Abstract
Planting the perennial biomass crop Miscanthus in the UK could offset 2–13 Mt oil eq. yr−1, contributing up to 10% of current energy use. Policymakers need assurance that upscaling Miscanthus production can be performed sustainably without negatively impacting essential food production or the wider environment. This study reviews a large body of Miscanthus relevant literature into concise summary statements. Perennial Miscanthus has energy output/input ratios 10 times higher (47.3 ± 2.2) than annual crops used for energy (4.7 ± 0.2 to 5.5 ± 0.2), and the total carbon cost of energy production (1.12 g CO2‐C eq. MJ−1) is 20–30 times lower than fossil fuels. Planting on former arable land generally increases soil organic carbon (SOC) with Miscanthus sequestering 0.7–2.2 Mg C4‐C ha−1 yr−1. Cultivation on grassland can cause a disturbance loss of SOC which is likely to be recovered during the lifetime of the crop and is potentially mitigated by fossil fuel offset. N2O emissions can be five times lower under unfertilized Miscanthus than annual crops and up to 100 times lower than intensive pasture. Nitrogen fertilizer is generally unnecessary except in low fertility soils. Herbicide is essential during the establishment years after which natural weed suppression by shading is sufficient. Pesticides are unnecessary. Water‐use efficiency is high (e.g. 5.5–9.2 g aerial DM (kg H2O)−1, but high biomass productivity means increased water demand compared to cereal crops. The perennial nature and belowground biomass improves soil structure, increases water‐holding capacity (up by 100–150 mm), and reduces run‐off and erosion. Overwinter ripening increases landscape structural resources for wildlife. Reduced management intensity promotes earthworm diversity and abundance although poor litter palatability may reduce individual biomass. Chemical leaching into field boundaries is lower than comparable agriculture, improving soil and water habitat quality.
Highlights
The IPCC 5th report (IPCC, 2014) makes clear that it is extremely likely that cumulative anthropogenic greenhouse gas emissions have led to unequivocal climate warming with temperature and precipitation extremes seen since the 1950s that are unprecedented over millennia
This study distils a large body of literature into simple statements around the environmental costs and benefits of producing Miscanthus in the UK, and while there is scope for further research, around hydrology at a commercial scale, biodiversity in older plantations or higher frequency sampling for N2O in land-use transitions to and from Miscanthus, clear indications of environmental sustainability do emerge
Any agricultural production is primarily based on human demand, and there will always be a trade-off between nature and humanity or one benefit and another; the literature suggests that Miscanthus can provide a range of benefits while minimizing environmental harm
Summary
The IPCC 5th report (IPCC, 2014) makes clear that it is extremely likely that cumulative anthropogenic greenhouse gas emissions have led to unequivocal climate warming with temperature and precipitation extremes seen since the 1950s that are unprecedented over millennia. The 2012 UK Bioenergy Strategy (DECC, 2012) suggests that the potential land available for Miscanthus that would not impinge on food production is in the range of 0.72–2.8 Mha which is well above the 2007 target (Fig. 2 puts the 0.35 Mha into context by showing current UK agricultural land use and 5 year trends) These strategy reports stress that while some energy crops may reduce soil erosion, improve biodiversity, and aid fuel security, production must take place ‘. Sample depths varied widely as did management regimes with some sites fertilized and others not Despite this variability, it seems likely that arable land converted to Miscanthus will sequester soil carbon; of the 14 comparisons, 11 showed overall increases in SOC over their total sample depths with suggested accumulation rates ranging from 0.42 to 3.8 Mg C haÀ1 yrÀ1. Net SOC (C3 and C4) accumulation rate since planting (over total sample depth) (Mg C haÀ1 yrÀ1)
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