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Early impacts of marginal land‐use transition to <i>Miscanthus</i> on soil quality and soil carbon storage across Europe

AbstractMiscanthus, a C4 perennial rhizomatous grass, is a low‐input energy crop suitable for marginal land, which cultivation can improve soil quality and promote soil organic carbon (SOC) sequestration. In this study, four promising Miscanthus hybrids were chosen to evaluate their short‐term potential, in six European marginal sites, to sequester SOC and improve physical, chemical, and biological soil quality in topsoil. Overall, no differences among Miscanthus hybrids were detected in terms of impacts on soil quality and SOC sequestration. SOC sequestration rate after 4 years was of +0.4 Mg C ha−1 year−1, but land‐use transition from former cropland or grassland showed contrasting SOC sequestration trajectories. In unfertilized marginal lands, cultivation of high‐yielding Miscanthus genotypes caused a depletion of K (−216 kg ha−1 year−1), followed by Ca (−56 kg ha−1 year−1), Mg (−102 kg ha−1 year−1) and to a lesser extent of N. On the contrary, the biological turnover of organic matter increased the available P content (+164 kg P2O5 ha−1 year−1). SOC content was identified as the main driver of changes in biological soil quality. High input of labile plant C stimulated an increment of microbial biomass and enzymatic activity. Here, a novel approach was applied to estimate C input to soil from different Miscanthus organs. Despite the high estimated plant C input to soil (0.98 Mg C ha−1 year−1), with significant differences among sites and Miscanthus hybrids, it was not identified as a driver of SOC sequestration. On the contrary, initial SOC and nutrients (N, P) content, as well as their elemental stoichiometric ratios with C, were the key factors controlling SOC dynamics. Introducing Miscanthus on marginal lands impacts positively soil biological quality over the short term, but targeted fertilization plans are needed to secure crop yield over the long term as well as the C sink capacity of this perennial cropping system.

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Hydrothermal carbonization: Sustainable pathways for waste‐to‐energy conversion and biocoal production

AbstractHydrothermal carbonization (HTC) technology emerges as a sustainable method to convert wet biomass, including food waste and municipal solid waste into high‐energy dense biocoal. This process, conducted at temperatures ranging from 180 to 260°C and pressures of 10–50 bar, effectively transforms the organic material in wet biomass into solid, liquid, and gaseous outputs. The solid product, biocoal, possesses a high carbon concentration and heating values on par with lignite coal, presenting a cleaner alternative to traditional fossil fuels. Despite operational commercial‐scale HTC facilities globally, further adoption across various feedstocks can improve waste management and energy production. The process can achieve energy yields up to 80%, particularly at temperatures favoring the generation of secondary char with higher heating values. HTC not only aids in reducing greenhouse gas emissions through carbon sequestration in solid waste but also promotes environmental sustainability by yielding nutrient‐rich by‐products for agriculture. As a versatile and energy‐efficient solution, HTC technology is a pivotal innovation in waste‐to‐energy conversion, addressing the imperative for sustainable waste management. Other supplementary benefits are presented; they include higher employability, reduction of a nation's reliance on imported energy, and better waste control, therefore considering all pillars of sustainability. Future research should focus on optimizing process efficiency and exploring the broader applicability of HTC to various biomass feedstocks, enhancing its role in the global pursuit of sustainable energy solutions.

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Altering plant carbon allocation to stems has distinct effects on rhizosphere soil microbiome assembly, interactions, and potential functions in sorghum

AbstractAltering plant carbon allocation from leaves to stems is key to improve biomass for forage, fuel, and renewable chemicals. The sorghum dry stalk (D) locus controls a quantitative trait for sugar accumulation, with enhanced carbon allocation in the stems of juicy green (dd) sorghum but reduced carbon allocation in that of dry white (DD) sorghum. However, it remains unclear whether altering sorghum sugar accumulation in stem affects below‐ground microbiome. Here we investigated sorghum rhizosphere soil microbiome in near isogenic lines with different magnitude of carbon allocations and accumulation in the stems. Results showed that enhanced carbon accumulation in stems of juicy green sorghum results in stronger selection in rhizosphere microbiome assembly. The rhizosphere soil microbial communities selected in juicy green sorghum tended to be fast‐growing microbial taxa which possessed potential functions that would promote higher potential capacity to use chemically labile carbon sources and potentially result in higher potential decomposition rates. We found the rhizosphere microbes selected by juicy green sorghum form weaker interactions than dry white sorghum. This is the first comprehensive study revealing how the different magnitude of carbon allocations to stems regulates microbial community assembly, microbial interaction, and microbial functions. This study indicates that future plant modification for bioenergy crops should also consider the impacts on belowground microbial community without compromising the sustainability.

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Estimating the energy return on investment of forestry biomass: Impacts of feedstock, production techniques and <scp>post‐processing</scp>

AbstractThe Energy Return On Investment (EROI) is a recognised indicator for assessing the relevance of an energy project in terms of net energy delivered to society. For woody biomass divergences remain on the right methodology to assess the EROI leading to large variations in the published estimates. This article presents an in‐depth discussion about the EROI of woody biomass in three different forms: woodchips, pellets and liquid fuels. The conceptualisation of EROI is further developed to reach a consistent definition for biomass post‐processed fuels. It considers, on top of the external energy investments, the grey energy associated with the energy used to enrich the fuel. With the proposed methodology, all woodchips have an EROI of the same order of magnitude, between 20 and 37, depending on forestry types, operations and machineries. For secondary residues, the first estimate is 170 if, as co‐products, no energy investment is allocated to the forestry operations and transport. On the basis of a mass allocation for forestry operations and transport, the EROI for secondary residues becomes of the same order of magnitude as that for wood chips. Woodchips can be further post‐processed into pellets or liquid fuels. Pellets have an EROI of 4–7 if the heat is externally supplied and 8–23 if internally supplied (self‐consumption of part of the raw material). Liquid fuels derived from primary wood and residues through gasification and Fischer‐Tropsch synthesis have an EROI between 4 and 16. Fuel enhancement with hydrogen (Power &amp; Biomass to Liquids) impacts negatively the EROI due to the low EROI of hydrogen produced from renewable electricity. However, these fuels offer other advantages such as improved carbon efficiency. A correct estimate of EROI for forestry biomass, as proposed in this work, is a necessary dimension in assessing the suitability of a project.

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Enviro‐economic and feasibility analysis of industrial hemp value chain: A systematic literature review

AbstractA recent renaissance of industrial hemp has been driven by a plethora of ecologically amicable products and their profitability. To identify its environment and economic fate across the value chain (VC), this study conducts a systematic review of 98 studies published in ScienceDirect, Web of Science, and Scopus‐indexed journals. The thematic content of the articles is categorized using three deductively derived classification categories: lifecycle analysis (n = 40), VC analysis (n = 30), and feasibility analysis (n = 28). Bibliometric analysis indicates that the majority (&gt;90%) of the studies were conducted in selected regions of Europe or North America, with further findings around regionally prioritized industrial hemp products, such as hempcrete in Southwest Europe, solid biofuel in North European states, and textile fiber and bio‐composites in East Europe and North America. Lifecycle analysis studies highlight nitrogenous fertilizer use during industrial hemp cultivation as a major ecological hotspot, which is taking a toll on the climate change index. However, hemp‐based products are generally climate‐friendly solutions when contrasted against their fossil fuel counterparts, with hempcrete in particular a highly touted carbon‐negative (−4.28 to −36.08 kg CO2 eq/m2) product. The review also identifies key issues within the hemp VC and presents innovative solutions alongside the recognition of value‐adding opportunities. Furthermore, feasibility analysis indicates unprofitability in using hemp for bioenergy production and there is a relative cost worthiness of hemp bio‐composites and hempcrete at the upstream level. Positive returns are observed under co‐production schemes. In contemplating the literature findings, we discussed and identified gap in existing literature for future exploration, including more studies to provide insights from the Global South, and the production of industrial hemp under a biophysically constrained landscape.

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Nitrogen acquisition and retention pathways in sustainable perennial bioenergy grass cropping systems

AbstractPerennial tall grasses show promise as bioenergy crops due to high productivity and efficient nutrient use. Ongoing research on bioenergy grasses seeks to reduce their reliance on synthetic nitrogen (N) fertilizer, the manufacture of which relies on fossil fuel combustion. Excessive use of fertilizers also causes adverse environmental consequences and leads to the evolutionary loss of plant traits beneficial to sustainable N cycle. Notably, perennial tall grasses have exhibited the potential to maintain high biomass yield without the need for N fertilizer or causing soil N depletion. Perennial grasses can be adept at interacting with their microbial partners to facilitate N acquisition and retention via mechanisms such as biological N fixation and nitrification inhibition. These inherent N management traits should be preserved and optimized at the this early stage of bioenergy grass breeding programs. This review examines the impact of external N on bioenergy grass production and explores the potential of leveraging advantageous N‐cycling attributes of perennial tall grasses, laying groundwork for future management and research efforts. With minimized dependency on external N input, the cultivation of perennial energy grasses will pave the way toward more resilient agricultural systems and play a significant role in addressing key global energy and environmental challenges.

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Formulating new types of rice husk biochar‐based fertilizers for the simultaneous slow‐release of nutrients and immobilization of cadmium

AbstractChina, as a significant global consumer of chemical fertilizers and a leading producer of rice, faces challenges associated with low fertilizer efficiency and fewer utilization options of rice husks. The development of rice husk biochar‐based fertilizers (RHBF) offers a strategic solution to address these issues. In this study, diverse biochar fertilizer production techniques were used to develop four types of fertilizers: blended RHBF, soaked RHBF, high‐pressure soaked RHBF, and pure rice husk biochar coated fertilizer. The nutrients slow‐releasing performance of these four RHBF were compared by hydrostatic and soil column intermittent leaching methods. Effects of their application on rice growth, yield, and cadmium reduction potential were analyzed and compared by the pot trial. Results demonstrated that nutrients of the four RHBF were generally released slower in the soil compared with the conventional compound fertilizer (CK). The slow nutrient release effect was more pronounced under high‐pressure soaked RHBF. Notably, in the soil column leaching experiment, the cumulative leaching rates of nitrogen and K2O for RHBF3 (12.0% and 13.9%) were greatly lower than those of CK (42.3% and 51.3%). Moreover, the application of RHBF induced a marked enhancement in the nutrient use efficiency, grain yield, harvest index, and photosynthetic characteristics compared to CK. The average agronomic efficiency of P2O5 for the four RHBF increased by 102.8% compared with CK, while the average grain yield of the four RHBF increased by 20.6%. In addition, RHBF showed a significant reduction in Cd mobilization by an average of 80.1% compared to CK. This study offers a promising model for enhancing the comprehensive performance of RHBF and optimizing traditional fertilizer application practices.

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