Interest in renewable energy generation and bio-based products have prompted the use of biomass sources such as annual and perennial crops. Perennial biomass crops such as miscanthus deliver more ecosystem services compared to annual crops. Among perennial crops, miscanthus is particularly distinctive for its high yield and low input requirements, increasing its potential for ecosystem services delivery and as a bioenergy feedstock. Miscanthus can be used for bioenergy production or as animal bedding among other uses. With regards to miscanthus bedding, on-farm cultivation of miscanthus could increase self-sufficiency of livestock farmers and avoid emissions associated with traditional straw bedding production and long-distance supply chains. Meanwhile, there is increasing demand for straw as a source of bioenergy, and there could soon be incentives to incorporate straw into arable soils in order to improve the sustainability of arable cropping systems. Miscanthus use as bedding fibre could therefore be associated with significant indirect effects in arable regions. This research therefore explored the potential of home-grown miscanthus production, capturing indirect effects of miscanthus bedding using a consequential life cycle assessment (CLCA) approach. Chapter 3 evaluated this potential of miscanthus for bioenergy and particularly for bedding by analysing burdens generated from the miscanthus portion of the farm using attributional life cycle assessment (ALCA). Emissions were calculated for miscanthus bedding cultivated on livestock farms without (F0) and with fertilizer (F1), and for miscanthus cultivated on the arable farm with a higher yield and fertilizer (F2) application rate. The economic potential of miscanthus was also analysed for both farm types using NPV models. Analysis was done for only the miscanthus component of the farms. Chapter 4 explored beyond the miscanthus area by evaluating direct and indirect effects of miscanthus bedding production at the livestock farm level. This was performed using a Consequential LCA model to capture livestock emissions, avoided burdens of straw transportation and provision of additional feed to offset pasture and/or animal displacement effects of miscanthus bedding cultivation. Compensation for displaced pasture and/or animals was evaluated via three farmer response decisions: buy extra concentrate feed (D1), utilize remaining pasture areas more efficiently (D2), or buy grass silage (D3). Chapter 5 and 6 further expanded the boundaries to integrate the wider market-induced effects of alternative use of straw for bioenergy and incorporation, respectively. Sensitivity analyses were conducted in both chapters involving D1-D3, F0 and F1, two miscanthus:straw substitution ratios, and two digestible energy (DE%) contents for replaced grass forage. These sensitivity analyses were augmented with scenario permutations around straw bioenergy displacement of electricity generation from natural gas (Ga) or coal (Co) in chapter 5, and analyses around carbon accumulation, subsequent arable crop yield effects of 0%, 6%, 13% following straw incorporation over time horizons of 20, 50, 100 years in chapter 6. The environmental balance potential of miscanthus bedding impacts across agricultural systems (livestock, arable farms) and energy systems was assessed using the following impact categories: global warming potential (GWP), resource depletion potential (RDP), acidification potential (AP) and eutrophication potential (EP). Results showed that miscanthus for bioenergy has lesser GWP, RDP and AP burdens than oil heat, but greater EP burdens if fertilized. Attributional LCA showed unfertilized and fertilized miscanthus bedding to be good alternatives to straw bedding. However, consequential LCA indicated that the environmental outcomes of miscanthus bedding production are likely to be beneficial under scenarios involving D2 and D3, but may be poor under scenarios with D1, because the environmental cost of additional concentrate feed production outweighed the benefits from straw incorporation, or fossil electricity substitution, depending on alternative use of diverted straw.
In conclusion, this PhD study applied consequential LCA in a novel manner to comprehensively account for major direct and indirect environmental effects of homegrown miscanthus bedding production on livestock farms. Novelty centres around LCA of miscanthus bedding, and application of consequential LCA to evaluate important indirect consequences of miscanthus cultivation and straw displacement not captured in previous attributional LCA studies. Results show that the integration of miscanthus bedding in livestock farms can be environmentally beneficial if improved forage management can mitigate for the land required to grow the miscanthus, even before benefits of alternative uses of displaced straw are considered.