Sustainable use of eucalypt biomass grown on short rotation coppice for bioenergy

Bioenergy is one of the alternatives to reduce the dependence of global energy on fossil fuels. The short rotation coppice (SRC) of eucalypt species appears as an interesting option for forest biomass production in a short time. However, the harvesting of whole trees (included the crown) in SRC systems has implications on sustainable land use. More information is required on the increase of biomass as renewable energy resource to achieve the sustainability of these crops. The main objective of this research was to evaluate the sustainable use of biomass from very high-density eucalypt plantations, managed at tropical conditions for bioenergy. To accomplish this objective, the tree was fractionated into three fractions: stem, branches, and leaves, and there was determination of the dry matter, energy yield, and nutrients export. This experiment used a short rotation coppice, a hybrid clone of Eucalyptus urophylla × Eucalyptus grandis, of 2 years old. According to the results obtained, the density planting and fertilization levels have a greater influence on the dry matter yield, energy yield, and nutrient exports. The higher density planting reaches mean values of 30.9 tonnes of dry matter per hectare (t DM ha⁻¹) and 743.3 GJ ha⁻¹. Considering the biomass yield and nutrients export of short rotation coppice of eucalypt, the higher density planting with the lower dose of fertilization is more indicative of sustainable use. The leaves have an important participation in nutrients export and should be retained in the soil of forest.     

Biomass production and soil nutrients in organic and inorganic fertilized willow biomass production systems

The use of organic waste materials as nutrient sources for willow biomass production is an attractive means to decrease fertilization costs, increase biomass production and reduce greenhouse gas emissions associated with the system. In this study, changes in soil nutrients and biomass production of two willow varieties (Salix miyabeana–SX64 and Salix purpurea–9882-34) in organic and synthetic fertilized systems were compared at three locations in Northeastern U.S.A: Middlebury VT (MID), Delhi NY (DEL) and Fredonia NY (FRE). A 150 and 200 kg available N ha⁻¹ of urea as commercial fertilizer (CF), biosolid compost (BC) and digested dairy manure (DM) and a control (CT0) treatments were applied in June 2008 to the willow which was re-sprouting after coppice. There was no significant difference (p > 0.05) in biomass production among the fertilization treatments at any of the three sites and for either of the varieties. First rotation biomass production of 9882-34 ranged from 9.0 to 11.6 Mg ha⁻¹ yr⁻¹ at DEL, 3.4–8.8 Mg ha⁻¹ yr⁻¹ at MID and 3.5–7.7 Mg ha⁻¹ yr⁻¹ at FRE. For SX64, biomass production ranged from 13.2 to 19.0 Mg ha⁻¹ yr⁻¹ at DEL, 9.0–15.0 Mg ha⁻¹ yr⁻¹ at Mid and 5.5–9.3 Mg ha⁻¹ yr⁻¹ at FRE. SX64 deployed small numbers of large stems and produced more biomass than 9882-34 which deployed large numbers of small stems. Application of BC significantly increased soil N and P levels at MID in both 2008 and 2009 (p < 0.05). At DEL, BC and DM treatments increased soil N, Ca, Mg and OM levels in both 2008 and 2009 (p < 0.05). The fertilization treatments had no significant effect on any soil nutrients at FRE. This study indicates that willow biomass can be produced without fertilizer additions in the first rotation across this range of sites due to the nutrient status of these sites and high internal nutrient cycling in these systems.     

Energy and CO2 analysis of poplar and maize crops for biomass production in north Italy

The rising price of fossil fuel and the increasing environmental concern encourage the use of biomasses as energy sources. Aim of this study was to compare two poplar SRC and vSRC (6 and 3 years rotation cycle) with an annual crop (maize), used for biomass production in north Italy.The average of the biomass production was 13.9 Mg DM ha⁻¹ per year for the SRC and vSRC poplar and 19.2 Mg DM ha⁻¹ for the maize.The energy consumption for the poplar cultivations was about 15 GJ ha⁻¹ per year, which represented only the 6% of the energy biomass product (about 257 GJ ha⁻¹ per year).The input value of the maize was higher (26.8 GJ ha⁻¹ per year). In this case, the input value was about the 7% of the energy content in the biomass product (about 370 GJ ha⁻¹ per year).During the vSRC cultivation an amount of 8090 kg CO₂ eq ha⁻¹ was emitted, 6420 kg CO₂ eq ha⁻¹ for the SRC and 26,370 kg CO₂ eq ha⁻¹ for the maize.Compared to the maize, the poplar SRC (or vSRC) crops are interesting from an energetic point of view, while maize requires less manpower, but it has major problems related to the landscape biodiversity.     

Carbon sequestration in willow (Salix spp.) plantations on former arable land estimated by repeated field sampling and C budget calculation

Short rotation coppice (SRC) plantations are of interest as producers of biomass for fuel, but also as carbon (C) sinks to mitigate CO₂ emissions. Carbon sequestration in biomass and soil was estimated in 5-year-old replicated SRC plantations with willows (Salix spp.) on former arable land at five sites in Sweden. Total standing C stocks, i.e. C stored in woody biomass above- and belowground, fine root standing crop, litter, and soil organic carbon (SOC) were estimated by repeated field sampling and C budget calculation.Overall, the SRC willow plantations represented a C sink after five years. Estimated increase of total standing C stock was 15% on average compared to pre-planting conditions. There was no change in SOC when including all sites. Analyses within sites revealed a decrease in SOC at one site, although the decrease was compensated for by C stored in willow biomass. After removal of stem biomass, C in other plant pools was sufficient to compensate for the SOC decrease. Remaining C in stumps, stool, and coarse roots was estimated at ca 20% of stem C.There was a discrepancy between SOC sequestration rates from soil sampling and C budget calculation, −2.1–1.0 and 0.15–0.45 Mg ha⁻¹ y⁻¹, respectively. Mineralization of old organic material from previous land-use and input to SOC from understory vegetation were not included in the calculations, which may explain part of the differences. The importance of understory litter in C budgets for young plantations was apparent, as it comprised 24–80% of aboveground litter C.     

Impact of different establishment methods in terms of tillage and weed management systems on biomass production of willow grown as short rotation coppice

To date little information is available on methods including soil preparation and weed control in SRC. For this purpose, in 2010, a field trial with willow cv. ‘Tordis’ was established in southwest Germany. Three different tillage systems (mouldboard plough, chisel plough + ley crop, no-till) were implemented in the establishment year in combination with eight chemical and mechanical weed management systems. Over a period of three years, plant and weed specific parameters were collected to determine the effect of tillage systems and weed treatments on final biomass production of willow. The highest biomass yields were obtained by mouldboard plough with chemical weed control (14.0 Mg ha⁻¹ dry matter) as well as by mouldboard plough with rotivation and band spraying of herbicides (14.2 Mg ha⁻¹ dry matter), followed by 13.7 Mg ha⁻¹ dry matter in no-till with broadcast application of herbicides. Chisel ploughing with ley crop led to lower willow yields in most weed treatments. It was assumed that chisel ploughing + ley crop would lead to a high competition for light, water and nutrients especially in the first year. Consequently, it is not recommended as an establishment method for willow. Additionally, mulching with wood chips and no weed management generally resulted in low biomass yields. Overall, the results suggest that the tillage system in combination with effective chemical or mechanical weed control is of major importance for the success of willow establishment.     

Simulated biomass,environmental impacts and best management practices for long-term switchgrass systems in a semi-arid region

Long-term information on switchgrass (Panicum virgatum L.) as a biomass energy crop grown on marginally saline soil and the associated impacts on soil carbon (C) and nitrogen (N) dynamics, greenhouse gas (GHG) emissions, and best management practices (BMPs) are limited. In this study, we employed the DAYCENT model, based on a 4-year switchgrass field experiment, to evaluate the long-term biomass yield potential and environmental impacts, and further to develop BMPs for switchgrass in a semi-arid region.The model showed that long-term (14-year) annual mean biomass yields were 9.6 and 5.2 Mg ha⁻¹ for irrigated and rainfed switchgrass systems, respectively. The simulated biomass yields correlated well with field-measured biomass with r² values of 0.99 and 0.89 for irrigated and rainfed systems, respectively. Soil organic carbon (SOC) and soil total nitrogen (STN) accumulated rapidly after switchgrass establishment, with mean accrual rates of 0.99–1.13 Mg C ha⁻¹ yr⁻¹ and 0.04–0.08 Mg N ha⁻¹ yr⁻¹, respectively. Based on the outputs of numerous long-term model simulations with variable irrigation water supplies and N rates, the irrigation regime and N rate with the highest yield to input ratio were chosen as BMPs. The DAYCENT model predicted-BMP was irrigating every 14 days at 70% potential evapotranspiration combined with an N rate of 67 kg ha⁻¹ yr⁻¹. Switchgrass established and produced biomass reasonably well in this semi-arid region; however, appropriate irrigation and N fertilization were needed for optimal biomass yield. Switchgrass had a great potential to sequester C into soils with low N₂O emissions while supplying significant quantities of biomass for biofuel synthesis.     

Switchgrass (Panicum virgatum L.) nutrients use efficiency and uptake characteristics,and biomass yield for solid biofuel production under Mediterranean conditions

Switchgrass produces high amounts of biomass that can be used for solid biofuel production. In this study, the dry biomass yield vs. N–P–K nutrient uptake relations as well as the N-mineralization and the N-fertilization recovery fraction for switchgrass (cv. Alamo) were determined under field conditions for three N-fertilization (0, 80 and 160 kg ha⁻¹) and for two irrigation (0 and 250 mm) levels, in two soils in central Greece with rather different moisture status over the period 2009–2012. It was found that dry biomass yield on the aquic soil may reach 27–30 t ha⁻¹ using supplemental irrigation, and remain at high levels (19–24 t ha⁻¹) without irrigation. In the xeric soil, however, lower biomass yields of 14–15 t ha⁻¹ may be produced with supplemental irrigation. The average N-concentration varies between 0.23% in stems and 1.10% in leaves, showing the very low needs in N. P-content varies between 0.16% in leaves and 0.03% in stems, whereas K-content fluctuates between 0.67% and 0.78%. Linear biomass yield-nutrient uptake relationships were found with high R², pointing to nutrient use efficiencies of 240 and 160 kg kg⁻¹, for N and K respectively. The base N-uptake ranged 70–84 kg ha⁻¹ in the aquic to 60 kg ha⁻¹ or less in the xeric soil. N-recovery fraction was about 30% in the aquic soil and lower in the xeric. Therefore, switchgrass is very promising for biomass production and its introduction in land use systems (especially in aquic soils of similar environments) should be seriously taken into consideration.     

Effects of delayed winter harvest on biomass yield and quality of napiergrass and energycane

Napiergrass (Cenchrus purpureus (Schumach.) Morrone) and energycane (Saccharum hyb.) are perennial grasses that are well-suited for biomass production in the southeastern USA. The purpose of this study was to determine the effects of delayed winter harvest on biomass yield and quality of these grasses. The study was conducted on two adjacent sites near Midville, GA. Each site used a split-plot design with four replications, with species as the main plot, and harvest times (December, January, or February) as sub-plots. Dry matter (DM) yields were measured by mechanical harvesting, and a sample of biomass was taken from each harvest for determination of ethanol production by simultaneous saccharification and fermentation (SSF). Biomass moisture, N, P, K, and ash mass fractions were also measured. Energycane DM yields were stable from December (46.8 Mg ha⁻¹) to January (42.9 Mg ha⁻¹), but then declined (36.8 Mg ha⁻¹), while napiergrass yields declined sharply from December (47.0 Mg ha⁻¹) to January (35.0 Mg ha⁻¹). Napiergrass moisture mass fraction was reduced by an average of 18% in February harvests compared to December. Mass fractions of N, K, and ash tended to decrease with later harvesting, but sometimes increased due to changes in biomass composition. Delaying harvest of napiergrass from December to January reduced N removal by an average of 144 kg ha⁻¹, while delaying harvest of energycane to February reduced N removal by an average of 54 kg ha⁻¹. In SSF, later-harvested energycane produced less ethanol per unit of DM while napiergrass was less affected by harvest date.     

Carbon and nutrients of Scots pine stands on sandy soils in Lithuania in relation to bioenergy sustainability

Sustainable forestry is based on the principle that harvesting practices should avoid negative influence on soil fertility, wood production and long-term soil carbon (C) stocks. We examined C and nutrient concentrations and stocks of Scots pine (Pinus sylvestris L.) stands on Arenosols in south-western Lithuania. The stands were 10, 20, 40, 50 and 65 years of age. C concentrations were relatively constant, while the concentrations of N, P, K, Ca, Mg and S often varied between compartments and stand ages.The total aboveground stocks of nitrogen (N) were estimated to be in the range of 185–260 kg ha⁻¹, and 78–189 kg ha⁻¹ for calcium (Ca), 75–104 kg ha⁻¹ for potassium (K), 22–33 kg ha⁻¹ for phosphorus (P), 21–41 kg ha⁻¹ for magnesium (Mg) and 16–28 kg ha⁻¹ for sulphur (S). Corresponding stocks of the crown alone were 139–207 kg ha⁻¹ of N, 54–88 kg ha⁻¹ of Ca, 44–79 kg ha⁻¹ of K, 15–26 kg ha⁻¹ of P, 15–23 kg ha⁻¹ of Mg, and 11–15 kg ha⁻¹ of S. Biomass, C and nutrient stocks in the crown did not change with age, whereas the stemwood stocks increased with stand age. The total removals of C and N over a whole 100-year rotation were simulated to be 129 Mg ha⁻¹ and 449 kg ha⁻¹, respectively. An example scenario was created to compare the magnitude of potential nutrient removals with the atmospheric influx, soil stocks, and the internal litterfall flux. We suggest that intensified utilisation of these stands for bioenergy may be sustainable.     

Characterization of fine root system and potential contribution to soil organic carbon of six perennial bioenergy crops

Perennial bioenergy crops provide biomass for renewable energy production, but also sequester atmospheric carbon (C) in the soil. Roots represent one of the most important soil C inputs-root length density (RLD, cm cm⁻³), root diameter and fine root biomass (FRB, Mg ha⁻¹) in the top 1 m of soil were characterized for three woody (poplar, black locust, willow) and three herbaceous (giant reed, miscanthus, switchgrass) perennial crops in the same location. The vertical distribution of FRB and RLD was described by fitting the “beta” (β) model to the experimental data. The herbaceous species had higher β values for FRB and RLD than woody crops, suggesting that the former explore the deeper soil layers with a greater proportion of roots. In particular, 3.7 Mg ha⁻¹, or 43% of the whole root mass, was found below the ploughing soil layer (0.3 m) for the herbaceous species, while only 1.2 Mg ha⁻¹, or 26% of the whole root mass, was allocated by woody crops to the same soil layer. In all the species, the majority of the sampled roots (99.1%) had a diameter lower than 2 mm, and in the first 10 cm of the soil the woody species tended to produce roots with a smaller diameter than those of the herbaceous species. Overall, the herbaceous crops have a higher potential to contribute to C storage in the deep soil layers, while the woody species, have a greater potential to affect soil organic carbon in the top soil layer.     

Effects of mechanical weed control or cover crop on the growth and economic viability of two short-rotation willow cultivars

Willow grown as short rotation coppice (SRC) is sensitive to weed competition, so herbicide treatment combined with mechanical weed control is recommended when establishing a plantation. This study compares that practice with two mechanical, row crop cultivator (RC) and row crop cultivator with torsion weeder (RCT), and two cultural treatments, cover crop (CC) and cut cover crop (CCC), to control weeds. Willow responses to these treatments were compared during the first three years after planting using two cultivars, Gudrun and Tordis with broad and narrow leaves, respectively. At harvest, the RCT treatment had produced 27% more biomass than the RC treatment (13.9 vs 11.0 Mg ha⁻¹ dry matter) and approximately three times more than the cultural treatments. However, the standard control treatment, herbicides and row crop cultivator (HRC), produced more than all other treatments (17.3 Mg ha⁻¹ dry matter). The two cultural treatments had higher plant mortality (CC 26.2% and CCC 32.8%) than the other treatments (HRC 2.7%, RC 7.0% and RCT 7.0%) after the first harvest cycle. No interaction between cultivar and treatment was found for willow shoot biomass, weed biomass or plant mortality. Overall, however, Gudrun had lower plant mortality and less weed biomass after the first harvest cycle than Tordis. All treatment and cultivar combinations gave positive financial annual returns when the whole life-span of the plantation was considered. This study suggests that without using herbicides, it is possible to establish a willow SRC plantation that produce enough to be economically viable.     

Nutrient sources and harvesting frequency on quality biomass production of switchgrass (Panicum virgatum L.) for biofuel

Improper management of cattle manure and poultry litter from confined animal farming are usually source of water pollution. However, appropriate application of these products on switchgrass (Panicum virgatum L.) field can enhance biomass yield and promote nutrient recycling. We evaluated the effects of harvest frequency and nutrient sources on yield and quality of switchgrass for biofuel feedstock. The experiment was carried out at Perkins and Lake Carl Blackwell, Oklahoma, from 2009 to 2011 using split plot design with four replications. The main plot treatments were two harvest frequencies single (June), and twice (June and November). The subplot treatments were nutrient sources: 1) cattle manure (CM), 2) poultry litter (PL), 3) urea (nitrogen at 150 kg ha⁻¹), 4) combined chemical fertilizer (nitrogen-P₂O₅–K₂O) with nitrogen at 150 kg ha⁻¹, P₂O₅ at 40 kg ha⁻¹, and K₂O at 20 kg ha⁻¹, 5) inter-seeded Crimson clover (Trifolium incarnatum L.), and 6) control. Mean biomass yield was higher (12.4 Mg ha⁻¹) in 2010 than other years possibly due to optimum moisture and temperature in 2010. At Perkins in 2010, application of CM and PL increased biomass yield significantly by 30 and 23% compared with combined chemical fertilizer (12.9 Mg ha⁻¹). The effect of nutrient sources on cellulose, hemicellulose and lignin content was not significant at both locations. Cumulative biomass from twice harvest was similar to single harvest except in 2011 due to dry weather after the first cut. The cellulose and lignin content were significantly higher for single harvest compared with twice harvest at both locations.     

Effect of fertilisation on biomass yield,ash and element uptake in SRC willow

Optimal fertilization of short rotation coppice (SRC) willow is important both in terms of economic yield and environmental effect. We measured biomass yield and nutrient uptake in two willow clones, Inger and Tordis, grown on a coarse sandy soil and within six different fertilization regimes. Fertilization treatments were carried out during two two-year harvest rotations, beginning in the 2nd growth year of the plantation. Willow was fertilized as follows with names referring to type of fertilizer and total quantities of nitrogen (kg ha⁻¹) in first and second year within both rotations: 1) Control₀₊₀, 2) NPK₁₂₀₊₀, 3) Slurry₁₈₀₊₀, 4) NPK_120+120, 5) NPK₂₄₀₊₀, 6) Slurry₃₆₀₊₀. Fertilization affected biomass yield significantly but interacted with rotation and clone. In first rotation, fertilization increased dry matter (DM) yield across clones significantly from 3.7 Mg ha⁻¹ y⁻¹ for Control₀₊₀ to 6.5, 6.4 and 5.6 for Slurry₃₆₀₊₀, NPK_120+120 and NPK₂₄₀₊₀, respectively. In second rotation, yield increased from 6.2 Mg ha⁻¹ y⁻¹ to 8.8, 8.2, 7.8 and 7.4 for Slurry₃₆₀₊₀, NPK₂₄₀₊₀, Slurry₁₈₀₊₀ and NPK_120+120, respectively. Biomass dry matter yield per ha increased linearly at 15 kg kg⁻¹ of applied total-N in both rotations. The yield increase in response to fertilization was generally larger in Inger than in Tordis. In general, element concentration in the harvested biomass was either unaffected or slightly reduced by fertilization. In conclusion, yield response to fertilization appears to be primarily related to the quantity of N applied but the effect depended on fertilizer type, harvest rotation and willow clone.     

Biochar and plant growth promoting rhizobacteria effects on switchgrass (Panicum virgatum cv. Cave-in-Rock) for biomass production in southern Québec depend on soil type and location

Switchgrass (Panicum virgatum L.) is a fast growing native C₄ perennial and a lignocellulosic biomass crop for North America. In combination with biochar, an active plant growth promoting rhizobacterial (PGPR) community can contribute to the long-term sequestration of carbon in soil, fix nitrogen, and enhance the availability of other nutrients to plants. Biochar and PGPR have the potential to improve grass biomass production, but they have not been tested together under high-latitude temperate zone field conditions. Therefore, the objective of this three-year field study was to determine whether there were effects on biomass yield and yield components of switchgrass (cv. Cave-in-Rock) due to a rhizobacterium that was able to mobilize soil phosphorus (Pseudomonas rhodesiae), a bacterial consortium that was able to supply nitrogen (Paenibacillus polymyxa, Rahnella sp., and Serrati sp.), and pine wood chip biochar applied as a soil amendment at 20 Mg ha⁻¹. The incorporation of biochar, or inoculation with the N-fixing consortium, and the combined inoculation of the experimental bacteria had positive effects on switchgrass height. At a loam soil site in Sainte-Anne-de-Bellevue, Québec, when nitrogen fertilizer was not applied, the addition of biochar had a positive effect on stand count (tillers m⁻¹ row). On the sandy soil in Sainte-Anne-de-Bellevue, when biochar was applied with 100 kg N ha⁻¹, biomass yield increased over the control but did not provide additional benefits over plots receiving only 50 kg N ha⁻¹. It remains unclear whether or not the increased C sequestration of this management system justifies increased N fertilizer usage.     

Yield potential and stand establishment for 20 candidate bioenergy feedstocks

Here we assess 20 bioenergy crop accessions across 10 species, and examine the influence of weed management and annual harvest treatments over three growing seasons in Virginia and one season in Kentucky. Species in this study include: Andropogon gerardii, Arundo donax, Miscanthus × giganteus (sterile triploid and seeded tetraploid), Miscanthus sinensis (ornamental and naturalized), Miscanthus sacchariflorus, Panicum virgatum, Phalaris arundinacea, Saccharum sp., Sorghum bicolor and the unconventional choice of Sorghum halepense. There was a large difference in yield between locations at the end of the planting year, with all accessions producing equivalent or greater biomass in Kentucky. Weed management did not impact yield in the establishment year, as biomass was predictably low. After the third growing season, only A. gerardii and two accessions of naturalized M. sinensis had noticeable reductions in yield due to competition from weeds. After three growing seasons, we obtained the highest yields from M. × giganteus (63, 51 and 39 Mg ha⁻¹ for ‘Illinois’, ‘PowerCane’ and ‘Nagara’ varieties, respectively), naturalized accessions of M. sinensis (54 Mg ha⁻¹), and A. donax (39 Mg ha⁻¹), using traditional cropping practices. Few accessions had low establishment rates limiting overall yields (<10 Mg ha⁻¹); however, when aboveground biomass was calculated on an individual plant basis, yields were comparable to high yielding species, encouraging further examination at higher population densities. Our results indicate that site characteristics such as soil parameters and water availability may be more important for yield than weed competition, especially over time.     

Energy characterisation of herbaceous biomasses irrigated with marginal waters

The paper reports the results of a research program aiming to evaluate the agronomic, and energy sustainability of the biomass production by perennial non-food herbaceous crops irrigated with different kinds of marginal waters. In four different sites (Bologna, Padova, Reggio Calabria, and Catania) the same four species (Arundo, Typha, Phragmites, and Lythrum), usually tested without irrigation, were planted and monitored during 2008–2010. The results show that a planting density of 10 m⁻² is necessary to obtain a maximum dry yield levels already from the second year of transplanting. The maximum productivity was obtained with Arundo (close to 100 Mg ha⁻¹ y⁻¹ in Bologna and 86 Mg ha⁻¹ y⁻¹ in Padova, 50–60 Mg ha⁻¹ y⁻¹ in the southern locations). Lythrum productivity ranged from 5.2 to 9.2 Mg ha⁻¹ y⁻¹ in all the RUs, with the exception of Reggio Calabria. Typha (around 10 Mg ha⁻¹ y⁻¹ at the third year) and Phragmites (5–8 Mg ha⁻¹ y⁻¹) gave significant production only in the northern locations. The HHVs were close to 15.5 MJ kg⁻¹ for Phragmites (except for Catania and Reggio Calabria with 20.0 MJ kg⁻¹) 18.0 MJ kg⁻¹ for the Arundo (except for Catania with 20.0 MJ kg⁻¹), 18.5 MJ kg⁻¹ for the Typha and Lythrum (except for Catania with 20.0 MJ kg⁻¹).     

Tree species composition,biomass and carbon stocks in two tropical forest of Assam

Tropical forests store higher above ground biomass (AGB) and AGB carbon (AGBC) than any other forest ecosystems. In the present study the tree composition, diversity, dominance and carbon stocks in the AGB and soil of tropical forests viz., the Gibbon wildlife sanctuary (GWS) and the Kholahat reserve forest (KRF) of Assam, India were assessed. Soil sampling, tree survey, girth above 1.3 m height of plants >10 cm girth of plants were assessed in 1000 m² quadrate. Allometric model for moist forest stands was used to determine AGB and AGBC. A total of 71 and 108 different tree species belong to 32 and 42 families were found in the GWS and KRF, respectively. In the GWF, the Shannon diversity index (1.22) and the Simpson index (0.085) were significant, while for the KRF these indices were insignificant. The basal area, AGB and AGBC in the GWS and KRF were 62.49–90.29 m² ha⁻¹, 135.30–146.42 Mg ha⁻¹, and 67.64–73.21 Mg ha⁻¹, respectively. The average soil carbon stock (SOC) in the upper, middle and lower layers was 57.74–78.44 kg m⁻², 39.22–64.93 kg m⁻² and 30.32–42.86 kg m⁻², respectively, in the GWS and KRF. However, compared to GWS, a higher AGB and AGBC were found in KRF. This finding reveals that the higher AGB, AGBC and SOC in the KRF were due to old growth matured forest with big and diverse tree species.     

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.     

Physiological adaptability of Poplar clones selected for bioenergy purposes under non-irrigated and suboptimal site conditions: A case study in Central Italy

New Poplar clones for biomass production are currently under evaluation in Italy to be cultivated in Mediterranean site conditions, where the evapotranspirative demand is not balanced by rainfall supply. The study aims to evaluate the dynamic responses of leaf gas exchanges, budding, foliar morphology and yield in three modern hybrids Poplar clones (AF2, AF6 and Monviso) under non-irrigated and suboptimal site conditions in a Short Rotation Forestry plantation of Central Italy. During the drought season, the stomatal closure was gradual in AF2 and AF6 but rapid in Monviso. These traits were associated with the best yields (expressed as dry matter) in AF2 (8.74 Mg ha⁻¹ year⁻¹) and AF6 (6.53 Mg ha⁻¹ year⁻¹) compared to Monviso (5.72 Mg ha⁻¹ year⁻¹). Monviso was advised as sensitive clone to summer drought even if it has showed higher photosynthetic potential traits such as earlier budding and maximum leaf area. AF2 and AF6 were advised as tolerant and moderately-tolerant clones to summer drought as they maintained higher and relatively-higher stomatal conductance (gs) values over a growing season, summer photosynthetic assimilation rates (A) and intrinsic water-use efficiency (A/gs ratio) compared to Monviso, respectively. We pointed out the occurrence of main physiological processes (budding, maximum and minimum gs, maximum leaf area) to highlight the key-periods leading the growth under these site conditions by identifying the air temperature thresholds and precipitation patterns along a growing season. We provided recommendations to Italian Poplar practitioners for cultivations of these clones in Mediterranean areas affected by summer drought.     

Relationships among Jatropha curcas seed yield and vegetative plant components under different management and cropping systems in Indonesia

An understanding of how Jatropha curcas seed yield relates to vegetative plant components under different management regimes is lacking. Such information is necessary to predict yields and design management strategies. This study investigated yield and vegetative plant component interactions, and the effects of management practices in monoculture, intercropping, and hedge cropping systems in Indonesia. Monoculture and intercropping experiments in Gunungkidul Regency used jatropha IP-1M material; hedge experiments in Sumbawa Regency used the Sumbawa provenance. In two-year-old monoculture, pruning significantly decreased yield from 109 kg ha⁻¹ to 28 kg ha⁻¹ due to a 40% decrease in canopy volume and LAI. In four-year-old jatropha intercropping, root barriers reduced yields 80% by limiting jatropha root access to soil moisture and nutrients in the maize plantings. Intercropping without root barrier and with leaf mulch produced the largest yields of 25 kg ha⁻¹. In hedge plantings, plant height influenced yield. Single rows of one-year-old monoculture produced 0.97 g m⁻¹ at 10 cm spacing, 1.69 g m⁻¹ at 30 cm, and 0.14 g m⁻¹ for 20 cm of mixed jatropha–gliricidia. Pruning significantly decreased LAI with 20 cm spacing indicating a higher proportion of above-ground biomass allocated for wood growth. Results indicate that seed yield across the three cropping systems can be determined by plant height and numbers of productive twig/branch, although number of inflorescences cluster per productive twig may be more important. Future research should focus on the transition of branches to reproductive phases, and on increasing numbers of productive twigs/branches and inflorescence clusters.