Yield parameters of Beta beets as a basis to estimate the biogas yield

Abstract

High biogas yields are expected from sugar beet because of its high root yield. But it has not been analysed yet, which varieties are best suited to reach the highest biogas yield. The study thus aimed at identifying a parameter to estimate the biogas yield of sugar beet. To get a broad variation of yields and beet qualities, field trials were conducted from 2008 to 2011 at 2 sites (Göttingen and Regensburg, Germany) with different sugar beet varieties and fodder beet. Different N application rates were included and furthermore, autumn sown beets (winter beet). Dry matter composition was analyzed, biogas yield and methane concentration were determined in batch experiments. Sugar beet reached root dry matter yields of more than 20tha–1 and thereby exceeded fodder beet. Moderate N application increased root dry matter yield, whereas higher N rates only enhanced the leaf dry matter yield. But most likely, leaves will not be considered for fermentation because of their low concentration of dry matter and organic dry matter. Winter beet reached total dry matter yields of 12tha–1, but dry matter was not as easily digestible as that of spring sown beets. Biogas yield showed a close linear relation to the root dry matter and the sugar yield as well. Sugar beet varieties can therefore be assessed for anaerobic digestion by their sugar yield. As sugar yield is already the main target, breeding for biogas beets will not be substantially different from that for beets used for sugar manufacture.