Recycling biomass waste to enhance future global soil productivity

Supervisors: Gareth Norton, Luke Beesley, Graeme Paton, Rupert Hough

Project Description:

Background: The growth of the renewable energy sector has led to the development and installation of efficient biomass boilers, the feed stock for which is normally virgin biomass, though some facilities accept waste woods, sewage sludges and heterogeneous materials The by-product of this form of energy generation is the solid ash which has a number of very useful applications in agriculture, such as increasing soil pH, and supplying macro and micronutrients, being notably high in P, K, Ca and Mg. As biomass boilers continue to increase in popularity, there is a need to find a sustainable use for the associated end-product and to ensure a reduction in the volume of ash being landfilled, in order to ensure as full use as possible is made of the potential resource value of ashes.

Hypothesis- sustainable soil application of wood ash will serve to reduce bio-energy by-product solids to landfill whilst enhancing agricultural soil performance

Project: The major aim of the project will be to assess the potential use of wood ash as a suitable amendment to agricultural soils. Specifically this will be achieved by;1) developing criteria for the selection of suitable ashes for soil application (ie local availability, chemical properties, ease of handling etc) 2) conducting experimental work with selected ashes to measure their  effect on soil chemical (pH, micronutrient availability and CEC) physical (bulk density and water retention, infiltration) and biological properties (microbial biomass / community composition, soil respiration) as well as their impact on crops (yield and macro and trace element composition). Ashes will also be assessed for potentially toxic substances and their transfer to the edible portion of crops (heavy metals and organic compounds).

Experiments will be conducted using a range of UK crops including wheat, barley, potatoes, biomass crops and grass used for livestock grazing. Experiments will initially be conducted at pot scale at University of Aberdeen glasshouse/environmental controlled facilities and then up-scaled intelligently to field plot trials at the James Hutton Institute’s experimental facilities.

The final stage will 3) create a tool to predict micro-nutrient value (and potentially yield of crops) from empirical chemical analysis of the ash product and the receiving soil. It is anticipated that modelling would be used to assess both beneficial as well as potentially toxic elements, and thus indicate under which circumstances different ashes could be safely applied to soils singly or repeatedly. This stage will make use of the advanced and comprehensive soils database information held at the James Hutton Institute.

Research training value of project: Skills to be developed for the student include: practical glass house and laboratory skills especially in the use of analytical chemistry techniques, field trials, mathematical modelling, quantitative risk assessment; more generic transferable skills such as presentation and writing, teaching and mentoring, and stakeholder interaction.


Gell, K., van Groenigen, J-W., Cayuela, M-L. (2011) Residues of bioenergy production chains as soil amendments: Immediate and temporal phytotoxicity. Journal of Hazardous Material, 186: 2017-2025.

Mollon, L.C., Norton, G.J., Trakal, L., Moreno-Jimenez, E., Elouali, F.Z., Hough, R.L., Beesley, L. (2016) Mobility and toxicity of heavy metal(loid)s arising from contaminated wood ash application to a pasture grassland soil. Environmental Pollution, 218: 419-427.

Saarsalmia, A., Smolandera, A., Kukkolaa, M., Moilanenb,M., Saramäkic, J. (2012) 30-Year effects of wood ash and nitrogen fertilization on soil chemical properties, soil microbial processes and stand growth in a Scots pine stand. Forest Ecology and Management, 278:63–70.