ARCHIVE: Fertiliser Manual (RB209)

Biomass Crops

In the UK two crops are being grown commercially specifically for biomass for use as a source of energy – willow (Salix spp) grown as short-rotation coppice (SRC) and Miscanthus (elephant grass, normally Miscanthus x giganteous). Other possible biomass crops such as switchgrass and poplar have only been grown in the UK under experimental conditions.

In addition to these dedicated biomass crops, some normal agricultural crops are also grown for energy purposes: these include wheat grain and sugar beet, both for bioethanol, and oilseed rape for biodiesel. Fertiliser requirement for these crops, if grown for energy use, is covered under the individual crops. Various agricultural by-products may be used for energy generation, such as incineration of cereal straw for electricity generation or anaerobic digestion of animal slurry for biogas generation.

One of the main reasons for growing crops for energy production is to replace some usage of fossil fuels and thus decrease greenhouse gas (GHG) emissions. Thus it is logical to ensure that GHG emissions associated with growing energy crops, directly or indirectly, are kept to a minimum. Nitrogen fertilisers lead to large emissions of GHGs – carbon dioxide (CO2) and nitrous oxide (N2O) during manufacture and additional N2O when applied to soil. N2O is a particularly powerful GHG, each molecule having the same greenhouse-warming potential a about 300 molecules of CO2. In total, the manufacture and use of each tonne of nitrogen-fertiliser is equivalent to at least 5 tonne CO2-equivalent. So it is important to consider the environmental effects of nitrogen fertiliser applications when growing crops for energy.

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