Showing papers in "Gcb Bioenergy in 2013"

Biochar and its effects on plant productivity and nutrient cycling: a meta‐analysis

Abstract: Biochar is a carbon-rich coproduct resulting from pyrolyzing biomass. When applied to the soil it resists decomposition, effectively sequestering the applied carbon and mitigating anthropogenic CO2 emissions. Other promoted benefits of biochar application to soil include increased plant productivity and reduced nutrient leaching. However, the effects of biochar are variable and it remains unclear if recent enthusiasm can be justified. We evaluate ecosystem responses to biochar application with a meta-analysis of 371 independent studies culled from 114 published manuscripts. We find that despite variability introduced by soil and climate, the addition of biochar to soils resulted, on average, in increased aboveground productivity, crop yield, soil microbial biomass, rhizobia nodulation, plant K tissue concentration, soil phosphorus (P), soil potassium (K), total soil nitrogen (N), and total soil carbon (C) compared with control conditions. Soil pH also tended to increase, becoming less acidic, following the addition of biochar. Variables that showed no significant mean response to biochar included belowground productivity, the ratio of aboveground : belowground biomass, mycorrhizal colonization of roots, plant tissue N, and soil P concentration, and soil inorganic N. Additional analyses found no detectable relationship between the amount of biochar added and aboveground productivity. Our results provide the first quantitative review of the effects of biochar on multiple ecosystem functions and the central tendencies suggest that biochar holds promise in being a win-win-win solution to energy, carbon storage, and ecosystem function. However, biochar's impacts on a fourth component, the downstream nontarget environments, remain unknown and present a critical research gap.

Production and characterization of slow pyrolysis biochar: influence of feedstock type and pyrolysis conditions

Abstract: Biochar was produced by fixed-bed slow pyrolysis from various feedstock biomasses under a range of process conditions. Feedstocks used were pine wood, wheat straw, green waste and dried algae. Process conditions varied were the highest treatment temperature (HTT) and residence time. The produced chars were characterized by proximate analysis, CHN-elemental analysis, pH in solution, bomb calorimetry for higher heating value, N2 adsorption for BET surface area and two biological degradation assays (oxygen demand, carbon mineralization in soil). In proximate analysis, it was found that the fixed carbon content (expressed in wt% of dry and ash-free biochar) in the biochar samples strongly depended on the intensity of the thermal treatment (i.e. higher temperatures and longer residence times in the pyrolysis process). The actual yield in fixed carbon (i.e. the biochar fixed carbon content expressed as wt% of the dry and ash-free original feedstock biomass weight) was practically insensitive to the highest treatment temperature or residence time. The pH in solution, higher heating value and BET surface positively correlated with pyrolysis temperature. Finally, soil incubation tests showed that the addition of biochar to the soil initially marginally reduced the C-mineralization rate compared against the control soil samples, for which a possible explanation could be that the soil microbial community needs to adapt to the new conditions. This effect was more pronounced when adding chars with high fixed carbon content (resulting from more severe thermal treatment), as chars with low fixed carbon content (produced through mild thermal treatment) had a larger amount of volatile, more easily biodegradable, carbon compounds.

Assessing potential of biochar for increasing water‐holding capacity of sandy soils

Abstract: Increasing the water-holding capacity of sandy soils will help improve efficiency of water use in agricultural production, and may be critical for providing enough energy and food for an increasing global population. We hypothesized that addition of biochar will increase the water-holding capacity of a sandy loam soil, and that the depth of biochar incorporation will influence the rate of biochar surface oxidation in the amended soils. Hardwood fast pyrolysis biochar was mixed with soil (0%, 3%, and 6% w/w) and placed into columns in either the bottom 11.4 cm or the top 11.4 cm to simulate deep banding in rows (DBR) and uniform topsoil mixing (UTM) applications, respectively. Four sets of 18 columns were incubated at 30 °C and 80% RH. Every 7 days, 150 mL of 0.001 M calcium chloride solution was added to the columns to produce leaching. Sets of columns were harvested after 1, 15, 29, and 91 days. Addition of biochar increased the gravity-drained water content 23% relative to the control. Bulk density of the control soils increased with incubation time (from 1.41 to 1.45 g cm−3), whereas bulk density of biochar-treated soils was up to 9% less than the control and remained constant throughout the incubation period. Biochar did not affect the CEC of the soil. The results suggest that biochar added to sandy loam soil increases water-holding capacity and might increase water available for crop use.

The effect of pyrolysis conditions on biochar stability as determined by three methods

Abstract: Biochar is the porous, carbonaceous material produced by thermochemical treatment of organic materials in an oxygen-limited environment. In general, most biochar can be considered resistant to chemical and biological decomposition, and therefore suitable for carbon (C) sequestration. However, to assess the C sequestration potential of different types of biochar, a reliable determination of their stability is needed. Several techniques for assessing biochar stability have been proposed, e.g. proximate analysis, oxygen (O): C ratio and hydrogen (H): C ratio; however, none of them are yet widely recognized nor validated for this purpose. Biochar produced from three feedstocks (Pine, Rice husk and Wheat straw) at four temperatures (350, 450, 550 and 650 °C) and two heating rates (5 and 100 °C min−1) was analysed using three methods of stability determination: proximate analysis, ultimate analysis and a new analytical tool developed at the UK Biochar Research Centre known as the Edinburgh accelerated ageing tool (Edinburgh stability tool). As expected, increased pyrolysis temperatures resulted in higher fractions of stable C and total C due to an increased release of volatiles. Data from the Edinburgh stability tool were compared with those obtained by the other methods, i.e. fixed C, volatile matter, O : C and H : C ratios, to investigate potential relationships between them. Results of this comparison showed that there was a strong correlation (R > 0.79) between the stable C determined by the Edinburgh stability tool and fixed C, volatile matter and O : C, however, H : C showed a weaker correlation (R = 0.65). An understanding of the influence of feedstock and production conditions on the long-term stability of biochar is pivotal for its function as a C mitigation measure, as production and use of unstable biochar would result in a relatively rapid return of C into the atmosphere, thus potentially intensifying climate change rather than alleviating it.

Impact of biochar field aging on laboratory greenhouse gas production potentials.

Abstract: Recent observations of decreased greenhouse gas (GHG) production from biochar amended soils have been used to further substantiate the environmental benefit of biochar production and soil incorporation strategies. However, the mechanisms behind this biochar-mediated response have not been fully elucidated. In addition, the duration of these GHG reductions is not known and is of pivotal importance for the inclusion of biochar into future bioenergy production and climate abatement strategies. In this study, the impacts of biochar field aging on the observed GHG production/consumption were evaluated. Two different wood-derived biochars and a macadamia nut shell biochar were weathered in an agricultural field in Rosemount, MN (2008–2011) and the impacts on net soil GHG production/consumption were assessed through laboratory incubations. For the three biochars evaluated here, weathering negated the suppression of N2O production that was originally observed from the fresh biochar in laboratory incubations. On the other hand, all three weathered biochars enhanced CO2 production (three- to tenfold compared with the fresh biochar amendments) in laboratory soil incubations, suggesting an enhanced microbial mineralization rate of the weathered biochar. This enhanced mineralization could be aided by the chemical oxidation of the biochar surfaces during weathering. Fresh biochar reduced observed soil methane oxidation rates, whereas the weathered biochars had no significant impacts on the observed soil methanotrophic activity. This study demonstrates that for these three biochars, weathering greatly alters the GHG response of the soil systems to biochar amendments.

Approaches for inclusion of forest carbon cycle in life cycle assessment – a review

Abstract: Forests are a significant pool of terrestrial carbon. A key feature related to forest biomass harvesting and use is the typical time difference between carbon release into and sequestration from the atmosphere. Traditionally, the use of sustainably grown biomass has been considered as carbon neutral in life cycle assessment (LCA) studies. However, various approaches to account for greenhouse gas (GHG) emissions and sinks of forest biomass acquisition and use have also been developed and applied, resulting in different conclusions on climate impacts of forest products. The aim of this study is to summarize, clarify, and assess the suitability of these approaches for LCA. A literature review is carried out, and the results are analyzed through an assessment framework. The different approaches are reviewed through their approach to the definition of reference land-use situation, consideration of time frame and timing of carbon emissions and sequestration, substitution credits, and indicators applied to measure climate impacts. On the basis of the review, it is concluded that, to account for GHG emissions and the related climate impacts objectively, biomass carbon stored in the products and the timing of sinks and emissions should be taken into account in LCA. The reference situation for forest land use has to be defined appropriately, describing the development in the absence of the studied system. We suggest the use of some climate impact indicator that takes the timing of the emissions and sinks into consideration and enables the use of different time frames. If substitution credits are considered, they need to be transparently presented in the results. Instead of carbon stock values taken from the literature, the use of dynamic forest models is recommended.

A method for screening the relative long‐term stability of biochar

Abstract: Biochar is being actively explored as a tool for long-term soil carbon sequestration. However, in order for this to be effective the long-term environmental stability of biochar must be assured. Here, we define and test an accelerated ageing method that seeks to reflect the oxidative nature of biochar degradation in soil. The method was applied to a systematic set of biochar samples produced from sugarcane bagasse, and a set of biochar samples produced from four different biomass sources. The stability of carbon in these samples was found to range between 41.6% and 76.1%, loosely correlating with biochar On:nC ratio (rn=n0.73). Increasing intensity of oxidative treatment eliminated more carbon. It also increased surface On:nC ratio in a manner reported for naturally aged charcoal samples. The method effectively discriminated biochar produced under contrasting pyrolysis conditions and could be used as a proxy for environmental ageing of approximately 100nyears under temperate conditions.

Co-generated fast pyrolysis biochar mitigates green-house gas emissions and increases carbon sequestration in temperate soils

Abstract: Char is a product of thermochemical conversion of biomass via pyrolysis, together with gas (syngas), liquid (bio-oil), and heat. Fast pyrolysis is a promising process for bio-oil generation, which leaves 10–30% of the original biomass as char. Char produced for soil application, is defined biochar (BC), and it may increase soil C storage, and reduce soil emissions of greenhouse gases (GHG), such as N2O and CH4 –potentially making fast pyrolysis bioenergy generation a C-negative system. However, differences in production conditions (e.g., feedstock, pyrolysis temperature and speed, post handling, and storage conditions) influence the chemical properties of BC and its net effect when added to soils. Understanding if fast pyrolysis BC can increase C sequestration and reduce GHG emissions will enable full assessment of the economic value and environmental benefits of this form of bioenergy. We characterized a BC produced by fast pyrolysis for bio-oil generation and examined GHG (CO2 ,N 2O and CH4) efflux, C partitioning using d 13 C, and soil C sequestration across four temperate soils and five BC rates; 0%, 1%, 5%, 10%, and 20% w/w. The fast pyrolysis process created a highly aromatic, low N, ashrich BC with a O : C ratio of 0.01, which we expected to be highly recalcitrant. Across soils, CO2 emissions increased linearly and N2O emissions decreased exponentially with increasing BC addition rates. Despite still being actively respired after 2 years, total BC-derived C-CO2 comprised less than the BC volatile C content (4%). Expressed as CO2 equivalents, CO2 was the primary GHG emitted (97.5%), followed by N2O. All GHG emissions were small compared to the total SOC sequestered in the BC. Fast pyrolysis produced a highly recalcitrant BC that sequestered C and reduced GHG emissions. The recovery and soil application of BC would contribute to a negative carbon balance for this form of bioenergy generation.

Infield greenhouse gas emissions from sugarcane soils in Brazil: effects from synthetic and organic fertilizer application and crop trash accumulation

Abstract: Bioethanol from sugarcane is becoming an increasingly important alternative energy source worldwide as it is considered to be both economically and environmentally sustainable. Besides being produced from a tropical perennial grass with high photosynthetic efficiency, sugarcane ethanol is commonly associated with low N fertilizer use because sugarcane from Brazil, the world's largest sugarcane producer, has a low N demand. In recent years, several models have predicted that the use of sugarcane ethanol in replacement to fossil fuel could lead to high greenhouse gas (GHG) emission savings. However, empirical data that can be used to validate model predictions and estimates from indirect methodologies are scarce, especially with regard to emissions associated with different fertilization methods and agricultural management practices commonly used in sugarcane agriculture in Brazil. In this study, we provide in situ data on emissions of three GHG (CO2, N2O, and CH4) from sugarcane soils in Brazil and assess how they vary with fertilization methods and management practices. We measured emissions during the two main phases of the sugarcane crop cycle (plant and ratoon cane), which include different fertilization methods and field conditions. Our results show that N2O and CO2 emissions in plant cane varied significantly depending on the fertilization method and that waste products from ethanol production used as organic fertilizers with mineral fertilizer, as it is the common practice in Brazil, increase emission rates significantly. Cumulatively, the highest emissions were observed for ratoon cane treated with vinasse (liquid waste from ethanol production) especially as the amount of crop trash on the soil surface increased. Emissions of CO2 and N2O were 6.9 kg ha−1 yr−1 and 7.5 kg ha−1 yr−1, respectively, totaling about 3000 kg in CO2 equivalent ha−1 yr−1.

Establishing release dynamics for plant nutrients from biochar.

Abstract: To assess the value of biochar to direct supply of crop nutrients we considered the release of phosphorus, magnesium and potassium from a hardwood biochar in a sequential leaching experiment with deionized water. Cumulative P release was proportionally large despite being quantitatively small, and the sixth extraction yielded 44–73% of the first, indicating that provision of soil P might be sustained for several seasons. Conversely, K release was quantitatively large but declined rapidly from first extraction to the last (6–18% of the first extraction). Only 6–27% of total Mg was recovered. These results indicate that these elements have contrasting associations with biochar that govern the trajectory and ultimate extent of their release. Fitting cumulative loss curves enabled these patterns to be quantitatively captured and compared and could provide a means to develop predictive capacity for the supply of nutrients from biochar to soil and plant.

Is biochar a source or sink for polycyclic aromatic hydrocarbon (PAH) compounds in agricultural soils

Abstract: Polycyclic aromatic hydrocarbons (PAHs) in the environment originate mainly from incomplete combustion of fossil fuels, and pose a significant human health risk. Soils act as environmental sinks for PAHs, as they become strongly absorbed onto soil particles; degradation is mainly driven by microbial catabolism, although it is dependent on PAH bioavailability. There is current interest in burying biochar in soil as a long-term soil carbon store; however, biochar inherently contains varying levels of PAHs and its application could contaminate soil, and its high sorptive capacity may facilitate the persistence of PAHs in the environment. The aim of this study was to determine the effect of adding biochar to soil on microbial mineralization of PAHs, and to quantify whether or not soils amended with biochar were less likely to leach PAHs. We used contrasting agricultural soils (Eutric Cambisol and Cambic Podzol) spiked with the labelled PAH compound 14 C-phenanthrene and amended with either wood biochar or rice husk biochar. Mineralization was quantified by measuring the release of 14 CO2 and simulated rain used to quantify leaching of PAH through biochar-amended soil. Rice husk biochar had higher concentrations of PAHs (64.65 mg kg 1 ) than wood biochar (9.56 mg kg 1 ), and both soil types contained quantifiable levels of PAHs. However, soil that had contained biochar for 3 years had significantly higher levels of PAH (1.95 mg kg 1 ) compared to unamended soil (1.13 mg kg 1 ). PAH catabolism in soil was reduced when amended with biochar, although biochar amendment did not consistently decrease PAH leaching. Biochar-mediated inhibition of PAH mineralization is a consequence of increased sorption and reduced bioavailability. Before large scale biochar addition to soils is adopted, future work is needed to address the dynamic between sorbent saturation and microbial activity and how this relates to the concentration of PAHs in soil solution and their persistence in the environment.

Distributed biochar and bioenergy coproduction: a regionally specific case study of environmental benefits and economic impacts

Abstract: Biochar has been advocated as a method of sequestering carbon while simultaneously improving crop yields and agro-ecosystem sustainability. It can be produced from a wide variety of biomass feedstocks using different thermochemical conversion technologies with or without the recovery of energy coproducts, resulting in chars of differing quality and a range of overall system greenhouse gas (GHG) mitigation outcomes. This analysis expands on previous sustainability studies by proposing a mechanistic life cycle GHG and economic operating cost assessment model for the coproduction of biochar and bioenergy from biomass residue feedstocks, with a case study for north-central Colorado presented. Production is modeled as a continuous function of temperature for slow pyrolysis, fast pyrolysis, and gasification systems. Biochar environmental benefits (C sequestration, N2O suppression, crop yield improvements) are predicted in terms of expected liming value and recalcitrance. System-level net GHG mitigation is computed, and net returns are estimated that reflect the variable economic costs of production, the agronomic value of biochar based on agricultural limestone or fertilizer displacement, and the value of GHG mitigation, with results compared to the alternate use of char for energy production. Case study results indicate that slow pyrolysis systems can mitigate up to 1.4 Mg CO2eq/Mg feedstock consumed, provided a favorable feedstock is utilized, production air pollutant emissions are mitigated, and energy coproducts are recovered. The model suggests that while financial returns are generally greater when char is consumed for energy (biocoal) than when used as a soil amendment (biochar), chars produced through high-temperature conversion processes will have greater GHG-mitigation value as biochar. The biochar scenario reaches economic parity at carbon prices as low as $50/Mg CO2eq for optimal scenarios, despite conservative modeling assumptions. This model is a step toward spatially explicit assessment and optimization of biochar system design across different feedstocks, conversion technologies, and agricultural soils.

Biochar in bioenergy cropping systems: impacts on soil faunal communities and linked ecosystem processes

Abstract: Biochar amendment of soil and bioenergy cropping are two eco-engineering strategies at the forefront of attempts to offset anthropogenic carbon dioxide (CO2) emissions. Both utilize the ability of plants to assimilate atmospheric CO2, and are thus intrinsically linked with soil processes. Research to date has shown that biochar and bioenergy cropping change both aboveground and belowground carbon cycling and soil fertility. Little is known, however, about the form and function of soil food webs in these altered ecosystems, or of the consequences of biodiversity changes at higher trophic levels for soil carbon sequestration. Hitherto studies on this topic have been chiefly observational, and often report contrasting results, thus adding little mechanistic understanding of biochar and bioenergy cropping impacts on soil organisms and linked ecosystem processes. This means it is difficult to predict, or control for, changes in biotic carbon cycling arising from biochar and bioenergy cropping. In this study we explore the potential mechanisms by which soil communities might be affected by biochar, particularly in soils which support bioenergy cropping. We outline the abiotic (soil quality-mediated) and biotic (plant- and microbe-mediated) shifts in the soil environment, and implications for the abundance, diversity, and composition of soil faunal communities. We offer recommendations for promoting biologically diverse, fertile soil via biochar use in bioenergy crop systems, accompanied by specific future research priorities.

Management swing potential for bioenergy crops

Abstract: Bioenergy crops are often classified (and subsequently regulated) according to species that have been evaluated as environmentally beneficial or detrimental, but in practice, management decisions rather than species per se can determine the overall environmental impact of a bioenergy production system. Here, we review the greenhouse gas balance and ‘management swing potential’ of seven different bioenergy cropping systems in temperate and tropical regions. Prior land use, harvesting techniques, harvest timing, and fertilization are among the key management considerations that can swing the greenhouse gas balance of bioenergy from positive to negative or the reverse. Although the management swing potential is substantial for many cropping systems, there are some species (e.g., soybean) that have such low bioenergy yield potentials that the environmental impact is unlikely to be reversed by management. High-yielding bioenergy crops (e.g., corn, sugarcane, Miscanthus, and fast-growing tree species), however, can be managed for environmental benefits or losses, suggesting that the bioenergy sector would be better informed by incorporating management-based evaluations into classifications of bioenergy feedstocks.

Miscanthus × giganteus and Arundo donax shoot and rhizome tolerance of extreme moisture stress

Abstract: Crops grown for bioenergy production are a mandated component of the United States energy portfolio. Giant miscanthus (Miscanthus × giganteus) is a leading bioenergy crop similar in habit to the invasive plant giant reed (Arundo donax). To characterize the environmental tolerance of giant miscanthus, we compared the soil moisture stress tolerance of giant miscanthus and giant reed under glasshouse conditions. We subjected both species to soil moisture conditions of severe drought (−4.2 MPa), mild drought (−0.5 MPa), field‐capacity (control), and flooded soils. These conditions were applied to two cohorts: one in which soil moisture conditions were imposed on newly planted rhizome fragments, and one in which conditions were imposed on established plants after 8 weeks of growth in field‐capacity soil. After 16 weeks, we harvested all plants, measured above‐ and belowground biomass, and evaluated the reproductive viability of rhizome fragments. The total biomass of each species under flooded conditions was not different from the field‐capacity control groups regardless of cohort. However, drought did affect the two cohorts differently. In the cohort treated after 8 weeks of growth, mild and severe drought conditions resulted in 56% and 66% reductions in biomass, averaged over both species, compared with the controls. In the cohort treated for the entire 16 weeks, mild and severe drought conditions resulted in 92% and 94% reductions in biomass. Rhizome fragments from both species and both cohorts showed 100% viability following flooded and control treatments; drought treatments reduced rhizome viability in both species, with a greater impact on giant miscanthus. Although giant miscanthus does not appear to have the potential to escape and establish in relatively dry upland ecosystems, it does show tolerance to flooded conditions similar to giant reed.

Measurement and modelling of CO2 flux from a drained fen peatland cultivated with reed canary grass and spring barley

Abstract: Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas (GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange (NEE) fluxes of CO2 as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass (RCG) and spring barley (SB) in a plot experiment (n = 3 for each cropping system). The CO2 flux was partitioned into gross photosynthesis (GP) and ecosystem respiration (RE). For the data analysis, simple yet useful GP and RE models were developed which introduce plot‐scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the RE model estimates the proportion of foliar biomass dependent respiration (Rfb) in the total RE. Annual RE was 1887 ± 7 (mean ± standard error, n = 3) and 1288 ± 19 g CO2‐C m−2 in RCG and SB plots, respectively, with Rfb accounting for 32 and 22% respectively. Total estimated annual GP was −1818 ± 42 and −1329 ± 66 g CO2‐C m−2 in RCG and SB plots leading to a NEE of 69 ± 36 g CO2‐C m−2 yr−1 in RCG plots (i.e., a weak net source) and −41 ± 47 g CO2‐C m−2 yr−1 in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO2 emissions during cultivation. However, in a broader GHG life‐cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial.

Soil carbon stocks and changes after oil palm introduction in the Brazilian Amazon

Abstract: As oil palm has been considered one of the most favorable oilseeds for biodiesel production in Brazil, it is important to understand how cultivation of this perennial crop will affect the dynamics of soil organic carbon (SOC) in the long term. The aim of this study was to evaluate the changes in soil C stocks after the conversion of forest and pasture into oil palm production in the Amazon Region. Soil samples were collected in March 2008 and September 2009 in five areas: native forest (NARF), pasture cultivated for 55 years (PAST), and oil palm cultivated for 4 (OP-4), 8 (OP-8) and 25 years (OP-25), respectively. Soils were sampled in March 2008 to evaluate the spatial variability of SOC and nitrogen (N) contents in relation to the spacing between trees. In September 2009, soils were sampled to evaluate the soil C stocks in the avenues (inter rows) and frond piles, and to compare the total C stocks with natural forest and pasture system. Soil C contents were 22–38% higher in the area nearest the oil palm base (0.6 m) than the average across the inter row (0–4.5 m from the tree), indicating that the increment in soil organic matter (SOM) must have been largely derived from root material. The soil C stocks under palm frond piles were 9–26% higher than in the inter rows, due to inputs of SOM by pruned palm fronds. The soil carbon stocks in oil palm areas, after adjustments for differences in bulk density and clay content across treatments, were 35–46% lower than pasture soil C stocks, but were 0–18% higher than the native forest soil C content. The results found here may be used to improve the life cycle assessment of biodiesel derived from palm oil.

Nature of water-biochar interface interactions

Abstract: A poplar biochar obtained by an industrial gasification process was saturated with water and analyzed using fast field cycling (FFC) NMR relaxometry in a temperature range between 299 and 353 K. Results revealed that the longitudinal relaxation rate increased with the increment of the temperature. This behavior was consistent with that already observed for paramagnetic inorganic porous media for which two different relaxation mechanisms can be accounted for: outer- and inner-sphere mechanisms. The former is due to water diffusing from the closest approach distance to infinity, whereas the second is due to water interacting by nonconventional H-bonds to the porous surface of the solid material. In particular, the inner-sphere relaxation appeared to be predominant in the water-saturated biochar used in the present study. This study represents a fundamental first step for the full comprehension of the role played by biochar in the draining properties of biochar-amended soils.

Effects of cross host species inoculation of nitrogen‐fixing endophytes on growth and leaf physiology of maize

Abstract: Plants that grow and thrive under abiotic stress often do so with the help of endophytic microorganisms. Although nitrogen-fixing (diazotrophic) endophytes colonize many wild plants, these natural relationships may be disrupted in cultivated crop species where breeding and genotype selection often occur under conditions of intensive fertilization and irrigation. Many energy crops including corn may still benefit from diazotrophic endophyte inoculations allowing for more efficient biomass production with less input of petroleum-derived fertilizer. A selection of diazotrophic endophytes isolated from willow (Salix sitchensis, Sitka willow) and poplar (Populus trichocarpa, black cottonwood) growing in nutrient-poor river sides were used as inoculum in three experiments testing the effect on plant growth and leaf level physiology of a sweet corn variety under various levels of applied nitrogen fertilizer. We report substantial growth promotion with improved leaf physiology of corn plants in response to diazotrophic endophyte inoculations. Significant gains of early biomass with a greater root : shoot ratio were found for plants receiving endophytic inocula over the uninoculated control groups regardless of the nitrogen level. Furthermore, inoculated plants exhibited consistently higher rates of net CO2 assimilation than did those without endophytic inoculation. These results have beneficial implications for enhanced plant growth in a low-input system on nutrient-poor sites. The immediate increase of root mass observed in endophyte inoculated plants has the potential to provide better establishment and early growth in resource-limited environments. The initial results of this study also indicate that the beneficial effect from endophytes isolated from poplar and willow species is not restricted to the species from which they were initially isolated.

Miscanthus biomass productivity within US croplands and its potential impact on soil organic carbon

Abstract: Interest in bioenergy crops is increasing due to their potential to reduce greenhouse gas emissions and dependence on fossil fuels. We combined process-based and geospatial models to estimate the potential biomass productivity of miscanthus and its potential impact on soil carbon stocks in the croplands of the continental United States. The optimum (climatic potential) rainfed productivity for field-dried miscanthus biomass ranged from 1 to 23 Mg biomass ha−1 yr−1, with a spatial average of 13 Mg ha−1 yr−1 and a coefficient of variation of 30%. This variation resulted primarily from the spatial heterogeneity of effective rainfall, growing degree days, temperature, and solar radiation interception. Cultivating miscanthus would result in a soil organic carbon (SOC) sequestration at the rate of 0.16–0.82 Mg C ha−1 yr−1 across the croplands due to cessation of tillage and increased biomass carbon input into the soil system. We identified about 81 million ha of cropland, primarily in the eastern United States, that could sustain economically viable (>10 Mg ha−1 yr−1) production without supplemental irrigation, of which about 14 million ha would reach optimal miscanthus growth. To meet targets of the US Energy Independence and Security Act of 2007 using miscanthus as feedstock, 19 million ha of cropland would be needed (spatial average 13 Mg ha−1 yr−1) or about 16% less than is currently dedicated to US corn-based ethanol production.

Nitrogen fertilization increases diversity and productivity of prairie communities used for bioenergy.

Abstract: Using prairie biomass as a renewable source of energy may constitute an important opportunity to improve the environmental sustainability of managed land. To date, assessments of the feasibility of using prairies for bioenergy production have focused on marginal areas with low yield potential. Growing prairies on more fertile soil or with moderate levels of fertilization may be an effective means of increasing yields, but increased fertility often reduces plant community diversity. At a fertile site in central Iowa with high production potential, we tested the hypothesis that nitrogen fertilization would increase aboveground biomass production but would decrease diversity of prairies sown and managed for bioenergy production. Over a 3 year period (years 2–4 after seeding), we measured aboveground biomass after plant senescence and species and functional-group diversity in June and August for multispecies mixtures of prairie plants that received no fertilizer or 84 kg N ha 1 year 1 . We found that nitrogen fertilization increased aboveground biomass production, but with or without fertilization, the prairies produced a substantial amount of biomass: averaging (±SE) 12.2 ± 1.3 and 9.1 ± 1.0 Mg ha 1 in fertilized and unfertilized prairies, respectively. Unfertilized prairies had higher species diversity in June, whereas fertilized prairies had higher species diversity in August at the end of the study period. Functionalgroup diversity was almost always higher in fertilized prairies. Composition of unfertilized prairies was characterized by native C4 grasses and legumes, whereas fertilized prairies were characterized by native C3 grasses and forbs. Although most research has found that nitrogen fertilization reduces prairie diversity, our results indicate that early-spring nitrogen fertilization, when used with a postsenescence annual harvest, may increase prairie diversity. Managing prairies for bioenergy production, including the judicious use of fertilization, may be an effective means of increasing the amount of saleable products from managed lands while potentially increasing plant diversity.

Torrefaction/biochar production by microwave and conventional slow pyrolysis - comparison of energy properties

Abstract: The energy efficiency of torrefaction/pyrolysis of biomass to fuel/biochar was studied using conventional (slow) and microwave (low temperature) pyrolysis. Conventional pyrolysis is approximately three times as energy efficient as microwave pyrolysis, in terms of the energy required to process a unit of feedstock. However, this is more than compensated for by the higher energy content of the condensable and gaseous coproducts from microwave pyrolysis, as these can be utilized to generate the electricity required to drive the process. It is proposed that the most efficient method of torrefaction/biochar production is a combination of conventional heating with ‘catalytic’ amount of microwave irradiation.

How effective are the sustainability criteria accompanying the European Union 2020 biofuel targets

Abstract: The expansion of biofuel production can lead to an array of negative environmental impacts. Therefore the European Union (EU) has recently imposed sustainability criteria on biofuel production in the Renewable Energy Directive (RED. In this article, we analyse the effectiveness of the sustainability criteria for climate change mitigation and biodiversity conservation. We first use a global agriculture and forestry model to investigate environmental effects of the EU member states National Renewable Energy Action Plans (NREAPs) without sustainability criteria. We conclude that these targets would drive losses of 2.2 Mha of highly biodiverse areas and generate 95 Mt CO2 eq of additional greenhouse gas (GHG) emissions. However, in a second step, we demonstrate that the EU biofuel demand could be satisfied "sustainably" according to RED despite its negative environmental effects. This is because the majority of global crop production is produced sustainably in the sense of RED and can provide more than 10 times the total European biofuel demand in 2020 if reallocated from sectors without sustainability criteria. This finding points to a potential policy failure of applying sustainability regulation to a single sector in a single region. To be effective this policy needs to be more complete in targeting a wider scope of agricultural commodities and more comprehensive in its membership of countries.

The role of forest residues in the accounting for the global warming potential of bioenergy

Abstract: Bioenergy makes up a significant portion of the global primary energy pie, and its production from modernized technology is foreseen to substantially increase. The climate neutrality of biogenic CO2 emissions from bioenergy grown from sustainably managed biomass resource pools has recently been questioned. The temporary change caused in atmospheric CO2 concentration from biogenic carbon fluxes was found to be largely dependent on the length of biomass rotation period. In this work, we also show the importance of accounting for the unutilized biomass that is left to decompose in the resource pool and how the characterization factor for the climate impact of biogenic CO2 emissions changes whether residues are removed for bioenergy or not. With the case of Norwegian Spruce biomass grown in Norway, we found that significantly more biogenic CO2 emissions should be accounted towards contributing to global warming potential when residues are left in the forest. For a 100‐year time horizon, the global warming potential bio factors suggest that between 44 and 62% of carbon‐flux, neutral biogenic CO2 emissions at the energy conversion plant should be attributed to causing equivalent climate change potential as fossil‐based CO2 emissions. For a given forest residue extraction scenario, the same factor should be applied to the combustion of any combination of stem and forest residues. Life cycle analysis practitioners should take these impacts into account and similar region/species specific factors should be developed.

Time‐dependent climate impact of a bioenergy system – methodology development and application to Swedish conditions

Abstract: The area of dedicated energy crops is expected to increase in Sweden. This will result in direct land use changes, which may affect the carbon stocks in soil and biomass, as well as yield levels an ...

Development and evaluation of ForestGrowth‐SRC a process‐based model for short rotation coppice yield and spatial supply reveals poplar uses water more efficiently than willow

Abstract: Woody biomass produced from short rotation coppice (SRC) poplar (Populus spp.) and willow (Salix spp.) is a bioenergy feedstock that can be grown widely across temperate landscapes and its use is likely to increase in future. Process-based models are therefore required to predict current and future yield potential that are spatially resolved and can consider new genotypes and climates that will influence future yield. The development of a process-based model for SRC poplar and willow, ForestGrowth-SRC, is described and the ability of the model to predict SRC yield and water use efficiency (WUE) was evaluated. ForestGrowth-SRC was parameterized from a process-based model, ForestGrowth for high forest. The new model predicted annual above ground yield well for poplar (r 2 = 0.91, RMSE = 1.46 ODT ha � 1 yr � 1 ) and willow (r 2 = 0.85, RMSE = 1.53 ODT ha � 1 yr � 1 ), when compared with measured data from seven sites in contrasting climatic zones across the United Kingdom. Average modelled yields for poplar and willow were 10.3 and 9.0 ODT ha � 1 yr � 1 , respectively, and interestingly, the model predicted a higher WUE for poplar than for willow: 9.5 and 5.5 g kg � 1 respectively. Using regional mapped climate and soil inputs, modelled and measured yields for willow compared well (r 2 = 0.58, RMSE = 1.27 ODT ha � 1 yr � 1 ), providing the first UK map of SRC yield, from a process-based model. We suggest that the model can be used for predicting current and future SRC yields at a regional scale, highlighting important species and genotype choices with respect to water use efficiency and yield potential.

The outcome is in the assumptions: analyzing the effects on atmospheric CO2 levels of increased use of bioenergy from forest biomass

Abstract: Recently, several studies have quantified the effects on atmospheric CO2 concentration of an increased harvest level in forests. Although these studies agreed in their estimates of forest productivity, their conclusions were contradictory. This study tested the effect of four assumptions by which those papers differed. These assumptions regard (1) whether a single or a set of repeated harvests were considered, (2) at what stage in stand growth harvest takes place, (3) how the baseline is constructed, and (4) whether a carbon-cycle model is applied. A main finding was that current and future increase in the use of bioenergy should be studied considering a series of repeated harvests. Moreover, the time of harvest should be determined based on economical principles, thus taking place before stand growth culminates, which has implications for the design of the baseline scenario. When the most realistic assumptions are used and a carbon-cycle model is applied, an increased harvest level in forests leads to a permanent increase in atmospheric CO2 concentration.

Life cycle assessment of eucalyptus short rotation coppices for bioenergy production in southern France

Abstract: Short rotation coppices (SRCs) are considered prime candidates for biomass production, yielding good-quality feedstock that is easy to harvest. Besides technical, social and economical aspects, environmental issues are important to take into account when developing SRCs. Here, we evaluated the environmental impacts of delivering 1 GJ of heat from eucalyptus SRC using life cycle assessment (LCA), based on management scenarios involving different rotations lengths, fertilizer input rates, stem densities and harvest methods. Compared to equivalent fossil chains, all eucalyptus scenarios achieved savings of fossil energy and greenhouse gas (GHG) emissions in the 80%-90% range, and had generally lower impacts, except for eutrophication. The 3-year rotation scenario was the most energy and GHG-intensive, while manual felling for the longer rotations resulted in 2-fold larger photochemical ozone impacts compared to the other scenarios. Transportation of wood chips and fertilization were the top two contributors to the impacts, the latter being more important with the shorter rotation lengths due to the evergreen character of eucalyptus. The possibility of including ecosystem carbon dynamics was also investigated, by translating the temporary sequestration of atmospheric CO2 in the above- and below-ground biomass of eucalyptus as CO2 savings using various published equivalence factors. This offset the life-cycle GHG emissions of heat provision from eucalyptus SRCs by 70 to 400%.

N2O fluxes of a bio‐energy poplar plantation during a two years rotation period

Abstract: Nitrous oxide emissions are of critical importance for the assumed climate neutrality of bio-energy. In this study we report on the N2O fluxes from a bio-energy poplar plantation measured with eddy covariance for 2 years, after conversion of agricultural fields to few months after harvesting of the plantation. A pulse peak of N2O was detected after the land use change and in the wake of the first heavy rainfall. The N2O-N emission during just a single week was 2.7 kg N2O-N ha−1 which represented approximately 42% of the total N2O-N emitted during the 2 years of measurements. After this peak emission, N2O fluxes were constantly rather low, not increasing after rainfall events any longer. Lowest emissions (and even N2O sink) occurred mostly during the end of the second growing season with maximum canopy development, and water table deeper than 80 cm. Gross primary production (GPP) explained 68% of the monthly averaged variability in N2O emission from August to December 2011. Probably N uptake by vegetation during the peak of the second growing season limited N2O emission, which in fact increased again after the plantation was coppiced. For the majority of the measuring period, N2O fluxes did not present a well-defined diurnal pattern, with the exception of two periods: (1) from 19–22 August 2010 and (2) from September–November 2011. In both cases wind speed played a major role in controlling the diurnal pattern in these fluxes (explaining up to 80% of the diurnal variability in N2O fluxes on 19–22 August 2010), whereas at the end of the second growing season (September–November 2011), GPP explained 73% of the diurnal pattern in N2O fluxes.

Characterization of culturable bacterial endophytes of switchgrass (Panicum virgatum L.) and their capacity to influence plant growth

Abstract: Switchgrass (Panicum virgatum L.) is a perennial warm season grass that is native to the plains of North America and is widely grown as a forage, bioenergy or groundcover crop. Despite its importance, a bottleneck in switchgrass production is poor seedling vigor, which as a perennial crop represents an important time for management. Herein, data identify a suite of culturable bacterial microflora extracted from switchgrass, and show their capability to influence host plant growth and development. A total of 307 bacterial isolates were cultured and isolated from surface sterilized switchgrass biomass and sequence identified into 76 strains (subspecies classification), 36 species and 5 phyla. Approximately 58% of bacterial strains, when reintroduced into surface‐sterilized switchgrass seeds, were documented to increase lamina length (cm from base to tip after 60 days growth) relative to uninoculated controls. Ecologically, Phylum Firmicutes was the most abundant bacterial classification and encompassed 75% of all isolates. Although the culturable bacterial community studies herein represent an unknown and assumedly minor proportion of the total microbiome, by focusing on culturable bacteria, we delineate functional feedback between the presence of isolated bacteria and switchgrass seedling growth.