Greenhouse gas emissions and abatement costs of biofuel production in South Africa

Transport accounts for about one quarter of South Africa's final energy consumption. Most of the energy used is based on fossil fuels causing significant environmental burdens. This threat becomes even more dominant as a significant growth in transport demand is forecasted, especially in South Africa's economic hub, Gauteng province. The South African government has realized the potential of biofuel usage for reducing oil import dependency and greenhouse gas (GHG) and has hence developed a National Biofuels Industrial Strategy to enforce their use. However, there is limited experience in the country in commercial biofuel production and some of the proposed crops (i.e. rapeseed and sugar beet) have not been yet cultivated on a larger scale. Furthermore, there is only limited research available, looking at the feasibility of commercial scale biofuel production or abatement costs of GHG emissions. To assess the opportunities of biofuel production in South Africa, the production costs and consumer price levels of the fuels recommended by the national strategy are analysed in this article. Moreover, the lifecycle GHG emissions and mitigation costs are calculated compared to the calculated fossil fuel reference including coal to liquid (CTL) and gas to liquid (GTL) fuels. The results show that the cost for biofuel production in South Africa are currently significantly higher (between 30% and 80%) than for the reference fossil fuels. The lifecycle GHG emissions of biofuels (especially for sugar cane) are considerably lower (up to 45%) than the reference fossil GHG emissions. The resulting GHG abatement costs are between 1000 and 2500 ZAR₂₀₀₇ per saved ton of carbon dioxide equivalent, which is high compared to the current European CO₂ market prices of ca. 143 ZAR₂₀₀₇ t^?1. The analysis has shown that biofuel production and utilization in South Africa offers a significant GHG‐mitigation potential but at relatively high cost.     

Environmental costs and benefits of growing Miscanthus for bioenergy in the UK

Planting the perennial biomass crop Miscanthus in the UK could offset 2–13 Mt oil eq. yr^?1, contributing up to 10% of current energy use. Policymakers need assurance that upscaling Miscanthus production can be performed sustainably without negatively impacting essential food production or the wider environment. This study reviews a large body of Miscanthus relevant literature into concise summary statements. Perennial Miscanthus has energy output/input ratios 10 times higher (47.3 ± 2.2) than annual crops used for energy (4.7 ± 0.2 to 5.5 ± 0.2), and the total carbon cost of energy production (1.12 g CO₂‐C eq. MJ^?1) is 20–30 times lower than fossil fuels. Planting on former arable land generally increases soil organic carbon (SOC) with Miscanthus sequestering 0.7–2.2 Mg C4‐C ha^?1 yr^?1. Cultivation on grassland can cause a disturbance loss of SOC which is likely to be recovered during the lifetime of the crop and is potentially mitigated by fossil fuel offset. N₂O emissions can be five times lower under unfertilized Miscanthus than annual crops and up to 100 times lower than intensive pasture. Nitrogen fertilizer is generally unnecessary except in low fertility soils. Herbicide is essential during the establishment years after which natural weed suppression by shading is sufficient. Pesticides are unnecessary. Water‐use efficiency is high (e.g. 5.5–9.2 g aerial DM (kg H₂O)^?1, but high biomass productivity means increased water demand compared to cereal crops. The perennial nature and belowground biomass improves soil structure, increases water‐holding capacity (up by 100–150 mm), and reduces run‐off and erosion. Overwinter ripening increases landscape structural resources for wildlife. Reduced management intensity promotes earthworm diversity and abundance although poor litter palatability may reduce individual biomass. Chemical leaching into field boundaries is lower than comparable agriculture, improving soil and water habitat quality.     

Economic and environmental performance of miscanthus cultivated on marginal land for biogas production

Environmental issues surrounding conventional annual biogas crops have led to growing interest in alternative crops, such as miscanthus. In addition to the better environmental performance, miscanthus can be grown on marginal land where no competition with feed and food crops is anticipated. On marginal land however, biomass yields are significantly lower than on good agricultural land. This raises the question of the economic and environmental sustainability of miscanthus cultivated on marginal land for biogas production. This study assessed the environmental and economic performance of miscanthus cultivated on marginal land for biogas production by conducting a Life‐Cycle Assessment and complementary Life‐Cycle Cost analysis. The functional unit chosen was 1 GJ of electricity (GJ_el.). The substitution of a fossil reference was included using a system expansion approach. Electricity generated by the combustion of miscanthus‐based biogas in a combined heat and power has considerably lower impacts on the environment than the fossil reference in most of the categories assessed. In the impact category “climate change”, the substitution of the marginal German electricity mix leads to a carbon mitigation potential of 256 kg CO₂e/GJ_el.. At 45.12 €/GJ_el., the costs of miscanthus‐based biogas generation and utilization are considerably lower than those of maize (61.30 €/GJ_el.). The results of this study clearly show that it can make economic and environmental sense to cultivate miscanthus on marginal land as a substrate for biogas production. The economic sustainability is however limited by the biomass yield. By contrast, there are no clear thresholds limiting the environmental performance. The decision needs to be made on a case‐by‐case basis depending on site‐specific conditions such as local biodiversity.     

Bioenergy crop greenhouse gas mitigation potential under a range of management practices

Perennial grasses have been proposed as viable bioenergy crops because of their potential to yield harvestable biomass on marginal lands annually without displacing food and to contribute to greenhouse gas (GHG) reduction by storing carbon in soil. Switchgrass, miscanthus, and restored native prairie are among the crops being considered in the corn and agricultural regions of the Midwest and eastern United States. In this study, we used an extensive dataset of site observations for each of these crops to evaluate and improve the DayCent biogeochemical model and make predictions about how both yield and GHG fluxes would respond to different management practices compared to a traditional corn‐soy rotation. Using this model‐data integration approach, we found 30–75% improvement in our predictions over previous studies and a subsequent evaluation with a synthesis of sites across the region revealed good model‐data agreement of harvested yields (r² > 0.62 for all crops). We found that replacement of corn‐soy rotations would result in a net GHG reduction of 0.5, 1.0, and 2.0 Mg C ha^?1 yr^?1 with average annual yields of 3.6, 9.2, and 17.2 Mg of dry biomass per year for native prairie, switchgrass, and miscanthus respectively. Both the yield and GHG balance of switchgrass and miscanthus were affected by harvest date with highest yields occurring near onset of senescence and highest GHG reductions occurring in early spring before the new crops emergence. Addition of a moderate length rotation (10–15 years) caused less than a 15% change to yield and GHG balance. For policy incentives aimed at GHG reduction through onsite management practices and improvement of soil quality, post‐senescence harvests are a more effective means than maximizing yield potential.     

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

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 (ΔT_s(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 ΔT_s(n). However, the first years after establishing the willow plantation it presented a warming contribution to ΔT_s(n). This behavior was due mainly to soil organic carbon (SOC) variation. A rapid initial increase in standing biomass counteracted the initial SOC loss.     

Productivity and water use efficiency of Agave americana in the first field trial as bioenergy feedstock on arid lands

Agave species are high‐yielding crassulacean acid metabolism (CAM) plants, some of which are grown commercially and recognized as potential bioenergy species for dry regions of the world. This study is the first field trial of Agave species for bioenergy in the United States, and was established to compare the production of Agave americana with the production of Agave tequilana and Agave fourcroydes, which are produced commercially in Mexico for tequila and fiber. The field trial included four experimental irrigation levels to test the response of biomass production to water inputs. After 3 years, annual production of healthy A. americana plants reached 9.3 Mg dry mass ha^?1 yr^?1 (including pup mass) with 530 mm of annual water inputs, including both rainfall and irrigation. Yields in the most arid conditions tested (300 mm yr^?1 water input) were 2.0–4.0 Mg dry mass ha^?1 yr^?1. Agave tequilana and Agave fourcroydes were severely damaged by cold in the first winter, and produced maximum yields of only 0.04 Mg ha^?1 yr^?1 and 0.26 Mg ha^?1 yr^?1, respectively. The agave snout weevil (Scyphophorus acupunctatus) emerged as an important challenge for A. americana cropping, killing a greater number of plants in the higher irrigation treatments. Physiological differences in A. americana plants across irrigation treatments were most evident in the warmest season, with gas exchange beginning up to 3 h earlier and water use efficiency declining in treatments with the greatest water input (780 mm yr^?1 water input). Yields were lower than previous projections for Agave species, but results from this study suggest that A. americana has potential as a bioenergy crop and would have substantially reduced irrigation requirements relative to conventional crops in the southwestern USA. Challenges for pest management and harvesting must still be addressed before an efficient production system that uses Agave can be realized.     

Genotypic variation of cell wall composition and its conversion efficiency in Miscanthus sinensis,a potential biomass feedstock crop in China

Plant cell walls are composed of cellulose microfibrils embedded in a cross‐linked‐net of matrix polysaccharides and co‐polymerized with lignin. The study presented the genotypic variations of cell wall composition, biohydrogen production, and lignocellulose degradation ratio in a collection of 102 Miscanthus sinensis (M. Sinensis, hereafter) accessions collected from a wide geographical range in China. Significant variations were observed for the determined traits, cellulose content, hemicellulose content, cellulose and hemicellulose degradation efficiency, and biohydrogen yield. The cellulose, hemicellulose, and lignin contents ranged from 30.20–44.25, 28.97–42.65, and 6.96–20.75%, respectively. The degradation ratio of cellulose and hemicellulose varied from 2.08% to 37.87% and from 14.71% to 52.50%, respectively. The feedstock was fermented to produce biohydrogen, and the production varied from 14.59 to 40.66 ml per gram of Miscanthus biomass. The expression profile of three cellulose synthase (MsCesA) genes was initially established to indicate the genotypic difference among the M. sinensis accessions. Pearson's correlations were conducted to reveal the perplexing relationship between the tested traits, biohydrogen yield, cell wall composition and their degradation efficiency. In addition, the relationship pattern, between the test traits and the geographic factors corresponding with the original place, was investigated. The result showed that the significant variation among the M. sinensis genotypes is the result of natural selection in different environments of their original habitats. Improvement in cell wall composition and structure and enhancement of lignocellulose degradation ratio could significantly increase sustainable bioenergy production.     

Mass balance and life cycle assessment of biodiesel from microalgae incorporated with nutrient recycling options and technology uncertainties

This article presents mass balances and a detailed life cycle assessment (LCA) for energy and greenhouse gases (GHGs) of a simulated microalgae biodiesel production system. Key parameters of the system include biomass productivity of 16 and 25 g m^?2 day^?1 and lipid content of algae of 40% and 25% for low and normal nitrogen conditions respectively. Based on an oil extraction efficiency from wet biomass of 73.6% and methane yields from anaerobically digested lipid‐extracted biomass of 0.31 to 0.34 l per gram of volatile solids, the mass balance shows that recycling growth media and recovering nutrients from residual biomass through anaerobic digestion can reduce the total demand for nitrogen by 66% and phosphorus by 90%. Freshwater requirements can be reduced by 89% by recirculating growth media, and carbon requirements reduced by 40% by recycling CO₂ from biogas combustion, for normal nitrogen conditions. A variety of technology options for each step of the production process and allocation methods for coproducts used outside the production system are evaluated using LCA. Extensive sensitivity and scenario analysis is also performed to provide better understanding of uncertainty associated with results. The best performing scenario consists of normal nitrogen cultivation conditions, bioflocculation and dissolved air flotation for harvesting, centrifugation for dewatering, wet extraction with hexane, transesterification for biodiesel production, and anaerobic digestion of biomass residual, which generates biogas used in a combined heat and power unit for energy recovery. This combination of technologies and operating conditions results in life cycle energy requirements and GHG emissions of 1.02 MJ and 71 g CO₂‐equivalent per MJ of biodiesel, with cultivation and oil extraction dominating energy use and emissions. Thus, even under optimistic conditions, the near‐term performance of this biofuel pathway does not achieve the significant reductions in life cycle GHG emissions hoped for from second‐generation biofuel feedstocks.     

Fuzzy GIS‐based multi‐criteria evaluation for US Agave production as a bioenergy feedstock

In the United States, renewable energy mandates calling for increased production of cellulosic biofuels will require a diversity of bioenergy feedstocks to meet growing demands. Within the suite of potential energy crops, plants within the genus Agave promise to be a productive feedstock in hot and arid regions. The potential distributions of Agave tequilana and Agave deserti in the United States were evaluated based on plant growth parameters identified in an extensive literature review. A geospatial suitability model rooted in fuzzy logic was developed that utilized a suite of biophysical criteria to optimize ideal geographic locations for this new crop, and several suitability scenarios were tested for each species. The results of this spatially explicit suitability model suggest that there is potential for Agave to be grown as an energy feedstock in the southwestern region of the United States – particularly in Arizona, California, and Texas – and a significant portion of these areas are proximate to existing transportation infrastructure. Both Agave species showed the highest state‐level renewable energy benefit in Arizona, where agave plants have the potential to contribute 4.8–9.6% of the states' ethanol consumption, and 2.5–4.9% of its electricity consumption, for A. deserti and A. tequilana, respectively. This analysis supports the feasibility of Agave as a complementary bioenergy feedstock that can be grown in areas too harsh for conventional energy feedstocks.     

Consequential life cycle assessment of biogas,biofuel and biomass energy options within an arable crop rotation

Feed in tariffs (FiTs) and renewable heat incentives (RHIs) are driving a rapid expansion in anaerobic digestion (AD) coupled with combined heat and power (CHP) plants in the UK. Farm models were combined with consequential life cycle assessment (CLCA) to assess the net environmental balance of representative biogas, biofuel and biomass scenarios on a large arable farm, capturing crop rotation and digestate nutrient cycling effects. All bioenergy options led to avoided fossil resource depletion. Global warming potential (GWP) balances ranged from ?1732 kg CO₂e Mg^?1 dry matter (DM) for pig slurry AD feedstock after accounting for avoided slurry storage to +2251 kg CO₂e Mg^?1 DM for oilseed rape biodiesel feedstock after attributing indirect land use change (iLUC) to displaced food production. Maize monoculture for AD led to net GWP increases via iLUC, but optimized integration of maize into an arable rotation resulted in negligible food crop displacement and iLUC. However, even under best‐case assumptions such as full use of heat output from AD‐CHP, crop–biogas achieved low GWP reductions per hectare compared with Miscanthus heating pellets under default estimates of iLUC. Ecosystem services (ES) assessment highlighted soil and water quality risks for maize cultivation. All bioenergy crop options led to net increases in eutrophication after displaced food production was accounted for. The environmental balance of AD is sensitive to design and management factors such as digestate storage and application techniques, which are not well regulated in the UK. Currently, FiT payments are not dependent on compliance with sustainability criteria. We conclude that CLCA and ES effects should be integrated into sustainability criteria for FiTs and RHIs, to direct public money towards resource‐efficient renewable energy options that achieve genuine climate protection without degrading soil, air or water quality.     

Influence of salt stress on C4 photosynthesis in Miscanthus sinensis Anderss.

• Miscanthus sinensis Anderss. is a good candidate for C₄ bioenergy crop development for marginal lands. As one of the characteristics of marginal lands, salinization is a major limitation to agricultural production. The present work aimed to investigate the possible factors involved in the tolerance of M. sinensis C₄ photosynthesis to salinity stress.
• Seedlings of two accessions (salt‐tolerant ‘JM0119’ and salt‐sensitive ‘JM0099’) were subjected to 0 mm NaCl (control) or 250 mm NaCl (salt stress treatment) for 2 weeks. The chlorophyll content, parameters of photosynthesis and chlorophyll a fluorescence, activity of C₄ enzymes and expression of C₄ genes were measured.
• The results showed that photosynthesis rate, transpiration rate, chlorophyll content, PSII operating efficiency, coefficient of photochemical quenching, activity of phosphoenolpyruvate carboxylase (PEPC) and pyruvate, orthophosphate dikinase (PPDK) and gene expression of PEPC and PPDK under salinity were higher after long‐term salinity exposure in ‘JM0119’ than in ‘JM0099’, while activity of NADP‐malate dehydrogenase (NADP‐MDH) and NADP‐malic enzyme (NADP‐ME), together with expression of NADP‐MDH and NADP‐ME, were much higher in ‘JM0099’ than in ‘JM0119’.
• In conclusion, the increased photosynthetic capacity under long‐term salt stress in the salt‐tolerant relative to the salt‐sensitive M. sinensis accession was mainly associated with non‐stomatal factors, such as reduced chlorophyll loss, higher PSII operating efficiency, enhanced activity of PEPC and PPDK and relatively lower activity of NADP‐ME.

     

Allelopathic and intraspecific growth competition effects establishment of direct sown Miscanthus

High yielding perennial crops are being developed as a sustainable feedstock for renewable energy and bioproducts. Miscanthus is a leading biomass crop, but most plantations comprise a sterile hybrid Miscanthus × giganteus that is clonally propagated. To develop new varieties across large areas, rhizome cloning is inefficient, time consuming and expensive. Alternative approaches use seed, and in temperate regions, this has been successfully applied by raising seedlings as plug plants in glasshouses before transfer to the field. Direct sowing has yet to be proven commercially viable because poor germination has resulted in inconsistent stand establishment. Oversowing using seed clusters is a common approach to improve the establishment of crops and it was hypothesized that such an approach will improve uniformity of density in early Miscanthus stands and thereby improve yield. Sowing multiple seeds creates potential for new interactions, and we identified at least two inhibitory mechanisms related to seed numbers. Germinating seed produced allelopathic effects on nearby seed thereby inhibiting plant growth. The inhibitory effect of Miscanthus seed on germination percentages was related to seed number within clusters. An extract from germinating Miscanthus seed inhibited the germination of Miscanthus seed. The extract was analysed by HPLC, which identified a complex mixture including several known allelopathic compounds including proanthocyanidins and vanillic acid. There was also evidence of root competition in soil in a controlled environment experiment. When the experiment on competition was replicated at field scale, the establishment rates were much lower and there was evidence of shoot competition. We conclude that the numbers of seed required to ensure an acceptable level of establishment in the field may be economically impractical until other agronomic techniques are included either to reduce the inhibitory effects of higher seed numbers or to reduce oversowing rates.     

Carbon sequestration in soil in a semi‐natural Miscanthus sinensis grassland and Cryptomeria japonica forest plantation in Aso,Kumamoto, Japan

Although Miscanthus sinensis grasslands (Misc‐GL) and Cryptomeria japonica forest plantations (Cryp‐FP) are proposed bioenergy feedstock systems, their relative capacity to sequester C may be an important factor in determining their potential for sustainable bioenergy production. Therefore, our objective was to quantify changes in soil C sequestration 47 years after a Misc‐GL was converted to a Cryp‐FP. The study was conducted on adjacent Misc‐GL and Cryp‐FP located on Mt. Aso, Kumamoto, Japan. After Cryp‐FP establishment, only the Misc‐GL continued to be managed by annual burning every March. Mass C and N, δ¹³C, and δ¹⁵N at 0–30 cm depth were measured in 5 cm increments. Carbon and N concentrations, C:N ratio, δ¹³C, and δ¹⁵N were measured in litter and/or ash, and rhizomes or roots. Although C input in Misc‐GL by M. sinensis was approximately 36% of that in Cryp‐FP by C. japonica, mean annual soil C sequestration in Misc‐GL (503 kg C ha^?1 yr^?1) was higher than that in Cryp‐FP (284 kg C ha^?1 yr^?1). This was likely the result of larger C input from aboveground litter to soil, C‐quality (C:N ratio and lignin concentration in aboveground litter) and possibly more recalcitrant C (charcoal) inputs by annual burning. The difference in soil δ¹⁵N between sites indicated that organic C with N had greater cycling between heterotrophic microbes and soil and produces more recalcitrant humus in Misc‐GL than in Cryp‐FP. Our data indicate that in terms of soil C sequestration, maintenance of Misc‐GL may be more advantageous than conversion to Cryp‐FP in Aso, Japan.     

Tissue chemistry and morphology affect root decomposition of perennial bioenergy grasses on sandy soil in a sub‐tropical environment

Second‐generation biofuels and bio‐based products derived from lignocellulosic biomass are likely to replace current fuels derived from simple sugars and starch because of greater yield potential and less competition with food production. Besides the high aboveground biomass production, these bioenergy grasses also exhibit extensive root systems. The decomposition of root biomass greatly influences nutrient cycling and microbial activity and subsequent accumulation of carbon (C) in the soil. The objective of this research was thus to characterize root morphological and chemical differences in six perennial grass species in order to better understand root decomposition and belowground C cycling of these bioenergy cropping systems. Giant reed (Arundo donax), elephantgrass (Pennisetum purpureum), energycane (Saccharum spp.), sugarcane (Saccharum spp.), sweetcane (Saccharum arundinaceum), and giant miscanthus (Miscanthus × giganteus) were established in Fall 2008 in research plots near Gainesville, Florida. Root decomposition rates were measured in situ from root decomposition bags over 12 months along with initial and final root tissue composition. Root potential decomposition rate constant (K) was higher in elephantgrass (3.64 g kg^?1 day^?1) and sweetcane (2.77 g kg^?1 day^?1) than in sugarcane (1.62 g kg^?1 day^?1) and energycane (1.48 g kg^?1 day^?1). Notably, K was positively related to initial root tissue total C (Total C), total fiber glucose (TFG), total fiber xylose (TFX), and total fiber carbohydrate (TFC) concentrations, but negatively related to total fiber arabinose (TFA) and lignin (TL) concentrations and specific root volume (SRV). Among the six species, elephantgrass exhibited root traits most favorable for fast decomposition: high TFG, high TFX, high TFC, high specific root length (SRL), and a low SRV, whereas giant reed, sugarcane, and energycane exhibited slow decomposition rates and the corresponding root traits. Thus, despite similar aboveground biomass yields in many cases, these species are likely to differentially affect soil C accumulation.     

Temperature and precipitation drive temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment

The aquatic pathway is increasingly being recognized as an important component of catchment carbon and greenhouse gas (GHG) budgets, particularly in peatland systems due to their large carbon store and strong hydrological connectivity. In this study, we present a complete 5‐year data set of all aquatic carbon and GHG species from an ombrotrophic Scottish peatland. Measured species include particulate and dissolved forms of organic carbon (POC, DOC), dissolved inorganic carbon (DIC), CO₂, CH₄ and N₂O. We show that short‐term variability in concentrations exists across all species and this is strongly linked to discharge. Seasonal cyclicity was only evident in DOC, CO₂ and CH₄ concentration; however, temperature correlated with monthly means in all species except DIC. Although the temperature correlation with monthly DOC and POC concentrations appeared to be related to biological productivity in the terrestrial system, we suggest the temperature correlation with CO₂ and CH₄ was primarily due to in‐stream temperature‐dependent solubility. Interannual variability in total aquatic carbon concentration was strongly correlated with catchment gross primary productivity (GPP) indicating a strong potential terrestrial aquatic linkage. DOC represented the largest aquatic carbon flux term (19.3 ± 4.59 g C m^?2 yr^?1), followed by CO₂ evasion (10.0 g C m^?2 yr^?1). Despite an estimated contribution to the total aquatic carbon flux of between 8 and 48%, evasion estimates had the greatest uncertainty. Interannual variability in total aquatic carbon export was low in comparison with variability in terrestrial biosphere–atmosphere exchange, and could be explained primarily by temperature and precipitation. Our results therefore suggest that climatic change is likely to have a significant impact on annual carbon losses through the aquatic pathway, and as such, aquatic exports are fundamental to the understanding of whole catchment responses to climate change.     

Sweetcane (Erianthus arundinaceus) as a native bioenergy crop with environmental remediation potential in southern China: A review

Sweetcane (Erianthus arundinaceus [Retzius] Jeswiet) is an ecologically dominant warm‐season perennial grass native to southern China. It traditionally plays an important role in sugarcane breeding due to its excellent biological traits and genetic relatedness to sugarcane. Recent studies have shown that sweetcane has a great potential in bioenergy and environmental remediation. The objective of this paper is to review the current research on sweetcane biology, phenology, biogeography, agronomy, and conversion technology, in order to explore its development as a bioenergy crop with environmental remediation potential. Sweetcane is resistant to a variety of stressors and can adapt to different growth environments. It can be used for ecological restoration, soil and water conservation, contaminated land repairing, nonpoint source pollutants barriers in buffer strips along surface waters, and as an ornamental and remediation plant on roadsides and in wetlands. Sweetcane exhibits higher biomass yield, calorific value and cellulose content than other bioenergy crops under the same growth conditions, thereby indicating its superior potential in second‐generation biofuel production. However, research on sweetcane as a bioenergy plant is still in its infancy. More works need be conducted on breeding, cultivation, genetic transformation, and energy conversion technologies.     

Using GIS and remote sensing to explore the influence of physical environmental factors and historical land use on bushland structure

Bushland is a vegetation type with a dense cover of woody plants of low stature and a grass understory. We explored the influence of environmental factors (precipitation, topography, geology, hydrology and waterhole density) and historical land use in the Tsavo ecosystem bushland. We mapped vegetation patterns in the region using remote sensing, GIS and field data and tested relationships with physical factors. We used regression analysis to explore the interaction of physical factors and human influence by including a protected and a nonprotected area, representing contrasting historical land use policies, as factors in the regression model. Bushland vegetation had the largest proportion in the region as a whole, but its proportion was notably greater in the nonprotected area. Precipitation, elevation, geology and historical land use were significant predictors of vegetation patterns in the regression models. Higher precipitation and elevation make woody plants superior competitors over grasses, resulting in predominance of bushland in such areas. Geologically, marine deposits result in shallow calcareous soils that favour grasses over trees, hence, absence of bushland. Wildlife management policies such as providing water for wildlife, protective boundaries and controlling wildfires influence distribution of wildlife and result in conditions that prevent regeneration and recruitment of trees.     

Greenhouse gas emissions from four bioenergy crops in England and Wales: Integrating spatial estimates of yield and soil carbon balance in life cycle analyses

Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops, Miscanthus ( Miscanthus × giganteus ), short rotation coppice (SRC) poplar ( Populus trichocarpa Torr. & Gray × P. trichocarpa , var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use – arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.     

Comparing annual and perennial crops for bioenergy production – influence on nitrate leaching and energy balance

Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass‐clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l^?1 nitrate‐N during the establishment year, but declined subsequently to <5 mg l^?1 nitrate‐N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha^?1 yr^?1 N in the first 3 years after planting. A similar trend was observed in grass‐clover where concentrations stabilized at 2–4 mg l^?1 nitrate‐N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha^?1 yr^?1 N. In winter wheat, an annual N leaching loss of 36–68 kg ha^?1 yr^?1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha^?1 yr^?1. Dry matter yields ranged between 5.9 and 14.8 Mg yr^?1 with lowest yield in the newly established willow and the highest yield harvested in grass‐clover. Grass‐clover gave the highest net energy yield of 244 GJ ha^?1 yr^?1, whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha^?1 yr^?1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops.