Poplar Short Rotation Research Articles

Environmental Effects over the First 2\xbd Rotation Periods of a Fertilised Poplar Short Rotation Coppice

A short rotation coppice (SRC) with poplar was established in a randomised fertilisation experiment on sandy loam soil in Potsdam (Northeast Germany). The main objective of this study was to assess if negative environmental effects as nitrogen leaching and greenhouse gas emissions are enhanced by mineral nitrogen (N) fertiliser applied to poplar at rates of 0, 50 and 75 kg N ha−1 year−1 and how these effects are influenced by tree age with increasing number of rotation periods and cycles of organic matter decomposition and tree growth after each harvesting event. Between 2008 and 2012, the leaching of nitrate (NO3−) was monitored with self-integrating accumulators over 6-month periods and the emissions of the greenhouse gases (GHG) nitrous oxide (N2O) and carbon dioxide (CO2) were determined in closed gas chambers. During the first 4 years of the poplar SRC, most nitrogen was lost through NO3− leaching from the main root zone; however, there was no significant relationship to the rate of N fertilisation. On average, 5.8 kg N ha−1 year−1 (13.0 kg CO2equ) was leached from the root zone. Nitrogen leaching rates decreased in the course of the 4-year study parallel to an increase of the fine root biomass and the degree of mycorrhization. In contrast to N leaching, the loss of nitrogen by N2O emissions from the soil was very low with an average of 0.61 kg N ha−1 year−1 (182 kg CO2equ) and were also not affected by N fertilisation over the whole study period. Real CO2 emissions from the poplar soil were two orders of magnitude higher ranging between 15,122 and 19,091 kg CO2 ha−1 year−1 and followed the rotation period with enhanced emission rates in the years of harvest. As key-factors for NO3− leaching and N2O emissions, the time after planting and after harvest and the rotation period have been identified by a mixed effects model.

Torrefaction of woody biomasses from poplar SRC and Portuguese roundwood: Properties of torrefied products

Torrefaction is an option for improving biomass properties for fuel application. Biomass undergoes chemical changes reflected on the upgrading of its properties as a biofuel, such as higher calorific power, lower O/C and H/C ratios, lower higroscopicity or better grindability. Objectives of this experimental study were to analyze the effects of torrefaction, under standart conditions of 265 °C, and residence time of 15 min in a nitrogen atmosphere and during a total 1h45m heating period, on a set of sixteen woody biomasses provenient from poplar short rotation coppice (SRC) and other Portuguese roundwoods. Average mass loss was higher than 40%. The set of poplar clones and common broom provided torrefied products with higher quality than the set of roundwood forest species. The results on other parameters for proximate and ultimate analysis corroborate this global picture. Correlation analysis showed a higher degree of interconnectedness between LHV and proximate analysis results, for poplar clones and common broom, comparatively with roundwood biomasses.

Poplar biomass production in short rotation under irrigation: A case study in the Mediterranean

In this study we analyzed the behavior of four poplar genotypes growing in the field under Mediterranean climatic conditions and different watering treatments ranging from optimal to deficient conditions. Behavior was assessed in relation to productivity, water-use efficiency, foliar nitrogen concentration as well as the relationship between these traits. Total aboveground biomass (Bt) was recorded at the end of the first rotation, while other variables such as carbon isotope discrimination (Δ13), net photosynthetic rate (A), stomatal conductance (gs), specific leaf area (SLA) and nitrogen concentration (NA) were also measured during the growth periods. ‘AF2’ and ‘Monviso’ were the most productive genotypes and also displayed the higher water-use efficiency. In contrast, ‘I-214’ and ‘Pegaso’ were significantly less productive and less efficient. However, these less productive genotypes displayed lower biomass reductions under non-optimal water conditions, probably due to their higher stomatal conductance and higher leaf nitrogen concentration under deficient water scenarios. The relationship between productivity and water use efficiency is analyzed and discussed. Biomass production was also modeled for the different watering scenarios. The study outcomes provided in this article will aid the development of appropriate management strategies as regards the establishment and management of poplar short rotation coppice (SRC) under scenarios with reduced water availability. It will also contribute towards identifying the most suitable genotypes for biomass production in the Mediterranean region and aid the selection of future lines for tree genetic improvements in the context of water scarcity.

Relationship between soil chemical composition and potential fuel quality of biomass from poplar short rotation coppices in Portugal and Belgium

Soil-woody biomass interactions are relevant for the productivity of bioenergy plantations and biomass quality. In this context, the main objective of this study was to evaluate and to quantify possible relationships between chemical variables of the soil and the produced biomass through a multivariate approach. This latter approach allows to overcome the complex issue of multi-collinearity among variables. Soil and woody biomass samples were collected from two poplar short rotation coppices in Santarém (Portugal) and in Lochristi (Belgium). The results from the analyses of those samples were integrated into three databases with soil, woody biomass and site plots as cases, and 23 physical and chemical properties as variables. The databases were subjected to a multivariate sequence of calculations, which included correlation, principal components, factorial and hierarchical clustering analyses. The calculations showed that the site plots and the woody biomass of genotypes in Lochristi were more homogeneous as compared to Santarém; they also confirmed the high interconnection between soil and woody biomass variables. The higher heating value of the woody biomass correlated well with the soil concentrations of P2O5, Mg, Ca, Na and organic C. Linear equations related the higher heating value to the most important soil and woody biomass variables. Finally, the results suggest that the annual monitoring of soil and biomass in SRC systems should be performed to optimize both productivity and woody biomass quality as a fuel.

On the Genetic Affinity of Individual Tree Biomass Allometry in Poplar Short Rotation Coppice

Woody biomass is one of our main resources available to enhance the bio-economy, but its production varies considerably depending on the species, the environment and crop management. The variability associated with these crops complicates the estimation of biomass through prediction models. The specificity of environment or genotype level limits the application of many of the models, which are often developed for use at local geographical levels. Although generalizations involve some loss of accuracy, the inclusion of a wide range of data for a wide range of environments and genotypes can improve model applicability. A total of 11,265 data from short-rotation, high-density poplar plantations (from 22 sites in Spain, covering 29 genotypes belonging to 7 different taxonomic groups) were used to develop biomass prediction models under Mediterranean conditions and to test whether similarities in individual tree biomass allometry occur within the taxonomic group level. A general model and both taxonomic group- and genotype-level models were fitted using weighted nonlinear regression. The simplified model, in which only the basal diameter is included, presented the best model performance, explaining 87% of the variability. The allometric similarities among different genotypes were evaluated in order to explore the relationship between the most frequently used poplar genotypes in the Mediterranean area, and although certain groups were identified, it was not possible to relate these similarities among different genotypes to their taxonomic group affinity. This was also confirmed by comparing the performance of the general models with the taxonomic group-level models when predicting at the genotype level. Although estimates made using the general models are relatively precise, the use of genotype-level models is recommended for more accurate predictions.

Is biomass liquefaction an option for the viability of poplar short rotation coppices? A preliminary experimental approach

Global renewable energy supply is expected to grow in the next three decades to address the issues related to mitigation of atmospheric carbon emissions. Within this scenario, biomass is a renewable resource that, due to its local availability is expected to play a prominent role. Cultivations specifically aimed to biomass production, such as woody short rotation coppices (SRCs), are a promising option for biomass supply in as much as these cultivations are carbon neutral along their life cycle. Nowadays, SRCs are not economically feasible and in the countries where they are implemented on a commercial scale, public subsidies are still needed. We propose that biomass liquefaction can be a possible route for the generation of high valued chemical products and thereby to potentiate the increase of areas allocated to SRCs and at the same time producing a liquid biofuel. By doing so, we believe that a parallel economic cycle can be generated allowing SRCs to be self-sustainable. The work on poplar biomass liquefaction developed so far discloses the high calorific value of bio-oil obtained in comparison with that from fossil fuels. Some preliminary chemical characteristics of the products obtained from liquefaction, are also presented.

A spatial explicit scenario method to support participative regional land-use decisions regarding economic and ecological options of short rotation coppice (SRC) for renewable energy production on arable land: case study application for the G\xf6ttingen district, Germany

BackgroundRenewable energy (RE) production is a land-use driver with increasing impact on landscape configuration and a matter of controversial debate. Woody biomass cropping provides an opportunity to interlink RE supply with spatial planning goals, RE concepts and rural development programmes since it tackles several issues, ranging from climate or soil protection to over food production and income diversification as well as new and additional regional value cluster. Participatory scenario generation supported by interactive visualization tools facilitates the development of joint goals regarding local land-use decisions.MethodsBased on a stakeholder dialogue in the rural district of Göttingen, two scenarios were quantified and analysed. Reflecting a farmer-oriented economic perspective in (a) “Income first” and an integration of economic and ecological aspects in (b) “Ecological benefits”, the two scenarios address opportunities and constraints of poplar short rotation coppice (SRC) in comparison to three common crop rotations in the case study area. Suitable SRC parcels were determined by linking yield modelling results of annual reference crops and poplar SRC with ecological indicators of water-induced soil erosion and ecotone density as well as with annuity calculation and a risk assessment (stochastic dominance) based on the Monte Carlo simulation of price and yield fluctuation.ResultsSRC was economically superior (stochastically first-order dominant) to all three reference crop rotations (oilseed rape-wheat-barley; maize-wheat-maize-wheat; oilseed rape-wheat-wheat) on 1800 ha or 4.9% of the arable land. With a positive annuity difference ranging between 63 and 236€ ha−1 a−1 SRC provides an opportunity to diversify farmers’ income. The primary energy supply from the suitable land parcels accounted for 130 GWh a−1 or 8% of the RE supply in 2030 strived for by local climate protection goals. Around 50% of the 1800 ha are suitable as focal areas for a joint consideration of farmers’ income, erosion protection and structural enrichment. The related average economic trade-off on annuity differences for the gain of substantially increased ecological benefits is about 17€ ha−1 a−1 (13%).ConclusionsLinking ecological criteria assessment with dynamic investment calculation and risk evaluation in a joint methodology revealed that SRC is an economic viable alternative for renewable energy production and can provide ecological synergies in terms of erosion protection and structural enrichment. The presented methodology is transferrable and allows to visualize stakeholder-based scenarios with an agreed identification of opportunities and constraints that come with SRC on arable land. This helps to better integrate local land-use decisions with formal and informal spatial planning goals.

Limitations for phytoextraction management on metal-polluted soils with poplar short rotation coppice—evidence from a 6-year field trial

ABSTRACTPoplar clones were studied for their phytoextraction capacity in the second growth cycle (6-year growth) on a site in the Belgian Campine region, which is contaminated with Cd and Zn via historic atmospheric deposition of nearby zinc smelter activities. The field trial revealed regrowth problems for some clones that could not be predicted in the first growth cycle. Four allometric relations were assessed for their capacity to predict biomass yield in the second growth cycle. A power function based on the shoot diameter best estimates the biomass production of poplar with R2 values between 0.94 and 0.98. The woody biomass yield ranged from 2.1 to 4.8 ton woody Dry Mass (DM) ha−1 y−1. The primary goal was to reduce soil concentrations of metals caused by phytoextraction. Nevertheless, increased metal concentrations were determined in the topsoil. This increase can partially be explained by the input of metals from deeper soil layers in the top soil through litterfall. The phytoextraction option with poplar short rotation coppice in this setup did not lead to the intended soil remediation in a reasonable time span. Therefore, harvest of the leaf biomass is put forward as a crucial part of the strategy for soil remediation through Cd/Zn phytoextraction.

Kinetics of Poplar Short Rotation Coppice Obtained from Thermogravimetric and Drop Tube Furnace Experiments

This article concentrates on the kinetics of poplar short rotation coppice obtained from thermogravimetric and drop tube furnace (DTF) experiments. Three poplar samples were studied, specifically, clone AF8 from two different plantations, one located in Italy (AF8-I) and another located in Portugal (AF8-P), and clone AF2 from a plantation located in Portugal. Initially, the combustion behavior of the three clones was evaluated by thermogravimetry. For the devolatilization zone, the thermogravimetric experiments yielded apparent activation energies of 109.7, 117.7, and 118.6 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. For the char oxidation stage, the apparent activation energies were 267.4, 252.0, and 264.3 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. Subsequently, the combustion behavior of the clone AF8-I was examined in a DTF. The data reported includes gas temperature and particle burnout measured along the DTF for five wall temperatures (900, 950, 1000, 1050, and 1100 °C). Th...

Early Clonal Survival and Growth of Poplars Grown on North Carolina Piedmont and Mountain Marginal Lands

The western half of North Carolina has abundant marginal pasturelands that vary greatly in altitude. Studies have demonstrated high Populus productivity on coastal plains and eastern Piedmont regions. Our objective was to identify best-performing Populus clones on marginal pasturelands representing upper Piedmont (Salisbury, 215 m above sea level, m.a.s.l.), northern Blue Ridge Mountains (Laurel Springs, 975 m.a.s.l.), and southern Blue Ridge Mountains (Mills River, 630 m.a.s.l.). At Salisbury, height and basal diameter (BD) were significantly related to clones (p < 0.0001), and some clones were affected by clone-spacing interaction while spacing affected aboveground wood volume significantly (p < 0.0001). At Mills River, clonal survival (p < 0.0011), height, and volume (p < 0.0051) varied with contrasting significance of some clonal differences between spacings. At Laurel Springs, survival varied among clones in 1 m × 1 m spacing (p = 0.003) but not 2 m × 2 m spacing while heights and volumes differed in both spacings (p < 0.0058). Clone 185 was consistently in the top 10 % for height, BD, and survival at all sites and spacings while other clones performed variably. Height-BD regressions were affected by clones, spacing, and sites. Volume had no clear correlations with precipitation, photosynthetically active radiation, temperature, and altitude across sites while height correlated with precipitation. Our results compared favorably with published results in other US regions, and show short rotation poplars have efficacy in Piedmont and mountain regions if the right clones in terms of growth/productivity, survival, and disease resistance are selected. Larger clonal performance variations are expected as competition increases, and highlight importance of experimentally determining suitable clones for specific sites.

Evaluation of Indirect Measurement Method of Seasonal Patterns of Leaf Area Index in a High-Density Short Rotation Coppice Culture of Poplar

Leaf area index (LAI) is an important determinant of biomass production and yield of short rotation bio-energy plantation. An accurate measurement of LAI is critical for quantifying light interception and penetration within the canopy, and subsequently understanding its influence on the stand carbon and energy balance. The aim of the current study is validation of the Sunscan Plant Canopy Analyzer which serves as an indirect method for the evaluation of the seasonal patterns of LAI, relation between LAI and above ground woody dry biomass and to determine the specific leaf area in short-rotation poplar hybrid clone J-105 (Populus nigra × P. maximowiczii) in uncoppiced (1st rotation) and coppiced (2nd rotation), respectively. LAI was measured in uncoppiced and coppiced by two different methods using indirect (SunScan Plant Canopy Analyzer) and direct (litterfall collection). Sunscan Plant Canopy Analyzer was compared against litterfall collection (only way to retrieve the actual LAI). Simple regression (R2 = 0.82) model was fitted to validate indirect measurement method and a very good agreement (82%) was observed in LAI values estimated from SunScan Plant Canopy Analyzer and from litterfall collection. Seasonal variability of LAI in a short rotation coppice (SRC) culture of poplar clone J-105 was evaluated over six years period (2008–2013), for uncoppiced (2008 and 2009) and coppiced (2010, 2011, 2012 and 2013) culture. The maximum canopy LAI (LAImax) reached 7.3 (uncoppiced) and 9.5 (coppiced). The linear regression (R2 = 0.93) for average LAI and above ground woody dry biomass was determined, and it was found that LAI acts an indicator of biomass productivity. Specific leaf area (SLA) was estimated in both uncoppiced and coppiced culture of poplar. The maximum SLA was found to be 138.9 cm2g−1 in uncoppiced and 126.9 cm2g−1 in coppiced. To conclude, the evaluated indirect LAI measurement method is portable, reliable and faster than direct LAI measurement in high density poplar short-rotation coppice culture.

Potential of poplar short rotation coppice cultivation for bioenergy in Southern Portugal

This manuscript examines the potential of poplar short rotation coppice cultivation for bioenergy in the Alentejo region, Southern Portugal. The biomass is intended to fulfil, at least, 10% (energy basis) of the fuel needs of two Portuguese coal-fired power plants (Sines and Pego), using co-firing technology. The study considers the overall production chain from cradle to power plant gate, cultivated in scrubland areas with duration of 12years, harvested every three years and with 6667 plants per ha, covering a land area of about 52,250ha. Three different biomass annual yields are assumed. The results show that the biomass selling prices range from 76.9 to 120.5Euroton−1, to match the production costs. The net energy of the overall project ranges from 34.7 to 75.4PJ and the project cost from 619 to 823.9MEuro. The main environmental impact of the project is the reduction of the CO2 emissions due to the biomass co-firing, instead of burning coal alone. The power plants can reduce CO2 emissions over the project lifetime between 8.2% and 16.5% of the current values. The financial analysis demonstrates that the project is not financially feasible without external grants, but a policy scenario of carbon allowances trading may be instrumental on turning it financially feasible, depending on allowances and coal market prices. Finally, with a reduction of 50% in the main costs, the project becomes financially feasible under a CO2 emissions trading scenario for a biomass yield of 20drytonha−1peryear.

Sub-Soiling and Genotype Selection Improves Populus Productivity Grown on a North Carolina Sandy Soil

This study reports the stem volume of 10 Populus genotypes in a randomized split-plot design with different tillage treatments (disking versus sub-soiling) after two years of growth. Height, diameter at breast height (DBH), stem aboveground volume index, survival, Melampsora rust resistance, leaf area index (LAI), chlorophyll content, and foliar nitrogen concentration (Foliar N) were measured to identify how tillage treatments might alter poplar growth. Stem volume index and LAI were positively correlated and differed significantly among tillage treatments, taxa, and genotypes. Melampsora rust resistance was also positively correlated with volume index, but significant differences were only detected among taxa and genotypes. Foliar N and chlorophyll did not correlate to stem volume for genotypes or tillage treatments. Overall, sub-soiling yielded 37% more estimated volume compared to disking. Within the sub-soiled treatments, four genotypes (140, 176, 185, and 356) had high survival (&gt;80%) and produced substantial stem volume (&gt;32 dm3·tree−1). These findings show that tillage practices do impact poplar stem volumes after two years and that sub-soiling improves productivity for poplar short rotation woody crops on loamy fine-sandy soils.

Poplar short rotation coppice is not a first choice crop for cattle slurry fertilization: Biomass yield and nitrogen-use efficiency

Little is known about the effect of cattle slurry fertilization on poplar short rotation coppice (SRC). This study addresses the following research questions: (i) is the biomass productivity of poplar SRC responsive to slurry application? (ii) what is the efficiency with which poplar SRC utilizes the N applied in the form of cattle slurry? (iii) does the ratio of carbon (C) to N (C/N) in harvested dry matter vary with rates of N fertilization? Fertilization treatments were: (i) no fertilization (control); (ii) cattle slurry 10mm, i.e. 10Lm−2 (CS10); (iii) cattle slurry 20mm, i.e. 20Lm−2 (CS20); and (iv) industrial fertilizers, consisting in 120kgNha−1 in the form of urea and 120kg P2O5 in the form of superphosphate (IF). The agronomic efficiency of applied N (AEN) varied from 5 to 14kg yield dry matter per kg N applied. The recovery efficiency of applied N (REN, kg N uptake per kg N applied) was merely 7.3–10.6%. The physiological efficiency of N uptake (PEN) was 79–123kg yield dry matter per kg N uptake. The threshold of 0.6% N, which is considered the guide value for high-quality biomass feedstock for combustion, was exceeded with the treatment CS20 in the first harvest cycle. Overall, our findings suggest that poplar SRC is not a first choice crop for cattle slurry application. In fact, N supply determined poor agronomic efficiency, a modest fraction of the N applied was recovered by the crop, and the rise of N concentration in the harvested biomass was detrimental for the quality of the feedstock product for combustion.

Selected environmental impacts of the technical production of wood chips from poplar short rotation coppice on marginal land

The use of marginal land for Short Rotation Coppice (SRC) might contribute to a sustainable energy supply in future. We assessed the environmental impacts of common production chains for manufacturing wood chips from SRC with poplar, including all the processes necessary to produce and deliver chips to a plant gate in 50 km distance from the field site (“cradle-to-plant gate”).To do so, we carried out a Life Cycle Analysis (LCA) including upstream processes. Results showed clearly that the specific environmental impacts were mainly caused by the processes “harvesting” and “transport”. Using a cut-and-chip harvesting system with a forage harvester generated low impacts during harvesting because of its high productivity. Using a cut-and-storage harvesting system with a whole rod harvester, however, didn't require accompanying tractor-trailer units during harvesting and allowed storing stems before chipping thereby, reducing the moisture content to approximately 30%. Consequently, the transport to the plant caused significantly lower environmental impacts at the same distance (50 km) which lead to a better result when looking at the overall production chain (26 vs. 36 kg CO2-eq Mgdm−1). Respective energy output to energy input ratios were 23:1 and 26:1.We also analysed the impacts of irrigation and fertigation as they might be options to increase biomass yield. Both treatments lead to considerably increased environmental impacts in all analysed categories which might be balanced only if the biomass yields increase substantially; an effect which could not be verified within the current study.

First vs. second rotation of a poplar short rotation coppice: leaf area development, light interception and radiation use efficiency

Given the high expectations for lignocellulosic biomass as one of the potential solutions for energy security and climate change mitigation, commercial scale studies over several rotations are crucial to assess the potential and the sustainability of short rotation coppice (SRC) cultures for bioenergy. The first and the second rotation of the SRC poplar (Populus) plantation of the present study differed significantly in biomass yield and in productivity determinants and their relationships. Coppicing enhanced leaf area development, radiation interception and woody biomass productivity. High total leaf area and radiation use efficiency (RUE) equally contributed to the high biomass yield during the establishment rotation, while RUE became the most important determinant of biomass yield after coppice. The study confirmed the significant genotypic variation in biomass productivity and its underlying determinants, also among more recently selected poplar genotypes. The absence of a correlation between intercepted radiation and RUE suggests the potential of selecting for genotypes combining high total leaf area and photosynthetic carbon uptake in future breeding programs for yield maximization towards sustainable bioenergy cultivation.

Geospatial assessment of potential bioenergy crop production on urban marginal land

Urban marginal land can be used for growing high yield bioenergy crops such as miscanthus and poplar. Here, a GIS-based modeling framework was created to assess potential urban marginal lands in Boston that include vacant lands and under-utilized public and private areas with adequate soil quality and sunlight. Using ArcGIS model builder as a spatial analysis tool, land parcels were screened for typical urban features such as buildings, driveways, parking lots, water and protected areas. The resultant layer was subjected to bio-geophysical modeling that includes soil quality, slope analysis and finally shadow analysis. Approximately 2660ha of potential marginal land was identified as suitable, representing 24% of total land area in Boston. Using crop yield information, it was estimated that this marginal land could be used to produce up to a total of nearly 42,130tons of high yield short rotation poplar biomass in a regular growing season. Also, bioenergy potential calculation revealed that for short rotation poplar, this amount of biomass can potentially yield up to 745 TJ (LHV) to 830 (HHV) TJ of yearly primary energy for the city of Boston that can be used for heat or electricity production, particularly for microgrid or district heating applications. This is equivalent to ∼0.6% of Massachusetts primary energy demand for 2012. Ongoing work will explore other urban regions of Massachusetts and the Eastern US that might be able to fulfill part of their energy demand locally while providing benefits in environmental quality, economic development, and urban resilience.

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.

Short Rotation Forestry (SRF) Versus Rapeseed Plantations: Insights from Soil Respiration and Combustion Heat Per Area

Bioenergy crops may be an important contributor to mitigating global warming risks. A comparison between willow and poplar Short Rotation Forestry and rapeseed cultivation was designed to evaluate the ratio between soil respiration and the combustion heat obtained from the extracted products per hectare. A manual dynamic closed chamber system was applied to measure CO2 emissions at the SRF and rapeseed sites during the growing season. Our results show that poplar and willow SRF has a very low ratio compared to rapeseed. We thus recommend poplar and willow SRF as renewable sources for bioenergy over the currently prevalent rapeseed production.

Harvesting systems for poplar short rotation coppice

The harvesting of wood species intended for energy production is one of the critical steps for the establishment of an economically viable supply chain. The review examines the state of the art of the main systems for collecting the short rotation coppice (SRC) by referring to poplar (Populus spp.), one of the main energy species for southern Europe. Starting from the early experiences of willow (Salix spp.) in Sweden, over time two approaches have established: the cut-and-chip and the harvest-and-storage system. In the work, the pros and cons of the two systems are analyzed and their efficiency compared, giving also some indication about the next evolution of the machines. Emerging systems showing an interesting future potential as bales production or the development of small-scale tractor-powered harvesters are also described. Finally, some economic considerations on differences between harvesting cost for the cut-and-chip and harvest-and-storage system are reported.