School of GeoSciences

School of GeoSciences

Dr Saran Sohi

I was recruited to lead soil science research in the UK Biochar Research Centre, Edinburgh, at its inception in late 2008 ( This is one of three core academic positions in UKBRC which has a strictly multi-disciplinary approach to evaluation of biochar, as a carbon storage technology with ancilliary benefits, both agronomic and socio-economic. The Centre has a team of 20 that includes a number of post-doctoral researchers, a lab manager and research assistants, plus a team of PhD students. Seasonally we host visitors from an extensive international network and a number of MSc and undergraduate reserach projects.

The purpose of my work is to establish a sound understanding of biochar function in soil, providing the predictive capacity required to 'prescribe' biochar in ways that firstly are safe, and secondly offer the best possible results in terms of soil and crop performance in diverse situations. The resolution and certainty of the understanding that we require is driven by the need to add value to biochar products in the agricultural enterprise, and thereby a mechanism to realise societal goals such as carbon storage, management of diffuse pollution and mitigation of trace gas emission from agriculture. My work is inextricably linked to my colleagues leading research into the optimising pyrolysis processes for the conversion of biomass into biochar, estimation of carbon-equivalent gains offered by pyrolysis-biochar systems, and scoping associated socio-economic issues including land-use.

We have established a "toolkit" by which biochar can be screened for five key functional properties in soil. Data gathered by applying these tests to a diverse set of biochar samples provides for optimisation of use under contrasting conditions and socio-economic circumstance. The dynamics of biochar effects on soil as well as their magnitude has been considered, accounting for the contrasting timescales over which different effects may be required. Simultaneously, the nature of the interaction between plant roots and biochar has been examined using mesocosms and triangulation with small scale field studies (in collaboration with Rothamsted Research). With Rothamsted Research I have instigated an isotope-tracer experiment that seeks to establish how biochar affects the stabilisation of carbon derived from exudatio by crop roots.

We are now at the stage where we are beginning to test out our holistic understanding of biochar in the context of what is already known of soil processes - in other words, using the knowledge gained through functional screening of biochar, to select biochar for its particular interactions with cereal crops, perennial grasses, bioenergy crops, etc., in different soil types and environmental conditions. We are in the latter stages of an initial five-year phase where we assess the general potential for biochar in managing waste, energy and crop production. The scale at which biochar can "work" in current and future context, assessed by validation of our current functional understanding of biochar in the field, will determine a second phase.

Soil Science research in UKBRC at the University of Edinburgh currently involves one post-doctoral researchers, one research scientist and a number of PhD students - the students affiliated either with the University of the Scotland's Rural College (SRUC). We link to a large network of national and international collaborators including our UKBRC partners, and guide a number of student research projects at MSc and BSc level.

My research background generally concerns the elucidation of soil organic matter dynamics. Modelling the measured dynamics of key soil physical fractions was the topic of my PhD and eight years post-doctoral work at Rothamsted Research, the BBSRC research institute based in Harpenden, Hertfordshire. Biochar should not be considered a distinct soil science discipline, and I seek to ensure that knowledge and experience gained from study and simulation of other recalcitrant organic matter fractions - and their interaction with more labile components - is not ignored in seeking understanding of biochar function. By way of example, existing understanding of the contrasting dynamics and interaction of soil fractions was used, in combination with simulation and isotope tracers, to assess the effect of charcoal in terra preta soils on the turnover of other soil carbon. This was my introduction to biochar soil science, and a consequence of collaborative research instigated at Cornell University, NY, where I worked in the group of Johannes Lehmann during 2005. This work is progressing towards publication.