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Nitrous oxide (N2O) is the third important long‐lived greenhouse gas next to carbon dioxide and methane and croplands are considered biogeochemical hotspots of soil N2O emissions. To reduce soil N2O and other greenhouse emissions, climate‐smart agricultural practices including biochar application have been applied. Many studies have been conducted with biochar application but results from these studies are not conclusive. To address this issue, meta‐analysis, a quantitative review that synthesizes results from multiple independent studies, has been widely used. The results from different meta‐analyses also differ but are seldomly evaluated. In this study, we evaluated meta‐analyses on the effects of biochar application on soil N2O emissions. A grand mean response ratio (RR) was further proposed to estimate an overall effect and the impacts of experiment setting, properties of biochar and soil, and agricultural practices. We found 18 meta‐analysis papers were published between 2014 and 2022. Sample size (publications or experiments) varied from less than 30 to more than 1000, with a mean sample size of 275. RR was calculated in all studies except one. While four meta‐analyses did not find a significant effect of biochar application on soil N2O emissions, all others reported reductions of soil N2O emissions, but the magnitude ranged from −10.5% to −54.8%. Synthesizing all results from these meta‐analyses, we found that biochar application overall significantly reduced the soil N2O emissions by 38.8%. The impacts increased with experimental duration till one and half years and reduced after that. Biochar application rate and C:N ratio had large influence on the effects of biochar application on soil N2O emissions. This study demonstrated that while meta‐analysis provides a more comprehensive and better estimation, the inconsistence among these studies may need to be further evaluated. A grand mean RR based on meta‐analyses could be more accurate and representative than single meta‐analysis. [ABSTRACT FROM AUTHOR]

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 and the use of inputs. Carbon dioxide ( CO2) fluxes of biomass are often not considered when calculating the climate impact in life cycle assessments ( LCA) assuming that the CO2 released at combustion has recently been captured by the biomass in question. With the extended time lag between capture and release of CO2 inherent in many perennial bioenergy systems, the relation between carbon neutrality and climate neutrality may be questioned. In this paper, previously published methodologies and models are combined in a methodological framework that can assist LCA practitioners in interpreting the time-dependent climate impact of a bioenergy system. The treatment of carbon differs from conventional LCA practice in that no distinction is made between fossil and biogenic carbon. A time-dependent indicator is used to enable a representation of the climate impact that is not dependent on the choice of a specific characterization time horizon or time of evaluation and that does not use characterization factors, such as global warming potential and global temperature potential. The indicator used to aid in the interpretation phase of this paper is global mean surface temperature change (Δ Ts( n)). A theoretical system producing willow for district heating was used to study land use change effects depending on previous land use and variations in the standing biomass carbon stocks. When replacing annual crops with willow this system presented a cooling contribution to Δ Ts( n). However, the first years after establishing the willow plantation it presented a warming contribution to Δ Ts( n). This behavior was due mainly to soil organic carbon ( SOC) variation. A rapid initial increase in standing biomass counteracted the initial SOC loss. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is carbon (C) flux neutral, i.e. the CO2 released from biofuel combustion approximately equals the amount of CO2 sequestered in biomass. This convention, widely adopted in life cycle assessment (LCA) studies of bioenergy systems, underestimates the climate impact of bioenergy. Besides CO2 emissions from permanent C losses, CO2 emissions from C flux neutral systems (that is from temporary C losses) also contribute to climate change: before being captured by biomass regrowth, CO2 molecules spend time in the atmosphere and contribute to global warming. In this paper, a method to estimate the climate impact of CO2 emissions from biomass combustion is proposed. Our method uses CO2 impulse response functions (IRF) from C cycle models in the elaboration of atmospheric decay functions for biomass-derived CO2 emissions. Their contributions to global warming are then quantified with a unit-based index, the GWPbio. Since this index is expressed as a function of the rotation period of the biomass, our results can be applied to CO2 emissions from combustion of all the different biomass species, from annual row crops to slower growing boreal forest. [ABSTRACT FROM AUTHOR]

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas ( GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta-analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential ( GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation. [ABSTRACT FROM AUTHOR]

Global warming necessitates urgent action to reduce carbon dioxide (CO2) emissions and remove CO2 from the atmosphere. Biochar, a type of carbonized biomass which can be produced from crop residues (CRs), offers a promising solution for carbon dioxide removal (CDR) when it is used to sequester photosynthetically fixed carbon that would otherwise have been returned to atmospheric CO2 through respiration or combustion. However, high‐resolution spatially explicit maps of CR resources and their capacity for climate change mitigation through biochar production are currently lacking, with previous global studies relying on coarse (mostly country scale) aggregated statistics. By developing a comprehensive high spatial resolution global dataset of CR production, we show that, globally, CRs generate around 2.4 Pg C annually. If 100% of these residues were utilized, the maximum theoretical technical potential for biochar production from CRs amounts to 1.0 Pg C year−1 (3.7 Pg CO2e year−1). The permanence of biochar differs across regions, with the fraction of initial carbon that remains after 100 years ranging from 60% in warm climates to nearly 100% in cryosols. Assuming that biochar is sequestered in soils close to point of production, approximately 0.72 Pg C year−1 (2.6 Pg CO2e year−1) of the technical potential would remain sequestered after 100 years. However, when considering limitations on sustainable residue harvesting and competing livestock usage, the global biochar production potential decreases to 0.51 Pg C year−1 (1.9 Pg CO2e year−1), with 0.36 Pg C year−1 (1.3 Pg CO2e year−1) remaining sequestered after a century. Twelve countries have the technical potential to sequester over one fifth of their current emissions as biochar from CRs, with Bhutan (68%) and India (53%) having the largest ratios. The high‐resolution maps of CR production and biochar sequestration potential provided here will provide valuable insights and support decision‐making related to biochar production and investment in biochar production capacity. [ABSTRACT FROM AUTHOR]

Biochar as a carbon-rich coproduct of pyrolyzing biomass, its amendment has been advocated as a potential strategy to soil carbon (C) sequestration. Updated data derived from 50 papers with 395 paired observations were reviewed using meta-analysis procedures to examine responses of soil carbon dioxide (CO2) fluxes, soil organic C (SOC), and soil microbial biomass C (MBC) contents to biochar amendment. When averaged across all studies, biochar amendment had no significant effect on soil CO2 fluxes, but it significantly enhanced SOC content by 40% and MBC content by 18%. A positive response of soil CO2 fluxes to biochar amendment was found in rice paddies, laboratory incubation studies, soils without vegetation, and unfertilized soils. Biochar amendment significantly increased soil MBC content in field studies, N-fertilized soils, and soils with vegetation. Enhancement of SOC content following biochar amendment was the greatest in rice paddies among different land-use types. Responses of soil CO2 fluxes and MBC to biochar amendment varied with soil texture and pH. The use of biochar in combination with synthetic N fertilizer and waste compost fertilizer led to the greatest increases in soil CO2 fluxes and MBC content, respectively. Both soil CO2 fluxes and MBC responses to biochar amendment decreased with biochar application rate, pyrolysis temperature, or C/N ratio of biochar, while each increased SOC content enhancement. Among different biochar feedstock sources, positive responses of soil CO2 fluxes and MBC were the highest for manure and crop residue feedstock sources, respectively. Soil CO2 flux responses to biochar amendment decreased with pH of biochar, while biochars with pH of 8.1-9.0 had the greatest enhancement of SOC and MBC contents. Therefore, soil properties, land-use type, agricultural practice, and biochar characteristics should be taken into account to assess the practical potential of biochar for mitigating climate change. [ABSTRACT FROM AUTHOR]

The application of organic materials to soil can recycle nutrients and increase organic matter in agricultural lands. Digestate can be used as a nutrient source for crop production but it has also been shown to stimulate greenhouse gas (GHG) emissions from amended soils. While edaphic factors, such as soil texture and pH, have been shown to be strong determinants of soil GHG fluxes, the impact of the legacy of previous management practices is less well understood. Here we aim to investigate the impact of such legacy effects and to contrast them against soil properties to identify the key determinants of soil GHG fluxes following digestate application. Soil from an already established field experiment was used to set up a pot experiment, to evaluate N2O, CH4 and CO2 fluxes from cattle‐slurry‐digestate amended soils. The soil had been treated with farmyard manure, green manure or synthetic N‐fertilizer, 18 months before the pot experiment was set up. Following homogenization and a preincubation stage, digestate was added at a concentration of 250 kg total N/ha eq. Soil GHG fluxes were then sampled over a 64 day period. The digestate stimulated emissions of the three GHGs compared to controls. The legacy of previous soil management was found to be a key determinant of CO2 and N2O flux while edaphic variables did not have a significant effect across the range of variables included in this experiment. Conversely, edaphic variables, in particular texture, were the main determinant of CH4 flux from soil following digestate application. Results demonstrate that edaphic factors and current soil management regime alone are not effective predictors of soil GHG flux response following digestate application. Knowledge of the site management in terms of organic amendments is required to make robust predictions of the likely soil GHG flux response following digestate application to soil. [ABSTRACT FROM AUTHOR]

Restoring overstocked forests by thinning and pyrolyzing residual biomass produces biochar and other value‐added products. Forest soils amended with biochar have potential to sequester carbon (C), improve soil quality, and alter greenhouse gas (GHG) emissions without depleting nutrient stocks. Yet, few studies have examined the effects of biochar on GHG emissions and tree growth in temperate forest soils. We measured GHG emissions, soil C content, and tree growth at managed forest sites in Idaho, Montana, and Oregon. We applied biochar amendments of 0, 2.5, or 25 Mg/ha to the forest soil surface. Flux of carbon dioxide and methane varied by season; however, neither were affected by biochar amendment. Flux of nitrous oxide was not detected at these nitrogen‐limited and unfertilized forest sites. Biochar amendment increased soil C content by 41% but did not affect tree growth. Overall, biochar had no detrimental effects on forest trees or soils. We conclude that biochar can be used harmlessly for climate change mitigation in forests by sequestering C in the soil. Forest soils amended with biochar made from forest residues have potential to modify tree growth, alter greenhouse gas emissions, and enhance long‐term soil carbon storage. In our study, various biochar amendments did not affect forest tree growth or greenhouse gas emissions but did increase soil carbon content up to 41%. We conclude that biochar can be safely applied to forest soils for the purpose of sequestering carbon. [ABSTRACT FROM AUTHOR]

Bioenergy as well as bioenergy with carbon capture and storage are key options to embark on cost-efficient trajectories that realize climate targets. Most studies have not yet assessed the influence on these trajectories of emerging bioeconomy sectors such as biochemicals and renewable jet fuels ( RJFs). To support a systems transition, there is also need to demonstrate the impact on the energy system of technology development, biomass and fossil fuel prices. We aim to close this gap by assessing least-cost pathways to 2030 for a number of scenarios applied to the energy system of the Netherlands, using a cost-minimization model. The type and magnitude of biomass deployment are highly influenced by technology development, fossil fuel prices and ambitions to mitigate climate change. Across all scenarios, biomass consumption ranges between 180 and 760 PJ and national emissions between 82 and 178 Mt CO2. High technology development leads to additional 100-270 PJ of biomass consumption and 8-20 Mt CO2 emission reduction compared to low technology development counterparts. In high technology development scenarios, additional emission reduction is primarily achieved by bioenergy and carbon capture and storage. Traditional sectors, namely industrial biomass heat and biofuels, supply 61-87% of bioenergy, while wind turbines are the main supplier of renewable electricity. Low technology pathways show lower biochemical output by 50-75%, do not supply RJFs and do not utilize additional biomass compared to high technology development. In most scenarios the emission reduction targets for the Netherlands are not met, as additional reduction of 10-45 Mt CO2 is needed. Stronger climate policy is required, especially in view of fluctuating fossil fuel prices, which are shown to be a key determinant of bioeconomy development. Nonetheless, high technology development is a no-regrets option to realize deep emission reduction as it also ensures stable growth for the bioeconomy even under unfavourable conditions. [ABSTRACT FROM AUTHOR]

Conversion of large areas of agricultural grassland is inevitable if European and UK domestic production of biomass is to play a significant role in meeting demand. Understanding the impact of these land-use changes on soil carbon cycling and stocks depends on accurate predictions from well-parameterized models. Key considerations are cultivation disturbance and the effect of autotrophic root input stimulation on soil carbon decomposition under novel biomass crops. This study presents partitioned parameters from the conversion of semi-improved grassland to Miscanthus bioenergy production and compares the contribution of autotrophic and heterotrophic respiration to overall ecosystem respiration of CO2 in the first and second years of establishment. Repeated measures of respiration from within and without root exclusion collars were used to produce time-series model integrations separating live root inputs from decomposition of grass residues ploughed in with cultivation of the new crop. These parameters were then compared to total ecosystem respiration derived from eddy covariance sensors. Average soil surface respiration was 13.4% higher in the second growing season, increasing from 2.9 to 3.29 g CO2-C m−2 day−1. Total ecosystem respiration followed a similar trend, increasing from 4.07 to 5.4 g CO2-C m−2 day−1. Heterotrophic respiration from the root exclusion collars was 32.2% lower in the second growing season at 1.20 g CO2-C m−2 day−1 compared to the previous year at 1.77 g CO2-C m−2 day−1. Of the total respiration flux over the two-year time period, aboveground autotrophic respiration plus litter decomposition contributed 38.46% to total ecosystem respiration while belowground autotrophic respiration and stimulation by live root inputs contributed 46.44% to soil surface respiration. This figure is notably higher than mean figures for nonforest soils derived from the literature and demonstrates the importance of crop-specific parameterization of respiration models. [ABSTRACT FROM AUTHOR]

The need for renewable energy sources will lead to a considerable expansion in the planting of dedicated fast-growing biomass crops across Europe. These are commonly cultivated as short-rotation coppice ( SRC), and currently poplar ( Populus spp.) is the most widely planted. In this study, we report the greenhouse gas ( GHG) fluxes of carbon dioxide ( CO2), methane ( CH4) and nitrous oxide (N2O) measured using eddy covariance technique in an SRC plantation for bioenergy production. Measurements were made during the period 2010-2013, that is, during the first two rotations of the SRC. The overall GHG balance of the 4 years of the study was an emission of 1.90 (±1.37) Mg CO2eq ha−1; this indicated that soil trace gas emissions offset the CO2 uptake by the plantation. CH4 and N2O contributed almost equally to offset the CO2 uptake of −5.28 (±0.67) Mg CO2eq ha−1 with an overall emission of 3.56 (±0.35) Mg CO2eq ha−1 of N2O and of 3.53 (±0.85) Mg CO2eq ha−1 of CH4. N2O emissions mostly occurred during one single peak a few months after the site was converted to SRC; this peak comprised 44% of the total N2O loss during the two rotations. Accurately capturing emission events proved to be critical for deriving correct estimates of the GHG balance. The nitrogen (N) content of the soil and the water table depth were the two drivers that best explained the variability in N2O and CH4, respectively. This study underlines the importance of the 'non- CO2 GHGs' on the overall balance. Further long-term investigations of soil trace gas emissions should monitor the N content and the mineralization rate of the soil, as well as the microbial community, as drivers of the trace gas emissions. [ABSTRACT FROM AUTHOR]

Soil amendment with pyrogenic organic matter (Py OM), also named biochar, is claimed to sequester carbon (C). However, possible interactions between Py OM and native soil organic carbon ( SOC) may accelerate the loss of SOC, thus reducing Py OM's C sequestration potential. We combined the results of 46 studies in a meta-analysis to investigate changes in CO2 emission of Py OM-amended soils and to identify the causes of these changes and the possible factors involved. Our results showed a statistically significant increase of 28% in CO2 emission from Py OM-amended soils. When grouped by Py OM C (PyC): SOC ratios, the group of studies with a ratio >2 showed a significant increase in CO2 emissions, but those with a ratio <2 showed no significant effect of Py OM application on CO2 emission. Our data are consistent with the hypothesis that increased CO2 emission after Py OM addition is additive and mainly derived from Py OM's labile C fractions. The PyC: SOC ratio provided the best predictor of increases in CO2 production after Py OM addition to soil. This meta-analysis highlights the importance of taking into account the amount of applied PyC in relation to SOC for designing future decomposition experiments. [ABSTRACT FROM AUTHOR]

The growing demand for bioenergy increases pressure on peatlands. The novel strategy of wet peatlands agriculture (paludiculture) may permit the production of bioenergy from biomass while avoiding large greenhouse gas emissions as occur during conventional crop cultivation on drained peat soils. Herein, we present the first greenhouse gas balances of a simulated paludiculture to assess its suitability as a biomass source from a climatic perspective. In a rewetted peatland, we performed closed-chamber measurements of carbon dioxide, methane, and nitrous oxide exchange in stands of the potential crops Phragmites australis, Typha latifolia, and Carex acutiformis for two consecutive years. To simulate harvest, the biomass of half of the measurement spots was removed once per year. Carbon dioxide exchange was close to neutral in all tested stands. The effect of biomass harvest on the carbon dioxide exchange differed between the 2 years. During the first and second year, methane emissions were 13-63 g m−2 a−1 and 2-5 g m−2 a−1, respectively. Nitrous oxide emissions lay below our detection limit. Net greenhouse gas balances in the study plots were close to being climate neutral during both years except for the Carex stand, which was a source of greenhouse gases in the first year (in CO2-equivalents: 18 t ha−1 a−1). Fifteen years after rewetting the net greenhouse gas balance of the study site was similar to those of pristine fens. In addition, we did not find a significant short-term effect of biomass harvest on net greenhouse gas balances. In our ecosystem, ~17 t ha−1 a−1 of CO2-equivalent emissions are saved by rewetting compared to a drained state. Applying this figure to the fen area in northern Germany, emission savings of 2.8-8.5 Mt a−1 CO2-equivalents could possibly be achieved by rewetting; this excludes additional savings by fossil fuel replacement. [ABSTRACT FROM AUTHOR]

Cellulosic ethanol is widely believed to offer substantial environmental advantages over petroleum fuels and grain-based ethanol, particularly in reducing greenhouse gas emissions from transportation. The environmental impacts of biofuels are largely caused by precombustion activities, feedstock production and conversion facility operations. Life cycle analysis ( LCA) is required to understand these impacts. This article describes a field-to-blending terminal LCA of cellulosic ethanol produced by biochemical conversion (hydrolysis and fermentation) using corn stover or switchgrass as feedstock. This LCA develops unique models for most elements of the biofuel production process and assigns environmental impact to different phases of production. More than 30 scenarios are evaluated, reflecting a range of feedstock, technology and scale options for near-term and future facilities. Cellulosic ethanol, as modeled here, has the potential to significantly reduce greenhouse gas ( GHG) emissions compared to petroleum-based liquid transportation fuels, though substantial uncertainty exists. Most of the conservative scenarios estimate GHG emissions of approximately 45-60 g carbon dioxide equivalent per MJ of delivered fuel (g CO2e MJ−1) without credit for coproducts, and 20-30 g CO2e MJ−1 when coproducts are considered. Under most scenarios, feedstock production, grinding and transport dominate the total GHG footprint. The most optimistic scenarios include sequestration of carbon in soil and have GHG emissions below zero g CO2e MJ−1, while the most pessimistic have life-cycle GHG emissions higher than petroleum gasoline. Soil carbon changes are the greatest source of uncertainty, dominating all other sources of GHG emissions at the upper bound of their uncertainty. Many LCAs of biofuels are narrowly constrained to GHG emissions and energy; however, these narrow assessments may miss important environmental impacts. To ensure a more holistic assessment of environmental performance, a complete life cycle inventory, with over 1100 tracked material and energy flows for each scenario is provided in the online supplementary material for this article. [ABSTRACT FROM AUTHOR]

Forests of the European Union ( EU) have been intensively managed for decades, and they have formed a significant sink for carbon dioxide ( CO2) from the atmosphere over the past 50 years. The reasons for this behavior are multiple, among them are: forest aging, area expansion, increasing plant productivity due to environmental changes of many kinds, and, most importantly, the growth rates of European forest having been higher than harvest rates. EU countries have agreed to reduce total emissions of GHG by 20% in 2020 compared to 1990, excluding the forest sink. A relevant question for climate policy is: how long will the current sink of EU forests be maintained in the near future? And could it be affected by other mitigation measures such as bioenergy? In this article we assess tradeoffs of bioenergy use and carbon sequestration at large scale and describe results of the comparison of two advanced forest management models that are used to project CO2 emissions and removals from EU forests until 2030. EFISCEN, a detailed statistical matrix model and G4M, a geographically explicit economic forestry model, use scenarios of future harvest rates and forest growth information to estimate the future carbon balance of forest biomass. Two scenarios were assessed: the EU baseline scenario and the EU reference scenario (including additional bioenergy and climate policies). Our projections suggest a significant decline of the sink until 2030 in the baseline scenario of about 25-40% (or 65-125 Mt CO2) compared to the models' 2010 estimate. Including additional bioenergy targets of EU member states has an effect on the development of this sink, which is not accounted in the EU emission reduction target. A sensitivity analysis was performed on the role of future wood demand and proved the importance of this driver for the future sink development. [ABSTRACT FROM AUTHOR]

The net CO2 exchange of forests was investigated to study net atmospheric impact of forest bioenergy production ( BP) and utilization in Finnish boreal conditions. Net CO2 exchange was simulated with a life cycle assessment tool over a 90-year period and over the whole Finland based on National Forest Inventory data. The difference in the net exchanges between the traditional timber production ( TP) and BP regime was considered the net atmospheric impact of forest bioenergy utilization. According to the results, forests became net sources of CO2 after about 20 years of simulation, and the net exchange was higher in the BP regime than in the TP regime until the middle of the simulation period. From 2040 onwards, the net exchange started to decrease in both regimes and became higher in the TP regime, excluding the last decade of the simulation. The shift of forests to becoming a CO2 source reflected the decrease in CO2 sequestration due to the increasing share of recently harvested and seedling stands that are acting as sources of CO2, and an increase of emissions from degradation of wood products. When expressed in terms of radiative forcing, the net atmospheric impact was on average 19% less for bioenergy compared with that for coal energy over the whole simulation period. The results show the importance of time dependence when considering dynamic forest ecosystems in BP and climate change mitigation. Furthermore, the results emphasize the dualistic role and possibilities of forest management in controlling the build and release of carbon into and from the stocks and in controlling the rate of the build speed, i.e. growth. This information is needed in identifying the capability and possibilities of ecosystems to produce biomass for energy, alongside other products and ecosystem services (e.g. pulp wood and timber), and simultaneously to mitigate climate change. [ABSTRACT FROM AUTHOR]

We studied the impact of reed canary grass ( RCG) cultivation on greenhouse gas emission in the following sites of an abandoned peat extraction area in Estonia: a bare soil ( BS) site, a nonfertilized P halaris (nfP) plot, a fertilized P halaris (fP) plot, and a natural bog ( NB) and a fen meadow ( FM) as reference areas. The C balance and global warming potential ( GWP) were estimated by measuring CO2, CH4, and N2O emissions and aboveground and belowground biomass variations. The high CO2 flux from the nfP and fP sites and the low CO2 emission from the BS are due to the enhancement of mineralization by plant growth on planted sites and inhibited mineralization by the recalcitrant C of BS. The NB site emitted 24 kg CH4 ha−1 yr−1, whereas the almost zero CH4 emission from the P halaris plots and the BS site was due to the high S concentration in peat, which probably inhibited methanogenesis. The N2O flux varied from <0.1 kg on the P halaris plots and the NB to 2.64 kg N2O ha−1 yr−1 on the FM. The highest yield of RCG was obtained in autumn (13.9 t and 8.0 t dw ha−1 on the fP and nfP, respectively). By spring, the biomass yield on the fP and nfP plot was 12.7 and 7.9 t dw ha−1, respectively. The C balance of nfP and fP plots was negative in comparison to the BS (−3322, −5983, and 2504 kg CO2 ha−1 yr−1, respectively). This indicates that the cultivation of RCG transformed them from a net source of C into a net sink of C. The GWP for the fP and nfP sites was −5981 and −3885 kg CO2 eq ha−1 yr−1, respectively. The BS site had a total GWP of 2544 kg CO2 eq ha−1 yr−1. [ABSTRACT FROM AUTHOR]

It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas ( GHG) footprint. We compared field emissions of nitrous oxide (N2O), methane ( CH4) and soil respiration rates from the C4 grass Miscanthus × giganteus and willow ( salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow , Miscanthus, wheat ( Triticum aetivum) and oilseed rape ( Brassica napus). N2O, CH4 fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange ( NEE) of carbon dioxide ( CO2) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N2O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 μg m−2 h−1 N2O-N from wheat and oilseed rape, and 4 and 0.2 μg m−2 h−1 N2O-N from Miscanthus and willow, respectively. Soil CH4 fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO2 was larger for Miscanthus (−770 g C m−2 h−1) than willow (−602 g C m−2 h−1) in the growing season of 2010. N2O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of 15N-labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer-induced increase in N2O emission in both crops. Denitrification rates (N2O + N2) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer. [ABSTRACT FROM AUTHOR]

The aim of this work was to study the sensitivity of carbon dioxide (CO2) emissions from wood energy to different forest management regimes when aiming at an integrated production of timber and energy biomass. For this purpose, the production of timber and energy biomass in Norway spruce [ Picea abies (L.) Karst] and Scots pine ( Pinus sylvestris L.) stands was simulated using an ecosystem model (SIMA) on sites of varying fertility under different management regimes, including various thinning and fertilization treatments over a fixed simulation period of 80 years. The simulations included timber (sawlogs, pulp), energy biomass (small-sized stem wood) and/or logging residues (top part of stem, branches and needles) from first thinning, and logging residues and stumps from final felling for energy production. In this context, a life cycle analysis/emission calculation tool was used to assess the CO2 emissions per unit of energy (kg CO2 MWh−1) which was produced based on the use of wood energy. The energy balance (GJ ha−1) of the supply chain was also calculated. The evaluation of CO2 emissions and energy balance of the supply chain considered the whole forest bioenergy production chain, representing all operations needed to grow and harvest biomass and transport it to a power plant for energy production. Fertilization and high precommercial stand density clearly increased stem wood production (i.e. sawlogs, pulp and small-sized stem wood), but also the amount of logging residues, stump wood and roots for energy use. Similarly, the lowest CO2 emissions per unit of energy were obtained, regardless of tree species and site fertility, when applying extremely or very dense precommercial stand density, as well as fertilization three times during the rotation. For Norway spruce such management also provided a high energy balance (GJ ha−1). On the other hand, the highest energy balance for Scots pine was obtained concurrently with extremely dense precommercial stands without fertilization on the medium-fertility site, while on the low-fertility site fertilization three times during the rotation was needed to attain this balance. Thus, clear differences existed between species and sites. In general, the forest bioenergy supply chain seemed to be effective; i.e. the fossil fuel energy consumption varied between 2.2% and 2.8% of the energy produced based on the forest biomass. To conclude, the primary energy use and CO2 emissions related to the forest operations, including the production and application of fertilizer, were small in relation to the increased potential of energy biomass. [ABSTRACT FROM AUTHOR]