Biomass equations for determining fractions of common and grey alders growing on abandoned farmland and some practical implications

A study was conducted in order to construct functions for above-ground biomass of fractions of young common alders (Alnus glutinosa (L.) Gaertn.) and grey alders (Alnus incana (L.) Moench.). The constructed functions were designed to be used to predict the amount of biofuel produced from small areas. Biomass production was estimated in 10 stands of common alder and 15 stands of grey alder, growing on abandoned farmland. The common alder stands were located in Sweden at latitudes ranging from 58° to 60° N, and their total age varied from 4 to 36 years. Grey alder stands were located at latitudes ranging from 60° to 66° N, and their total age varied from 5 to 35 years. A modified ‘mean tree technique’ was used to estimate biomass production, i.e. the tallest tree was chosen for sampling. The mean total dry weight above the stump level for common alder stands was 39 tonnes ha⁻¹ with a range of 5 to 140 d.w. ha⁻¹ and 61 tonnes ha⁻¹ with a range of 3 to 140 tonnes d.w. ha⁻¹ for grey alder stands. The mean annual increment for common alder stands was 3.11 tonnes ha⁻¹ y⁻¹ (0.50–7.71) and 4.38 tonnes ha⁻¹ y⁻¹ (0.66–9.32) for grey alder stands. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and leaf area index (LAI), among other measures, were estimated. The mean LAI for common alder stands was 3.16 and 2.03 for grey alder stands. The specific leaf area per tree for common alder was 16.1 m² kg⁻¹ and 14.4 m² kg⁻¹ for grey alder. Practical implications of the findings are discussed.     

Increment and biomass in hybrid poplar and some practical implications

Growth data were collected from 41 stands of poplar (Populus sp.) growing on former farmland in Sweden, situated between latitudes 55 and 63° N. The mean age of the poplar was 20 years (range 4-73), the mean stand density 1327 stems ha⁻¹ (range 155-4690), and the mean diameter at breast height (over bark) 210 mm (range 49-447 mm). Soil types in the poplar stands were mainly clay (25 stands), other sediments (six stands) and sandy-silty till (10 stands).The mean total standing dry weight above stump level (≈200 mm) for poplar was 141.9 ± 13.9 ton ha⁻¹ with a range of 19-438 ton ha⁻¹. In addition to estimating conventional dry weights of trees and tree components, SLA, PLA and LAI, among other measures, were estimated and were in agreement with published figures.The results indicate that poplar stands could produce 70-105 ton ha⁻¹ after 10-15 years growth mainly used for biofuel. Otherwise, the stands could be thinned for pulpwood and timber production with a rotation period of 25-30 years and the thinnings used for biofuel.     

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.     

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.     

Biomass equations for determining fractions of pendula and pubescent birches growing on abandoned farmland and some practical implications

Biomass production was estimated in 10 stands each of pendula birch (Betula pendula Roth) and pubescent birch (Betula pubescens Ehrh.) growing on abandoned farmland. The pendula birch stands were located in Sweden at latitudes ranging from 66° to 58°N, and their total age varied from 8 to 32 years. Pubescent birch stands were located at latitudes ranging from 66° to 60°N, and their total age varied from 6 to 20 years. A modified “mean tree technique” was used to estimate biomass production; i.e. the tallest tree was chosen for sampling. The actual mean total dry weight above stump level was 71 tonnes ha⁻¹ (range, 6 to 175 tonnes d.w. ha⁻¹) for pendula birch stands and 27.3 tonnes ha⁻¹ (range, 7 to 61 tonnes d.w. ha⁻¹) for pubescent birch stands. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and LAI, among other measures, were estimated.     

Yield comparison of four lignocellulosic perennial energy crop species

From 2006 to 2009, block template experiments were conducted to evaluate the biomass yield of four crop species—Amur silvergrass, Giant Miscanthus, Virginia fanpetals, and two Basket willow clones—at the University of Life Science, Lublin, Poland. The dry matter (d m) yields and number of shoots were determined each November, while biomass moisture levels were determined every November and March. The averages of the 4-year research datasets indicated that Giant Miscanthus produced the greatest biomass (16.5 t ha⁻¹ d m), while the two Basket willow clones (8.8–10.2) t ha⁻¹ d m, and Amur silvergrass (6.2 t ha⁻¹ d m) produced the lowest biomass. The mean yield of Virginia fanpetals was 13.0 t ha⁻¹ d m. The largest number of shoots per one m² were produced by Miscanthus species (55 units), with Basket willow and Virginia fanpetals producing half this amount (24–28 units). Similar moisture levels were obtained for Basket willow biomass harvested in autumn (49.5–54.6)% and winter (48.4–49.7)%. The biomass moisture levels of the other species in March was approximately two times lower (14–29)% than that in November (27–70)%.In a second experiment, the effect of varying plant density (10 000 and 30 000 plants per ha) on the yield of Giant Miscanthus was investigated. Double the biomass yield was obtained in crops with a density of 30 000 plants per hectare compared to 10 thousand. The higher yields were accompanied by larger, heavier, taller, but thinner shoots.     

Evaluation of sorghum hybrids for biomass production in central Italy

Two field experiments were carried out in 2005 and 2006 in central Italy in order to evaluate the biomass production and quality in eight sorghum hybrids, to define their biomass partitioning among leaves, panicles and stems and to identify which were the most adapted at early harvest. Sorghum showed a high potential in terms of biomass production in central Italy, with biomass dry yield of 25 t ha⁻¹ in average, adopting low input in terms of irrigation and fertilization. The most productive hybrids were H133 (26.3 t ha⁻¹) and H952 (25.9 t ha⁻¹) among the biomass hybrids and SS506 (27.3 t ha⁻¹) among the forage hybrids. The trends of dry weight and moisture content of biomass during the different hybrids growth cycles allowed to estimate the biomass production of each hybrids, hypothesizing an early harvest at 20 August with in-field drying of biomass. Early harvest reduced dry weight of biomass from 4.6% to 21.7%, depending of hybrids; SS506 and H128 showed to be the most adapted at early harvest. HHV and LHV of biomass showed average values higher in biomass hybrids (18.4 and 17.5 MJ kg⁻¹ d.m.) than in forage hybrids (17.7 and 16.8 MJ kg⁻¹ d.m.); while, ash content average values were lower in biomass hybrids (6.8% d.m.) than in forage hybrids (7.7% d.m.). The highest values of leaves + panicles partitioning in the forage hybrids increased ash content, reducing the quality of their biomass for thermal utilization; the biomass hybrids should be therefore preferable.     

Above ground standing biomass and carbon storage in village bamboos in North East India

Bamboo forms an important component in the traditional landscape of North East India. For biomass estimation of village bamboos of Barak Valley, North East India, allometric relationships were developed by harvest method describing leaf, branch and culm biomass with DBH as an independent variable using a log linear model. The culm density of the stand was 8950 culms ha⁻¹ during 2005 of which 67% of growing stock was represented by Bambusa cacharensis, 17.88% by Bambusa vulgaris and 15.12% by Bambusa balcooa. Above ground stand biomass was 121.51 t ha⁻¹ of which 86% was contributed by culm component followed by branch (10%) and leaf (4%). With respect to species, B. cacharensis made up to 46% of total stand biomass followed by B. vulgaris (28%) and B. balcooa (26%). Carbon storage in the above ground biomass was 61.05 t ha⁻¹. Allocation of C was more in culm components (53.05 t ha⁻¹) than in branch (5.81 t ha⁻¹) and leaf (2.19 t ha⁻¹). Carbon storage in the litter floor mass was 2.40 t ha⁻¹, of which leaf litter made up the highest amount (1.37 t ha⁻¹) followed by sheath (0.86 t ha⁻¹) and branch (0.17 t ha⁻¹). Carbon stock in the soil up to 30 cm depth was 57.3 t ha⁻¹. Gross C stock in the plantation was estimated to be 120.75 t ha⁻¹. Carbon storage estimated in the bamboo stand of present study offers insights into the opportunity of village bamboos in the rural landscape for carbon storage through carbon sequestration. Management and utilization of village bamboos as a potential source of carbon sink by smallholder farmers are discussed in the context of their livelihood security and the Millennium Development Goals of the United Nations.     

Above-ground biomass production and nutrient accumulation in young stands of silver birch on abandoned agricultural land

During the last decade, more than 400 000 ha of agricultural land was abandoned in Estonia. Such areas are often characterized by rapid natural afforestation with silver birch, which has led to an increase both in the woodland area and in the area of silver birch stands. However, many bioenergetic aspects related to birch stands growing on arable land are still poorly understood. The main aim of the present study was to investigate the above-ground biomass production, nutrient (NPK) accumulation, and foliar characteristics of young silver birch stands on abandoned agricultural land. Five 8-year-old stands of silver birch growing on different soil types were included in the study.The density of the studied stands varied from 3060 to 36 200 trees per ha and their above-ground biomass varied from 6.0 to 22.9 t DM ha⁻¹. The largest share in the above-ground biomass of the birches (59–80%) was from the stems. The mean stem mass of the birches ranged from 0.29 to 1.79 kg, and the mean total above-ground biomass ranged from 0.36 to 3.03 kg. The leaf area index for the studied stands varied from 1.21 to 4.64 m² m⁻², being the highest for the stand of medium density. Mean single leaf area varied from 9.4±0.2 to 15.4±0.3 cm², leaf weight per area varied from 61.1±0.4 to 77.5±0.5 g m², and specific leaf area varied from 13.2±0.1 to 16.8±0.1 m² kg⁻¹. However, no significant differences were found between stand density and the foliar characteristics. There was a strong positive correlation between soil nitrogen concentration and leaf nitrogen concentration (R=0.92); regarding phosphorus concentration, the corresponding correlation was weak (R=0.52) and regarding potassium concentration, no significant correlation was found. The amount of nitrogen accumulated in the above-ground part of the silver birch stands varied between 42.4 and 145.8 kg ha⁻¹, the amount of phosphorus, between 5.9 and 27.9 kg ha⁻¹, and the amount of potassium, between 7.2 and 78.6 kg ha⁻¹. The N:P:K ratios for the foliage were comparable. It is evident that the proportion of nitrogen and phosphorus are close to optimum, while the N:K ratio was lower than optimum value in all cases.     

Aboveground tree biomass in a recovering tropical sal (Shorea robusta Gaertn. f.) forest of Eastern Ghats,India

Aboveground biomass of individual tree species by component and total biomass per unit area for four different stages of a recovering tropical dry deciduous forest stands, dominated by sal (Shorea robusta Gaertn. f.) of the Eastern Ghats, India were investigated during 2001–2002. Different periods of recovering (2, 4, 6, and 10-year) forest stands (84°13′E, 20°29′N) were selected in the Kandhamal district of Orissa, India and sample trees of all species were harvested. Tree species diversity was 23, 23, 21 and 22 in 2, 4, 6, and 10-year recovering stands, respectively. Species-wise Ixora pavetta showed the highest biomass in 2 and 4-year stands while Shorea robusta in 6 and 10-year stands. Component-wise, in all species, bole–wood contribution ranged between 22.6% and 60.9%. Aboveground tree biomass, in all the stands, was dominated by Shorea robusta, which ranged between 12.68 and 231.91 Mg ha⁻¹. Total aboveground tree biomass was 30.12, 49.21, 107.54 and 261.08 Mg ha⁻¹ in 2, 4, 6 and 10-year stands, respectively.     

Long-term yield potential of switchgrass-for-biofuel systems

Limited information is available regarding biomass production potential of long-term (>5- yr-old) switchgrass (Panicum virgatum L.) stands. Variables of interest in biomass production systems include cultivar selection, site/environment effects, and the impacts of fertility and harvest management on productivity and stand life. We studied biomass production of two upland and two lowland cultivars under two different managements at eight sites in the upper southeastern USA during 1999–2001. (Sites had been planted in 1992 and continuously managed for biomass production.) Switchgrass plots under lower-input management received 50 kg N ha⁻¹ yr⁻¹ and were harvested once, at the end of the season. Plots under higher-input management received 100 kg N ha⁻¹ (in two applications) and were harvested twice, in midsummer and at the end of the season. Management effects on yield, N removal, and stand density were evaluated. Annual biomass production across years, sites, cultivars, and managements averaged 14.2 Mg ha⁻¹. Across years and sites, a large (28%) yield response to increased inputs was observed for upland cultivars; but the potential value of higher-input management for lowland cultivars was masked overall by large site×management interactions. Nitrogen removal was greater under the higher-input system largely due to greater N concentrations in the midsummer harvests. Management recommendations (cultivar, fertilization, and harvest frequency), ideally, should be site and cultivar dependent, given the variable responses reported here.     

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.     

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.     

Effects of a 20-year old Miscanthus × giganteus stand and its removal on soil characteristics and greenhouse gas emissions

Miscanthus is a perennial rhizomatous C4 grass with high yield potentials and low nutrient needs, thus a promising candidate for the production of cellulosic biomass. While optimal management options and yields attainable on a commercial scale are still debated, no study has yet addressed its removal and potential effects on following crops. Here, we present results from a trial involving a 20-year old Miscanthus stand on i) soil C, N, P and K stocks, compared with an adjacent field cultivated with a rotation of annual arable food crops, ii) the greenhouse gases (GHG) emissions following the removal of Miscanthus and iii) the immediate short-term effects on the following land use (re-cultivation to wheat or set-aside).Compared to the adjacent field under annual crops, the Miscanthus plot had a larger soil organic C stock (by 13 t C ha⁻¹) but a similar N stock, and lower P and K stocks (with differences of 100 kg P ha⁻¹ and 1170 kg K ha⁻¹, respectively). These losses imply that some degree of fertilization may be necessary as compensation. The effects of Miscanthus removal for the following wheat were significant on crop N content but negligible on grain yield.1.5 t CO₂ ha⁻¹ of CO₂ were released after the Miscanthus removal and the N₂O emissions increased from 150 g N₂O-N ha⁻¹ to 493 g N₂O-N ha⁻¹ during the following year. These results highlight the importance of investigation of the end-of-life stage of perennial crops for an accurate assessment of their environmental impacts.     

A novel approach to simulate growth of multi-stem willow in bioenergy production systems with a simple process-based model (3PG)

An important requirement for commercialization of willow biomass production in short-rotation crop (SRC) plantations is the reliable and cost-efficient estimation of biomass yield. Predictions and simulations of willow stand biomass have been problematic due to issues with modeling the multi-stem growth form of willow. The aim of this paper was to develop a new approach for managing allometric measurements from multi-stemmed willow for stand growth simulations. The 3PG model (Physiological Principles in Predicting Growth) was parameterized for willow and was used for biomass yield simulation for an entire 22-yr cycle (seven 3-yr rotations) of willow in SRC plantations. The multi-stemmed growth form was transformed into a single-stem modeling form by deriving whole plant willow allometric relationships using detailed stem-level measurements of basal area, stem biomass and volume. 3PG model predictions for plant diameter, height, biomass, and stand biomass and volume were within the 95% confidence range of mean plot values. Model simulations showed that after seven 3-yr rotations only 20% of planted cuttings would survive (a decrease from 15,152 to 3022 plants ha⁻¹), but stand volume would increase continuously with each subsequent rotation. 3PG predictions for cumulative (for 22 yr) aboveground biomass was 272 Mg ha⁻¹ and mean annual yield was 12 Mg ha⁻¹ yr⁻¹, comparing favorably with other findings. To our knowledge, this work is the first where the 3PG model was calibrated and used for willow species. Once parameterized for a specific willow clone, 3PG can predict biomass accumulation for any agricultural land in North America using only available soil and climate data.     

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.     

Soil carbon accrual in particle-size fractions under Miscanthus x. giganteus cultivation

The energy crop Miscanthus x. giganteus is a deep rooting perennial rhizomatous C4 grass with great biomass production, even under temperate German climate conditions. Accordingly we hypothesized that this crop may accumulate great amounts of carbon in soil, particularly in deeper soil layers. We sampled several former C3-derived arable fields that had been cropped with Miscanthus for 0–19 years. We were able to trace the origin and turnover of soil organic C (SOC) on the basis of natural ¹³C/¹²C abundance measurements. The analysis was performed on bulk soil samples and on particle-size fractions that are known to comprise SOC of different availability for decay. Miscanthus-derived C accumulated at a rate of 1800 kg ha⁻¹ y⁻¹ down to a soil depth of 100 cm. Only about 50% of this C accrual occurred in the surface soil (0–10 cm). The C accumulation differed among size fractions. Miscanthus-derived C in the coarse-POM fraction increased rapidly during the first years of Miscanthus cultivation until a steady state was reached after approximately seven years. The stocks of Miscanthus-derived C associated with the clay fraction increased at a rate of 230 kg ha⁻¹ y⁻¹ in 0–5 cm, 45 kg ha⁻¹ y⁻¹ in 20–30 cm and 38 kg ha⁻¹ y⁻¹ in 50–75 cm. The C accumulation rate decreased with increasing soil depth. In particular, Miscanthus-derived C associated with the clay fraction led to increasing SOC stocks, even below the former Ap; that is, below a depth that would respond sensitively to a future land use change.     

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.     

Sweet sorghum as a bioenergy crop: Literature review

Sweet sorghum (Sorghum bicolor L. Moench) is a widely adapted sugar crop with high potential for bioenergy and ethanol production. Sweet sorghum can yield more ethanol per unit area of land than many other crops especially under minimum input production. Sweet sorghum is well-adapted to marginal growing conditions such as water deficits, water logging, salinity, alkalinity, and other constraints. Sweet sorghum potential exists for ethanol yield of 6000 L ha⁻¹ with more than three units of energy attained per unit invested. Traditionally, sweet sorghum has served as a syrup crop and its culture and production are well understood. Sweet sorghum is genetically diverse and variations exits for characteristics such as Brix % (13–24), juice sucrose concentration (7.2–15.5%), total stalk sugar yield (as high as 12 Mg ha⁻¹), fresh stalk yield (24–120 Mg ha⁻¹), biomass yield (36–140 t ha⁻¹) and others indicating potential for improvement. Transitioning sweet sorghum to a bioenergy crop is hampered by inadequate technology for large-scale harvest, transport and storage of the large quantities of biomass and juice produced, especially where the harvest window is short. Conversion of sweet sorghum to ethanol can be achieved by fermenting juice expressed from stems or directly fermenting chopped stalks. Integration of the fermentation and distillation of sweet sorghum juice in corn ethanol plants has not yet been achieved.     

Determination of biomass accumulation in mixed belts of Salix,Corylus and Alnus species in combined food and energy production system

Given the energetic, demographic and the climatic challenges faced today, we designed a combined food and energy (CFE) production system integrating food, fodder and mixed belts of Salix, Alnus and Corylus sp. as bioenergy belts. The objective was to assess the shoot dry weight-stem diameter allometric relationship based on stem diameter at 10 (SD₁₀) and 55 cm (SD₅₅) from the shoot base in the mixed bioenergy belts. Allometric relations based on SD₁₀ and SD₅₅ explained 90–96% and 90–98% of the variation in shoot dry weights respectively with no differences between the destructive and the non-destructive methods. The individual stool yields varied widely among the species and within willow species with biomass yield range of 37.60–92.00 oven dry tons (ODT) ha⁻¹ in 4-year growth cycle. The biomass yield of the bioenergy belt, predicted by allometric relations was 48.84 ODT ha⁻¹ in 4-year growth cycle corresponding to 12.21 ODT ha⁻¹ year⁻¹. The relatively high biomass yield is attributed to the border effects and the ‘fertilizing effect’ of alder due to nitrogen fixation, benefitting other SWRC components. On termination of 4-year growth cycle, the bioenergy belts were harvested and the biomass yield recorded was 12.54 ODT ha⁻¹ year⁻¹, in close proximity to the biomass yield predicted by the allometric equations, lending confidence and robustness of the model for biomass yield determination in such integrated agro-ecosystem.