Philip Stack

PhD Title

Potential for carbon sequestration in upland grassland soils

PhD Supervisors

Dr Joanna Cloy, Prof Bryan Griffiths, Dr John Holland, Dr Oliver Knox (SRUC) & Dr Saran Sohi (University of Edinburgh)


This SRUC-funded project aims to investigate carbon and nitrogen cycling in Scottish upland grazed grassland soils at two sites: Boghall Glen in the Pentland hills and Kirkton farm in the southern Highlands. Rough upland grassland accounts for a large proportion of Scotland’s agricultural land area (60%) and has relevance to national greenhouse gas (GHG) inventories due to the large quantity of carbon stored in its soils and the methane and nitrous oxide (N2O) emissions associated with its current primary land use, the grazing of domestic ruminant livestock.

To investigate the effects of changes in vegetation and manure deposition on soil organic carbon cycling in these soils, a natural abundance 13C tracer in the form of dung from sheep fed exclusively maize has been applied to intact soil cores subject to various vegetation treatments. Maize, a subtropical grass, photosynthesises via the C4 pathway imbuing its biomass with a 13C isotope ratio distinct from that of native British flora, and permitting its use here as a natural abundance tracer. Cohorts of these soil cores will be periodically destructively sampled and changes in the quantity and isotopic ratio of distinct soil organic carbon fractions over time used to follow the incorporation of the 13C tracer into the soil.

Agricultural grasslands are a major source of N2O, a large portion of which is derived from the deposition of animal excreta at pasture. The IPCC guidelines for calculating inventories suggest using a default N2O emission factor of 1% for dung and urine deposited onto pasture. I am currently carrying out a field experiment to investigate the appropriateness of this emission factor for the soils and climate encountered in the Scottish uplands. Static gas chambers have been deployed in a randomised block design at semi-improved grassland fields at the Boghall and Kirkton sites since spring 2015. Chambers in each block have been treated randomly with sheep dung, synthetic sheep urine, a combination of both or have been left as unamended controls. Sampling of soil gas flux and key soil parameters has been carried out since treatment application to enable calculation of an excreta emission factor for these sites and investigate variations in nitrous oxide flux.

Research Interests

Agricultural greenhouse gas emissions; soil carbon and nitrogen cycling; the use of stable isotope tracers to elucidate soil biochemical cycles; sustainable use of the Scottish uplands

Qualifications and past experience 

  • 2013, Research assistant in the University of Edinburgh on topics relating to changes in soil carbon stocks.
  • 2011-2012, Junior researcher in the VU University Amsterdam Development of isotope fractionation – reactive transport models to describe isotope fractionation during chloroethene degradation in groundwater
  • M.Sc. (with distinction) in Environmental Engineering (Queens University Belfast)
  • B.Sc. (1st class Hons) in Environmental Science (University College Cork)


Stack P. & Rock L., 2011, A δ34S isoscape of total sulphur in soils across Northern Ireland, Applied Geochemistry 26, 1478–1487

Philip Stack

PhD Student

Address: Crop & Soils Systems, Scotland’s Rural College (SRUC), Peter Wilson Building, Kings Buildings, West Mains Road, Edinburgh EH9 3JG.

Telephone: 01315354326