Ranking Yield of Energy Crops: A Meta-Analysis Using Direct and Indirect Comparisons.

Energy crop yields vary between species, but no global study has been carried out to rank energy crops on the basis of existing yield data. We carried out a systematic literature review, and extracted 856 yield data from 28 published papers for 36 energy crop species. A statistical analysis, based on direct and indirect comparisons, was performed to compare the mean yield values of the energy crops included in the database. For direct comparisons, the difference between crops grown at the same site-years was determined, whereas indirect comparisons involved an assessment of the differences between crops grown at different site-years (making use of a third reference crop grown at the same site-years as the crops to be compared). Overall, direct and indirect comparisons generated similar energy crop rankings. Miscanthus x giganteus was significantly more productive than most of the other energy crops included in our database. Arundo donax and Pennisetum purpureum were significantly more productive than Miscanthus x giganteus, but both were studied in a limited number of sites. By contrast, Erianthus, Phragmites australis, Phalaris arundinacea, Miscanthus sacchariflorus and Miscanthus sinensis were the least productive energy crop. Our database was also used to develop a Bayesian statistical model which predicts yields of energy crops using location-specific measurements. The practical value of this model was illustrated in a case study.