Browsing by Subject "Biogasnutzung"

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    How can miscanthus be integrated most efficiently into agricultural production systems?
    (2019) Mangold, Anja; Lewandowski, Iris
    The demand for biomass is increasing steadily, as fossil resources are gradually being replaced by biomass within the context of a developing bioeconomy. Plant-based feedstocks currently used for this replacement virtually all come from annual crops. However, perennial crops such as miscanthus are expected to be more environmentally benign due to their generally low-input requirements and high yield potential. Despite these advantages, the current cultivation area of miscanthus in Europe is quite low. One reason for this is that the cultivation and utilization of miscanthus faces several challenges. For example, the most common propagation method via rhizomes is very labour-intensive and thus expensive, leading to high establishment costs. Seed propagation is a promising option to reduce costs, but is not suitable for sterile genotypes. Another challenge to be overcome is the problem of re-integrating former miscanthus fields into crop rotations. The crop following miscanthus needs to be highly competitive in order not to be impaired by resprouting miscanthus shoots and thus able to achieve high yields. Additionally, there is only little information available on the effect of miscanthus cultivation and its subsequent removal on soil N content. This information is however crucial, for example to avoid environmental problems being caused by a potential nitrogen leaching after a miscanthus removal. If miscanthus is to be utilized as a biogas substrate, there are further challenges to be overcome. Firstly, the optimal harvest date needs to be defined with regard to the methane hectare yield and resilience of the crop to green cutting. Secondly, as a continuous supply of biomass throughout the year is necessary, ensiling will become a relevant topic. However, information is still required on the optimal harvest date to achieve a sufficient silage quality and the effects of ensiling on methane hectare yield. Finally, the suitability of miscanthus for biogas production is also influenced by biomass quality such as the proportions of leaf and stem. This has already been established for miscanthus utilization in combustion but has not yet been sufficiently investigated for anaerobic digestion. In summary, there are a number of uncertainties involved in miscanthus establishment, removal and utilization, which currently hamper its integration into agricultural production systems. From a bioeconomic point of view, this integration needs to be conducted as efficiently as possible in terms of nutrient-use, environmental and land-use efficiency. The aim of this study was to contribute to the filling of these knowledge gaps. To answer these knowledge gaps, several miscanthus field trials and laboratory experiments were conducted: a novel propagation method was tested; the re-integration of miscanthus fields into a crop rotation was analysed; and the effect of genotype, harvest date and ensiling on the digestibility and methane hectare yield was investigated. The results illustrate some possibilities of improving the nutrient-use, environmental and land-use efficiency of miscanthus biomass production along its supply chain: It was shown that miscanthus propagation via collars is feasible and a promising alternative to rhizome propagation, as the multiplication rate of collars is comparable to that of rhizome propagation. As the harvesting of collars is likely to be less labour-intensive and is less destructive for the mother field than rhizome propagation, this method is more favourable for both economic and ecological reasons. The re-integration of miscanthus into crop rotations revealed maize to be a suitable crop after miscanthus, as it coped with the prevailing soil conditions and suppressed resprouting miscanthus efficiently, resulting in satisfactory yields. The soil mineral nitrogen (Nmin) content was found to increase during the vegetation period following a miscanthus removal, but was generally on a low level (average: 17.3 kg Nmin ha-1). Additionally, it was found that, in Germany, miscanthus should be harvested in mid-October to maximize methane yields and nutrient recycling but minimize yield reduction. In addition, silage quality was best when miscanthus was harvested on this date. As leaf proportion correlated positively with substrate-specific methane yield (SMY) and thus genotypes with a higher leaf proportion were found to have a higher SMY, methane hectare yields could be increased even further by using genotypes with a high leaf proportion. In summary, the approaches developed in this study allow to considerably improve the ecological and economic performance of miscanthus production by increasing nutrient-use,environmental impact and land-use, and thus simplifying implementation into practice.