Circular Biomass Valorization for Ireland’s Horticulture: Land-Use Linked GIS Projection and Multivariate Screening for Peat-Alternative Growing Media

Ireland’s peat-reduction policy and circular bioeconomy initiatives are increasing the demand for peat‑alternative growing media and creating a timely opportunity to recover value from underutilised, regionally dispersed biomass. This study asked how Ireland can prioritise locally available biomass and processing routes for peat substitution by integrating spatial supply evidence with substrate-relevant performance screening.

County-level availability of less-accessible bioresources (soft rush, bracken, gorse, and nettles) was projected from land-use data's mathematical models and mapped using Geographic Information Systems (GIS) to identify regional “hotspots” for targeted sourcing. In parallel, candidate growing‑media constituents: willow, bracken, and cereal straws (barley, wheat, oat, and rye) were characterised in raw/chipped/shredded and milled forms for bulk density (BD), moisture, pH, electrical conductivity (EC), and particle size distribution (PSD).

The PSD fractions were treated as compositional data using a centered log‑ratio (CLR) and integrated with the other variables via principal component analysis (PCA), yielding interpretable clustering that separate processing-driven physical properties from feedstock-driven chemical constraints. GIS results show uneven regional biomass potential, concentrated in western and southern counties, supporting regional-based circular bioeconomy interventions. Multivariate results demonstrate that mechanical processing (especially milling) dominates physical behaviour by shifting material toward fine fractions and increasing BD, while pH and EC differentiate feedstocks chemically. Bracken remains a consistent outlier with relatively high EC and low pH, indicating that conditioning/pre-treatment is necessary before application.

The GIS-based bioresource assessment with multivariate decision workflow links “where biomass is” with “how it behaves” while correctly handling compositional particle-size data. The results suggest that policy and investment should not only target biomass recovery regions but also enable fit-for-purpose preprocessing infrastructure and quality control. This integrated approach reduces risk in peat-substitution for soilless horticulture, accelerates shortlisting of feedstock–process combinations for pilot trials, and provides evidence for techno-economic assessment and circular resource recovery planning in Ireland.