Listen: Sustainable cellulosic biofuels: A soils-centric perspective

At the 2018 Professor GW Leeper Memorial Lecture, Professor G. Philip Robertson from Michigan State University explored the sustainability promise of switchgrass as both a biofuel and a carbon sink.

Switchgrass is an abundant native plant of the central North American tallgrass prairie, with a notable ability to produce moderate to high yields on marginal farmland. It is cultivated for soil conservation, forage production, ornamental ground cover, sequestration of atmospheric carbon dioxide and as a crop for cellulosic biofuels like ethanol and butanol.

switch grass
Switchgrass is one of several promising cellulosic biofuel species that can provide high yields and greenhouse gas mitigation. Photo: Kurt Stepnitz, Michigan State University via Science.

Scientists have explored switchgrass as a renewable bioenergy crop since the 1980s. Professor Robertson has been one of the leading figures in this research and in the 2018 Leeper lecture, he explored its potential from a number of perspectives:

  • To improve US energy independence through use as a biofuel
  • As climate mitigation, both in the form of avoided CO2 emissions as a substitute for petroleum, and for its negative emissions contribution through bioenergy carbon capture and storage
  • Its contribution to North American biodiversity.

Professor Robertson is University Distinguished Professor of Ecosystem Ecology in the Department of Plant, Soil and Microbial Sciences at Michigan State University. He is currently science director for the US Department of Energy’s Great Lakes Bioenergy Research Center, and from 1988-2016 he directed the US National Science Foundation’s Long-Term Ecological Research (LTER) Program in Agricultural Ecology.

You can listen to the 2018 Leeper Lecture below; Professor Robertson’s slides are available here.

While switchgrass’ benefits are clearest in its native North American environment, Professor Robertson concluded that it and other cellulosic biofuels are central to almost all climate mitigation pathways with a reasonable certainty of limiting the global temperature increase to 1.5 °C by 2100.

“Petroleum use related to transportation is responsible for about 34 per cent of the total greenhouse gas footprint in the US, and so clearly [when building] a decarbonised economy it’s crucial to bring the transportation sector into alignment,” he said.

“Avoiding CO2 emissions is one aspect of this, but there’s also the aspect of negative emissions [via carbon sequestered in the perennial crops], which is a bit of a sleeper issue.”

But Professor Robertson also warned that their benefits are not guaranteed, as prior and future land use could limit the benefits of switchgrass and other biofuels. Replacing food and animal feed crops with biofuels may lead farmers to produce these elsewhere and excessive fertilisation or the replacement of existing carbon storage with biofuel crops could result in a net increase in greenhouse gas emissions. Choosing the most appropriate crop for the environment is also crucial.

      Professor delivering a lecture
Professor Robertson said biofuels planted on marginal agricultural land could deliver climate mitigation

Professor Robertson identified marginal land – privately held nonurban land which is not used for cropping or grazing and is not forest or wetland – as the areas with the most unambiguous sustainability benefit: US legislation mandates the production of 136 billion litres of ethanol biofuel by 2022, and Professor Robertson said switchgrass production on half of available marginal land in 10 US states could meet approximately 25 per cent of this requirement.

The Leeper Lecture concluded the Faculty of Veterinary and Agricultural Sciences’ Research Week 2018, which saw staff and outside experts deliver seminars and public events celebrating and progressing research in the Faculty.

The lecture is an annual public lecture hosted by the Victorian branch of Soil Science Australia and is part of the Faculty of Veterinary and Agricultural Sciences’ Dean’s Lecture Series.

Geoffrey Winthrop Leeper (1903-1986) was an agricultural chemist with a lifelong interest in soils. He joined the University of Melbourne’s School of Agriculture in 1933 and was promoted to professor in 1962.

As an academic, he was known for his insistence on academic rigour and accuracy, his appreciation of plain language and rational thinking and his contributions to teaching, particularly in soil science and inorganic chemistry. He is immortalised in a gargoyle statue at the University’s Trinity College, where he was born and resided during his studies.

Story and images by Stuart Winthrope. Banner image: Around 75 people attended the 2018 Leeper Lecture including leaders and staff in the Faculty of Veterinary and Agricultural Sciences, members of the Victorian branch of Soil Science Australia, students and members of the public.