Browsing by Subject "Nutrient relocation"

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    Introducing new miscanthus hybrids into the European bioeconomy : the effect of environment and management on biomass quantity and quality
    (2023) Magenau, Elena; Lewandowski, Iris
    Miscanthus has been identified as a promising lignocellulosic perennial biomass crop for temperate climates and different (marginal) soils in terms of yield and ecological benefits. The cultivation of miscanthus brings numerous ecological advantages, such as a reduction in soil erosion, protection of aquatic ecosystems from alteration through eutrophication, and increasing heterogeneity in annual arable landscapes leading to increased biodiversity compared to annual crops. Reasons for this are its perenniality, the long period of time it stands on the field, and its low fertiliser and plant protection demands. Nevertheless, the area under cultivation in Europe is limited. The reasons are that the scientific yield levels are not reached commercially, and the only commercially cultivated hybrid Miscanthus × giganteus (M×g) is sterile. Miscanthus is therefore currently propagated and established via rhizomes, which limits upscaling. However, the seed-based hybrids tested so far do not reach the potential of M×g in terms of yield, quality, and ecological impact under a wide range of climatic conditions. To improve the integration of miscanthus as a biomass crop in the growing European bioeconomy, it is required to reach high and stable yields over several years (security of biomass supply) and a low ecological impact by low nutrient offtakes under different European climates. Therefore, it is essential to gain agronomic knowledge on how genetic (G), location-specific environment (E), and management (M) factors and the interactions between them affect the security of biomass supply and ecosystem services of novel seed-based hybrids. Against this background, the research objectives of this study are: 1) to investigate the effect of the onset of the growing season on biomass supply security and how it is affected by late spring frosts, 2) to assess G × E interaction effects on miscanthus biomass security, and 3) to assess G × E × M interaction effects on nutrient offtake, yield and quality of miscanthus biomass. For this purpose, new seed- and rhizome-based miscanthus hybrids were compared with the commercially grown M×g and evaluated for biomass yield, quality, and nutrient offtakes (a key parameter defining the ecological impact) under different European conditions to determine biomass supply security and ecological effects. The effect of the management parameters cutting height and harvest time was also analysed. The results show that to reach a high biomass supply security, avoiding damage by late spring frosts is essential. An effective mechanism is a low frost sensitiveness of the emerging shoots and to produce new shoots over the whole growth period, as observed for the seed-based M. sinensis × sinensis (M sin×sin). By contrast, a late emergence and producing fewer, thicker but frost-susceptible shoots at the beginning of the growing season, as observed for rhizome-based M×g and rhizome- and seed-based M. sacchariflorus × sinensis (M sac×sin), endangers the biomass supply security in case of frost after emerging. Over the first three years, the establishment process of miscanthus depended on location and hybrid. The M sin×sin hybrids flowered and senesced earlier than the taller M sac×sin hybrids. Active senescence, probably initiated by flowering, increases biomass quality by reducing the moisture and nutrient content. Following the third growing season, the highest yields were recorded at the low-altitude site in northern Italy and the lowest on a industrially damaged marginal land site in northern France. Moisture contents at spring harvest were lowest in Croatia and highest in Wales, United Kingdom. A lower moisture content is highly desirable for transport, storage and most end-use applications. Overall, lower moisture contents at harvest were found in M sin×sin hybrids than in M sac×sin. As expected, delaying the harvest until spring reduced yield and nutrient contents. At lower latitudes, the late-ripening M sac×sin combined high yields with low nutrient contents when harvested in spring. At the most elevated latitude location (Wales), the early-ripening M sin×sin combined high biomass yields with low nutrient offtakes. The M×g clone with intermediate flowering and senescence showed similarly low nutrient contents at all locations. An increased cutting height at spring harvest decreased yields by 270 kg ha-1 (0.83%) with each 1-cm increase in cutting height up to 40 cm. Although whole shoot mineral concentrations were significantly influenced by both hybrid and year interactions, total nutrient contents did not differ significantly from those in the lower basal sections. In years with wet conditions before harvest, an increase in cutting height of 10 cm decreased moisture content by up to 8%, whereas the effect during dry conditions was marginal. To achieve high biomass supply security and increased ecological benefits in miscanthus cultivation, the results of this study lead to the recommendation to cultivate M sin×sin hybrids at locations with a high risk of late spring frosts, as observed in northern European sites, and M sac×sin hybrids at locations where the risk is low, as observed in southern Europe. In southern Europe, M sac×sin hybrids achieved high yields with low nutrient and moisture contents as they made use of the long vegetation period. In general, M sin×sin has a shorter growth period than M sac×sin hybrids, making it the perfect hybrid for northern Europe, where the vegetation period is short. To ensure biomass supply in regions with extreme minimum winter temperatures and late spring frosts, miscanthus should be harvested in spring due to the thicker mulch layer, which functions as insulation. To ensure biomass supply security, a successful establishment is essential. Therefore, during the establishment phase, harvest should generally take place in spring, as the establishment period is crucial for securing biomass yield throughout the cultivation period. Weakening or even loss of plants during this period will lead to higher weed pressure and lower than optimal yields. The harvest cutting height should be as low as possible to achieve a higher yield without an over-proportional increase in nutrient offtake. However, cutting height needs to be adapted according to local conditions by finding an optimum between biomass loss and the risk of damage to harvest machinery and contamination of the biomass by soil. Should the moisture content of the biomass be too high for safe storage due to wet conditions during harvest, the cutting height can be increased to avoid costly post-harvest drying procedures. This study recommends hybrids for specific locations in Europe, provides important data for determining harvest timing and height, and key data on the ecological impact. It shows that the cultivation of miscanthus in Europe, taking into account the G × E × M interactions, has the potential to secure the biomass supply for the growing bioeconomy while positively influencing the provision of ecosystem services. Furthermore, integrating miscanthus into the agricultural system increases its resilience by diversifying the crops grown, the structure of the agricultural landscape and farmers income.
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    The potential of miscanthus as biogas feedstock
    (2020) Kiesel, Andreas; Lewandowski, Iris
    Of all renewable energy forms, biomass accounts for the by far largest proportion of gross inland energy consumption in Europe. As the biogas sector in particular can provide demand-driven electricity generation, energy storage and flexible utilization options including biofuels, it is likely to play an important role in future energy systems in future. In Germany, the largest biogas market in Europe, energy crops provide the highest proportion of biogas input substrates, with maize being the most dominant. The environmental impact of biogas production is mainly attributed to energy crop production, with the risks of maize cultivation being particularly criticized. Perennial biomass crops have the potential to reduce the environmental impact of the biogas sector and miscanthus is an especially promising candidate crop due to its high yields. However, preliminary observations have indicated that the green harvest of miscanthus necessary for biogas production leads to a strong yield depression in the subsequent year. The aim of this thesis was to determine and understand the mechanisms influencing the green-cut tolerance of miscanthus and to assess the potential of different green-harvest regimes for biogas production. Here, ‘green-cut tolerance’ is defined as the crop’s ability to regrow in the year after the green harvest is performed without yield depression. A further aim of this thesis was to investigate the environmental performance of miscanthus-based biogas production and to determine its energy efficiency compared to other utilization options. Field trials were conducted to assess the potential of miscanthus hybrids for biogas production, the green-cut tolerance of Miscanthus x giganteus (Mxg), and how both are influenced by management practices (harvest regime x nitrogen fertilization). A Life-Cycle Assessment was performed to evaluate the environmental impact of biogas production from perennial C4 grasses, including miscanthus, and to assess the optimization potential compared to the standard biogas crop maize. The suitability of miscanthus biomass was investigated for the utilization options bioethanol, biogas and combustion, and the energy efficiency of these was compared based on their net energy yield. The results revealed that Mxg harvested in October showed the highest average biomass yield, the highest methane yield (approx. 6000 m3 methane ha-1) of all harvest regimes, and a higher substrate-specific methane (SMY) yield than for biomass harvested after winter. An earlier green harvest (July, August) improved the SMY, but led to a sharp biomass and thus methane yield decline in the second year and was identified as unsuitable for Mxg. As increased nitrogen fertilization showed no effect on the yield in any of the harvest regimes, it can be disregarded as a management practice for improving green-cut tolerance. Instead, harvest date was found to have a strong influence on green-cut tolerance and sufficient time for relocation of carbohydrates needs to be allowed before a green cut is performed. This finding is crucial for the utilization of miscanthus biomass harvested green and also for the breeding of new varieties with improved green-cut tolerance. Breeding targets for optimized biogas varieties should include to increase the SMY and biomass yield and to widen the possible harvest window. Selecting genotypes that relocate carbohydrates to the rhizomes earlier would allow an earlier green harvest without yield decline the following year, but this may involve a trade-off with the SMY. The suitability of miscanthus for the utilization options assessed was found to be influenced by biomass composition, which in turn was affected by genotype and harvest date. Lignin content had a negative effect on biomass quality for biogas and bioethanol production and increased with later harvest dates. Hemicellulose had a positive effect on biomass quality for bioethanol production through the improvement of the saccharification potential. Low ash, potassium and chloride content enhanced biomass quality for combustion by increasing the ash melting temperatures and decreased with a delay in harvest to after winter. For the biogas and bioethanol utilization pathways, novel miscanthus varieties with low lignin content need to be developed, whereas for combustion varieties with a high lignin content are more favourable. The Life Cycle Assessment revealed that the use of miscanthus has a high potential to reduce the environmental impacts of biogas crop production and thus the biogas sector. Miscanthus had a more favourable performance than the annual biogas crop maize in each impact category considered and the highest reduction potential compared to the fossil reference in the impact categories climate change, fossil fuel depletion and marine eutrophication. The choice of biomass utilization pathway had a considerable effect on the energy yield per unit area, with combustion showing the overall highest energy yield potential for electricity production. However, for the combustion pathway, miscanthus is generally harvested after winter and this is accompanied by biomass yield losses of 35% compared to peak yield. In the biogas pathway, miscanthus can be harvested close to peak yield, leading to an only 10% lower energy yield than that of combustion. When considering the use of miscanthus for biofuel production, the highest area efficiency was found for the direct use of biomethane, followed by battery electric vehicles fuelled by electricity from biomass combustion, and the lowest for the direct use of bioethanol. However, the low conversion efficiency of bioethanol production did not consider energy generation from by-products. In this thesis it was determined that the green-cut tolerance of miscanthus is influenced by the carbohydrate relocation to the rhizomes and thus by harvest date. Miscanthus harvested in October shows a high potential as feedstock for biogas production due to its high yield and sufficient digestibility, can help improve the biogas sector’s environmental performance and contribute to an increase in greenhouse gas mitigation. The digestibility of miscanthus biomass for biogas production could be improved by breeding and selecting genotypes with low lignin contents and by applying suitable pretreatment methods. Increased digestibility could also help to overcome potential trade-offs between early carbohydrate relocation and SMY. The efficiency of biomass utilization greatly depends on the utilization option, with a high efficiency being identified for biomethane as a transportation fuel and for peak-load power generation. It was shown that miscanthus is a suitable crop for the provision of sustainably produced biomass as a feedstock for the growing European bioeconomy that provides additional ecosystem services, e.g. groundwater and surface water protection.