A growing bioeconomy requires increasing amounts of biomass from residues, wastes, and industrial crops for bio‐based products and bioenergy. There is much discussion about how industrial crop ...cultivation could promote social–ecological outcomes such as environmental protection, biodiversity conservation, climate change adaptation, food security, greenhouse gas mitigation, and landscape appearance. In Germany, maize (Zea mays L.) is the main biogas substrate source, despite being associated with problems such as erosion, biodiversity losses, an increase in wild boar populations and lowered landscape diversity. The cultivation of perennial wild plant mixtures (WPM) addresses many of these problems. Despite being less developed than maize, WPM cultivation has received notable attention among scientists in Germany over the past decade. This is mainly because WPMs clearly outperform maize in social–ecological measures, despite their methane yield performance. This review summarizes and discusses the results of 12 years of research and practice with WPMs as a social‐ecologically more benign bioenergy cropping system.
Perennial wild plant mixtures contain annual, biennial, and perennial wild plant species and can be grown for over five years. They provide numerous ecosystem services including biomass for renewable energy, environmental protection, biodiversity conservation, carbon storage, and landscape improvement. This makes perennial wild plant mixtures a promising biomass cropping system for a transition to a social‐ecologically more sustainable bioeconomy.
The growing bioeconomy will require a greater supply of biomass in the future for both bioenergy and bio-based products. Today, many bioenergy cropping systems (BCS) are suboptimal due to either ...social-ecological threats or technical limitations. In addition, the competition for land between bioenergy-crop cultivation, food-crop cultivation, and biodiversity conservation is expected to increase as a result of both continuous world population growth and expected severe climate change effects. This study investigates how BCS can become more social-ecologically sustainable in future. It brings together expert opinions from the fields of agronomy, economics, meteorology, and geography. Potential solutions to the following five main requirements for a more holistically sustainable supply of biomass are summarized: (i) bioenergy-crop cultivation should provide a beneficial social-ecological contribution, such as an increase in both biodiversity and landscape aesthetics, (ii) bioenergy crops should be cultivated on marginal agricultural land so as not to compete with food-crop production, (iii) BCS need to be resilient in the face of projected severe climate change effects, (iv) BCS should foster rural development and support the vast number of small-scale family farmers, managing about 80% of agricultural land and natural resources globally, and (v) bioenergy-crop cultivation must be planned and implemented systematically, using holistic approaches. Further research activities and policy incentives should not only consider the economic potential of bioenergy-crop cultivation, but also aspects of biodiversity, soil fertility, and climate change adaptation specific to site conditions and the given social context. This will help to adapt existing agricultural systems in a changing world and foster the development of a more social-ecologically sustainable bioeconomy.
Biofuel production from crop residues is widely recognized as an essential component of developing a bioeconomy, but the removal of crop residues still raises many questions about the sustainability ...of the cropping system. Therefore, this study reviews the sustainability effects of crop residues removal for biofuel production in terms of crop production, soil health and greenhouse gas emissions. Most studies found little evidence that residue management had long‐term impacts on grain yield unless the available water is limited. In years when water was not limiting, corn and wheat removal rates ≥90% produced similar or greater grain yield than no removal in most studies. Conversely, when water was limiting, corn grain yield decreased up to 21% with stover removal ≥90% in some studies. Changes in soil organic fractions and nutrients depended largely on the amount of residue returned, soil depth and texture, slope and tillage. Reductions in organic fractions occurred primarily with complete stover removal, in the top 15–30 cm in fine‐textured soils. Soil erosion, water runoff and leaching of nutrients such as total nitrogen (N) and extractable soil potassium decreased when no more than 30% of crop residues were removed. Stover management effects on soil bulk density varied considerably depending on soil layer, and residue and tillage management, with removal rates of less than 50% helping to maintain the soil aggregate stability. Reductions in CO2 and N2O fluxes typically occurred following complete residue removal. The use of wheat straw typically increased CH4 emissions, and above or equal to 8 Mg/ha wheat straw led to the largest CO2 and N2O emissions, regardless of N rates. Before using crop residues for biofuel production, it should therefore always be checked whether neutral to positive sustainability effects can be maintained under the site‐specific conditions.
Biofuel production from crop residues is widely recognized as an essential component of developing a bioeconomy, but the removal of crop residues still raises many questions about the overall sustainability of the cropping system. Before using crop residues for biofuel production, it should therefore always be checked whether neutral to positive sustainability effects can be maintained under the site‐specific conditions.
The cultivation of perennial wild plant mixtures (WPMs) is becoming increasingly important in Germany for providing sustainably produced bioenergy. However, perennial energy cropping systems always ...raise the question of how to reclaim the land for arable crops. This study examined this issue by looking at how a former WPM area was returned to arable cropping for an organic farm. From 2013 to 2018, the WPM area was harvested annually in the autumn. From 2019 to 2020, it was co-managed with the surrounding land as a semi-intensive grassland under a three-cut regime. The area was then ploughed in the spring of 2021 to grow silage maize. Weeds were controlled mechanically once. Nevertheless, the perennial wild plant species grew vigorously, with common tansy (Tanacetum vulgare L.) standing out with a total fresh matter share of 29.0%. This maize–WPM mixture achieved a dry matter yield of 15.5 ± 5.5 Mg ha−1, which was notably but not significantly (p < 0.05) lower than that of silage maize growing next to the former WPM area (23.4 ± 5.5 Mg ha−1). After silage maize, winter wheat was sown in the autumn of 2021 and further regrowth of common tansy was observed in the spring of 2022. Yield and quality effects must therefore be given special consideration in the first arable crop following WPM cultivation.
Giant reed (GR) and reed canary grass (RCG) have emerged as promising perennial industrial crops for providing sustainable bioenergy from marginal land. However, there is great uncertainty among ...farmers and researchers about where these crops can be grown in the future due to climate change, which complicates a timely transition to a bioeconomy. Therefore, this study quantifies marginal land and suitable cropping areas for GR and RCG in Europe, as well as their overlap. To derive these areas, the present (1991–2020) and future (2071–2100, RCP8.5) growing degree days, growing season length, annual precipitation, and aridity index were analyzed using the E‐OBS observational dataset and EURO‐CORDEX regional climate simulations. The study concludes that while marginal land will decrease by ~18%, GR and RCG will profit from the changing European climate, increasing by ~24% and ~13%, respectively. Looking at regions of overlap between marginal land and the selected crops, a decrease of ~87% and an increase of ~462% is projected for RCG and GR, respectively. This is due to marginal land shifting southward, benefitting the warm‐season grass GR, while RCG prefers cooler climates.
Giant reed and reed canary grass have emerged as promising perennial industrial crops for providing sustainable bioenergy from marginal land. However, there is great uncertainty about where these crops can be grown in the future due to climate change. Therefore, this study quantifies marginal land, climatologically suitable cropping areas for the two crops, and the overlap between these regions in Europe at the end of the century under a climate change scenario. The provided framework can be used to examine European marginal land's suitability for other promising bioenergy crops, thereby fostering the EU's growing bioeconomy, while simultaneously reducing land competition.
Lignocellulosic biomass from marginal land is needed for a social–ecologically sustainable bioeconomy transition. However, how much biomass can be expected? This study addresses this question by ...reviewing the limitations of current biomass yield modeling for lignocellulosic crops on marginal land and deriving recommendations to overcome these limitations. It was found that on the input side of biomass yield models, geographically limited research and the lack of universally understood definitions impose challenges on data collection. The unrecognized complexity of marginal land, the use of generic crop growth models together with data from small-scale field trials and limited resolution further reduce the comparability of modeling results. On the output side of yield models, the resistance of modeled yields to future variations is highly limited by the missing incorporation of the risk of land use changes and climatic change. Moreover, several limitations come with the translation of modeled yields into bioenergy yields: the non-specification of conversion factors, a lack of conversion capacities, feedstock yield–quality tradeoffs, as well as slow progress in breeding and the difficulty of sustainability criteria integration into models. Intensified political support and enhancement of research on a broad range of issues might increase the consistency of future yield modeling.
The cultivation of perennial wild plant mixtures (WPMs) in biogas cropping systems dominated by maize (Zea mays L.) restores numerous ecosystem functions and improves both spatial and temporal ...agrobiodiversity. In addition, the colorful appearance of WPM can help enhance landscape beauty. However, their methane yield per hectare (MYH) varies greatly and amounts to only about 50% that of maize. This study aimed at decreasing MYH variability and increasing accumulated MYH of WPM by optimizing the establishment method. A field trial was established in southwest Germany in 2014, and is still running. It tested the effects of three WPM establishment procedures (E1: alone without maize, in May, E2: undersown in cover crop maize in May, E3: WPM sown after whole‐crop harvest of spring barley Hordeum vulgare L. in June) on both MYH and species diversity of two WPMs S1, S2). Mono‐cropped maize and cup plant (Silphium perfoliatum L.) were used as reference crops. Of the WPM treatments tested, S2E2 achieved the highest (19,296 mN3/ha, 60.5% of maize) and S1E1 the lowest accumulated MYH (8,156 mN3/ha, 25.6% of maize) in the years 2014–2018. Cup plant yielded slightly higher than S2E2 (19,968 mN3/ha, 62.6% of maize). In 2014, the WPM sown under maize did not significantly affect the cover crop performance. From 2015 onward, E1 and E2 had comparable average annual MYH and average annual number of WPM species. With a similar accumulated MYH but significantly higher number of species (3.5–10.2), WPM S2E2 outperformed cup plant. Overall, the long‐term MYH performance of WPM cultivation for biogas production can be significantly improved by undersowing with maize as cover crop. This improved establishment method could help facilitate the implementation of WPM cultivation for biogas production and thus reduce the trade‐off between bioenergy and biodiversity.
The cultivation of perennial wild plant mixtures (WPMs) as biogas substrate combines the production of biomass with the provision of ecosystem services. However, the methane yield per hectare (MYH) is low compared to other biogas crops such as maize and cup plant. In this study, a 5 year field trial investigated the effect of different WPM establishment procedures on the long‐term MYH. While the establishment after spring barley failed, the establishment under maize (a) significantly increased the long‐term MYH of WPM, (b) reduced the risk of establishment failures, and (c) maintained the species diversity from the second year onward.
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