Water and radiation use efficiency of sugarcane for bioethanol production in South Africa, benchmarked against other selected crops

Abstract

There are indications that high-fibre sugarcane genotypes may produce more biomass and use resources more efficiently than conventional sugarcane cultivars. The objective of this research was to gather quantitative information on resource use for selected conventional and high-fibre sugarcane genotypes and benchmark it against other bioethanol crops. Although conventional sugarcane initially grew slower than sorghum and Napier grass, it produced very high biomass (about 70 t ha⁻¹) and theoretical ethanol (first- and secondgenerations) yields (about 27 kL ha⁻¹) at 12 months, and used water relatively efficiently (about 5 kg m⁻³ and 2 kL m⁻³), out-performing all other crops except sorghum. The contribution of cellulosic ethanol to total ethanol yield varied hugely, from 89% for the high-fibre sugarcane hybrid to about 48% for conventional sugarcane, to as low as 14% for sugar beet. The high-fibre sugarcane hybrid grew faster initially and produced more biomass at eight months (56 t ha⁻¹ vs 45 t ha⁻¹) than the conventional types, but then flowered, reducing its growth rates markedly thereafter. It was also less sensitive to mild drought conditions. The results suggest that cellulosic ethanol production may be a feasible option that could be incorporated into conventional or biomass sugarcane production systems.

Keywords: bioethanol crops, biomass, high-fibre sugarcane, stalk fibre composition, theoretical ethanol yield