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Bioresource Technology 99 (2008) 479–485
Influence of harvest time on fuel characteristics of five potential energy crops in northern China
Shaojun Xiong a,b,*, Quan-Guo Zhang a, Da-Yong Zhang a, Rolf Olsson b
a College of Life Science, Beijing Normal University, Beijing 100875, China b Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, Box 4097, SE-904 03 Umea˚, Sweden
Received 4 September 2006; received in revised form 17 January 2007; accepted 21 January 2007 Available online 26 March 2007
Abstract
Five potential energy crops in northern China were examined for fuel characteristics over different harvest times to test whether or not a delayed harvest improves fuel quality in a semiarid area in China as is the case in northern Europe and North America. The five crops include indigo bush (Amorpha fruticosa), sand willow (Salix cheilophila), switch grass (Panicum virgatum), reed canary grass (Phalaris arundinacea), and sainfoin (Onobrychis viciifolia). These crops are considered as fuels for thermal conversion. From September 2002 to April 2003, biomass was sampled monthly, and the effects of harvest time on the fuel characteristics of the five crops were studied. With respect to ash and some undesired element contents in biomass, a delayed harvest in spring resulted in a better fuel quality than a traditional harvest in autumn. Of the five species, indigo bush and sand willow had the lowest ash contents when harvested in spring. Switch grass is a promising herbaceous energy crop in semiarid areas in terms of its yield, fuel characteristics, and low water use. Chlorine had the most significant correlation with harvest time and ash content in the biomass. In a comparison with the biofuel crops in Europe and North America, a much higher proportion of chlorine was found in all examined plants. The results from this study indicate that an energy crop with delayed harvest may extend fuel resources and conserve soil in semiarid regions in northern China, practices that will help maintain and improve economical and ecological sustainability. 2007 Elsevier Ltd. All rights reserved.
Keywords: Energy crop; Delayed harvest; Fuel characteristics; Semiarid; China
1. Introduction 2000). The most promising energy crops in these regions include willow (Salix ssp.), switchgrass (Panicum virgatum), In the last 20 years, interest in using biomass for energy and reed canary grass (Phalaris arundinacea). Studies production has been growing (IEA, 1998a,b; Agarwal and (Obernberger et al., 1997; Landstrom et al., 1996; Burvall, Agarwal, 1999b; Bain and Overend, 2002). This renewable 1997) indicate that the yield and fuel characteristics of energy resource may help mitigate greenhouse gas and energy crops may vary from place to place. Little is known, reduce acid rain. In addition, energy crop cultivation can however, whether or not these energy crops can be used for maintain and improve ecological and social sustainability. thermal conversion in the semiarid regions in north China. Researchers have identified quite a few species as cur- Although delayed harvest (winter or following spring rent/potential energy crops in Europe and North America harvest, Olsson et al., 1989) decreases yield (Hadders and (IEA, 1998b; Venendaal et al., 1997; Samson and Duxbury, Olsson, 1997; Lewandowski and Heinz, 2003), it is impor- tant in the biofuel production economy because it cuts off artificial drying cost while providing hygienically acceptable * Corresponding author. Address: Unit of Biomass Technology and biomass material (Olsson et al., 1989; Landstrom et al., Chemistry, Swedish University of Agricultural Sciences, Box 4097, SE-904 03 Umea˚, Sweden. Tel.: +46 90 786 8778; fax: +46 90 786 8799. 1996; Burvall, 1997). It has also been demonstrated that E-mail address: [email protected] (S. Xiong). the delayed harvest system could improve fuel quality and
0960-8524/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.01.034 转载 中国科技论文在线 http://www.paper.edu.cn
480 S. Xiong et al. / Bioresource Technology 99 (2008) 479–485 reduce fertilization costs. Delayed harvest reduces undesir- region with a typical inland climate. Yearly precipitation able components such as Cl, K, Ca, P, S, and N in biomass is about 360 mm (average of 30 years) and 50–60% of the (Burvall, 1997; Lewandowski and Heinz, 2003), which in yearly rain falls in July, August, and September. Winter turn likely contributes to a low emissions of environmentally is usually dry with a mean value of less than 5 mm rainfall harmful substances such as NOx (Agarwal and Agarwal, from December to February in last 10 years (Fig. 1). 1999a,b; Obernberger et al., 1997; Lewandowski and Heinz, Monthly mean temperature is 9.0 C for January and 2003; Paulrud and Nilsson, 2001) and less sintering and cor- 23.5 C for July. The frost-free period is about 135–138 rosion problems (Agarwal and Agarwal, 1999a; Miles et al., days from May to September. 1996). In addition, delayed harvest may decrease the amount The site is part of the energy crop plantation of Shanxi of nutrients removed from the soil (Hadders and Olsson, Laowan Bioenergy Technology Corp. This loess soil has 1997; Agarwal and Agarwal, 1999a). Current knowledge, been cultivated for a long time. In May 2002, available however, is obtained mostly from northern Europe and N, P, and K content were 52.4, 5.9, and 125 mg/kg, respec- North America where rain and snow may play an important tively. The total nitrogen and organic matter in the soil role in nutrient leaching from crops to soil during late were about 0.04% and 0.57%. We chose and studied the autumn, winter, and early spring. Little is known about species from the following six plots each named for the spe- whether delayed harvest is important for energy crop cies genus: (1) Amorpha (indigo bush); (2) Salix (sand wil- production for biofuels in dry areas. low); (3) Panicum 01 (switch grass); (4) Panicum 02 (switch The cultivation of energy crops is important in northern grass); (5) Phalaris (reed canary grass); and (6) Onobrychis China because of economical growth and environmental (sainfoin). These plots make it possible to compare the fuel degradation related to soil erosion and over-farming. An qualities among different species and between different integration of re-vegetation and energy cropping with a yearly leys of the same species switch grass. The informa- delayed harvest may be effectively applied in large areas tion about the five species and their establishment are sum- to protect soils from erosion. To address these goals, we marized in Table 1. In November 2002, all the plots were conducted a field study to examine the fuel characteristics almost equally divided by a path (3.5 m in width) into of three known species (sand willow, Salix cheilophila, two subplots. switchgrass, and reed canary grass) and two legumes (indigo Before and during the study period, two shrubs were bush Amorpha fruticosa and sainfoin Onobeychis viciaefolia) irrigated once re-growth started in the spring and once in a semiarid area in northern China between 2001 and after defoliation in late autumn 2002 (relevant to about 2003. The two legumes were included because they produce 15–20 mm precipitation each time). No water was added high biomass and control soil erosion especially in north- for herbaceous species except for natural precipitation dur- west China (Yang, 1996; Wei et al., 2001; Huang and ing the period. Neither fertilizers nor pesticides were sup- Sun, 2006); however, their feasibility as a biofuel is unclear. plied during the study period. In Europe, it is typical to harvest short rotation energy woods and energy grass the third year after planting (Vene- ndaal et al., 1997). However, in the semi-arid climates of 120
China, harvesting these crops in the second year may be 100 10-year average preferred. The production in the second year of Amorpha Study period and Salix was as high as 13–17 t/ha (room dry) and switch 80 grass was as high as 9 t/ha (room dry) (Xiong, personal 60 observations), but there is little knowledge about the fuel characteristics of these young shoots. Such knowledge is 40 needed to evaluate the feasibility of these biofuels. 20
In this paper, we present the results of fuel characteris- Monthly precipitation (mm) tics of the five crops that were cultivated in Shanxi Province 0 (northern China) and harvested at different times from Sep- 30 tember 2002 to April 2003. The purpose of this study was 25 10-year average to increase the understanding on how the delayed harvest 20 Study period system influences the fuel characteristics of the five poten- 15 tial energy crops in a semiarid region. 10 5 2. Methods 0 -5 2.1. Study site -10 -15 Monthly mean temperature (°C) The study site was located in Ying Xian (39 330N, 113 May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 0 11 E), Shanxi Province (northern China), a region of the Fig. 1. Monthly precipitation and mean temperature during the study east Loess Plateau (1010 m in altitude). It is a semiarid period versus historical data (1994–2003). 中国科技论文在线 http://www.paper.edu.cn
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Table 1 Species used in the study English name Latin name Cultivar Life Biomass yield Examined Year of Distribution form (t/ha)a area (m2) establishment Indigo bush, Amorpha Laizhou Shrub 13.4 3600 2001 Native in USA, but now in many false indigo fruticosa areas of Asia and Europe Sand willow Salix Wuliu Shrub 16.9 2400 2001 Native in China chelophila Switch grass Panicum Cave in Grass 9.3 4500 2001 Native in North America, but virgatum rock 4.4 180 2002 cultivated in Asia since 1960s Reed canary Phalaris Bamse Grass 1.8 240 2002 Widespread species in Europe, Asia grass arundinacea and North America Sainfoin Onobrichis Gansu Forb 3.1 240 2002 Native in USA, now cultivated in viciifolia north China a Data are room-dry values and collected from field observations in the study area in October 2002. Three 2 · 2 m subplots were used to estimate the biomass of indigo bush, sand willow, and second lay switch grass, but two subplots for reed canary grass, sainfoin, and the first ley switch grass were used in the study plots.
2.2. Sampling and analyses 50 ml of 2 mol L 1 KCl for 1 h. To determine available P and K in the soil, an ammonium-lactate and acetic acid Samples from the plots were taken once every month buffer was used for the extraction. from September 2002 to April 2003. Except for the first An estimation of biomass was conducted in October sample (taken on 23 September), most samplings were 2002 and by means of harvesting all crops at 5 cm above made on the 15th day every month. On each occasion, ground within a square of 2 · 2 m and drying at room tem- three shrub and 10 herbaceous plants from each of subplot perature for one month. Three 2 · 2 m squares were used were randomly chosen and cut at 5 cm above ground. The to estimate the biomass of indigo bush, sand willow, and two sub-samples from the same plot were then merged into second ley switch grass, but two squares were used for reed one sample. The samples were cut into small pieces (10– canary grass, sainfoin, and the first ley switch grass in each 15 cm long), put in paper bags, dried, and analyzed. The of study plots. air-dried samples (in room 18–22 C for more than one Except for the biomass, all other data are based on oven- month) were milled to less than 1 mm for further analyses. dry mass basis. SPSS software (V.10, SPSS Incorporated, Before analysing the samples, a part of the air-dried sam- 2000) was used to analyze the data. A Pearson correlation ples were used to determine moisture at 105 C for 8 h. test was performed to determine the correlation between In total, 48 samples of five target species were studied. the harvest time and fuel characteristics, such as the heat The calorific heat value of crops was measured using an values, ash content, and concentrations of chemical compo- Auto-Calculating Bomb Calorimeter (CA-4P, Shimadzu nents in biomass. A Mann–Whitney test was conducted to Corporation, Japan). Ash content was analysed by weigh- determine the difference in fuel characteristics of switch ing the residuals after an ignition of biomass samples in a grass between those established in 2001 and 2002. muffle furnace at 550 C. Analyses of C, H, N, and S con- tents were conducted using an elemental analyzer (Vario, 3. Results Elementar GmbH, Germany) at 950 C in the combustion tube and 550 C in the reducing tube. P, K, Na, and Ca 3.1. Fuel characteristics versus harvest time were extracted in nitric acid at 160 C (4 h) and then deter- mined using an inductively coupled plasma spectrometer 3.1.1. Calorific heat value (ULTIMA, Jobin Yvon GmbH, Germany, [EPC 1996]). Sand willow had the highest calorific heat value (18.55– Si was determined using the Gravimetric method (ISO 19.56 MJ/kg), and reed canary grass had the lowest heat 5997: 1984). The determination of total Cl was done using value (16.33–17.58 MJ/kg). There was no significant corre- the silver-nitrate titration method. Most analyses were per- lation between the heat value and harvest time for any formed at the Analytical and Testing Centre, Beijing Nor- species (Fig. 2). mal University, China, except those for ash and Cl, which were made at the Institute of Plant Nutrition and 3.1.2. Ash content Resources, Beijing Municipal Academy of Agricultural There was a general reduction of ash content (%) and Forestry Sciences, Beijing, China. Because the S con- between September and April for all examined species centration was too low and untraceable in most of the sam- (Fig. 2) although significant correlation between the ash ples (<0.001%), it was excluded from the final analyses. All content and time appeared only for Amorpha (Pearson cor- the soil nutrient analyses were also conducted at the labs of relation test, R = 0.815, P = 0.014, N = 8) and Onobrychis þ Beijing Normal University. Available N (NO3 and NH4 ) (R = 0.913, P = 0.002). The lowest levels of ash content in soil was measured by extraction of soil sample with were found in the biomass of Amorpha (2.82%) and Salix 482 S. Xiong et al. / Bioresource Technology 99 (2008) 479–485 R=-0.91 R=-0.722 R=-0.821 R=-0.869 R=-0.701 R=-0.886
Onobrychis < 0.05) Pearson correlation P SONDJ FMA established 2001 (switch grass); 0 1 0 http://www.paper.edu.cn 1 0 0 8 6 4 2 1 0 5 0 2 1 0 0.2 0.1 1.5 0.5 20 18 16 50 45 40 15 10 1.5 0.5 0.6 0.4 0.2 2 1 0 R=-0.879 R=-0.778 R=-0.799 Panicum virgatum
Phalaris R=0.788 R=-0.875 01 = -value indicates a significant ( (sainfoin). SONDJ FMA R 0 1 0 1 0 0 2 1 0 8 6 4 5 0 2 1 0 4 2 0 50 45 40 20 18 16 15 10 0.2 0.1 1.5 0.5 1.5 0.5 0.6 0.4 0.2 Panicum (sand willow); Onobrychis viciifolia
Panicum 02 = 1 0 0 1 0 SONDJ FMA 5 0 8 6 4 2 1 0 15 10 50 45 40 1.5 0.5 1.5 0.5 20 18 16 0.2 0.1 Onobrychis 0 2 1 0 Salix cheilophila 2 1 0 0.6 0.4 0.2 = Salix
Panicum 01 (reed canary grass); (indigo bush); SONDJ FMA 1 0 0 0 1 0 2 1 0 5 0 8 6 4 2 1 0 2 1 0 1.5 0.5 0.6 0.4 0.2 15 10 20 18 16 50 45 40 0.2 0.1 1.5 0.5 Phalaris arundinacea Amorpha fruticosa R=0.804 R=-0.748 = =
Salix Phalaris Amorpha SONDJ FMA 0 1 0 1 0 0 5 0 8 6 4 2 1 0 2 1 0 20 18 16 50 45 40 15 10 0.2 0.1 1.5 0.5 1.5 0.5 0.6 0.4 0.2 2 1 0 established 2002; R=-0.82 R=-0.857
Amorpha Panicum virgatum SONDJ FMA 02 = 5 0 8 6 4 2 1 0 1 0 0 15 10 50 45 40 1 0 0
20 18 16 2 1 0 2 1 0
1.5 0.5
0.2 0.1 1.5 0.5 0.6 0.4 0.2 MJ/kg (%) Ash (%) C (%) H (%) N (%) P (%) K (%) Ca (%) Cl (‰) Na (%) Si Fig. 2. The fuel characteristics of examined species over time. All data are based on dry weight. Heat value = net calorific heat value. An between the fuel characteristic andPanicum harvest time. 中国科技论文在线 中国科技论文在线 http://www.paper.edu.cn
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(3.33%) in April; the highest one was in Phalaris in Decem- with time in a comparison with other examined elements ber (14.7%). The first year ley Panicum had apparently (Fig. 2). Except Panicum, strong correlations between Cl higher ash content in biomass than the second year ley and harvest time were observed for most species (Amorpha, (9.1 versus 7.9% in October, 5.19 versus 3.48% in April). R = 0.857, P = 0.006; Salix, R = 0.748, P = 0.033; Phalaris, R = 0.875, P = 0.004; Onobrichis, R = 0.886, 3.1.3. Carbon and hydrogen P = 0.003). Except for indigo bush whose carbon content (%) increased significantly with harvest time (R = 0.804, P = 3.1.7. Si and Na 0.016), most plants did not significantly change its carbon The content of Si (%) in Panicum and Phalaris tended to content over the time, although an increase of carbon con- increase in spring, but the correlation was only significant tent between March and April was observed in all cases for Phalaris (R = 0.788). There were no correlations for (Fig. 2). The hydrogen content (%) in biomass for all the the other species. No statistically significant correlation studied species had no statistically significant changes with was found between the harvest time and Na content (&), the time. although an obvious decrease occurred in most cases in April (Fig. 2). 3.1.4. N, P, and K N, P, and K content (%, for all) tended to decrease in 3.2. Influence of plant age (ley year) general from September to March for most plants (Fig. 2). The major reduction, however, occurred between Switch grass in the second year ley had significantly September and October in most cases. Between March higher C concentration (P = 0.028, Mann–Whitney test, and April, some species (such as Amorpha and Salix) two-tailed; same below) but lower ash (P = 0.007), Si increased in the N, P, and K content. In general, Phalaris (P = 0.002) and N content (P = 0.005) than that in the first and Onobrychis had more considerable changes in their N, year ley. P, and K contents with harvest time than the others. There is a significant correlation (P < 0.05) between the nutrient 3.3. A general comparison of fuel characteristics content and harvest time in Phalaris and Onobrichis (Fig. 2). A general comparison of fuel characteristics between the 3.1.5. Calcium examined crops and those in Europe and Northern Amer- Calcium content (%) decreased generally with harvest ica is summarized in Table 2. For all species, chlorine pro- time, although a significant correlation was found for Ono- portions in spring-harvested material were remarkably brychis only (R = 0.869, P = 0.008). In almost all the higher, but sodium and sulphur contents were generally cases, a decrease of Ca content in biomass appeared mostly lower than those reported in Europe and Canada (Table between September and November; the lowest level was 2). Silicon contents were lower in biomass of Amorpha reached in April. and Salix, but much higher in Phalaris than those reported. In addition, the calorific heat value of switch grass was 3.1.6. Chlorine 6–11% lower depending on ley year, but the potassium Chlorine concentration in biomass decreased also with was much higher than the spring-harvested material in time in all the plots and had the most significant changes Canada.
Table 2 Fuel characteristics of examined species Parameter (Oven-dried basis) Data from this study (harvested in April) Reference values Amorpha Salix Panicum 01 Panicum 02 Phalaris Onobrychis Salixa Phalarisb Panicumc Net calorific heat value (MJ/kg) 17.85 19.09 17.42 16.50 16.33 16.73 18.8 17.60 18.50 Ash (%) 2.82 3.37 3.48 5.19 9.81 4.43 2.0 5.6 3.50 Carbon (%) 48.06 49.35 46.88 46.51 43.83 46.48 49.0 46.0 Hydrogen (%) 6.41 6.31 6.03 6.07 6.01 6.14 6.2 5.5 Nitrogen (%) 0.74 0.46 0.24 0.60 0.74 0.68 0.5 0.88 0.33 Phosphorus (%) 0.05 0.05 0.02 0.04 0.06 0.05 0.08 0.11 Potassium (%) 0.21 0.19 0.21 0.27 0.21 0.31 0.3 0.27 0.06 Calcium (%) 0.38 0.48 0.25 0.28 0.32 0.79 0.5 0.20 Chlorine (%) 0.14 0.21 0.21 0.50 0.25 0.32 0.03 0.09 0.02 Silicon (%) 0.07 0.11 0.93 1.12 3.01 0.28 <0.72 1.85 1.03 Sodium (%) 0.008 0.007 0.010 0.009 0.009 0.010 <0.045 0.02 Sulphur (%) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.05 0.09 Source: a CEN, 2005; b Burvall, 1997; c Samson et al., 2000. 中国科技论文在线 http://www.paper.edu.cn
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4. Discussion The effect of harvest time on fuel characteristics varies with species. In the examined species in this study, indigo The results from this study demonstrate that delayed bush and sand willow are the most promising energy crops harvest is important in biofuel production even in the semi- for combustion. They have the highest calorific heat values arid region in northern China. A harvest in April resulted (17.85 and 19.09 MJ/kg, respectively), but the lowest ash in a considerable reduction of ash content and a lower rate and Cl content in April. K, Na, and Si in the biomass for of elements such as Cl in biomass (Fig. 2); high levels of ash both species remained low almost during the entire study content and the undesirable elements were almost always period from autumn to spring and were even on average found in the biomass from late September, a normal har- lower than those reported in Europe (CEN, 2005). In these vest time. Although a total quantity of precipitation from perspectives, the delayed harvested biomass of second year 23 September to 15 April was about 60 mm (abort sand willow and indigo bush can be very good biofuel com- 20 mm rain fell in March and April, Fig. 1), a decrease in pared to the wood fuels in Europe. The fact that N, P, and ash and undesirable element contents in the spring-har- K levels increased in April could be the result of re-growth vested biomass was similar to those in wetter regions, such that was started one week before the scheduled sampling as northern Europe and Canada (Burvall, 1997; Hadders and harvesting. As long as re-growth starts, the plants start and Olsson, 1997; Lewandowski and Heinz, 2003). Spring to absorb nutrients from the soil. Harvesting earlier than harvest can apparently provide better quality biomass mid-April could increase the effectiveness of indigo bush materials for combustion than a traditional autumn har- and sand willow as biofuels. vest in a semiarid region. This study cannot prove the effectiveness of Phalaris and The mechanism for the reduction in ash and some ele- Onobrychis as biofuels because only the first ley crops were ments in the delayed harvest material may be attributed included in this study; however, Panicum is definitely a to a re-translocation of nutrient components to under- very good energy crop in a semiarid such as northern ground organs (i.e., rhizomes and roots) before winter, a China. The first year ley switch grass had ash content as leakage of elements as the result of rain, and a loss of leaves low as 5.19% in April; this is similar to a 3–4 year old reed during the winter and spring (Landstrom et al., 1996; Had- canary grass and miscantus in Europe (Burvall, 1997; ders and Olsson, 1997; Lewandowski and Heinz, 2003). Lewandowski and Heinz, 2003), but the second year ley Although this study could not distinguish these processes, showed even better results (Fig. 2). In addition, a higher the semi-arid environment in this study suggests the leach- heat value but lower contents of most examined undesir- ing by water is unlikely to be a dominant process as is the able elements were also found in the second year ley bio- case in Europe and Northern America (Lewandowski mass. The trend of better fuel with elder crop will et al., 2003). The plant physiological re-translocation of probably continue until a progressed maturity is reached the mineral elements before winter and loss of leaves during (c.f. Lewandowski et al., 2003). Panicum is a C4 grass, a winter may be more important. In the field, we observed a grass that needs much less water than the shrub species decreased biomass yield in spring harvested energy crops to produce the same amount of biomass (Samson et al., possibly due to leaf falling. However, future researches 2000). The fact that switch grass could reach a yield of should cover a determination of the relative importance of 4–5 t/ha in the first year and 9 t/ha (room dry, Table 1) the three processes. Nevertheless, these processes may result in the second year without irrigation in this study indicates in a recycling of some mineral elements within the ecosys- that this species may effectively adapt to the semiarid envi- tem and end up as both economical and ecological benefits, ronment. Switch grass stands normally reach two-third of such as conservation of soil nutrients and a reduction in use their capacity during the second year and attain a full yield of fertilizers as well as improvement fuel quality. in the third or fourth year when it is mature (c.f. Lewan- The fact that spring harvest may improve biofuel quality dowski et al., 2003). even in semiarid northern China has also a tremendous Compared with other elements examined, chlorine con- implication for soil conservation. Soil erosion is a severe tent fluctuated the most over the study period (Fig. 2). problem hindering sustainable agriculture in semiarid These changes were closely correlated to the pattern of region in northern China (Huang and Sun, 2006). Many ash content over time. As indicated by a separate analysis farmlands, which originated from semiarid grasslands (Pearson correlation test, two-tailed, P < 0.05, except for and were resulted from the enlargement of farmland in Phalaris), when the ash content increased, the chlorine con- the 1950–1970s, have become infertile because of intensive tent increased. Although the chlorine content was dramat- monoculture and soil erosion for so many years. Topsoil ically reduced by spring harvest for all species (Fig. 2), the (where most organic and nutrients exist) becomes thinner level was still several to tens times higher than those and thinner with time because the winds carry the soil reported in northern Europe and North America (Table away. While a cultivation of energy crops provides an alter- 2) and could be problematic for combustion and gasifica- native to traditional agriculture, a delayed harvest will pro- tion (Burvall, 1997; Agarwal and Agarwal, 1999a; Miles vide prolonged vegetation cover and therefore protect soil et al., 1996). Chlorine is soluble and readily washed out from erosion by wind during winter and spring when the of the crop throughout the winter in European climates, sand-dust storms mostly happen. but it may remain high in the examined biomass growing 中国科技论文在线 http://www.paper.edu.cn
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in a semi-arid environment where little rain is available Agarwal, G.D., Agarwal, A.K., 1999b. Environmental implications of during the winter. using biomass as an alternative source of energy: a critical assessment. Future studies should consider also the influences of TERI Information Monitor on Environmental Science 4 (2), 79–86. Bain, R.L., Overend, R.P., 2002. Biomass for heat and power. Forest soils, year ley, and their interaction with delayed harvest Products Journal 52 (2), 12–19. on the fuel characteristics of the energy crops in the semi- Burvall, J., 1997. Influence of harvest time and soil type on fuel quality in arid environment. A full understanding of these processes reed canary grass (Phalaris arundinacea L.). Biomass and Bioenergy 12 may help to explain the differences in fuel characteristics (3), 149–154. between this study and those reports in Europe and North- CEN, 2005. Technic Specifications. CEN/TS 14961:2005. Solid biofuels – Fuel Specifications and Classes. ern America (Table 2). In addition, the mechanisms Hadders, G., Olsson, R., 1997. Harvest of grass for combustion in late responsible for these differences need to be studied. summer and in spring. Biomass and Bioenergy 12 (3), 171–175. Huang, Y., Sun, W.J., 2006. Changes in topsoil organic carbon of 5. Conclusions croplands in mainland China over the last two decades. Chinese Science Bulletin 51, 1785–1803. International Energy Agency (IEA), 1998a. Renewables in power gener- A delayed harvest (a spring harvest) resulted in a better ation: towards a better environment. IEA Publications, Paris, 1998. fuel quality of examined energy crops than a traditional International Energy Agency, 1998b. CADDET Renewable Energy harvest (an autumn harvest). Among the five species stud- Technologies. Mini-review of energy from crops and crop residues. ied, two shrubs – indigo bush and sand willow – had the IEA CADDET Centre for Renewable Energy, Harwell, 1998. lowest ash content in spring, although they were second Landstrom, S., Lomakka, L., Andersson, S., 1996. Harvest in spring improves yield and quality of reed canary grass as a bioenergy crop. year crops after establishment. Switch grass, however, is Biomass and Bioenergy 11, 333–341. the most promising herbaceous energy crop in terms of Lewandowski, I., Heinz, A., 2003. Delayed harvest of miscanthus – its yield and fuel characteristics. The second year ley switch Influences on biomass quantity and quality and environmental impacts grass produced nearly twice as much yield as the first year of energy production. European Journal of Agronomy 19, 45–63. ley. Chlorine had the most significant correlation with har- Lewandowski, I., Scurlock, J.M.O., Lindvall, E., Christou, M., 2003. The development and current status of perennial rhizomatous grasses as vest time and ash content in the biomass. Although a much energy crops in US and Europe. Biomass and Bioenergy 25, 335– higher proportion of chlorine was found in all examined 361. plants in a comparison with the biofuel crops in Europe Miles, R., Miles, J.R., Baxter, L., Bryer, R., Jenkins, B., Oden, L., 1996. and North America, some other fuel characteristics (such Boiler deposits from firing biomass fuels. Biomass and Bioenergy 10 as ash content) of the second year sand willow and indigo (2–3), 125–138. Obernberger, I., Biedermann, F., Widmann, W., Riedl, R., 1997. bush as well as switch grass are comparable to those wood Concentrations of inorganic elements in biomass fuels and recovery fuels and energy grasses used in Europe. in the different ash fractions. Biomass and Bioenergy 12 (3), 211– Implications of this study are significant with respect to 224. economical and ecological sustainability: an energy crop Olsson, R., Sandstrom, T., Dahlgren, O., Andersson, L.-O., 1989. with delayed harvest may not only provide a renewable Sameldning Energigra¨s-torv: Miljo¨ och Ekonomi. Report No. 63, Statens lantbrukskemiska laboratorium, Swedish University of Agri- and good quality energy source, but can also help soil con- cultural Sciences, Umea˚, 1989. servation in semiarid regions. More studies, however, are Paulrud, S., Nilsson, C., 2001. Briquetting and combustion of spring- needed to examine the effects of energy crops on water harvested reed canary-grass: effect of fuel composition. Biomass and and nutrient relations in a semiarid region and to analyse Bioenergy 20 (1), 25–35. ecological and economical value of energy crop cultivation. Samson, R., Duxbury, P., 2000. Assessment of pelletized biofuels. Report of Resource Efficient Agricultural Production Canada, available from: