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Yield, energy parameters and chemical composition of short-rotation willow biomass
Industrial Crops and Products 46 (2013) 60–65
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Yield, energy parameters and chemical composition of short-rotation willow biomass Mariusz J. Stolarski a , Stefan Szczukowski a , Józef Tworkowski a , Andrzej Klasa b,∗ a b
Department of Plant Breeding and Seed Production, University of Warmia and Mazury in Olsztyn, Poland Department of Agrochemistry and Environmental Protection, University of Warmia and Mazury in Olsztyn, Poland
a r t i c l e
i n f o
Article history: Received 29 August 2012 Received in revised form 9 January 2013 Accepted 10 January 2013 Keywords: SRWC Biomass Salix viminalis Yield Energy Cellulose Lignin
a b s t r a c t In this paper, the yielding capacity of four willow (Salix viminalis L.) clones grown as short-rotation plantations in a four-year cutting cycle is presented. Some chemical parameters of harvested biomass were analyzed, i.e. its elemental composition (C, H, S) and contents of cellulose, lignin and hemicelluloses. The yield of dry oven biomass amounted on average to 14.1 Mg ha−1 year−1 and its gain of energy was equal to 242.3 GJ ha−1 year−1 . Willow of clone UWM 042 showed the highest (633 cm) and the thickest (31.0 mm) stems and the biomass yield of this clone (16.4 Mg ha−1 year−1 ) was significantly higher than the yield of cv. Start (14.0 Mg ha−1 year−1 ). The moisture content of biomass amounted on average to 46.9% while ash content was 2.1% in oven dry biomass and the lowest in the trial ash content was found in the biomass of clone UWM 042. The highest content of carbon (52.2% C ODM) and hydrogen (7.1% H ODM) was found in biomass samples of the clone UWM 033. The content of cellulose in the biomass of the studied clones (ranged from 43.9 to 45.3%) was higher while lignin content (19.9–20.7% ODM) was lower than in the biomass of cv. Start taken as standard. Biomass obtained from the new clone UWM 042 showed higher yield and better parameters compared to cv. Start (registered in Poland). © 2013 Elsevier B.V. All rights reserved.
1. Introduction Short-rotation woody crops have been promoted as a sustainable method of biomass production (Bergkvist and Ledin, 1998; Keoleian and Volk, 2005; Rivera-Tinoco and Bouallou, 2010; Wilkinson et al., 2007) for heat and/or power generation. Recently, another perspective of effective biomass utilization as a stock material for ethanol (Hahn-Hagerdal and Pamment, 2004; Linde et al., 2008) or methanol production has been reported (Ciechanowicz and Szczukowski, 2009a; Holmgren et al., 2012; Kumabe et al., 2008; Xuan et al., 2009). One of the most important current aims of technology is to reach a high rate of economic growth using energy generated by other processes than combustion. One of the postulated sources of such energy is fuel cell utilization, which generates power directly from hydrogen atoms (Ciechanowicz and Szczukowski, 2009b). Rapid development of fuel cell technology (among anther PEFC, DMFC, SOFC) can generate high market demand for methanol, which is considered to be a safe, liquid source of hydrogen. It is possible to work out a system of methanol production from coal and biomass using high energy neutrons (Ciechanowicz, 2007, 2010) which are carbon neutral and economically sound.
∗ Corresponding author. E-mail address: [email protected] (A. Klasa). 0926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2013.01.012
In this system, which could be treated as a sustainable alternative to an oil-based economy, some key factors are as follows: high yield and quality of biomass from short-rotation woody crops, an appropriate method of thermal conversion of biomass to easily transportable materials (charcoal or bio-oil), additional process of syngas production from biogas and, one of the most important issues, is implementation of muon-catalyzed nuclear fusion (http://www.biodatabase.de/Muon-catalyzed%20fusion). In numerous research reports (Mitchell, 1995; Volk et al., 2006; Tworkowski et al., 2006), it was stated that willow grown in SRWC systems is able to achieve high biomass yields and, after harvest in a dormant period (usually winter), in the following spring is able to re-grow vigorously. Moreover, short-rotation willow coppice plantations can be established on fields unsuitable for food or ´ feed production (Budzynski et al., 2009). The results of earlier studies conducted at our University (Szczukowski et al., 2002; Stolarski, 2009) have shown that willow biomass quality was related to species, cultivar and cutting cycle length. The obtained results have provided information concerned the variability of morphological traits in clones of Salix viminalis as well as their yielding ability and biomass quality in the aspect of studied genotypes biomass suitability to thermal conversion and methanol production. Other authors (Kaakinen et al., 2007) have reported that the chemical composition of willow bio-fuel is affected by the type of habitat. Therefore, the aim of this study was to determine yield of willow grown in a quadrennial cutting cycle as well as quantification of
M.J. Stolarski et al. / Industrial Crops and Products 46 (2013) 60–65 Table 1 Physico-chemical properties of soil. Item
Unit
pH H2 O pH KCl CaCO3 Organic matter Organic matter C-organic N total C:N S Hh T V% = S × 100 T−1
– – % % Mg ha−1 % % – cmol(+) kg−1 cmol(+) kg−1 cmol(+) kg−1 %
Horizon (depth cm) 0–35
35–80
80–150
7.6 7.2 1.44 8.35 350.7 3.54 0.354 9.60 34.3 1.3 35.6 96.3
7.7 7.2 1.42 9.91 – – – – 33.9 1.6 35.5 95.5
7.4 7.0 3.15 14.24 – – – – 34.4 2.2 37.6 91.4
various biomass parameters which are important for its thermal processing. 2. Materials and method 2.1. Experimental site A field trial was conducted in northern Poland in the Kwidzyn Vistula River Valley in the village of Obory (53◦ 43 N, 18◦ 53 E), ´ 80 km south of Gdansk. The annual precipitation amounts to 400–500 mm, the growing period lasts from 200 to 210 days and the annual average temperature is ca. 8 ◦ C. The experiment was carried out on alluvial soil classified as heavy-textured Fluvisol. The soil reaction in the area of the trial was close to neutral (pHKCl 7.0–7.2) (Table 1). The groundwater table during the experiment was at the 45–80 cm level and the soil was periodically flooded. It can be evaluated as being very suitable for growing short-rotation willow coppice. The forecrop for willow was alfalfa. Before willow planting in summer 2000, glyphosate was applied at the rate of 5 l ha−1 to destroy alfalfa and perennial weeds. Harrowing was then conducted and mineral fertilizers were applied at the following rates: 26.2 kg P kg ha−1 and 74.7 kg K ha−1 . In the late autumn, depth ploughing (at a depth of 35 cm) was performed. In the following early spring, shallow harrowing was conducted once and manual planting of 20 cm long cuttings at a density of 18,000 plants ha−1 was then performed. A standard system of twin rows (with a distance between rows of 0.75 m and 1.5 m between double rows) was applied. Just after planting, herbicide Azotop 50 WP (simazine) was applied at the rate of 2 kg ha−1 . During the growing period manual weeding was conducted twice. In the spring 2002 nitrogen fertilizer at the rate of 60 kg N ha−1 was applied. In 2003, biomass was harvested in a triennial cutting cycle. In the fourth growing season (in 2003), the following rates of fertilizers were applied: nitrogen 100 kg N ha−1 , 26.2 kg P kg ha−1 and 74.7 kg K ha−1 . Potassium and phosphorus were applied in the spring before the start of re-growth as potassium chloride and superphosphate. Nitrogen was applied as ammonium nitrate in split rates of 50 kg N ha−1 at the same time as P and K fertilizers and at the end of May. No fertilizers or weeding were applied in the seasons from 2005 to 2007. 2.2. Field trial This report concerns growing seasons from 2004 to 2007. The experimental factor was willow genotype: one registered in Poland cultivar START and three high-yielding varieties from our collection (designated as UWM 033, UWM 042, UWM 046) were studied.
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The field experiment was performed using the same design as a commercial short-rotation willow plantation. All genotypes represented the species S. viminalis. Each genotypes was grown in 12 rows on an area of 2430 m2 in a strip 13.5 wide and 180.0 m long. The total area of the field trial was 9720 m2 . For each strip, four 75 m2 randomized sub-plots were established to determine plant density, biometrical parameters and willow biomass yield. 2.3. Procedure of determination of plant density, biometrical traits and biomass yield Before harvesting in the winter 2007 after the end of the growing period the plant density was determined on each 75 m2 subplot. The percentage of plant losses seven years after planting was determined. On each subplot, 20 plants were chosen at random to determine the number of growing stems, their height and stem diameter (these measurements were done 0.5 m above ground level). Harvesting was performed manually using a circular saw blade. The biomass harvested from each plot was registered and the fresh matter yield per 1 ha was calculated. Samples of biomass one randomly chosen plant per plot (each plant ca. 3 kg in three replicates) were chipped and mixed and laboratory sub-samples were taken (ca. 1 kg per plot). 2.4. Procedure of laboratory analyses In the laboratory, the moisture content in biomass was determined by drying sub-samples of 200 g weight (in three replicates) of biomass at 105 ◦ C. The yield of dry oven biomass and its caloric value on the basis of fresh matter yield and the net calorific value (GJ ha−1 year−1 ) were then calculated. Dried samples of weight ca. 20 g per plot were ground in a basic IKA KMF 10 analytical mill using sieve 0.25 mm. Samples of weight of 1.5 g were then ashed at 550 ◦ C and the gross calorific value was determined in an IKA C 2000 calorimeter using the dynamic method. The net calorific value of fresh biomass was determined. The content of carbon, hydrogen and sulfur in the biomass of tested clones was determined in an ELTRA CHS 500 automatic analyzer. The chemical composition of the willow wood was analyzed in Poznan´ at the Institute of Wood Technology. The biomass was ground into 0.5–1 mm particles and the following measurements were taken: content of wood fraction dissolved in hot and cold water, content of wood fraction dissolved in an ethanol–benzene mixture (1:1), content of fraction dissolved in an alkaline solution (in 1% water solution of NaOH); content of cellulose by Seifert, lignin content by Tappi and pentozane content by Tollens. 2.5. Statistical procedures Statistical analyses were based on the model of total randomized design according to the following formula, which assumes no adjustment for spatial effects within the field layout: yij = + i + εij where yij being any observation for which X1 = i (i and j denote the level of the factor and the replication within the level of the factor, respectively), is the general location parameter; i is the effect of having treatment level i; εij is a random error with the level of the factor and the replication within the level of the factor, respectively. For the studied traits, the average values and standard error of mean were presented (SEM). In the case where significant effects of treatments were found, an SNK multiple test (Student,
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Table 2 Growth parameters and annual yield of willow. Clone/cultivar
Plant height (m)
UWM 033 UWM 042 UWM 046 START Mean
5.80 6.33 6.06 6.03 6.06
± ± ± ± ±
0.16b 0.17a 0.20ab 0.11ab 0.16
Stem diameter (mm) 28.7 31.0 28.9 30.8 29.9
± ± ± ± ±
Plant mortality (%)
Number of shoots per stool
0.7 2.3 1.4 2.6 0.6
5.0 3.5 3.9 3.2 3.9
± ± ± ± ±
0.7 0.6 0.6 0.3 0.3
26.4 18.1 25.7 24.3 23.6
± ± ± ± ±
Yield (Mg ODM ha−1 year−1 )
1.8 4.3 6.3 7.1 1.9
13.7 16.4 12.3 14.0 14.1
± ± ± ± ±
0.7ab 0.8a 0.8b 0.7ab 0.9
± Standard error of mean; lack of letter denotes lack of significant differences the same lower letter denotes homogenous group according to SNK test.
Newman–Keuls) was used and homogenous groups were recognized at the level of ˛ = 0.05. All tests were done using STATISTICA 8.0 PL software.
3. Results 3.1. Plant density, morphological traits and biomass yield In 2007 (seven years after planting), the survival rate amounted to 76% and the average plant density was 13,800 plants ha−1 (Table 2). The lowest rate of mortality was found for clone UWM 042 and, in the case of clone UWM 033, losses were higher by 8%. The number of stems per stool ranged from 3.2 to 5.0 recorded for plants of clone UWM 033 and for cultivar Start, respectively. Fouryear-old stems showed considerable height at each treatment – above 6 m. The highest and thickest stems were noted for clone UWM 042. The yield of oven dry biomass gained in a quadrennial cutting cycle amounted to 14.1 Mg ha−1 year−1 (Table 2). The highest significant yield was found for clone UWM 042, while in another overlapping homogeneous group there were average values for cv. Start and cultivar UWM 033 and to the third homogeneous group only cv. UWM 046 was classified. In terms of energy content, willow biomass showed an average 240 GJ ha−1 year−1 and the variability of this parameter was similar to the previously-described yield variability (Fig. 1). In case of the biomass of clone UWM 042, this value was close to 300 GJ ha−1 year−1 . The yield of ODM harvested in the first harvest averaged 5 Mg ha−1 year−1 lower than in the second rotation with a relatively narrow degree of variability between 7.9 and 11.9 Mg ha−1 year−1 for clones UWM 046 and UWM 042, respectively.
3.2. Ash and moisture content, heating value and the chemical composition of biomass In a biomass of willow of clone UWM 042, a significantly lower ash content (1.79% of oven dry matter) was found compared to other studied clones which all had similar levels of ash (Table 3). The gross calorific value of biomass averaged 19.33 MJ kg−1 ODM (oven dry matter) and the values were similar for all studied willow clones and the same low level of variability was noted for the net calorific value of fresh willow biomass, which ranged from 9.07 to
Fig. 1. Energy value of obtained biomass yield (GJ ha−1 year−1 ).
Table 4 Content of carbon, hydrogen and sulfur in willow biomass (% of ODM). Clone/cultivar
C
H
UWM 033 UWM 042 UWM 046 START Mean
52.2 51.4 51.3 50.8 51.4
± ± ± ± ±
0.1a 0.2b 0.2bc 0.1 c 0.2
7.1 7.0 6.9 6.8 6.9
S ± ± ± ± ±
0.1a 0.1b 0.0b 0.0b 0.1
0.035 0.040 0.051 0.031 0.039
± ± ± ± ±
0.001c 0.001b 0.001a 0.002d 0.004
Legend as in Table 2.
9.17 MJ kg−1 . The moisture content of willow biomass gained in the quadrennial cutting cycle was on a similar level ca. 46.9%. The elemental composition of willow biomass is presented in Table 4. In a biomass of willow clone UWM 033, the highest carbon (52.2% C ODM−1 ) and hydrogen (7.1% H ODM−1 ) contents were found. The lowest sulfur content (0.031% S ODM−1 ) was determined in the cv. Start biomass. In the biomass of the other studied willow clones, the sulfur content ranged between 0.035 and 0.051% S in ODM. The highest hot- and cold-water-extracted matter fraction and the fraction extractable in an ethanol–benzene mixture were both determined in the biomass of clone UWM 042, although it was not statistically proven (Table 5).
Table 3 Ash and moisture content, calorific value of willow biomass. Clone/cultivar
Moisture content (%)
UWM 033 UWM 042 UWM 046 START Mean
47.0 46.7 47.1 46.7 46.9
Legend as in Table 2.
± ± ± ± ±
0.2 0.5 0.2 0.3 0.1
Ash content (% of DM) 2.33 1.79 2.17 2.11 2.10
± ± ± ± ±
0.08a 0.07b 0.03a 0.09a 0.11
Gross calorific value (MJ kg−1 ODM) 19.34 19.35 19.30 19.34 19.33
± ± ± ± ±
0.03 0.02 0.03 0.01 0.01
Net calorific value (MJ kg−1 fresh matter) 9.11 9.17 9.07 9.17 9.13
± ± ± ± ±
0.04 0.11 0.06 0.06 0.02
M.J. Stolarski et al. / Industrial Crops and Products 46 (2013) 60–65 Table 5 Content of substances dissolved in hot and cold water and extractable in ethanol–benzene mixture (% of absolute dry matter). Clone/cultivar
Fraction extractable in: Cold water
UWM 033 UWM 042 UWM 046 START Mean
3.01 3.54 3.08 2.99 3.15
± ± ± ± ±
Hot water
0.13 0.25 0.12 0.01 0.13
5.24 5.82 5.20 5.24 5.37
± ± ± ± ±
0.10 0.33 0.06 0.07 0.15
Ethanol–benzene mixture 3.43 3.89 3.41 3.56 3.57
± ± ± ± ±
0.25 0.15 0.19 0.02 0.11
A generally high content of cellulose in the biomass of four-year willow stems was found (Table 6). Very similar values of this parameter were found in the biomass of two clones UWM 046 and UWM 033 which was significantly higher compared to cv. Start. If the results are presented as cellulose annual yield, it can be seen that clone UWM 042 gave the highest significant yield of this compound. The lignin content in the biomass of studied willow clones ranged in a rather narrow scope of variability. The content of hemicelluloses (treated as a fraction dissolved in a 1% NaOH solution) appeared to be the highest in the biomass of clone UWM 033 (22.9% ODM). The lowest significant value of this parameter was determined in the cv. Start biomass. The content of pentozanes ranged from 16.9 to 18.9% ODM and the significantly lowest value was found for clone UWM 033. 4. Discussion Biomass yield gained in a quadrennial cutting cycle can be considered as rather high (averaging 14 Mg ODM ha−1 year−1 ). The biomass yield of clone UWM 042 amounted to 16 Mg ODM ha−1 year−1 . This high yield was the final effect of the interaction between high planting density (14,800 plants ha−1 ), high stems (above 6 m) and a high number of relatively thick (above 30 mm in diameter) stems per stool. An additional benefit of growing that specific willow genotype was the highest yield of cellulose (7.2 Mg ha−1 year−1 ) obtained in the trial, which would potentially achieve a high efficiency of methanol production. In Canada, the high yield of short-rotation willow and poplar grown at the planting density of 18,000 plants ha−1 has also been obtained (Labrecque and Teodorescu, 2005). In the quadrennial cutting cycle among tested genotypes, the highest yield was found for Salix miyabeana (SX64) and Salix sachalinensis (SX61) at 16.9 and 15.6 Mg ODM ha−1 year−1 , respectively. The highest yield among tested S. viminalis clones was found for clone SVQ and it was only 9 Mg ODM ha−1 year−1 . The highest yield of poplar in a quadrennial cutting cycle was found for clone NM Populus maximowiczii × Populus nigra (NM6) (18.0 Mg ODM ha−1 year−1 ). A similar yield level was found for poplar grown in a quadrennial cutting cycle in Italy (Guidi et al., 2009). Other authors reported (Deckmyn et al., 2004) that the annual yield of poplar biomass increased with the age of plants up to a maximum between the third and fourth growing seasons.
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In our earlier studies (Stolarski et al., 2008; Szczukowski et al., 2005) in quadrennial cutting cycles while using higher planting densities, but from plots with a smaller area, the biomass yield was higher in some cases by up to 33% than in this experiment. In many field trials, it was found that using longer cutting cycles from biennial, i.e. triennial or quadrennial, resulted in a higher annual yield (Adegbidi et al., 2001; Kopp et al., 1997; Smaliukas et al., 2007; Stolarski et al., 2006). In our other studies (Stolarski, 2009), it was shown that the highest willow biomass yield was achieved in a triennial cutting cycle (averaging 17.23 Mg ODM ha−1 year−1 ). In biennial and annual cutting cycles, yield reductions of 4.6 and 30.9% were noted, respectively. The biomass yield gained in a quadrennial cutting cycle in Wales (Randerson et al., 2000) with a similar planting density than was applied in the current study was considerably lower than that achieved in our trials, but in Wales no fertilizers were applied for four seasons. Willow biomass obtained in a quadrennial cutting cycle demonstrated high quality as a wood fuel and potential raw material for methanol production. In clone UWM 042, the contents of carbon and hydrogen were higher while the ash level was lower than in the biomass of the willow cultivar Start (registered in Poland). In our earlier studies (Stolarski, 2009), it was found that prolonging cutting cycles from annual to biennial and triennial resulted in a decrease in the biomass humidity, bark and alkali element contents. Woodchips made of biomass obtained in a triennial cutting cycle showed higher heating value and a higher content of carbon and hydrogen than in a biomass obtained in shorter cutting cycles. Adler et al. (2005) reported that willow gained in short cutting cycles produced thin stems with a high bark content. In our earlier studies (Stolarski et al., 2005), it was stated that ash and the macronutrient contents in shoots harvested in an annual cutting cycle were considerably higher than respective values of biomass in a quadrennial cutting cycle and the analyzed parameters had higher values in bark compared to wood tissues. Similar relationships were observed by Klasnja et al. (2002). It is known that the chemical composition of willow biomass is related to the species and age of the plant (Stolarski et al., 2005; ´ Wróblewska and Czajka, 2003). Surminski (1990) reported that the concentration of particular wood compounds in willow biomass was related only to plant age and species did not affect it. Generally, biomass harvested from young woody plants contained less cellulose, hemicellulose and lignin than more mature wood (Rowell et al., 1997). The cited authors have shown that there is a decrease in the content of fractions extractable in water and alkali solutions and an increase in cellulose, hemicellulose and lignin in bamboo shoots of older plants. In our studies, when the biomass of different clones were harvested in the same cutting cycle, it was found that the content of cellulose and hemicellulose was higher while the lignin concentration was lower compared to the registered cultivar Start. While estimating the suitability of willow biomass as a raw material for the pulp and paper industry, the most critical is the cellulose-to-lignin content ratio. It affects the pulping parameters
Table 6 Content and yield of cellulose, lignin, hemicelluloses and pentozanes in willow biomass. Clone/cultivar
Cellulose (% of ODM)
UWM 033 UWM 042 UWM 046 START Mean
45.0 43.9 45.3 42.4 44.1
Legend as in Table 2.
± ± ± ± ±
0.2a 0.1b 0.3a 0.1c 0.2
Cellulose yield (Mg ha−1 year−1 ) 6.2 7.2 5.6 5.9 6.2
± ± ± ± ±
0.3b 0.4a 0.3b 0.3b 0.4
Lignin (% of ODM) 20.7 19.9 20.0 21.1 20.4
± ± ± ± ±
0.2 0.5 0.2 0.0 0.3
Hemicellulose (% of ODM) 22.9 21.7 22.2 20.6 21.8
± ± ± ± ±
0.2a 0.1b 0.1b 0.1c 0.1
Pentozanes (% of ODM) 16.9 18.9 18.0 18.5 18.1
± ± ± ± ±
0.2c 0.1a 0.1b 0.2a 0.4
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of biomass and the strength of the obtained cellulose fibers, which together determine the economics of pulp production. In our experiment, the tested biomass showed a normal cellulose-tolignin ratio, which amounted to 2.2 and ranged between 2.0 for biomass of cv. Start and 2.3 for biomass of clone UWM 046. From literature data, it is evident that the cellulose-to-lignin ratio is higher in wood from broadleaf trees and in mature tissues than in wood from coniferous and juvenile trees, respectively. Absolute values ranged from 1.2 to 2.9 (Klasnja et al., 2002; Stolarski et al., 2005; Wróblewska and Czajka, 2003). Zabaniotou et al. (2008) analyzed different lignocellulosic biomass processed by different methods. They concluded that when biomass has more cellulose and hemicellulose content, its efficiency in hydrogen production was higher irrespective of the technology applied. According to Florin and Harris (2007), interest in achieving hydrogen economy is growing and that biomass may be considered to be a versatile and fully renewable source of hydrogen. They pointed out that there are a number of technologies for processing biomass into hydrogen. They expressed the view that none of the proposed methods can be considered as mature enough to meet the future demands for H2 . The concept of closed cycles of energy resources is the core of sustainable economic development. Biomass-based hydrogen production systems seem to meet these demands. Orecchini and Bocci (2007) stated that gasification/anaerobic digestion plus reforming can be already treated as competitive technology. Thus, biomass hydrogen production can play a very important role in the world’s energy supply. In their extensive review, Huber et al. (2006) identified several pathways leading to the synthesis of biofuels (including hydrogen) from biomass and analyzed how the biofuel industry is still in its infancy and that more research activity will be required for its development. They also reported that in the following chain: (i) growth of biomass feedstock, (ii) biomass conversion into a biofuel and (iii) fuel utilization; second step required special attention because existing technologies of biomass conversion vary considerably in their efficiency. It is possible to develop a methanol producing system using a carbon source from biomass and hard coal using high energy neutron sources. One of the most essential factors in the system of methanol production which can be understand as a sound alternative for oil is a reliable supply of high quality biomass from short-rotation plantations and finding the best thermal conversion technology of this raw material. In a methanol production system, the share of particular components, i.e. biomass, hard coal and high energy neutrons, can contribute to creating a carbon neutral system of methanol production which could be economically acceptable in the global economy because methanol produced from SRWC biomass using high energy neutrons can be widely used as car fuel with zero CO2 emissions (Ciechanowicz, 2007, 2010).
5. Conclusions An appropriate selection of a S. viminalis clone for growing in quadrennial cutting cycle on fertile alluvial soil achieved a high yield of biomass with good quality parameters which can improve its thermal conversion and bio-methanol synthesis. Clone UWM 042 gave a higher yield of better quality biomass compared to the Polish willow cultivar Start. The obtained results show that selection of willow clone for growing in a SRWC system can affect both yield and quality.
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Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Yield, energy parameters and chemical composition of short-rotation willow biomass Mariusz J. Stolarski a , Stefan Szczukowski a , Józef Tworkowski a , Andrzej Klasa b,∗ a b
Department of Plant Breeding and Seed Production, University of Warmia and Mazury in Olsztyn, Poland Department of Agrochemistry and Environmental Protection, University of Warmia and Mazury in Olsztyn, Poland
a r t i c l e
i n f o
Article history: Received 29 August 2012 Received in revised form 9 January 2013 Accepted 10 January 2013 Keywords: SRWC Biomass Salix viminalis Yield Energy Cellulose Lignin
a b s t r a c t In this paper, the yielding capacity of four willow (Salix viminalis L.) clones grown as short-rotation plantations in a four-year cutting cycle is presented. Some chemical parameters of harvested biomass were analyzed, i.e. its elemental composition (C, H, S) and contents of cellulose, lignin and hemicelluloses. The yield of dry oven biomass amounted on average to 14.1 Mg ha−1 year−1 and its gain of energy was equal to 242.3 GJ ha−1 year−1 . Willow of clone UWM 042 showed the highest (633 cm) and the thickest (31.0 mm) stems and the biomass yield of this clone (16.4 Mg ha−1 year−1 ) was significantly higher than the yield of cv. Start (14.0 Mg ha−1 year−1 ). The moisture content of biomass amounted on average to 46.9% while ash content was 2.1% in oven dry biomass and the lowest in the trial ash content was found in the biomass of clone UWM 042. The highest content of carbon (52.2% C ODM) and hydrogen (7.1% H ODM) was found in biomass samples of the clone UWM 033. The content of cellulose in the biomass of the studied clones (ranged from 43.9 to 45.3%) was higher while lignin content (19.9–20.7% ODM) was lower than in the biomass of cv. Start taken as standard. Biomass obtained from the new clone UWM 042 showed higher yield and better parameters compared to cv. Start (registered in Poland). © 2013 Elsevier B.V. All rights reserved.
1. Introduction Short-rotation woody crops have been promoted as a sustainable method of biomass production (Bergkvist and Ledin, 1998; Keoleian and Volk, 2005; Rivera-Tinoco and Bouallou, 2010; Wilkinson et al., 2007) for heat and/or power generation. Recently, another perspective of effective biomass utilization as a stock material for ethanol (Hahn-Hagerdal and Pamment, 2004; Linde et al., 2008) or methanol production has been reported (Ciechanowicz and Szczukowski, 2009a; Holmgren et al., 2012; Kumabe et al., 2008; Xuan et al., 2009). One of the most important current aims of technology is to reach a high rate of economic growth using energy generated by other processes than combustion. One of the postulated sources of such energy is fuel cell utilization, which generates power directly from hydrogen atoms (Ciechanowicz and Szczukowski, 2009b). Rapid development of fuel cell technology (among anther PEFC, DMFC, SOFC) can generate high market demand for methanol, which is considered to be a safe, liquid source of hydrogen. It is possible to work out a system of methanol production from coal and biomass using high energy neutrons (Ciechanowicz, 2007, 2010) which are carbon neutral and economically sound.
∗ Corresponding author. E-mail address: [email protected] (A. Klasa). 0926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2013.01.012
In this system, which could be treated as a sustainable alternative to an oil-based economy, some key factors are as follows: high yield and quality of biomass from short-rotation woody crops, an appropriate method of thermal conversion of biomass to easily transportable materials (charcoal or bio-oil), additional process of syngas production from biogas and, one of the most important issues, is implementation of muon-catalyzed nuclear fusion (http://www.biodatabase.de/Muon-catalyzed%20fusion). In numerous research reports (Mitchell, 1995; Volk et al., 2006; Tworkowski et al., 2006), it was stated that willow grown in SRWC systems is able to achieve high biomass yields and, after harvest in a dormant period (usually winter), in the following spring is able to re-grow vigorously. Moreover, short-rotation willow coppice plantations can be established on fields unsuitable for food or ´ feed production (Budzynski et al., 2009). The results of earlier studies conducted at our University (Szczukowski et al., 2002; Stolarski, 2009) have shown that willow biomass quality was related to species, cultivar and cutting cycle length. The obtained results have provided information concerned the variability of morphological traits in clones of Salix viminalis as well as their yielding ability and biomass quality in the aspect of studied genotypes biomass suitability to thermal conversion and methanol production. Other authors (Kaakinen et al., 2007) have reported that the chemical composition of willow bio-fuel is affected by the type of habitat. Therefore, the aim of this study was to determine yield of willow grown in a quadrennial cutting cycle as well as quantification of
M.J. Stolarski et al. / Industrial Crops and Products 46 (2013) 60–65 Table 1 Physico-chemical properties of soil. Item
Unit
pH H2 O pH KCl CaCO3 Organic matter Organic matter C-organic N total C:N S Hh T V% = S × 100 T−1
– – % % Mg ha−1 % % – cmol(+) kg−1 cmol(+) kg−1 cmol(+) kg−1 %
Horizon (depth cm) 0–35
35–80
80–150
7.6 7.2 1.44 8.35 350.7 3.54 0.354 9.60 34.3 1.3 35.6 96.3
7.7 7.2 1.42 9.91 – – – – 33.9 1.6 35.5 95.5
7.4 7.0 3.15 14.24 – – – – 34.4 2.2 37.6 91.4
various biomass parameters which are important for its thermal processing. 2. Materials and method 2.1. Experimental site A field trial was conducted in northern Poland in the Kwidzyn Vistula River Valley in the village of Obory (53◦ 43 N, 18◦ 53 E), ´ 80 km south of Gdansk. The annual precipitation amounts to 400–500 mm, the growing period lasts from 200 to 210 days and the annual average temperature is ca. 8 ◦ C. The experiment was carried out on alluvial soil classified as heavy-textured Fluvisol. The soil reaction in the area of the trial was close to neutral (pHKCl 7.0–7.2) (Table 1). The groundwater table during the experiment was at the 45–80 cm level and the soil was periodically flooded. It can be evaluated as being very suitable for growing short-rotation willow coppice. The forecrop for willow was alfalfa. Before willow planting in summer 2000, glyphosate was applied at the rate of 5 l ha−1 to destroy alfalfa and perennial weeds. Harrowing was then conducted and mineral fertilizers were applied at the following rates: 26.2 kg P kg ha−1 and 74.7 kg K ha−1 . In the late autumn, depth ploughing (at a depth of 35 cm) was performed. In the following early spring, shallow harrowing was conducted once and manual planting of 20 cm long cuttings at a density of 18,000 plants ha−1 was then performed. A standard system of twin rows (with a distance between rows of 0.75 m and 1.5 m between double rows) was applied. Just after planting, herbicide Azotop 50 WP (simazine) was applied at the rate of 2 kg ha−1 . During the growing period manual weeding was conducted twice. In the spring 2002 nitrogen fertilizer at the rate of 60 kg N ha−1 was applied. In 2003, biomass was harvested in a triennial cutting cycle. In the fourth growing season (in 2003), the following rates of fertilizers were applied: nitrogen 100 kg N ha−1 , 26.2 kg P kg ha−1 and 74.7 kg K ha−1 . Potassium and phosphorus were applied in the spring before the start of re-growth as potassium chloride and superphosphate. Nitrogen was applied as ammonium nitrate in split rates of 50 kg N ha−1 at the same time as P and K fertilizers and at the end of May. No fertilizers or weeding were applied in the seasons from 2005 to 2007. 2.2. Field trial This report concerns growing seasons from 2004 to 2007. The experimental factor was willow genotype: one registered in Poland cultivar START and three high-yielding varieties from our collection (designated as UWM 033, UWM 042, UWM 046) were studied.
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The field experiment was performed using the same design as a commercial short-rotation willow plantation. All genotypes represented the species S. viminalis. Each genotypes was grown in 12 rows on an area of 2430 m2 in a strip 13.5 wide and 180.0 m long. The total area of the field trial was 9720 m2 . For each strip, four 75 m2 randomized sub-plots were established to determine plant density, biometrical parameters and willow biomass yield. 2.3. Procedure of determination of plant density, biometrical traits and biomass yield Before harvesting in the winter 2007 after the end of the growing period the plant density was determined on each 75 m2 subplot. The percentage of plant losses seven years after planting was determined. On each subplot, 20 plants were chosen at random to determine the number of growing stems, their height and stem diameter (these measurements were done 0.5 m above ground level). Harvesting was performed manually using a circular saw blade. The biomass harvested from each plot was registered and the fresh matter yield per 1 ha was calculated. Samples of biomass one randomly chosen plant per plot (each plant ca. 3 kg in three replicates) were chipped and mixed and laboratory sub-samples were taken (ca. 1 kg per plot). 2.4. Procedure of laboratory analyses In the laboratory, the moisture content in biomass was determined by drying sub-samples of 200 g weight (in three replicates) of biomass at 105 ◦ C. The yield of dry oven biomass and its caloric value on the basis of fresh matter yield and the net calorific value (GJ ha−1 year−1 ) were then calculated. Dried samples of weight ca. 20 g per plot were ground in a basic IKA KMF 10 analytical mill using sieve 0.25 mm. Samples of weight of 1.5 g were then ashed at 550 ◦ C and the gross calorific value was determined in an IKA C 2000 calorimeter using the dynamic method. The net calorific value of fresh biomass was determined. The content of carbon, hydrogen and sulfur in the biomass of tested clones was determined in an ELTRA CHS 500 automatic analyzer. The chemical composition of the willow wood was analyzed in Poznan´ at the Institute of Wood Technology. The biomass was ground into 0.5–1 mm particles and the following measurements were taken: content of wood fraction dissolved in hot and cold water, content of wood fraction dissolved in an ethanol–benzene mixture (1:1), content of fraction dissolved in an alkaline solution (in 1% water solution of NaOH); content of cellulose by Seifert, lignin content by Tappi and pentozane content by Tollens. 2.5. Statistical procedures Statistical analyses were based on the model of total randomized design according to the following formula, which assumes no adjustment for spatial effects within the field layout: yij = + i + εij where yij being any observation for which X1 = i (i and j denote the level of the factor and the replication within the level of the factor, respectively), is the general location parameter; i is the effect of having treatment level i; εij is a random error with the level of the factor and the replication within the level of the factor, respectively. For the studied traits, the average values and standard error of mean were presented (SEM). In the case where significant effects of treatments were found, an SNK multiple test (Student,
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M.J. Stolarski et al. / Industrial Crops and Products 46 (2013) 60–65
Table 2 Growth parameters and annual yield of willow. Clone/cultivar
Plant height (m)
UWM 033 UWM 042 UWM 046 START Mean
5.80 6.33 6.06 6.03 6.06
± ± ± ± ±
0.16b 0.17a 0.20ab 0.11ab 0.16
Stem diameter (mm) 28.7 31.0 28.9 30.8 29.9
± ± ± ± ±
Plant mortality (%)
Number of shoots per stool
0.7 2.3 1.4 2.6 0.6
5.0 3.5 3.9 3.2 3.9
± ± ± ± ±
0.7 0.6 0.6 0.3 0.3
26.4 18.1 25.7 24.3 23.6
± ± ± ± ±
Yield (Mg ODM ha−1 year−1 )
1.8 4.3 6.3 7.1 1.9
13.7 16.4 12.3 14.0 14.1
± ± ± ± ±
0.7ab 0.8a 0.8b 0.7ab 0.9
± Standard error of mean; lack of letter denotes lack of significant differences the same lower letter denotes homogenous group according to SNK test.
Newman–Keuls) was used and homogenous groups were recognized at the level of ˛ = 0.05. All tests were done using STATISTICA 8.0 PL software.
3. Results 3.1. Plant density, morphological traits and biomass yield In 2007 (seven years after planting), the survival rate amounted to 76% and the average plant density was 13,800 plants ha−1 (Table 2). The lowest rate of mortality was found for clone UWM 042 and, in the case of clone UWM 033, losses were higher by 8%. The number of stems per stool ranged from 3.2 to 5.0 recorded for plants of clone UWM 033 and for cultivar Start, respectively. Fouryear-old stems showed considerable height at each treatment – above 6 m. The highest and thickest stems were noted for clone UWM 042. The yield of oven dry biomass gained in a quadrennial cutting cycle amounted to 14.1 Mg ha−1 year−1 (Table 2). The highest significant yield was found for clone UWM 042, while in another overlapping homogeneous group there were average values for cv. Start and cultivar UWM 033 and to the third homogeneous group only cv. UWM 046 was classified. In terms of energy content, willow biomass showed an average 240 GJ ha−1 year−1 and the variability of this parameter was similar to the previously-described yield variability (Fig. 1). In case of the biomass of clone UWM 042, this value was close to 300 GJ ha−1 year−1 . The yield of ODM harvested in the first harvest averaged 5 Mg ha−1 year−1 lower than in the second rotation with a relatively narrow degree of variability between 7.9 and 11.9 Mg ha−1 year−1 for clones UWM 046 and UWM 042, respectively.
3.2. Ash and moisture content, heating value and the chemical composition of biomass In a biomass of willow of clone UWM 042, a significantly lower ash content (1.79% of oven dry matter) was found compared to other studied clones which all had similar levels of ash (Table 3). The gross calorific value of biomass averaged 19.33 MJ kg−1 ODM (oven dry matter) and the values were similar for all studied willow clones and the same low level of variability was noted for the net calorific value of fresh willow biomass, which ranged from 9.07 to
Fig. 1. Energy value of obtained biomass yield (GJ ha−1 year−1 ).
Table 4 Content of carbon, hydrogen and sulfur in willow biomass (% of ODM). Clone/cultivar
C
H
UWM 033 UWM 042 UWM 046 START Mean
52.2 51.4 51.3 50.8 51.4
± ± ± ± ±
0.1a 0.2b 0.2bc 0.1 c 0.2
7.1 7.0 6.9 6.8 6.9
S ± ± ± ± ±
0.1a 0.1b 0.0b 0.0b 0.1
0.035 0.040 0.051 0.031 0.039
± ± ± ± ±
0.001c 0.001b 0.001a 0.002d 0.004
Legend as in Table 2.
9.17 MJ kg−1 . The moisture content of willow biomass gained in the quadrennial cutting cycle was on a similar level ca. 46.9%. The elemental composition of willow biomass is presented in Table 4. In a biomass of willow clone UWM 033, the highest carbon (52.2% C ODM−1 ) and hydrogen (7.1% H ODM−1 ) contents were found. The lowest sulfur content (0.031% S ODM−1 ) was determined in the cv. Start biomass. In the biomass of the other studied willow clones, the sulfur content ranged between 0.035 and 0.051% S in ODM. The highest hot- and cold-water-extracted matter fraction and the fraction extractable in an ethanol–benzene mixture were both determined in the biomass of clone UWM 042, although it was not statistically proven (Table 5).
Table 3 Ash and moisture content, calorific value of willow biomass. Clone/cultivar
Moisture content (%)
UWM 033 UWM 042 UWM 046 START Mean
47.0 46.7 47.1 46.7 46.9
Legend as in Table 2.
± ± ± ± ±
0.2 0.5 0.2 0.3 0.1
Ash content (% of DM) 2.33 1.79 2.17 2.11 2.10
± ± ± ± ±
0.08a 0.07b 0.03a 0.09a 0.11
Gross calorific value (MJ kg−1 ODM) 19.34 19.35 19.30 19.34 19.33
± ± ± ± ±
0.03 0.02 0.03 0.01 0.01
Net calorific value (MJ kg−1 fresh matter) 9.11 9.17 9.07 9.17 9.13
± ± ± ± ±
0.04 0.11 0.06 0.06 0.02
M.J. Stolarski et al. / Industrial Crops and Products 46 (2013) 60–65 Table 5 Content of substances dissolved in hot and cold water and extractable in ethanol–benzene mixture (% of absolute dry matter). Clone/cultivar
Fraction extractable in: Cold water
UWM 033 UWM 042 UWM 046 START Mean
3.01 3.54 3.08 2.99 3.15
± ± ± ± ±
Hot water
0.13 0.25 0.12 0.01 0.13
5.24 5.82 5.20 5.24 5.37
± ± ± ± ±
0.10 0.33 0.06 0.07 0.15
Ethanol–benzene mixture 3.43 3.89 3.41 3.56 3.57
± ± ± ± ±
0.25 0.15 0.19 0.02 0.11
A generally high content of cellulose in the biomass of four-year willow stems was found (Table 6). Very similar values of this parameter were found in the biomass of two clones UWM 046 and UWM 033 which was significantly higher compared to cv. Start. If the results are presented as cellulose annual yield, it can be seen that clone UWM 042 gave the highest significant yield of this compound. The lignin content in the biomass of studied willow clones ranged in a rather narrow scope of variability. The content of hemicelluloses (treated as a fraction dissolved in a 1% NaOH solution) appeared to be the highest in the biomass of clone UWM 033 (22.9% ODM). The lowest significant value of this parameter was determined in the cv. Start biomass. The content of pentozanes ranged from 16.9 to 18.9% ODM and the significantly lowest value was found for clone UWM 033. 4. Discussion Biomass yield gained in a quadrennial cutting cycle can be considered as rather high (averaging 14 Mg ODM ha−1 year−1 ). The biomass yield of clone UWM 042 amounted to 16 Mg ODM ha−1 year−1 . This high yield was the final effect of the interaction between high planting density (14,800 plants ha−1 ), high stems (above 6 m) and a high number of relatively thick (above 30 mm in diameter) stems per stool. An additional benefit of growing that specific willow genotype was the highest yield of cellulose (7.2 Mg ha−1 year−1 ) obtained in the trial, which would potentially achieve a high efficiency of methanol production. In Canada, the high yield of short-rotation willow and poplar grown at the planting density of 18,000 plants ha−1 has also been obtained (Labrecque and Teodorescu, 2005). In the quadrennial cutting cycle among tested genotypes, the highest yield was found for Salix miyabeana (SX64) and Salix sachalinensis (SX61) at 16.9 and 15.6 Mg ODM ha−1 year−1 , respectively. The highest yield among tested S. viminalis clones was found for clone SVQ and it was only 9 Mg ODM ha−1 year−1 . The highest yield of poplar in a quadrennial cutting cycle was found for clone NM Populus maximowiczii × Populus nigra (NM6) (18.0 Mg ODM ha−1 year−1 ). A similar yield level was found for poplar grown in a quadrennial cutting cycle in Italy (Guidi et al., 2009). Other authors reported (Deckmyn et al., 2004) that the annual yield of poplar biomass increased with the age of plants up to a maximum between the third and fourth growing seasons.
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In our earlier studies (Stolarski et al., 2008; Szczukowski et al., 2005) in quadrennial cutting cycles while using higher planting densities, but from plots with a smaller area, the biomass yield was higher in some cases by up to 33% than in this experiment. In many field trials, it was found that using longer cutting cycles from biennial, i.e. triennial or quadrennial, resulted in a higher annual yield (Adegbidi et al., 2001; Kopp et al., 1997; Smaliukas et al., 2007; Stolarski et al., 2006). In our other studies (Stolarski, 2009), it was shown that the highest willow biomass yield was achieved in a triennial cutting cycle (averaging 17.23 Mg ODM ha−1 year−1 ). In biennial and annual cutting cycles, yield reductions of 4.6 and 30.9% were noted, respectively. The biomass yield gained in a quadrennial cutting cycle in Wales (Randerson et al., 2000) with a similar planting density than was applied in the current study was considerably lower than that achieved in our trials, but in Wales no fertilizers were applied for four seasons. Willow biomass obtained in a quadrennial cutting cycle demonstrated high quality as a wood fuel and potential raw material for methanol production. In clone UWM 042, the contents of carbon and hydrogen were higher while the ash level was lower than in the biomass of the willow cultivar Start (registered in Poland). In our earlier studies (Stolarski, 2009), it was found that prolonging cutting cycles from annual to biennial and triennial resulted in a decrease in the biomass humidity, bark and alkali element contents. Woodchips made of biomass obtained in a triennial cutting cycle showed higher heating value and a higher content of carbon and hydrogen than in a biomass obtained in shorter cutting cycles. Adler et al. (2005) reported that willow gained in short cutting cycles produced thin stems with a high bark content. In our earlier studies (Stolarski et al., 2005), it was stated that ash and the macronutrient contents in shoots harvested in an annual cutting cycle were considerably higher than respective values of biomass in a quadrennial cutting cycle and the analyzed parameters had higher values in bark compared to wood tissues. Similar relationships were observed by Klasnja et al. (2002). It is known that the chemical composition of willow biomass is related to the species and age of the plant (Stolarski et al., 2005; ´ Wróblewska and Czajka, 2003). Surminski (1990) reported that the concentration of particular wood compounds in willow biomass was related only to plant age and species did not affect it. Generally, biomass harvested from young woody plants contained less cellulose, hemicellulose and lignin than more mature wood (Rowell et al., 1997). The cited authors have shown that there is a decrease in the content of fractions extractable in water and alkali solutions and an increase in cellulose, hemicellulose and lignin in bamboo shoots of older plants. In our studies, when the biomass of different clones were harvested in the same cutting cycle, it was found that the content of cellulose and hemicellulose was higher while the lignin concentration was lower compared to the registered cultivar Start. While estimating the suitability of willow biomass as a raw material for the pulp and paper industry, the most critical is the cellulose-to-lignin content ratio. It affects the pulping parameters
Table 6 Content and yield of cellulose, lignin, hemicelluloses and pentozanes in willow biomass. Clone/cultivar
Cellulose (% of ODM)
UWM 033 UWM 042 UWM 046 START Mean
45.0 43.9 45.3 42.4 44.1
Legend as in Table 2.
± ± ± ± ±
0.2a 0.1b 0.3a 0.1c 0.2
Cellulose yield (Mg ha−1 year−1 ) 6.2 7.2 5.6 5.9 6.2
± ± ± ± ±
0.3b 0.4a 0.3b 0.3b 0.4
Lignin (% of ODM) 20.7 19.9 20.0 21.1 20.4
± ± ± ± ±
0.2 0.5 0.2 0.0 0.3
Hemicellulose (% of ODM) 22.9 21.7 22.2 20.6 21.8
± ± ± ± ±
0.2a 0.1b 0.1b 0.1c 0.1
Pentozanes (% of ODM) 16.9 18.9 18.0 18.5 18.1
± ± ± ± ±
0.2c 0.1a 0.1b 0.2a 0.4
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of biomass and the strength of the obtained cellulose fibers, which together determine the economics of pulp production. In our experiment, the tested biomass showed a normal cellulose-tolignin ratio, which amounted to 2.2 and ranged between 2.0 for biomass of cv. Start and 2.3 for biomass of clone UWM 046. From literature data, it is evident that the cellulose-to-lignin ratio is higher in wood from broadleaf trees and in mature tissues than in wood from coniferous and juvenile trees, respectively. Absolute values ranged from 1.2 to 2.9 (Klasnja et al., 2002; Stolarski et al., 2005; Wróblewska and Czajka, 2003). Zabaniotou et al. (2008) analyzed different lignocellulosic biomass processed by different methods. They concluded that when biomass has more cellulose and hemicellulose content, its efficiency in hydrogen production was higher irrespective of the technology applied. According to Florin and Harris (2007), interest in achieving hydrogen economy is growing and that biomass may be considered to be a versatile and fully renewable source of hydrogen. They pointed out that there are a number of technologies for processing biomass into hydrogen. They expressed the view that none of the proposed methods can be considered as mature enough to meet the future demands for H2 . The concept of closed cycles of energy resources is the core of sustainable economic development. Biomass-based hydrogen production systems seem to meet these demands. Orecchini and Bocci (2007) stated that gasification/anaerobic digestion plus reforming can be already treated as competitive technology. Thus, biomass hydrogen production can play a very important role in the world’s energy supply. In their extensive review, Huber et al. (2006) identified several pathways leading to the synthesis of biofuels (including hydrogen) from biomass and analyzed how the biofuel industry is still in its infancy and that more research activity will be required for its development. They also reported that in the following chain: (i) growth of biomass feedstock, (ii) biomass conversion into a biofuel and (iii) fuel utilization; second step required special attention because existing technologies of biomass conversion vary considerably in their efficiency. It is possible to develop a methanol producing system using a carbon source from biomass and hard coal using high energy neutron sources. One of the most essential factors in the system of methanol production which can be understand as a sound alternative for oil is a reliable supply of high quality biomass from short-rotation plantations and finding the best thermal conversion technology of this raw material. In a methanol production system, the share of particular components, i.e. biomass, hard coal and high energy neutrons, can contribute to creating a carbon neutral system of methanol production which could be economically acceptable in the global economy because methanol produced from SRWC biomass using high energy neutrons can be widely used as car fuel with zero CO2 emissions (Ciechanowicz, 2007, 2010).
5. Conclusions An appropriate selection of a S. viminalis clone for growing in quadrennial cutting cycle on fertile alluvial soil achieved a high yield of biomass with good quality parameters which can improve its thermal conversion and bio-methanol synthesis. Clone UWM 042 gave a higher yield of better quality biomass compared to the Polish willow cultivar Start. The obtained results show that selection of willow clone for growing in a SRWC system can affect both yield and quality.
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