Energy crop production in double-cropping systems: Results from an experiment at seven sites

Abstract

Energy crop production for fermentation in biogas plants significantly increased in the last years. At present maize is the most common energy crop for biogas production due to high dry matter and methane yields together with advanced breeding activities. In Germany nearly 80% of all energy crop biogas production is based on maize for silage. This dominance frequently causes environmental risks like soil erosion, nutrient losses and increased use of pesticides. Furthermore it puts societies’ acceptance towards biogas production increasingly at risk. Thus, the development of innovative cropping systems is essential for a sustainable energy crop production.This paper reviews results from 3 years field trials at seven locations with 12 different double-cropping systems (turnip rape, rye and mixture of rye–winterpea as first crops and maize, sorghum, sunflower and mixture of maize–sunflower as succeeding second crops) in comparison with three sole crops systems as references: maize and sunflower after mustard as catch crop and energy rye, harvested at dough ripeness as whole-crop silage.Double-cropping systems with rye or rye–pea as first crop and maize as second crop achieved highest DM yields of 23tDMha−1 on average, followed by sole cropped maize and double-cropping system of turnip rape and maize. Sole-cropped sunflowers had the lowest yield with nearly 15tDMha−1, followed by winter rye harvested at dough ripeness. Yields of other double-cropping systems had an intermediate position between those treatments. Methane yield per hectare was positively correlated with DM yield. Double cropping systems mostly achieved lower DM contents than sole cropping systems due to later sowing and altered photoperiodic influences. Further research on cultivars suitable for late sowing dates is necessary.Methane yield of crops was very similar with 282–298Nlkg−1 oDM, except for sorghum with 255Nlkg−1 oDM on average. Hence, differences in chemical components did not result in large changes regarding to methane yield, again except for sorghum, probably due to higher lignin contents.Double-cropping systems had mostly higher yield stability than sole cropping systems. The cultivation of two crops within 1 year may also spread the risk of weather extremes among two crops (or more if mixtures are grown) resulting in higher yield stability. This property is getting increasingly important with regard to climate change. Hence, double-cropping systems may contribute to a more sustainable energy crop production.