The study was carried out in the Midwest on poorly fertile or degraded set-aside land.
It shows that mixtures of native grasses sequester more carbon in the soil than is used in their production and processing - making their ethanol carbon-negative.
The more diverse the mixture, the more carbon they sequester and the greater the amount of above-ground biomass produced, said researcher Dr Jason Hill of Stanford University. Extrapolation of the team’s results suggests carbon storage will continue for about 100 years.
The team also compared the 28.4 gigajoules per hectare energy yield for ethanol produced from mixed grasses using new technologies that break down cellulose with the 18.8GJ/ha for corn-based ethanol.
But this does not take into account the ethanol that could be produced from the cellulose in other parts of the corn.
These would increase bioethanol production per hectare of corn by 300-600%, according to industry estimates (ENDS Report 382, pp 26-29 ). While not carbon-negative, these yields are likely to appeal more to industry.
Native grasses would also need to prove their worth against miscanthus and coppiced woodland when cellulose-based ethanol production eventually becomes commercially viable in the UK.
Nevertheless, native grasses grown on set-aside land boast other benefits such as providing wildlife habitats, reducing fertiliser and pesticide pollution, and quelling fears about biofuels outcompeting food crops.