthus are less than for coal or natural gas.

If you’d like to know more you can read the full paper on the study here.

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