Land use change to bioenergy: A meta-analysis of soil carbon and GHG emissions

A systematic review and meta-analysis were used to assess the current state of knowledge and quantify the effects of land use change (LUC) to second generation (2G), non-food bioenergy crops on soil organic carbon (SOC) and greenhouse gas (GHG) emissions of relevance to temperate zone agriculture. Following analysis from 138 original studies, transitions from arable to short rotation coppice (SRC, poplar or willow) or perennial grasses (mostly Miscanthus or switchgrass) resulted in increased SOC (+5.0 ± 7.8% and +25.7 ± 6.7% respectively). Transitions from grassland to SRC were broadly neutral (+3.7 ± 14.6%), whilst grassland to perennial grass transitions and forest to SRC both showed a decrease in SOC (−10.9 ± 4.3% and −11.4 ± 23.4% respectively). There were insufficient paired data to conduct a strict meta-analysis for GHG emissions but summary figures of general trends in GHGs from 188 original studies revealed increased and decreased soil CO₂ emissions following transition from forests and arable to perennial grasses. We demonstrate that significant knowledge gaps exist surrounding the effects of land use change to bioenergy on greenhouse gas balance, particularly for CH₄. There is also large uncertainty in quantifying transitions from grasslands and transitions to short rotation forestry. A striking finding of this review is the lack of empirical studies that are available to validate modelled data. Given that models are extensively use in the development of bioenergy LCA and sustainability criteria, this is an area where further long-term data sets are required.     

Change in carbon footprint of canola production in the Canadian Prairies from 1986 to 2006

Accounting for greenhouse gas (GHG) emissions at the production stage of a bioenergy crop is essential for evaluating its eco-efficiency. The objective of this study was to calculate the change in GHG emissions for canola (Brassica napus L.) production on the Canadian Prairies from 1986 to 2006. Net GHG emissions in the sub-humid and semi-arid climatic zones were estimated for fallow-seeded and stubble-seeded canola in intensive-, reduced- and no-tillage systems, with consideration given to emissions associated with synthetic nitrogen (N) fertilizer input, mineralized N from crop residues, N leaching and volatilization, farm operations, the manufacturing and transportation of fertilizer, agrochemicals and farm machinery, and emission and removal of CO₂ associated with changes in land use (LUC) and land management (LMC). The GHG emissions on an area basis were higher in stubble-seeded canola than in fallow-seeded canola but, the opposite was true on a grain dry matter (DM) basis. Nitrous oxide emissions associated with canola production, CO₂ emissions associated with farm energy use and the manufacturing of synthetic N fertilizer and its transportation contributed 49% of the GHG emissions in 1986 which increased to 66% in 2006. Average CO₂ emissions due to LUC decreased from 27% of total GHG emissions in 1986 to 8% in 2006 and soil C sequestration due to LMC increased from 8% to 37%, respectively. These changes caused a reduction in net GHG emission intensities of 40% on an area basis and of 65% on a grain DM basis. Despite the reduction in GHG emission intensities, GHG emissions associated with canola in the Prairies increased from 3.4 Tg CO₂ equiv in 1986 to 3.8 Tg CO₂ equiv in 2006 because of the more than doubling of canola production.     

A conceptual framework for estimating the climate impacts of land-use change due to energy crop programs

In this paper I discuss general conceptual issues in the estimation of the impacts of CO₂ emissions from soils and biomass, over time, as a result of land-use change (LUC) due to increased demand for energy crops. The effect of LUC on climate depends generally on the magnitude and timing of changes in soil and plant carbon, and in particular on the timing and extent of the reversion of land to original ecosystems at the end of the bioenergy program. Depending on whether one counts the climate impacts of any reversion of land uses, and how one values future climate-change impacts relative to present impacts, one can estimate anywhere from zero to very large climate impacts due to land-use change (LUC). I argue that the best method is to estimate the net present value (NPV) of the impacts of climate change due to LUC. With this approach, one counts the reversion impacts at the end of the program and applies a continuous discounting function to future impacts to express them in present terms. In this case, the impacts of CO₂ emissions from the initial LUC then are at least partially offset by the impacts of CO₂ sequestration from reversion.     

The GHG balance of biofuels taking into account land use change

The contribution of biofuels to the saving of greenhouse gas (GHG) emissions has recently been questioned because of emissions resulting from land use change (LUC) for bioenergy feedstock production. We investigate how the inclusion of the carbon effect of LUC into the carbon accounting framework, as scheduled by the European Commission, impacts on land use choices for an expanding biofuel feedstock production. We first illustrate the change in the carbon balances of various biofuels, using methodology and data from the IPCC Guidelines for National Greenhouse Gas Inventories. It becomes apparent that the conversion of natural land, apart from grassy savannahs, impedes meeting the EU's 35% minimum emissions reduction target for biofuels. We show that the current accounting method mainly promotes biofuel feedstock production on former cropland, thus increasing the competition between food and fuel production on the currently available cropland area. We further discuss whether it is profitable to use degraded land for commercial bioenergy production as requested by the European Commission to avoid undesirable LUC and conclude that the current regulation provides little incentive to use such land. The exclusive consideration of LUC for bioenergy production minimizes direct LUC at the expense of increasing indirect LUC.     

Nitrogen fertilization of switchgrass increases biomass yield and improves net greenhouse gas balance in northern Michigan, U.S.A

Nitrogen (N) fertilization can increase bioenergy crop production; however, fertilizer production and application can contribute to greenhouse gas (GHG) emissions, potentially undermining the GHG benefits of bioenergy crops. The objective of this study was to evaluate the effects of N fertilization on GHG emissions and biomass production of switchgrass bioenergy crop, in northern Michigan. Nitrogen fertilization treatments included 0 kg ha⁻¹ (control), 56 kg ha⁻¹ (low) and 112 kg ha⁻¹ (high) of N applied as urea. Soil fluxes of CO₂, N₂O and CH₄ were measured every two weeks using static chambers. Indirect GHG emissions associated with field activities, manufacturing and transport of fertilizer and pesticides were derived from the literature. Switchgrass aboveground biomass yield was evaluated at the end of the growing season. Nitrogen fertilization contributed little to soil GHG emissions; relative to the control, there were additional global warming potential of 0.7 Mg ha⁻¹ y⁻¹ and 1.5 Mg ha⁻¹ y⁻¹ as CO₂ equivalents (CO₂eq), calculated using the IPCC values, in the low and high N fertilization treatments, respectively. However, N fertilization greatly stimulated CO₂ uptake by switchgrass, resulting in 1.5- and 2.5-fold increases in biomass yield in the low and high N fertilization treatments, respectively. Nitrogen amendments improved the net GHG benefits by 2.6 Mg ha⁻¹ y⁻¹ and 9.4 Mg ha⁻¹ y⁻¹ as CO₂eq relative to the control. Results suggest that N fertilization of switchgrass in this region could reduce (15-50%) the land base needed for bioenergy production and decrease pressure on land for food and forage crop production.     

Applying resource efficiency principles to the analysis of EU-27 bioenergy options by 2020 – Findings from a recent study for the European Environment Agency

The Renewable Energy Directive sets a target for the European Union (EU) to consume 20% of its final energy from renewable sources by 2020 and further targets are under discussion. EU renewable energy targets will lead to a substantial increase in the demand for bioenergy. As for other sectors, it is important, therefore, to apply the principles of the EU Resource efficiency roadmap to bioenergy production: producing more output with less material input and minimising adverse environmental impacts during the entire production life cycle. This paper uses that concept to analyse the most resource efficient ways for reaching the 2020 bioenergy targets (as set out in National Renewable Energy Action Plans).Scenario analysis with three different storylines is used to model environmental and land use implications plus total bioenergy potential and GHG reductions in 2020 from the agricultural, forest, and waste sectors. These storylines vary in environmental ambition level and economic and political assumptions and explore plausible bioenergy development paths. They show substantial variance in terms of environmental impact and the GHG efficiency between different bioenergy pathways.The modelling shows that under Storyline 1 bioenergy targets of the National Renewable Energy Action Plans would be achieved with CO₂ eq emissions of 44 kg GJ⁻¹, i.e. 62% less GHG emission than if the energy were generated using fossil fuels. In contrast, stricter environmental constraints in Storyline 3 lead to a substantially lower CO₂ eq burden of 25 kg GJ⁻¹, which represents an 80% reduction compared to fossil fuels.     

Spatial variation of environmental impacts of regional biomass chains

In this study, the spatial variation of potential environmental impacts of bioenergy crops is quantitatively assessed. The cultivation of sugar beet and Miscanthus for bioethanol production in the North of the Netherlands is used as a case study. The environmental impacts included are greenhouse gas (GHG) emissions (during lifecycle and related to direct land use change), soil quality, water quantity and quality, and biodiversity. Suitable methods are selected and adapted based on an extensive literature review. The spatial variation in environmental impacts related to the spatial heterogeneity of the physical context is assessed using Geographical Information System (GIS). The case study shows that there are large spatial variations in environmental impacts of the introduction of bioenergy crops. Land use change (LUC) to sugar beet generally causes more negative environmental impacts than LUC to Miscanthus. LUC to Miscanthus could have positive environmental impacts in some areas. The most negative environmental impacts of a shift towards sugar beet and Miscanthus occur in the western wet pasture areas. The spatially combined results of the environmental impacts illustrate that there are several trade offs between environmental impacts: there are no areas were no negative environmental impacts occur. The assessment demonstrates a framework to identify areas with potential negative environmental impacts of bioenergy crop production and areas where bioenergy crop production have little negative or even positive environmental impacts.     

Soil CO2–C flux and carbon storage in the dry tropics: Impact of land-use change involving bioenergy crop plantation

The study was conducted to evaluate the impact of land-use change in the dry tropics on soil CO₂–C flux and soil organic carbon (SOC) storage, along with the major factors controlling them i.e. soil microbial biomass (SMB), belowground net productivity (BNP), and soil aggregate size fractions. Land-use change, in this study, involved conversion of natural forest, to degraded forest and then to an agroecosystem or a bioenergy crop plantation of Jatropha curcas. The soil CO₂–C flux was highest in the agroecosystem followed in decreasing order by degraded forest, bioenergy crop plantation and smallest in the natural forest. The inverse trend was found in case of SOC storage, SMB and BNP. The proportion of macroaggregate in the soil follows the trend of SOC storage, whereas mesoaggregate follows the trend of CO₂–C flux across all land-use types. The CO₂–C flux showed significant negative correlation with BNP, SMB, macroaggregate size fraction, and SOC. Our study suggests that the flux of soil CO₂–C was regulated directly by the soil aggregate fraction and not by SMB or BNP. However, soil aggregate formation was, in turn, related to the SMB and/or below BNP. Macroaggregates appear to protect the SOC, which results in lower CO₂–C flux and higher SOC storage. It can be concluded that the bioenergy crops plantation on degraded forest lands in the dry tropics, may increase C storage in soil and reduce soil CO₂–C flux, thereby helping in the mitigation of global climate change in addition to providing feed stocks for fossil fuel substitution.     

On sustainability of bioenergy production: Integrating co-emissions from agricultural intensification

Biomass from cellulosic bioenergy crops is seen as a substantial part of future energy systems, especially if climate policy aims at stabilizing CO₂ concentration at low levels. However, among other concerns of sustainability, the large-scale use of bioenergy is controversial because it is hypothesized to increase the competition for land and therefore raise N₂O emissions from agricultural soils due to intensification. We apply a global land-use model that is suited to assess agricultural non-CO₂ GHG emissions. First, we describe how fertilization of cellulosic bioenergy crops and associated N₂O emissions are implemented in the land-use model and how future bioenergy demand is derived by an energy-economy-climate model. We then assess regional N₂O emissions from the soil due to large-scale bioenergy application, the expansion of cropland and the importance of technological change for dedicated bioenergy crops. Finally, we compare simulated N₂O emissions from the agricultural sector with CO₂ emissions from the energy sector to investigate the real contribution of bioenergy for low stabilization scenarios.As a result, we find that N₂O emissions due to energy crop production are a minor factor. Nevertheless, these co-emissions can be significant for the option of removing CO₂ from the atmosphere (by combining bioenergy use with carbon capture and storage (CCS) options) possibly needed at the end of the century for climate mitigation. Furthermore, our assessment shows that bioenergy crops will occupy large shares of available cropland and will require high rates of technological change at additional costs.     

Carbon dioxide emissions from switchgrass and cottonwood grown as bioenergy crops in the Lower Mississippi River Alluvial Valley

Marginal land of the Lower Mississippi Alluvial Valley (LMAV) has the potential to be utilized for substantial production of bioenergy feedstocks. However, resulting ecosystem services associated with dedicated bioenergy crop production, such as soil respiration and carbon dioxide (CO₂) emissions, which play an important role in global carbon (C) cycling, are not well understood. The objective of this study was to evaluate the effects of land use [i.e., switchgrass (Panicum virgatum) and eastern cottonwood (Populus deltoides) grown as dedicated bioenergy crops and a soybean (Glycine max)-grain sorghum (Sorghum bicolor) agroecosystem rotation] on monthly respiration and estimated annual CO₂ emissions for 2012 and 2013 from a silt -loam soil in east-central Arkansas. Peak monthly fluxes achieved each year differed (p < 0.05) somewhat among ecosystems. Annual CO₂ emissions differed among ecosystems (p < 0.001), but not between years (p = 0.45). Cottonwood emitted less CO₂ in both years (7.3 and 7.4 Mg ha⁻¹ for 2012 and 2013, respectively) compared to the other two ecosystems, while emissions from the switchgrass did not differ from those from the soybean in 2012 (10.3 and 9.5 Mg ha⁻¹, respectively) or grain sorghum in 2013 (9.7 and 9.2 Mg ha⁻¹, respectively). Results showed established bioenergy feedstock cropping systems do not have greater soil CO₂ emissions compared with a traditional soybean-grain sorghum crop rotation. Results also indicated that different bioenergy feedstocks can produce different quantities of CO₂ emissions, which may be important to consider when converting marginal lands to bioenergy feedstock cropping systems.     

Economic and greenhouse gas emission analysis of bioenergy production using multi-product crops—case studies for the Netherlands and Poland

In the face of climate change that may result from greenhouse gas (GHG) emissions, the scarcity of agricultural land and limited competitiveness of biomass energy on the market, it is desirable to increase the performance of bioenergy systems. Multi-product crops, i.e. using a crop partially for energy and partially for material purposes can possibly create additional incomes as well as additional GHG emission reductions. In this study, the performance of several multi-product crop systems is compared to energy crop systems, focused on the costs of primary biomass fuel costs and GHG emission reductions per hectare of biomass production. The sensitivity of the results is studied by means of a Monte-Carlo analysis. The multi-product crops studied are wheat, hemp and poplar in the Netherlands and Poland. GHG emission reductions of these multi-product crop systems are found to be between 0.2 and 2.4 Mg CO_2eq/(ha yr) in Poland and 0.9 and 7.8 Mg CO_2eq/(ha yr) in the Netherlands, while primary biomass fuel costs range from −4.1 to −1.7 €/GJ in the Netherlands and from 0.1 to 9.8 €/GJ in Poland. Results show that the economic attractiveness of multi-product crops depends strongly on material market prices, crop production costs and crop yields. Net annual GHG emission reductions per hectare are influenced strongly by the specific GHG emission reduction of material use, reference energy systems and GHG emissions of crop production. Multi-product use of crops can significantly decrease primary biomass fuel costs. However, this does not apply in general, but depends on the kind of crops and material uses. For the examples analysed here, net annual GHG emission reductions per hectare are not lowered by multi-product use of crops. Consequently, multi-product crops are not for granted an option to increase the performance of bioenergy systems. Further research on the feasibility of large-scale multi-product crop systems and their impact on land and material markets is desirable.     

Life cycle GHG emissions from Malaysian oil palm bioenergy development: The impact on transportation sector's energy security

Malaysia's transportation sector accounts for 41% of the country's total energy use. The country is expected to become a net oil importer by the year 2011. To encourage renewable energy development and relieve the country's emerging oil dependence, in 2006 the government mandated blending 5% palm-oil biodiesel in petroleum diesel. Malaysia produced 16 million tonnes of palm oil in 2007, mainly for food use. This paper addresses maximizing bioenergy use from oil-palm to support Malaysia's energy initiative while minimizing greenhouse-gas emissions from land-use change. When converting primary and secondary forests to oil-palm plantations between 270–530 and 120–190 g CO₂-equivalent per MJ of biodiesel produced, respectively, is released. However, converting degraded lands results in the capture of between 23 and 85 g CO₂-equivalent per MJ of biodiesel produced. Using various combinations of land types, Malaysia could meet the 5% biodiesel target with a net GHG savings of about 1.03 million tonnes (4.9% of the transportation sector's diesel emissions) when accounting for the emissions savings from the diesel fuel displaced. These findings are used to recommend policies for mitigating GHG emissions impacts from the growth of palm oil use in the transportation sector.     

Estimating GHG emission mitigation supply curves of large-scale biomass use on a country level

This study evaluates the possible influences of a large-scale introduction of biomass material and energy systems and their market volumes on land, material and energy market prices and their feedback to greenhouse gas (GHG) emission mitigation costs. GHG emission mitigation supply curves for large-scale biomass use were compiled using a methodology that combines a bottom-up analysis of biomass applications, biomass cost supply curves and market prices of land, biomaterials and bioenergy carriers. These market prices depend on the scale of biomass use and the market volume of materials and energy carriers and were estimated using own-price elasticities of demand. The methodology was demonstrated for a case study of Poland in the year 2015 applying different scenarios on economic development and trade in Europe. For the key technologies considered, i.e. medium density fibreboard, poly lactic acid, electricity and methanol production, GHG emission mitigation costs increase strongly with the scale of biomass production. Large-scale introduction of biomass use decreases the GHG emission reduction potential at costs below 50 €/Mg CO_2eq with about 13–70% depending on the scenario. Biomaterial production accounts for only a small part of this GHG emission reduction potential due to relatively small material markets and the subsequent strong decrease of biomaterial market prices at large scale of production. GHG emission mitigation costs depend strongly on biomass supply curves, own-price elasticity of land and market volumes of bioenergy carriers. The analysis shows that these influences should be taken into account for developing biomass implementations strategies.     

Agricultural and agro-industrial residues-to-energy: Techno-economic and environmental assessment in Brazil

This study aims to quantify the environmentally sustainable and economically feasible potentials of agricultural and agro-industrial residues to generate electricity via direct combustion in centralised power plants in Brazil. Further, the energy savings and greenhouse gas (GHG) reduction potential of replacing natural gas-based electricity by bioenergy have been assessed. To this end, a methodology has been developed based on an integrated evaluation, incorporating statistical and geographical information system (GIS)-based analysis, and a life-cycle-assessment approach. Results reveal that the environmentally sustainable generation potential is nearly 141 TWh/year, mainly concentrated in the South, Southeast, and Midwest regions of the country. Sugarcane, soybean and maize crop residues are the major feedstocks for available bioenergy. On the other hand, the economic potential is far lower, accounting to 39 TWh/year. The total GHG mitigation is nearly 18 million tonne CO₂e and could reach 64 million tonne CO₂e yearly, if the technical potential is considered. The gap between technical and economic potentials implies that constraints to bioenergy are not related to a lack of resources, but rather associated to economic, logistical, regulatory and political barriers.     

Large-scale bioenergy production from soybeans and switchgrass in Argentina: Part B. Environmental and socio-economic impacts on a regional level

The feasibility of deploying a socio-economic and environmental impact analysis for large-scale bioenergy production on a regional level is analyzed, based on a set of defined criteria and indicators. The analysis is done for La Pampa province in Argentina. The case study results in conclusions in how far the criteria can be verified ex ante based on available methodologies and data sources. The impacts are analyzed for two bioenergy chains (soybeans and switchgrass) for a set of defined land use scenarios. The carbon stock change for switchgrass ranges from 0.2 to 1.2 ton C/ha/year and for soybean from ?1.2 to 0 ton C/ha/year, depending on the scenario. The GHG emission reduction ranges from 88% to 133% for the switchgrass bioenergy chain (replacing coal or natural gas) and from 16% to 94% for the soybean bioenergy chain (replacing fossil fuel) for various lifetime periods. The annual soil loss, compared to the reference land use system is 2–10 ton/ha for the soybean bioenergy chain and 1–2 ton/ha for the switchgrass bioenergy chain. In total, nine sustainability principles are analyzed. In the case of switchgrass, most environmental benefits can be achieved when produced on suitable land of abandoned cropland. Soybean production for bioenergy shows a good overall sustainability performance if produced on abandoned cropland. The production of switchgrass on degraded grassland shows socio-economic and environmental benefits, which is not the case for soybean production. The production of bioenergy production on non-degraded grassland is not preferred. It is concluded that the scenario approach enables understanding of the complexity of the bioenergy chain and the underlying factors influencing the sustainability principles. It is difficult to give ex ante a final conclusion whether a bioenergy chain is sustainable or not as this depends not only on the previous land use system but also on other factors as the selection of the bioenergy crop, the suitable agroecological zone and the agricultural management system applied. The results also imply that it is possible to steer for a large part the sustainability performance of a bioenergy chain during project development and implementation. Land use planning plays a key role in this process.     

Miscanthus and willow heat production—An effective land-use strategy for greenhouse gas emission avoidance in Ireland?

Recent decoupling of EU direct payments from agricultural production, to land-area-based payments, has accelerated the national trend of declining livestock numbers, presenting opportunities for new agricultural products. This paper uses life-cycle analyses to quantify the national magnitude and area-based efficiency of greenhouse gas (GHG) emission reductions possible from utilising indigenously grown willow and Miscanthus as heating fuels in domestic/commercial premises. Willow and Miscanthus fuel-chain emissions were calculated at 0.045 and 0.062 kg CO₂ eq. kWh_th, compared with 0.248, 0.331 and 0.624 kg CO₂ eq. kWh_th for gas, oil and electric heat, respectively. Long-term soil C sequestration where willow and Miscanthus are grown on tillage land could exceed fuel-chain emissions, resulting in heat production better than C-neutral. Net GHG emission reductions ranged from 7671 kg CO₂ eq. ha⁻¹ a⁻¹ where willow displaced grassland and gas to 34,187 kg CO₂ eq. ha⁻¹ a⁻¹ where Miscanthus displaced set-aside and electric heat. A simple, indicative scenario assumed that energy-crops were grown on set-aside and destocked grassland in the ratio of 1:2, and displaced a total of 4728 GWh_th combined gas, oil and electric heat. Consequent net GHG emission reductions arising from sole utilisation of either willow or Miscanthus equated to 2.6% or 2.5% of 2004 national emissions, and required just 2.9% or 2.1% of Ireland's agricultural land area. Net total emission reductions were relatively insensitive to variation in yield and cultivation emissions, but large reductions associated with electric-heat displacement will decline as electricity production becomes less GHG-intensive, and may not be representative of other countries. Energy-crop heat production offers considerably greater GHG emission reduction potential compared with agricultural destocking alone, and appears to represent an efficient land-use option for this purpose.     

Greenhouse gas balances and mitigation costs of 70 modern Germany-focused and 4 traditional biomass pathways including land-use change effects

With Germany as the point of energy end-use, 70 current and future modern pathways plus 4 traditional biomass pathways for heat, power and transport have been compiled and examined in one single greenhouse gas (GHG) balancing assessment. This is needed to broaden the narrow focus on biofuels for transport and identify the role of bioenergy in GHG mitigation. Sensitivity analysis for land-use changes and fossil reference systems are included. Co-firing of woody biomass and fermentation of waste biomass are the most cost-efficient and effective biomass applications for GHG emission reduction in modern pathways. Replacing traditional biomass with modern biomass applications offers an underestimated economic potential of GHG emission reduction. The range of maximum CO₂ equivalent GHG reduction potential of bioenergy is identified in a range of 2.5-16 Gt a⁻¹ in 2050 (5-33% of today’s global GHG emissions), and has an economic bioenergy potential of 150 EJ a⁻¹.     

Net N2O and CH4 soil fluxes of annual and perennial bioenergy crops in two central German regions

The area used for bioenergy feedstock production is increasing because substitution of fossil fuels by bioenergy is promoted as an option to reduce greenhouse gas (GHG) emissions. However, agriculture itself contributes to rising atmospheric nitrous oxide (N₂O) and methane (CH₄) concentrations. In this study we tested whether the net exchanges of N₂O and CH₄ between soil and atmosphere differ between annual fertilized and perennial unfertilized bioenergy crops. We measured N₂O and CH₄ soil fluxes from poplar short rotation coppice (SRC), perennial grass-clover and annual bioenergy crops (silage maize, oilseed rape, winter wheat) in two central German regions for two years. In the second year after establishment, the N₂O emissions were significantly lower in SRC (<0.1 kg N₂O–N ha⁻¹ yr⁻¹) than grassland (0.8 kg N₂O–N ha⁻¹ yr⁻¹) and the annual crop (winter wheat; 1.5 kg N₂O–N ha⁻¹ yr⁻¹) at one regional site (Reiffenhausen). However, a different trend was observed in the first year when contents of mineral nitrogen were still higher in SRC due to former cropland use. At the other regional site (Gierstädt), N₂O emissions were generally low (<0.5 kg N₂O–N ha⁻¹ yr⁻¹) and no crop-type effects were detected. Net uptake of atmospheric CH₄ varied between 0.4 and 1.2 kg CH₄–C ha⁻¹ yr⁻¹ with no consistent crop-type effect. The N₂O emissions related to gross energy in the harvested biomass ranged from 0.07 to 6.22 kg CO₂ equ GJ⁻¹. In both regions, Gierstädt (low N₂O emissions) and more distinct Reiffenhausen (medium N₂O emissions), this energy yield-related N₂O emission was the lowest for SRC.     

Energy and greenhouse gas balances of cassava-based ethanol

Biofuel production has been promoted to save fossil fuels and reduce greenhouse gas (GHG) emissions. However, there have been concerns about the potential of biofuel to improve energy efficiency and mitigate climate change. This paper investigates energy efficiency and GHG emission saving of cassava-based ethanol as energy for transportation. Energy and GHG balances are calculated for a functional unit of 1 km of road transportation using life-cycle assessment and considering effects of land use change (LUC). Based on a case study in Vietnam, the results show that the energy input for and GHG emissions from ethanol production are 0.93 MJ and 34.95 g carbon dioxide equivalent per megajoule of ethanol respectively. The use of E5 and E10 as a substitute for gasoline results in energy savings, provided that their fuel consumption in terms of liter per kilometer of transportation is not exceeding the consumption of gasoline per kilometer by more than 2.4% and 4.5% respectively. It will reduce GHG emissions, provided that the fuel consumption of E5 and E10 is not exceeding the consumption of gasoline per kilometer by more than 3.8% and 7.8% respectively. The quantitative effects depend on the efficiency in production and on the fuel efficiency of E5 and E10. The variations in results of energy input and GHG emissions in the ethanol production among studies are due to differences in coverage of effects of LUC, CO₂ photosynthesis of cassava, yields of cassava, energy efficiency in farming, and by-product analyses.     

GHG balances of bioenergy systems – Overview of key steps in the production chain and methodological concerns

This paper deals with a methodology for calculating the greenhouse gas (GHG) balances of bioenergy systems producing electricity, heat and transportation biofuels from biomass residues or crops. Proceeding from the standard Life-Cycle Assessment (LCA) as defined by ISO 14040 norms, this work provides an overview of the application of the LCA methodology to bioenergy systems in order to estimate GHG balances. In this paper, key steps in the bioenergy chain are identified and the bioenergy systems are compared with fossil reference systems producing the same amount of final products/services. The GHG emission balances of the two systems can thus be compared. Afterwards, the most important methodological assumptions (e.g. functional unit, allocation, reference system, system boundaries) and key aspects affecting the final outcomes are discussed. These key aspects are: changes in organic carbon pools, land-use change effects (both direct and indirect), N₂O and CH₄ emissions from agricultural soils and effects of crop residue removal for bioenergy use. This paper finally provides some guidelines concerning the compilation of GHG balances of bioenergy systems, with recommendations and indications on how to show final results, address the key methodological issues and give homogenous findings (in order to enhance the comparison across case studies).