Feasibility assessment of poplar bioenergy systems in the Southern Europe

A detailed reliability assessment of bioenergy production systems based on poplar cultivation was made. The aim of this assessment was to demonstrate the Economic feasibility of implementing poplar biomass production for power generation in Spain. The assessment considers the following chain of energy generation: cultivation and harvesting, and transportation and electricity generation in biomass power plants (10, 25 and 50 MW). Twelve scenarios were analysed in accordance with the following: two harvesting methods (high density packed stems and chip production in the field), two crop distributions around the power plant and three power plant sizes. The results show that the cost of biomass delivered at power plant ranges from 18.65 to 23.96 € Mg^?1 dry basis. According to power plant size, net profits range from 3 to 22 million € per yr.Sensibility analyses applied to capital cost at the power plant and to biomass production in the field demonstrate that they do not affect the feasibility of these systems. Reliability is improved if benefits through selling CO₂ emission credits are taken into account.This study clears up the Economic uncertainty of poplar biomass energy systems that already has been accepted as environmentally friendlier and as offering better energetic performance.     

Biomass production from traditional coppice management in northern Italy

Traditional coppice stands cover millions of hectares throughout Europe and offer large amounts of biomass. The study analyzed 10 commercial coppice harvesting operations in northwestern Italy, where modern machines were deployed. Removals, prices, work, revenues and costs were carefully determined. Firewood was the main product, representing between 70% and 100% of the total product mass and value. Traditional coppice stands often yield over 200 m³ of energy biomass per hectare, at the time of cut. Cable yarding operations were better organized than ground-based operations, which explained why they incurred the same harvesting cost, despite the more challenging site conditions under which they were deployed. Mean harvesting cost was 45 € m⁻³, of which about 10% was needed for felling, 70% for extraction and processing, and the remaining 20% for loading and transportation. All operations accrued some profit, which varied between 13 and 43 € m⁻³ or between 1600 and 8600 € ha⁻¹, depending on operational efficiency, value recovery and stand yield.     

Recovery of logging residues for energy from spruce (Pices abies) dominated stands

Vast quantities of logging residue are left behind on clearcut areas. Given the suitable transportation distance, environmental and economic circumstances, they provide a possible alternative for fossil fuels. However, distribution of residual biomass over large areas during the logging operation and trampling by machines hinders the recovery. The recovery enhancing effect of three single-grip harvester work techniques on the productivity of logging residue recovery for energy was studied. Forwarder productivity, distribution of effective work time, forwarding distance, load size and the residue yield were studied.A heavy forwarder with an enlarged 22 m³ load space was used. The average load size was 9 tonnes. More than 50% of the forwarder's work time was spent on loading the residues. The recovery output of the trampled residues from the strip road after a conventional harvesting method was 11.4 t/E₀-h for a 9 tonnes load and a 300 m transportation distance. In contrast, the single-grip harvester methods that aimed at the post-logging residue recovery increased the recovery output to 12.0–13.3 t/E₀-h. The load size was a more significant factor than the forwarding distance in terms of machine productivity. The yield of residue recovery after the conventional roundwood harvesting method was 58.4% and from 66.8% to 78.7% for the alternative single-grip-harvester methods.     

Ethanol from lignocellulosic biomass: techno-economic performance in short-, middle- and long-term

The state of the art of hydrolysis-fermentation technologies to produce ethanol from lignocellulosic biomass, as well as developing technologies, is evaluated. Promising conversion concepts for the short-, middle- and long-term are defined. Their technical performance was analysed, and results were used for economic evaluations. The current available technology, which is based on dilute acid hydrolysis, has about 35% efficiency (HHV) from biomass to ethanol. The overall efficiency, with electricity co-produced from the not fermentable lignin, is about 60%. Improvements in pre-treatment and advances in biotechnology, especially through process combinations can bring the ethanol efficiency to 48% and the overall process efficiency to 68%. We estimate current investment costs at 2.1 k€/kW_HHV (at 400 MW_HHV input, i.e. a nominal 2000 tonne dry/day input). A future technology in a 5 times larger plant (2 GW_HHV) could have investments of 900 k€/kW_HHV. A combined effect of higher hydrolysis-fermentation efficiency, lower specific capital investments, increase of scale and cheaper biomass feedstock costs (from 3 to 2 €/GJ_HHV), could bring the ethanol production costs from 22 €/GJ_HHV in the next 5 years, to 13 €/GJ over the 10–15 year time scale, and down to 8.7 €/GJ in 20 or more years.     

Energy policy tools for agricultural residues utilization for heat and power generation: A case study of sugarcane trash in Thailand

Cane trash could viably substitute fossil fuels in heat and power generation projects to avoid air pollution from open burning and reduce greenhouse gas (GHG) emission. It is competitive with bituminous and other agro-industrial biomass. Using cane trash for heat generation project could provide a higher reliability and return on investment than power generation project. The heat generation project could be viable (Financial Internal Rate of Return, FIRR = 36–81%) without feedstock subsidy. With current investment and support conditions, the capacity of 5 MW option of power generation project is the most viable (FIRR = 13.6–15.3%); but 30 MW, 1 MW and 10 MW options require feedstock subsidy 450–1100 Baht/t-cane trash to strengthen financial viability. Furthermore, the revenue from carbon credit sales could compensate the revenue from current energy price adder and increases 0.5–1.0% FIRR of power generation project. Using cane trash for 1 MW power generation could reduce GHG emission 637–861 t CO₂eq and avoid air pollutant emissions of 3.35 kg nitrogen oxides (NO_x), 0.41 kg sulfur oxides (SO_x) and 2.05 kg volatile organic compounds (VOC). Also, 1 t steam generation from cane trash could avoid pollutant emissions of 0.6 kg NO_x, 0.07 kg SO_x, and 0.37 kg VOC. The potential of cane trash to cause fouling/slagging as well as erosion are not significantly different from other biomass, but chlorinated organic compounds and NO_x could be higher than bituminous and current biomass feedstock at sugar mill (bagasse and rice husk).     

Performance of simulated flexible integrated gasification polygeneration facilities,Part B: Economic evaluation.

This paper investigates the economics of integrated gasification polygeneration (IG-PG) facilities and assesses under which market conditions flexible facilities outperform static facilities. In this study, the facilities use Eucalyptus wood pellets (EP), torrefied wood pellets (TOPS) and Illinois #6 coal as feedstock to produce electricity, FT-liquids, methanol and urea. All facilities incorporate CCS. The findings show production costs from static IG-PG facilities ranging between 12 and 21 €/GJ using coal, 19–33 €/GJ using TOPS and 22–38 €/GJ using EP, which is above the average market prices. IG-PG facilities can become competitive if capital costs drop by 10%–27% for coal based facilities. Biomass based facilities will need lower biomass pellet prices or higher CO₂ credit prices. Biomass becomes competitive with coal at a CO₂ credit price of 50–55 €/t CO₂. Variations in feedstock, CO₂ credit and electricity prices can be offset by operating a feedstock flexible IG-PG facility, which can switch between coal and TOPS, thereby altering its electricity production. The additional investment is around 0.5% of the capital costs of a dedicated coal based IG-PG facility. At 30 €/t CO₂, TOPS will be the preferred feedstock for 95% of the time at a feedstock price of 5.7 €/GJ. At these conditions, FT-liquids (gasoline/diesel) can be produced for 15.8 €/GJ (116 $/bbl). Historic records show price variations between 5.7 and 7.3 €/GJ for biomass pellet, 1.0–5.6 €/GJ for coal and 0–32 €/t CO₂. Within these price ranges, coal is generally the preferred feedstock, but occasionally biomass is preferred. Lower biomass prices will increase the frequency of switching feedstock preference from coal to biomass, raising the desire for flexibility. Of the three investigated chemicals, an IG-PG facility producing FT-liquids benefits the most from flexibility. Our study suggests that if the uncertainty in commodity prices is high, a small additional investment can make flexible IG-PG facilities attractive.     

Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal

Based on the results of previous studies, the efficiency of a Brayton/Hirn combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO₂ removal by chemical absorption reached 33.94%, considering also the separate CO₂ compression process. The specific CO₂ emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO₂ chemical absorption (38–39% efficiency, 130 kg/MW h specific CO₂ emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilisation. The LCA shows the important environmental advantages of biomass utilisation in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilisation.     

Biomass yield and energy analysis of soybean production in relation to fertilizer-NPK and organic manure

The study attempts to quantify the root biomass and density, nodulation, crop biomass and grain yield of soybean, to analyze crop growth and energy (renewable and non-renewable) inputs in relation to fertilizer-NPK and organic manure. Observations were recorded from soybean grown with no fertilizer, NPK and NPK + FYM (farmyard manure). The root biomass (BM_root) increased significantly with NPK + FYM compared to NPK and control. The trend of BM_root was best fitted with a third order polynomial. Root length density was higher in NPK + FYM. Biomass of stem, petiole and leaf were significantly greater in NPK + FYM than other treatments, relative contribution to total biomass at physiological maturity were stem 29%, petiole 9%, leaf 17% and pod 46%; quadratic regression models best represented the stem, petiole and leaf biomass data. A maximum LAI of 4.88, total biomass of 633 g m^?2 at maturity, CGR of 18.4 g m^?2 d^?1 were recorded in NPK + FYM. Grain yields increased by 72.5 and 98.5%, and stover yields by 56.0 and 94.8% in NPK and NPK + FYM, respectively over control. Though the total energy input in NPK + FYM was greater than those in NPK and control, the share of renewable energy was much higher with greater net energy output and non-renewable energy productivity in NPK + FYM than NPK. The use efficiency of non-renewable energy was also higher in NPF + FYM. Thus, a combination of NPK-fertilizer and organic manure (FYM) could be the viable nutrient management option for soybean production.     

Outlook for advanced biofuels

To assess which biofuels have the better potential for the short-term or the longer term (2030), and what developments are necessary to improve the performance of biofuels, the production of four promising biofuels—methanol, ethanol, hydrogen, and synthetic diesel—is systematically analysed. This present paper summarises, normalises and compares earlier reported work. First, the key technologies for the production of these fuels, such as gasification, gas processing, synthesis, hydrolysis, and fermentation, and their improvement options are studied and modelled. Then, the production facility's technological and economic performance is analysed, applying variations in technology and scale. Finally, likely biofuels chains (including distribution to cars, and end-use) are compared on an equal economic basis, such as costs per kilometre driven. Production costs of these fuels range 16–22 €/GJ_HHV now, down to 9–13 €/GJ_HHV in future (2030). This performance assumes both certain technological developments as well as the availability of biomass at 3 €/GJ_HHV. The feedstock costs strongly influence the resulting biofuel costs by 2–3 €/GJ_fuel for each €/GJ_HHV feedstock difference. In biomass producing regions such as Latin America or the former USSR, the four fuels could be produced at 7–11 €/GJ_HHV compared to diesel and gasoline costs of 7 and 8 €/GJ (excluding distribution, excise and VAT; at crude oil prices of ∼35 €/bbl or 5.7 €/GJ). The uncertainties in the biofuels production costs of the four selected biofuels are 15–30%. When applied in cars, biofuels have driving costs in ICEVs of about 0.18–0.24 €/km now (fuel excise duty and VAT excluded) and may be about 0.18 in future. The cars’ contribution to these costs is much larger than the fuels’ contribution. Large-scale gasification, thorough gas cleaning, and micro-biological processes for hydrolysis and fermentation are key major fields for RD&D efforts, next to consistent market development and larger scale deployment of those technologies.     

The economical and environmental performance of miscanthus and switchgrass production and supply chains in a European setting

The purpose of this study is to analyse the economical and environmental performance of switchgrass and miscanthus production and supply chains in the European Union (EU25), for the years 2004 and 2030. The environmental performance refers to the greenhouse gas (GHG) emissions, the primary fossil energy use and to the impact on fresh water reserves, soil erosion and biodiversity. Analyses are carried out for regions in five countries. The lowest costs of producing (including storing and transporting across 100 km) in the year 2004 are calculated for Poland, Hungary and Lithuania at 43–64 € per oven dry tonne (odt) or 2.4–3.6 € GJ^?1 higher heating value. This cost level is roughly equivalent to the price of natural gas (3.1 € GJ^?1) and lower than the price of crude oil (4.6 € GJ^?1) in 2004, but higher than the price of coal (1.7 € GJ^?1) in 2004. The costs of biomass in Italy and the United Kingdom are somewhat higher (65–105 € odt^?1 or 3.6–5.8 € GJ^?1). The doubling of the price of crude oil and natural gas that is projected for the period 2004–2030, combined with nearly stable biomass production costs, makes the production of perennial grasses competitive with natural gas and fossil oil. The results also show that the substitution of fossil fuels by biomass from perennial grasses is a robust strategy to reduce fossil energy use and curb GHG emissions, provided that perennial grasses are grown on agricultural land (cropland or pastures). However, in such case deep percolation and runoff of water are reduced, which can lead to overexploitation of fresh water reservoirs. This can be avoided by selecting suitable locations (away from direct accessible fresh water reservoirs) and by limiting the size of the plantations. The impacts on biodiversity are generally favourable compared to conventional crops, but the location of the plantation compared to other vegetation types and the size and harvesting regime of the plantation are important variables.     

Biomass resources assessment for power generation: A case study from Haryana state,India

India generates over 370 million tonnes of biomass every year. In addition to the direct harvesting from plants, biomass is also produced as a by product in many agro based industries such as rice husk from rice mill, saw dust from saw mill, bagasse from sugar mills etc. It has been estimated that about 17 GW of power can be generated through cogeneration, combustion and gasification routes from the available biomass. However, for this potential to be realized, data on production, present usage patterns, prices and seasonal fluctuation on biomass is essentially required. The present article is based on the resource assessment of non-plantation surplus biomass with a view to using it for energy production and its utilization in the state of Haryana, India.Being an agricultural state, Haryana has a huge potential of biomass availability in the form of crop residue and saw dust. In the agricultural sector, a total 24.697 Mt y^?1 of residue is generated, of which 71% is consumed in various domestic and commercial activities within the state. While in agro based industrial sector, a total of 646 kt y^?1 of sawdust is generated, of which only 6.65% is consumed in the state. Of the total generated biomass in the state, 45.51% is calculated as basic surplus, 37.48% as productive surplus and 34.10% as net surplus. The power generation potential from all these three categories of surplus biomass is 1.499 GW, 1.227 GW and 1.120 GW respectively.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Estimates of technically available woody biomass feedstock from natural forests and willow biomass crops for two locations in New York State

A Geographic Information System (GIS) was used to estimate the technically available woody biomass from forests and willow biomass crops within a 40 km radius of Syracuse and Tupper Lake, NY. Land cover and land use data were used to identify the available land base and restrictions were applied for slope, parcel size and designated wetlands. Approximately 222,984 oven-dry tonnes (odt) of forest biomass are technically available annually around Syracuse, from 165,848 hectares (ha) of timberland. There are 67,880 ha of agricultural land technically available for growing willow biomass crops, which could produce 38,181 odt yr^?1 if 5% of this land was used and yields were 11.25 odt ha^?1 yr^?1. There are approximately 215,300 odt of forest biomass technically available annually around Tupper Lake from 211,500 ha of timberland. There are 781 ha of technically available agricultural land in this area so willow biomass production would be minimal. While these two areas have different land cover and land use characteristics, both have the potential to produce significant amounts of woody biomass.     

The capacitive characteristics of supercapacitors consisting of activated carbon fabric–polyaniline composites in NaNO3

A sandwich-type supercapacitor consisting of two similar activated carbon fabric–polyaniline (ACF–PANI) composite electrodes was demonstrated to exhibit excellent performance (i.e., highly reversibility and good stability) in NaNO₃. Polyaniline with the charge density of polymerization less than or equal to 9 C cm⁻² synthesized by means of a potentiostatic method showed a high specific capacitance of 300 F g⁻¹. Influences of the polymerization charge density (i.e., the polymer loading) on the capacitive characteristics of ACF–PANI composites were compared systematically. The capacity of an ACF–PANI electrode reach ca. 3.4 F cm⁻² (a 100% increase in total capacity) when the charge density of polymerization is equal to 9 C cm⁻². The surface morphology of these ACF–PANI composites was examined by a scanning electron microscope (SEM).     

Effects of process factors on biological activity of granular sludge grown in an UASFF bioreactor

Control and operation of a hybrid granular sludge reactor are mainly related to biological behavior of the granules under different process conditions. In this study, a 1-l digester was used to examine biological activity of the granules grown in a hybrid anaerobic reactor (AHR). The biogas production process was modeled and analyzed with three-process variables viz., influent COD (3000, 6500 and 10,000 mg COD/l), biomass concentration (2000, 4000 and 6000 mg VSS/l) and initial alkalinity (200, 1100 and 2000 mg CaCO₃/l). Experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). In order to carry out a comprehensive analysis of the biogas production process, the indicative parameters viz., specific methanogenic activity (SMA), bicarbonate alkalinity produced-to-COD removed ratio, and COD removal were studied as the response. The maximum SMA was modeled to be 0.99 g CH₄-COD/g VSS d under COD_in, initial bicarbonate alkalinity (BA) and biomass concentrations of 10,000 mg COD/l, 2000 mg CaCO₃/l and 2000 mg VSS/l, respectively, while the observed value was 1.039 g CH₄-COD/g VSS d. The maximum COD removal was achieved at the condition when the influent COD was within the range of 4250–5250 mg/l and initial BA was more than 1100 mg CaCO₃/l. Initial BA and COD_in played an important role in the production of bicarbonate alkalinity during the digestion process.     

Alkalinity and high total solids affecting H2 production from organic solid waste by anaerobic consortia

The optimization of total solids in the feed (%TS) and alkalinity ratio (γ) for H₂ production from organic solid wastes under thermophilic regime was carried out using response surface methodology based on a central composite design. The total solids levels were 20.9, 23.0, 28.0, 33.0 and 35.1% whereas the levels of alkalinity ratio (defined as g phosphate alkalinity/g dry substrate) were 0.15, 0.20, 0.30, 0.41 and 0.45. High levels of TS and γ affected in a negative way the H₂ productivity and yield; both response variables significantly increased upon decreasing the TS content and alkalinity ratio. The highest H₂ productivity and yield were 463.7 N mL/kg-d and 54.8 N mL/g VS_rem, respectively, predicted at 20.9% TS and alkalinity ratio 0.25 (0.11 g CaCO₃/g dry substrate). The alkalinity requirements for hydrogenogenic processes were lower than those reported for methanogenic processes (0.11 vs. 0.30 g CaCO₃/g COD). Adequate alkalinity ratio was necessary to maintain optimal biological activity for hydrogen production; however, excessive alkalinity negatively affected process performance probably due to an increase of osmotic pressure. Interestingly, reactor pH depended only on the alkalinity ratio, thus the buffer capacity was able to maintain a constant pH independently of TS levels. At γ = 0.15–0.30 the pHs were in the range 5.56–5.95, which corresponded to the highest hydrogen productivities and yields. Finally, the highest metabolite accumulation corresponded with the highest removal efficiencies but not with high H₂ productivities and yields. Therefore, it seems that organic matter removal was channeled toward solvent generation instead of hydrogen production at high TS and γ levels. This is the first study that shows the requirements of alkalinity in solid substrate fermentation conditions for H₂ production processes and their interaction with the content of total solids in the feed.     

Comparison of Arundo donax L. and Miscanthus x giganteus in a long-term field experiment in Central Italy: Analysis of productive characteristics and energy balance

Miscanthus x giganteus (miscanthus) and Arundo donax L. (giant reed) are two perennial crops which have been received particular attention during the last decade as bioenergy crops. The main aim of the present study was to compare the above-ground biomass production and the energy balance of these perennial rhizomatous grasses in a long-term field experiment. The crops were cultivated from 1992 to 2003 in the temperate climate of Central Italy with 20,000 plants ha^?1, 100–100–100 kg N, P₂O₅, K₂O per hectare, and without irrigation supply. For each year of trial, biomass was harvested in autumn to estimate biometric characteristics and productive parameters. Besides, energy analysis of biomass production was carried out determining energy output, energy input, energy efficiency (output/input) and net energy yield (output–input). Results showed high above-ground biomass yields over a period of 10 years for both species, with better productive performances in giant reed than in miscanthus (37.7 t DM ha^?1 year^?1 vs 28.7 t DM ha^?1 year^?1 averaged from 2 to 12 years of growth). Such high yields resulted positively correlated to number of stalks (miscanthus), plant height and stalk diameter (giant reed). Moreover, these perennial species are characterised by a favourable energy balance with a net energy yield of 467 and 637 GJ ha^?1 (1–12 year mean) for miscanthus and giant reed respectively.With such characteristics, both grasses could be proposed as biomass energy crops in Southern Europe with a significant and environmentally compatible contribution to energy needs.     

Wood ash effects on plant and soil in a willow bioenergy plantation

Intensive management for biomass production results in high rates of nutrient removal by harvesting. We tested whether wood ash generated when burning wood for energy could be used to ameliorate negative soil effects of short-rotation harvesting practices. We measured the temporal and spatial dynamics of soil nutrient properties after wood ash applications in a willow plantation in central New York State and determined the influence of wood ash application on willow growth. Wood ash was applied annually for 3 years at the rates of 10 and 20 Mg ha⁻¹ to coppiced willow, Salix purpurea, clone SP3. Wood ash application significantly increased soil pH in the 0–10 cm soil layer from 6.1 in the control to 6.9 and 7.1 in the 10 and 20 Mg ha⁻¹ treated plots. Wood ash application significantly increased soil extractable phosphorus, potassium, calcium, and magnesium concentrations. Potassium was the element most affected by wood ash treatment at all soil depths. Wood ash had no significant effect on nutrient concentrations of foliar, litter, and stem tissue. Wood ash did not affect either individual plant growth or plot biomass production, which declined over the course of the study; it did increase the size of stems, but this effect was balanced by a decrease in the number of stems. Applying nitrogen as well as wood ash might be required to maintain the productivity of this SRIC system.     

Biomass and volume yield after 6 years in multiclonal hybrid poplar riparian buffer strips

In this paper the potential of five hybrid poplar clones (Populus spp.) to provide biomass and wood volume in the riparian zone is assessed in four agroecosystems of southern Quebec (Canada). For all variables measured, significant Site effects were detected. Survival, biomass yield and volume yield were highest at the Bromptonville site. After 6 years of growth, total aboveground biomass production (stems + branches + leaves) reached 112.8 tDM/ha and total leafless biomass production (stems + branches) reached 101.1 tDM/ha at this site, while stem wood volume attained 237.5 m³/ha. Yields as low as 14.2 tDM/ha for total biomass and 24.8 m³/ha for total stem volume were also observed at the Magog site. Highest yields were obtained on the most fertile sites, particularly in terms of NO₃ supply rate. Mean stem volume per tree was highly correlated with NO₃ supply rate in soils (R² = 0.58, p < 0.001). Clone effects were also detected for most of the variables measured. Total aboveground biomass and total stem volume production were high for clone 3729 (Populus nigra × P. maximowiczii) (73.1 tDM/ha and 134.2 m³/ha), although not statistically different from clone 915311 (P. maximowiczii × P. balsamifera). However, mean whole-tree biomass (including leaves) was significantly higher for clone 3729 (38.8 kgDM/tree). Multifunctional agroforestry systems such as hybrid poplar riparian buffer strips are among the most sustainable ways to produce a high amount of biomass and wood in a short time period, while contributing to alleviate environmental problems such as agricultural non-point source pollution.     

Above-ground biomass production and allometric relations of Eucalyptus globulus Labill. coppice plantations along a chronosequence in the central highlands of Ethiopia

Eucalyptus plantations are extensively managed for wood production in the central highlands of Ethiopia. Nevertheless, little is known about their biomass (dry matter) production, partitioning and dynamics over time. Data from 10 different Eucalyptus globulus stands, with a plantation age ranging from 11 to 60 years and with a coppice-shoot age ranging from 1 to 9 years were collected and analyzed. Above-ground tree biomass of 7–10 sampled trees per stand was determined destructively. Dry weights of tree components (W_c; leaves, twigs, branches, stembark, and stemwood) and total above-ground biomass (W_a) were estimated as a function of diameter above stump (D), tree height (H) and a combination of these. The best fits were obtained, using combinations of D and H. When only one explanatory variable was used, D performed better than H. Total above-ground biomass was linearly related to coppice-shoot age. In contrast a negative relation was observed between the above-ground biomass production and total plantation age (number of cutting cycles). Total above-ground biomass increased from 11 t ha^?1 at a stand age of 1 year to 153 t ha^?1 at 9 years. The highest dry weight was allocated to stemwood and decreased in the following order: stemwood > leaves > stembark > twigs > branches. The equations developed in this study to estimate biomass components can be applied to other Eucalyptus plantations under the assumption that the populations being studied are similar with regard to density and tree size to those for which the relationships were developed.