Potential Bioenergy Crop Research Articles

Potential of Miscanthus × giganteus as fuel in a suspended furnace

ABSTRACT Miscanthus is one of the potential bioenergy crops in the world. This non-woody biomass can grow almost anywhere and does not require high cultivation costs. Its energy content is approximately 525 GJ/ha/year, the highest among other non-woody biomass. This research aims to study the potency of Miscanthus × giganteus as fuel in a suspended furnace. Some combustion characteristics of Miscanthus particles were determined experimentally and numerically. At a 40°C/min heating rate, the particle's initial and active decomposition temperatures are 197 and 352°C, respectively. The study also reveals that the combustion mode of the Miscanthus particles was affected by the furnace temperature. At furnace temperatures of 300–400°C, the combustion mode of the Miscanthus particles refers to the simultaneous combustion model. While, at temperatures 450–600°C, its combustion produces extensive flames and is called the sequential combustion model. The extensive flames are useful in cyclone furnaces to maintain combustion stability. Under cold modelling, the average drag time of the representative particles with an equivalent diameter of 1384 µm, in a typical furnace, is 26.82 s, much higher than its combustion time of 11.25 s. This indicates that the particles can be burned out in a suspended state.

Recent advances in the processing of Napier grass (Pennisetum purpureum Schumach) as a potential bioenergy crop for bioethanol production

Pennisetum purpureum is an easily cultivated fast-growing perennial grass with great potential as a bioenergy crop due to its high biomass production. Recent advancements in the processing of P. purpureum for the generation of bioethanol are highlighted in this review paper. Various pretreatment methods, namely, enzymatic, acid, and alkaline pretreatment have been investigated to enhance the efficiency of cellulose hydrolysis, which is a crucial step in bioethanol production. Moreover, genetic engineering approaches for enhancing the biomass yield and reducing the lignin are being discussed in this review. The production of bioethanol can be increased by several fermentation processes, including saccharification, separated hydrolysis, simultaneous saccharification, and fermentation. This comprehensive review explores recent advancements in bioethanol production, encompassing technological innovations, diversification of feedstock sources, genetic engineering methodologies, inventive pretreatment techniques, refinements in enzymatic hydrolysis, and enhancements in fermentation, ultimately highlighting the potential of P. purpureum as a sustainable bioethanol source while addressing the challenges and opportunities in its commercial-scale production.

Changes in soil pore structure generated by the root systems of maize, sorghum and switchgrass affect in situ N2O emissions and bacterial denitrification

AbstractDue to the heterogeneous nature of soil pore structure, processes such as nitrification and denitrification can occur simultaneously at microscopic levels, making prediction of small-scale nitrous oxide (N2O) emissions in the field notoriously difficult. We assessed N2O+N2 emissions from soils under maize (Zea mays L.), switchgrass (Panicum virgatum L.), and energy sorghum (Sorghum bicolor L.), three potential bioenergy crops in order to identify the importance of different N2O sources to microsite production, and relate N2O source differences to crop-associated differences in pore structure formation. The combination of isotopic surveys of N2O in the field during one growing season and X-ray computed tomography (CT) enabled us to link results from isotopic mappings to soil structural properties. Further, our methodology allowed us to evaluate the potential for in situ N2O suppression by biological nitrification inhibition (BNI) in energy sorghum. Our results demonstrated that the fraction of N2O originating from bacterial denitrification and reduction of N2O to N2 is largely determined by the volume of particulate organic matter occluded within the soil matrix and the anaerobic soil volume. Bacterial denitrification was greater in switchgrass than in the annual crops, related to changes in pore structure caused by the coarse root system. This led to high N-loses through N2 emissions in the switchgrass system throughout the season a novel finding given the lack of data in the literature for total denitrification. Isotopic mapping indicated no differences in N2O-fluxes or their source processes between maize and energy sorghum that could be associated with the release of BNI by the investigated sorghum variety. The results of this research show how differences in soil pore structures among cropping systems can determine both N2O production via denitrification and total denitrification N losses in situ.

A comprehensive study of essential properties of Conocarpus Erectus as a potential bioenergy crop

A comprehensive study of essential properties of Conocarpus Erectus as a potential bioenergy crop

Biofuel production, study & characterisation from macro-algae (Azolla pinnata)

The demands for energy and the scarcity in fossil fuel are constantly increasing. This has resulted in the search for sustainable, renewable, and low cost biofuel that has triggered the search for potential bioenergy crops. Aquatic plants that can grow rapidly with minimum resources and can produce biomass in bulk amounts are driving the attention of scientists and researchers throughout the world. The production of biofuels from such organic materials and waste components can result in developing of sustainable alternative that will not only be beneficial to the environment but also to public health. In this study, one such aquatic macro algae Azolla pinnata proved to be potential source for biofuel production. The evaluation of its growth was done and trans-esterification of Azolla pinnata lipid was carried out to produce biofuel. The species have a unique combination of physical, chemical and nutrients composition that makes it a boon to mankind. This macro algae was subjected to series of laboratory testing and evaluation for its characterization such as acid value test, trans-esterification, fatty acid methyl esters (FAMEs) test, gas chromatography which showed the feasibility of algal based biofuel. The comparison of properties of extracted biofuel (physicochemical) from Azollla pinnta was done with standardized ASTM D6751 values. The outcome of produced biofuel was very close to conventional fuel.

Genotyping by sequencing-based linkage map construction and identification of quantitative trait loci for yield-related traits and oil content in Jatropha (Jatropha curcas L.).

Jatropha (Jatropha curcas L.) has been considered as a potential bioenergy crop and its genetic improvement is essential for higher seed yield and oil content which has been hampered due to lack of desirable molecular markers. An F2 population was created using an intraspecific cross involving a Central American line RJCA9 and an Asiatic species RJCS-9 to develop a dense genetic map and for Quantitative trait loci (QTL) identification. The genotyping-by-sequencing (GBS) approach was used to genotype the mapping population of 136 F2 individuals along with the two parental lines for classification of the genotypes based on single nucleotide polymorphism (SNPs). NextSeq 2500 sequencing technology provided a total of 517.23million clean reads, with an average of ~ 3.8million reads per sample. We analysed 411 SNP markers and developed 11 linkage groups. The total length of the genetic map was 4092.3cM with an average marker interval of 10.04cM. We have identified a total of 83 QTLs for various yield and oil content governing traits. The percentage of phenotypic variation (PV) was found to be in the range of 8.81 to 65.31%, and a QTL showed the maximum PV of 65.3% for a total seed number on the 6th linkage group (LG). The QTLs detected in this study for various phenotypic traits will lay down the path for marker-assisted breeding in the future and cloning of genes that are responsible for phenotypic variation.

Bioenergy Crops as a Promising Alternative to Fossil Fuels in Louisiana: A Geographic Information System (GIS) Perspective

Rising greenhouse gas emissions are causing climate change, and the world’s focus has shifted to the need to reduce our reliance on fossil fuels. There has been a rise in the published literature on the utilization of crops for bioenergy production in Louisiana. However, very few scholarly documents have used Geographic Information Systems (GIS) to map the distribution of potential bioenergy crops in Louisiana. This study seeks to fill the void by evaluating the potential of bioenergy crops in Louisiana for energy production using GIS. Given this objective, the agricultural census data for 1999, 2009, 2019, and 2020 obtained from the U.S. Department of Agriculture were used in the analysis. The quantities of various crops produced in the state were loaded into an attribute table and joined to a shapefile using ArcGIS software. The symbology tool’s graduated option was used to create five maps representing each of the bioenergy crops in Louisiana. The findings of the GIS analysis show that some of the parishes, such as Franklin produced the most bushels of corn (13,795,416), Iberia produced the most tons of sugarcane (1,697,980), East Carroll produced the most bushels of soybean (8,237,991), Tensas harvested the most bales of cotton (80,898) and Avoyelles produced the most bushels of sorghum (630,694). The abundance and availability of crops as raw materials for energy production will translate into lower prices in terms of energy use, making bioenergy crops a promising alternative to fossil fuels. In addition, gasoline price data from 1993-2022 was obtained from U.S. Energy Information Administration. A regression model for the average annual gasoline price over the years was constructed. The results show that the average annual gasoline price variation with respect to years is statistically significant (p 0.05). This suggests that gasoline prices will generally rise despite a price drop over the years. The paper concludes by outlining policy recommendations in the form of assessing the availability and viability of other crop types, such as wheat, oats, and rice, for energy production in the state.

Assessment of Drought Tolerance of Miscanthus Genotypes through Dry-Down Treatment and Fixed-Soil-Moisture-Content Techniques

Miscanthus, a high-yielding, warm-season C4 grass, shows promise as a potential bioenergy crop in temperate regions. However, drought may restrain productivity of most genotypes. In this study, total 29 Miscanthus genotypes of East-Asian origin were screened for drought tolerance with two methods, a dry-down treatment in two locations and a system where soil moisture content (SMC) was maintained at fixed levels using an automatic irrigation system in one location. One genotype, Miscanthus sinensis PMS-285, showed relatively high drought-tolerance capacity under moderate drought stress. Miscanthus sinensis PMS-285, aligned with the M. sinensis ‘Yangtze-Qinling’ genetic cluster, had relatively high principal component analysis ranking values in both two locations experiments, Hokkaido University and Brigham Young University. Genotypes derived from the ‘Yangtze-Qinling’ genetic cluster showed relatively greater photosynthetic performance than other genetic clusters, suggesting germplasm from this group could be a potential source of drought-tolerant plant material. Diploid genotypes showed stronger drought tolerance than tetraploid genotypes, suggesting ploidy could be an influential factor for this trait. Of the two methods, the dry-down treatment appears more suitable for selecting drought-tolerant genotypes given that it reflects water-stress conditions in the field. However, the fixed-SMC experiment may be good for understanding the physiological responses of plants to relatively constant water-stress levels.

Integrative Effects of Treated Wastewater and Synthetic Fertilizers on Productivity, Energy Characteristics, and Elements Uptake of Potential Energy Crops in an Arid Agro-Ecosystem

Using wastewater in agriculture is a desirable alternative source of irrigation and is gaining attraction worldwide. Therefore, this study was designed to assess the effect of treated municipal wastewater (TWW) and groundwater (GW), along with half and full doses of the recommended NPK dose on the plant growth, total biomass, gross energy, and macro- and trace element content and uptake of safflower (Carthamus tinctorius L.), canola (Brassica napus L.), and triticale (X Triticosecale Wittmack) grown in old and virgin soil as potential bioenergy crops. The results showed that crops planted in old or virgin soil irrigated with TWW had higher values of plant height, leaf area per plant, total chlorophyll content, total biomass, and gross and net energy contents compared to those irrigated with GW grown in virgin soil. Similarly, crops grown in old soil irrigated with TWW showed higher concentrations in dry matter and uptake for both macronutrients (N, P, and K) and trace elements (B, Zn, Mn, Cu, Cd, Pb, and Ni) compared to those planted in virgin soil and irrigated with GW. Furthermore, the application of the recommended half dose of NPK in old and virgin soil irrigated with TWW showed occasionally comparable results to that of a full recommended dose of NPK for most of the measured parameters. Importantly, the recommended half dose applied to old soil irrigated with TWW resulted in a significant improvement in all measured parameters compared to virgin soil irrigated with GW, along with a full recommended dose of NPK. Briefly, TWW can be used to irrigate crops grown for bioenergy purposes, since it did not pose any harmful effect for energy crops. In addition, it provides additional nutrients to soil and thus decreases the required rate of synthetic fertilizer by up to 50% without any significant decreases in the final production of crops.

Impacts of Long- and Short-Term of Irrigation with Treated Wastewater and Synthetic Fertilizers on the Growth, Biomass, Heavy Metal Content, and Energy Traits of Three Potential Bioenergy Crops in Arid Regions

The availability of suitable water is an important factor for increasing the cultivated areas and sustainability in arid (i.e., less than 200 mm precipitation per year) and semiarid regions (i.e., 200–700 mm precipitation per year). Therefore, this study aimed to analyze the impact of treated wastewater (TWW) and groundwater (GW) as well as synthetic fertilizers (50% and 100% of the recommended NPK dose; 150–150–60 kg N–P2O5–K2O ha−1) on the growth, biomass, energy traits, and macro and trace elements of maize (Zea mays L.), sorghum (Sorghum bicolor L.), and pearl millet (Pennisetum glaucum L) grown in old cultivated (first location; L1) and virgin soil (L2 and L3) as potential bioenergy crops. The soil in L1 has been irrigated with treated wastewater for the last 15 years and continued to be irrigated with treated wastewater in this investigation. The virgin soil was divided into two parts: the first part was irrigated with TWW, and the second part was irrigated with GW. The experiments were laid out in a split-plot with a randomized complete block design with water treatments (TWW in old and virgin soil, and GW in virgin soil) in main plots, and the two treatments of fertilization (50% and 100% of the recommended NPK dose) were distributed randomly in subplots. Compared with the crops irrigated with GW, the crops irrigated with TWW, whether grown on old or virgin soil, showed higher plant height, total chlorophyll content, leaf area per plant, total biomass, energy content, and gross energy with low ash. They also contained higher (but lower than permissible limits) concentrations of macro-elements (NPK) and trace elements (Fe, Mn, Cu, Zn, Cd, Pb, Ni, and Co). In addition, the application of a 50% recommended dose of NPK with TWW showed equivalent results to a 100% recommended dose of NPK on all measured parameters with few exceptions. In conclusion, the TWW can be used to irrigate field crops allocated for bioenergy production in arid regions because it does not harm the plants and environment. In addition, the 50% recommended dose of NPK fertilizer exerted no negative effects on the growth and energy production of field crops, thereby protecting the environment and reducing the leaching of excessive fertilizers into GW.

Changes in phenotype and gene expression under lead stress revealed key genetic responses to lead tolerance in Medicago sativa L.

Lead (Pb) is a serious heavy metal soil pollutant. It can be absorbed and accumulated by plant roots and impact plant growth. Medicago sativa L. (alfalfa) is a low-input forage and potential bioenergy crop, and improving its yield and quality has always been a focus of the alfalfa breeding industry. Little is known about the mechanism by which alfalfa responds to Pb stress at the molecular level. In this study, three alfalfa genotypes (a lead-resistant type (LR), a lead-sensitive type (LS) and an intermediate type (IN)) with contrasting abilities to resist lead were exposed to different durations of Pb treatment. Next-generation sequencing (NGS)-based RNA-seq technology was employed to characterize the root transcriptomes of three genotypes of alfalfa and identify differentially expressed genes (DEGs) during Pb stress. Genotypes LR and LS displayed different mechanisms of tolerance. In LR, the accumulation of more resistant substances was induced by the upregulation of sucrose synthase, glucan endo-1,3-beta-glucosidase, beta-amylase 3, probable trehalose-phosphate phosphatase J, 6-phosphofructo-2-kinase delta-1-pyrroline-5-carboxylate synthase (P5CS) and δ-ornithine aminotransferase (δ-OAT). In addition, flavin monooxygenase (YUCCA), 4-coumarate:CoA ligase-like protein (4CL), cinnamoyl-CoA reductase-like protein (CCR), ferulate 5-hydroxylase (F5H) and caffeic acid O-methyltransferase (COMT) were upregulated, leading to root development in a short time under Pb stress. Further study of the expression levels of metal transport-related genes, such as NRAMP (metal transporter), MATE (multidrug and toxin extrusion), HIPPs (heavy metal-associated isoprenylated plant proteins), MTP (metal tolerance protein), and ABC transporter, suggested that these genes were differentially expressed after lead treatment in the three alfalfa genotypes. Our research provides useful information for further studies on the molecular mechanism of Pb resistance in Medicago sativa L.

Intraspecific Variability in Root Traits and Edaphic Conditions Influence Soil Microbiomes Across 12 Switchgrass Cultivars

Microbial communities help plants access nutrients and tolerate stress. Some microbiomes are specific to plant genotypes and, therefore, may contribute to intraspecific differences in plant growth and be a promising target for plant breeding. Switchgrass (Panicum virgatum) is a potential bioenergy crop with broad variation in yields and environmental responses; recent studies suggest that associations with distinct microbiomes may contribute to variation in cultivar yields. We used a common garden experiment to investigate variation in 12 mature switchgrass cultivar soil microbiomes and, furthermore, to examine how root traits and soil conditions influence microbiome structure. We found that average root diameter varied up to 33% among cultivars and that the cultivars also associated with distinct soil microbiomes. Cultivar had a larger effect on the soil bacterial than fungal community but both were strongly influenced by soil properties. Root traits had a weaker effect on microbiome structure but root length contributed to variation in the fungal community. Unlike the soil communities, the root bacterial communities did not group by cultivar, based on a subset of samples. Microbial biomass carbon and nitrogen and the abundance of several dominant bacterial phyla varied between ecotypes but overall the differences in soil microbiomes were greater among cultivars than between ecotypes. Our findings show that there is not one soil microbiome that applies to all switchgrass cultivars, or even to each ecotype. These subtle but significant differences in root traits, microbial biomass, and the abundance of certain soil bacteria could explain differences in cultivar yields and environmental responses.

Variability in structural carbohydrates, lipid composition, and cellulosic sugar production from industrial hemp varieties

The aim of this study was to determine carbohydrate recovery from hemp for ethanol production and quantify biodiesel from TAG (Triacylglycerol) present in hemp. The structural composition of five different hemp varieties (Seward County-SC, York County-YC, Loup County-LC, 19 m96136-19 m, and CBD Hemp-CBD) were analyzed. Concentration of glucan and xylan ranged between 32.63 to 44.52% and 10.62 to 15.48% respectively. The biomass was then pretreated with Liquid hot water followed by disk milling and then hydrolyzed enzymatically to yield monomeric sugars. High glucose (63-85%) and xylose (73-88%) recovery was achieved. Lipids were extracted from hemp using hexane and isopropanol and then transesterified to produce biodiesel. Approximately, 50% of total fatty acids in SC, LC, and CBD hemp were linoleic acid. Palmitic acid was present between 32 to 50% in varieties YC and 19 m. Highest TAG concentration at 25% of total lipids was observed in CBD hemp. The analysis on lipid composition and high sugar recovery demonstrates hemp as a potential bioenergy crop for ethanol and biodiesel coproduction.

Development of a Prebiotic Oligosaccharide Rich Functional Beverage from Sweet Sorghum Stalk Biomass

Sweet sorghum with sugar-rich stalks is considered a potential bioenergy crop. In this study, the sucrose in stalk juice was transformed into oligosaccharides by employing microbial and enzymatic methods. The maximum oligosaccharide yield of 10–14 g L−1 was obtained from 20 g L−1 sucrose in the sweet sorghum juice, representing conversion of about 82%–87% sucrose. The caloric value of the modified sweet sorghum juice was reduced by more than 50%. The probiotic bacteria exhibited a noteworthy growth profile in the modified sweet sorghum juice enriched with the non-digestible oligosaccharides. The antioxidative properties of the sweet sorghum stalk juice were not altered in the bioprocessed juice. The modified juice did not show any significant change in sensory properties after sucrose to oligosaccharide transformation. Furthermore, the oligosaccharides in the juice exhibited tolerance to heat exposure and, therefore, is feasible for food processing applications. The results suggested sweet sorghum as low-cost biomass for the development of plant-based functional products.

Effects of bioenergy on biodiversity arising from land-use change and crop type.

Understanding how the world's flora and fauna will respond to bioenergy expansion is critical. This issue is particularly pronounced considering bioenergy's potential role as a driver of land-use change, the variety of production crops being considered and currently used for biomass, and the diversity of ecosystems that can potentially supply land for bioenergy across the planet. We conducted 2 global meta-analyses to determine how 8 of the most commonly used bioenergy crops may affect site-level biodiversity. One search was directed at finding data on biodiversity in different production land uses and the other at extracting energy-yield estimates of potential bioenergy crops. We used linear mixed-effect models to test whether effects on biodiversity varied with different individual bioenergy crop species, estimated energy yield, first- or second-generation crops, type of reference ecosystem considered, and magnitude of vertical change in habitat structure between any given crop and the reference ecosystem. Species diversity and abundance were generally lower in crops considered for bioenergy relative to the natural ecosystems they may replace. First-generation crops, derived from oils, sugars, and starches, tended to have greater effects than second-generation crops, derived from lignocellulose, woody crops, or residues. Crop yield had nonlinear effects on abundance and, to a lesser extent, overall biodiversity; biodiversity effects were driven by negative yield effects for birds but not other taxa. Our results emphasize that replacing natural ecosystems with bioenergy crops across the planet will largely be detrimental for biodiversity, with first generation and high-yield crops having the strongest negative effects. We argue that meeting energy goals with bioenergy using existing marginal lands or biomass extraction within existing production landscapes may provide more biodiversity-friendly alternatives than conversion of natural ecosystems for biofuel production.

Molecular Mechanisms of the Floral Biology of Jatropha curcas: Opportunities and Challenges as an Energy Crop.

Fossil fuel sources are a limited resource and could eventually be depleted. Biofuels have emerged as a renewable alternative to fossil fuels. Jatropha has grown in significance as a potential bioenergy crop due to its high content of seed oil. However, Jatropha’s lack of high-yielding seed genotypes limits its potential use for biofuel production. The main cause of lower seed yield is the low female to male flower ratio (1:25–10), which affects the total amount of seeds produced per plant. Here, we review the genetic factors responsible for floral transitions, floral organ development, and regulated gene products in Jatropha. We also summarize potential gene targets to increase seed production and discuss challenges ahead.

Nitrous oxide emissions associated with ammonia-oxidizing bacteria abundance in fields of switchgrass with and without intercropped alfalfa.

The nitrogen (N) fertilizer required to supply a bioenergy industry with sufficient feedstocks is associated with adverse environmental impacts, including loss of oxidized reactive nitrogen through leaching and the production of the greenhouse gas nitrous oxide (N2 O). We examined effects on crop yield, N fate and the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to conventional fertilizer application or intercropping with N-fixing alfalfa, for N delivery to switchgrass (Panicum virgatum), a potential bioenergy crop. Replicated field plots in Prosser, WA, were sampled over two seasons for reactive nitrogen, N2 O gas emissions, and bacterial and archaeal ammonia monooxygenase gene (amoA) counts. Intercropping with alfalfa (70:30, switchgrass:alfalfa) resulted in reduced dry matter yields compared to fertilized plots, but three times lower N2 O fluxes (≤ 4 g N2 O-N ha-1 d-1 ) than fertilized plots (12.5 g N2 O-N ha-1 d-1 ). In the fertilized switchgrass plots, AOA abundance was greater than AOB abundance, but only AOB abundance was positively correlated with N2 O emissions, implicating AOB as the major producer of N2 O emissions. A life cycle analysis of N2 O emissions suggested the greenhouse gas emissions from cellulosic ethanol produced from switchgrass intercropped with alfalfa cultivation would be 94% lower than emissions from equivalent gasoline usage.

Assessment of Suitability of Tree Species for Bioenergy Production on Burned and Degraded Peatlands in Central Kalimantan, Indonesia

Large areas of deforested and degraded land, particularly degraded peatlands, need a viable long-term solution for restoration, ideally one that ensures energy security without compromising food security or biodiversity conversation. To address a knowledge gap on the most adaptive bioenergy crop(s) for degraded lands, this research project assessed the survival and growth performance of potential bioenergy crops to restore burned and degraded peatlands. Our methodology compared the bioenergy species with the potential to survive in extreme environments, i.e., gamal [Gliricidia sepium (Jacq.) Walp.], kaliandra (Calliandra calothyrsus Meissner), kemiri sunan [Reutealis trisperma (Blanco) Airy Shaw], and nyamplung (Calophyllum inophyllum L.). Observed parameters are plant survival rates, tree height, and circular stem growth. The experiment was conducted between March 2016 to February 2017 in a two-hectare demonstration plot on burned and degraded peatland in Buntoi village, Pulang Pisau, Central Kalimantan province. Using a split plot design, two treatments were given to each species, i.e., monoculture plantation and agroforestry (intercropped with Ananas comosus (L.) Merr.); with each treatment, the species were replicated on two separate plots. Results indicate that nyamplung is the most adoptable species followed by kemiri sunan, however both species performed very well under agroforestry treatment when compared with monoculture. Further study is needed to assess the productivity and associate biofuel yield.

Miscanthus, switchgrass, giant reed, and bulbous canary grass as potential bioenergy crops in a semi-arid Mediterranean environment

Perennial grasses have received particular attention as bioenergy crops in recent years due to their high biomass productivity and environmental benefits. The objective of the present study was to compare four perennial grasses: miscanthus (Miscanthus x giganteus Keng), switchgrass (Panicum virgatum L.), giant reed (Arundo donax L.), and bulbous canary grass (Phalaris aquatica L.) in terms of biomass yield, energy balance, and biomass quality under four nitrogen fertilization rates (0, 100, 150, 200 kg ha–1y–1) and 2 harvest times (autumn, winter) over three growing seasons in the Mediterranean environment of Turkey. The crop biomass and net energy yields were optimized with none or 100 kg ha–1 y–1 N input in the study. Although the winter harvest resulted in significant yield reductions in all of the grass species, it improved the biomass quality of miscanthus, switchgrass, and giant reed due to reduced moisture and ash contents. On the contrary, the autumn harvest resulted in a considerably lower moisture and ash contents in bulbous canary grass, mainly because of leaf defoliation the during summer dormancy period. Giant reed produced the highest average biomass yield (between 12.86 and 36.78 t ha–1) over the three years, followed by miscanthus (between 12.75 and 23.54 t ha–1), switchgrass (between 11.88 and 18.91 t ha–1), and bulbous canary grass (between 5.21 and 10.83 t ha–1). On the other hand, bulbous canary grass provided the highest average energy ratio (19.7–64.5) over the three years, due mainly to a lack of energy input for irrigation. These results suggest that satisfactory biomass production can be achievable from miscanthus, switchgrass, and giant reed in the semi-arid Mediterranean environment under adequate moist conditions, but the irrigation requirement increases the energy cost, thus decreasing the energy ratio. In this respect, bulbous canary grass may be evaluated as an alternative bioenergy crop in the dry marginal lands of Mediterranean for sustainable biomass production.

The impacts of four potential bioenergy crops on soil carbon dynamics as shown by biomarker analyses and DRIFT spectroscopy

AbstractPerennial bioenergy crops accumulate carbon (C) in soils through minimally disturbing management practices and large root inputs, but the mechanisms of microbial control over C dynamics under bioenergy crops have not been clarified. Root‐derived C inputs affect both soil microbial contribution to and degradation of soil organic matter resulting in differing soil organic carbon (SOC) concentrations, storage, and stabilities under different vegetation regimes. Here, we measured biomarker amino sugars and neutral sugars and used diffuse reflectance mid‐infrared Fourier transform spectroscopy (DRIFTS) to explore microbial C contributions, degradation ability, and SOC stability, respectively, under four potential bioenergy crops, M.×giganteus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), a mixed prairie, and a maize (Zea mays L.)–maize–soybean (Glycine max(L.) Merr.) (MMS) rotation over six growing seasons. Our results showed that SOC concentration (g/kg) increased by 10.6% in mixed prairie over the duration of this experiment and SOC storage (Mg/ha) increased by 17.0% and 15.6% in switchgrass and mixed prairie, respectively. Conversion of row crops to perennial grasses maintained SOC stability and increased bacterial residue contribution to SOC in M.×giganteus and switchgrass by 20.0% and 15.0%, respectively, after 6 years. Degradation of microbe‐derived labile SOC was increased in M.×giganteus, and degradation of both labile and stable SOC increased in MMS rotation. These results demonstrate that microbial communities under perennial grasses maintained SOC quality, while SOC quantity increased under switchgrass and mixed prairie. Annual MMS rotation displayed decreases in aspects of SOC quality without changes in SOC quantity. These findings have implications for understanding microbial control over soil C quantity and quality under land‐use shift from annual to perennial bioenergy cropping systems.