Research paperSorghum, a sustainable feedstock for biogas production? Impact of climate, variety and harvesting time on maturity and biomass yield

- Maturity level of 5 sorghum varieties as a function of harvesting date was related.
- Optimal degree of maturity as a function of growing degree days was shown.
- Specific methane yield per hectare is similar to maize.
- Sorghum can be used as catch but also main crop for biogas production.

The experiments comprised three vegetation periods of five sorghum varieties. Novel data on the development of biomass yield, maturity level and biogas production were gained. Dry matter (DM) biomass yield ranged between 15.7 and 20.67 t ha−1 when sorghum was grown as main crop. The variety SOR 4 achieved a methane yield of 6500 m3 ha−1. The suitability of different sorghum varieties as summer catch crops was measured and assessed by combining growing degree days (GDD; temperatures > 10 °C) and maturity stage. This paper introduces a correlation of yields in course of the vegetation period with GDD values which enables to transfer yield and economic efficiency predictions from present results to other sites.Sorghum is able to provide high-yields when used as catch crop, whereby an adapted varietal selection is indispensable. The sorghum variety SOR 2 (year2) of 1100 growing degree days (GDD) proofed to be fast ripening and is especially suitable as a summer catch crop. This variety achieved mean DM yields of 12.4 t ha−1 when used as summer catch crop.Within this study crop maturities between 20 and 45% DM were investigated. Within this range, no decrease in specific methane yield with the increase in maturity and DM yield was observed.The three year experimental data also included one year with low precipitation. The statistical analysis did not reveal a significant influence of the precipitation on the biomass yield which confirms the drought resistance of sorghum. This result is especially important in view of adaptation to climate change.