Enhancing the sustainability of perennial bioenergy crops using companion crops

Biogeochemical Cycles



Companion cropping in rotational agriculture has shown potential for improving sustainability, reducing the need for fertilisers and herbicides, and benefiting soil health and wider ecosystem services. The overarching aim of this project is to explore if these benefits can be transferred to the perennial bioenergy crop Short Rotation Coppice (SRC) willow.

SRC willow is a leading perennial bioenergy crop in temperate regions including the UK (Rowe, Street and Taylor, 2009). SRC is a low input, fast growing crop with above-ground biomass coppiced on a 3-5 year cycle and a life span of >25 years. Large scale expansion of this crop expected as part of the UKs plan to tackle the climate emergency (Committee on Climate Change, 2019) but the agronomic understanding of the crop is limited leaving significant scope for improving sustainability. Recent studies in similar perennial crops have demonstrated that companion cropping, with nitrogen (N) fixing species, can reduce weed competition and the need for herbicides, replace N fertiliser and contribute to soil carbon storage (Warwick et al., in press; Guenon et al., 2016; Nabel et al., 2018). These results are exciting, with potential to reduce the carbon footprint and economic costs of SRC crop expansion. However, further evidence on the benefits of companion cropping is urgently needed.

In this PhD you will explore the impacts of companion cropping on SRC willow yield and the underlying mechanisms. Focusing on changes in soil physico-chemical and biological properties (microbes and soil fauna), and weed suppression. This will be linked to a wider assessment of the economic and environmental implications. There will also be an opportunity to explore co-production of grazing animals in SRC plantations, with low density sheep grazing in mature SRC plantations already being trialled by the PhD projects commercial partner (Iggesund), the leading UK Company in SRC development. This holistic approach gives the opportunity to link novel research in plant-soil interactions with strategies to tackle climate change.

Click on an image to expand

Image Captions

Sheep grazing in a SRC willow plantation


This project will explore three questions:
1) Does companion cropping improve the environmental sustainability of SRC willow by improving soil C storage, soil health and diversity?
2) Does companion cropping improve SRC economic viability by reducing the need for fertiliser and herbicides?
3) Does companion cropping increase the multifunctional use of SRC by providing improved fodder resources for sheep?

Building on existing collaborations with Iggesund Paperboard, the UK leader in SRC willow cultivation, the student will undertake field trials of companion planting incorporating N fixing species in established and new commercial SRC plantations. The student will be able to select trial locations from Iggesund’s extensive network of plantations (>150) allowing them to explore cover crop performance under a range of crop ages, soil types and abiotic conditions.

The student will undertake an initial identification and in-field screening process to select the best performing cover crops from a range of candidate species, assessing establishment, survival rates, weed suppression and influence of SRC yields.

Following this the student will be encouraged to utilise the best performing cover crop species (2-3) to develop their own field and lab experiments to explore the mechanisms linking companion crops and impacts on willow performance as well as fodder crop provision. There will be opportunities to investigate impacts on N and C cycling, soil biodiversity (fauna and microbial), soil structure, SRC N uptake and utilisation and forage quality.

Additional data from Iggesund on costs of SRC production and management will also enable cost benefit and a cost minimization analysis to be performed, assessing both companion crop implementation and potential to reduce herbicide and fertiliser cost. There will also be opportunity to expand this analysis to incorporate the valuation of natural capital and ecosystems services.

Project Timeline

Year 1

Literature review and selection of candidate companion crop species. Development of method for initial screening of candidate species, selection of trial locations. In-house training in plant and biogeochemical analyses at CEH Lancaster.

Establishment and monitoring candidate screening trial; including measurements of productivity, establishment, weed suppression, SRC yield indicators

Year 2

Selection of and assessment of most promising candidate species, Undertaking investigation of the mechanisms by which companion planting affects SRC yield and soil health/sustainability and fodder provisioning.

Apply for travel grant to attend a UK conference e.g. Supergen Bioenergy Hub Conference

Year 3

Completion of field trials and data analysis.
Undertake economic and environmental sustainability assessments drawing on field trial data and input from industrial partner Iggesund

Year 3.5

Completion of economic and environmental sustainability assessment
Thesis write up and submission.
Presentation at international conference e.g. European Biomass Conference and Exhibition

& Skills

A comprehensive training programme will be provided by CEH and the IAPETUS DTP programme, providing both specialist scientific training and generic transferable and professional skills (including: career planning and enhancing employability, presentation skills, learning and teaching in higher education, analysis and presentation of data, thesis and scientific writing skills, statistical analysis). The student will also receive in-house training at CEH Lancaster in plant-soil biogeochemical analyses (e.g. N Ionic exchange resin) and measures of soil microbial activity (e.g. extracellular enzyme activity) and soil health (e.g. soil aggregation and fauna diversity assessments).

The student will be encouraged to attend project specific postgraduate training through NERC advanced training courses and will also be eligible to join the Supergen Bioenergy Hub ECR network (SHARE). SHARE provides access to bursaries for travel, training workshops and networking opportunities designed to help ECR working within bioenergy to developed interdisciplinary skills and knowledge of the bioenergy field.

The student will spend 4 weeks internship with industrial supervisor Neil Watkins the alternative fuels manager for Iggesund Paper Mill in Workington. Neil is responsible for sourcing the 50,000 tonnes of sustainable UK willow biomass per year required by Iggesund onsite biomass heat and power plant. His work covers grower recruitment, media, crop management, agronomic development, economic and biomass sustainability and supply. This internship will therefore provide the student with unique experience and knowledge of all aspects of the industrial use of bioenergy crops

References & further reading

Committee on Climate Change (2019) Net Zero The UK’s contribution to stopping global warming. Available at: file:///C:/Users/rebrow/Downloads/Net-Zero-The-UKs-contribution-to-stopping-global-warming.pdf.

Guénon, R. et al. (2016) ‘Carbon and nutrient dynamics in short-rotation coppice of poplar and willow in a converted marginal land, a case study in central France’, Nutrient Cycling in Agroecosystems.

Humpenöder, F. et al. (2018) ‘Large-scale bioenergy production: how to resolve sustainability trade-offs?’, Environmental Research Letters., 13(2), p. 024011.

Nabel, M. et al. (2018) ‘Legume Intercropping with the Bioenergy Crop Sida hermaphrodita on Marginal Soil’, Frontiers in Plant Science. Frontiers, 9, p. 905. doi: 10.3389/fpls.2018.00905.

Rowe, R. L. et al. (2016) ‘Initial soil C and land-use history determine soil C sequestration under perennial bioenergy crops’, GCB Bioenergy, 8(6), pp. 1046–1060. doi:.

Rowe, R. L., Street, N. R. and Taylor, G. (2009) ‘Identifying potential environmental impacts of large-scale deployment of dedicated bioenergy crops in the UK’, Renewable and Sustainable Energy Reviews, 13(1), pp. 271–290.

Warwick, K. et al. (no date) ‘Biomass and integrated forage/biomass yields of switchgrass as affected by intercropped cool-and warm-season legumes’, Journal soil and water conservation ,71(1)

Iggesund : www.biofuel.iggesund.co.uk

Further Information

Dr. Rebecca Rowe
Centre for Ecology & Hydrology
Library Avenue
T: 01524 595983

Apply Now