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Woody biofuel production from short rotation coppice in Italy: Environmental-impact assessment of different species and crop management
Biomass and Bioenergy 94 (2016) 209e219
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Research paper
Woody biofuel production from short rotation coppice in Italy: Environmental-impact assessment of different species and crop management Jacopo Bacenetti a, *, Sara Bergante b, Gianni Facciotto b, Marco Fiala a degli Studi di Milano, Via AgriFood LCA LAB, Department of Agricultural and Environmental Sciences, Production, Landscape, Agroenergy, Universita Giovanni Celoria 2, 20133, Milano, Italy b di ricerca per le Produzioni Legnose fuori Foresta (PLF), Strada Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria (CREA), Unita Frassineto 35, 15033, Casale Monferrato, AL, Italy a
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 January 2016 Received in revised form 16 July 2016 Accepted 5 September 2016
Short Rotation Coppices (SRC) can be a suitable solution for the production of biomass, mainly due to the easy-to-harvest good-quality feedstock. Besides technical, social and economic aspects, environmental issues are important to be taken into account when developing SRC. Although some studies focused on environmental sustainability of SRC were carried out only few compare different arboreous species using primary data. In this study, the environmental evaluation of SRC plantations carried out with 14 poplar and 6 willow clones was performed using primary data collected during experimental field tests over 12 years. Twelve impact potentials were evaluated using the characterization factors reported by the ILCD method: climate change (CC), ozone depletion (OD), Human toxicity, cancer effects (HTc), Human toxicity, non-cancer effects (HT), particulate matter (PM), photochemical ozone formation (POF), acidification (TA), freshwater eutrophication (FE), terrestrial eutrophication (TE), marine eutrophication (ME), freshwater ecotoxicity (FEx) and mineral, fossil and renewable resource depletion (MFRD). Both for poplar and for willow, among the different clones the environmental performance greatly vary mainly due to the yield. The choice of the most productive clones involves a reduction of the environmental impact of the produced biomass of about 35% (respect to the average results both for poplar and willow). However, biofuel production from willow SRC achieves lower environmental burdens respect to poplar SRC considering both the average biomass yield and the most productive clones. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Chips wood Poplar Willow Woody biomass Renewable energy Experimental trials
1. Introduction In Europe, energy policies are increasingly promoting the generation of energy from renewable sources (i.e., the European Union [EU] target of 27% renewable energy by 2030 and 40% of greenhouse gas [GHG] emission reduction) [1]. Among the different renewable sources, woody biomass is an interesting solution for energy generation in rural areas for both electricity [2] and heat production [3,4]. Woody biomass can be produced from forestry management but also from dedicated plantations in which woody species are grown for energy purposes [5e7]. In more detail, regarding the latter, the Short Rotation Coppice (SRC) plantations
* Corresponding author. E-mail address: [email protected] (J. Bacenetti). http://dx.doi.org/10.1016/j.biombioe.2016.09.002 0961-9534/© 2016 Elsevier Ltd. All rights reserved.
are cultivations of woody crops (poplar, willow, black locust, and other fast-growth species) characterized by short cutting cycles (1, 2, or 5e6 years), high plant density (from 1000 to 12,000 trees per hectare), and a crop cycle ranging from 10 to 15 years, over which several harvests take place [7e11]. Over the years, thanks to public subsidy frameworks, in Italy, about 10,000 ha of SRC were realized mainly in northern regions (Lombardy and Veneto) [7,8,12e16]. Poplar clones (Populus spp.) are the most used for SRC, but experiences were also carried out with new clones of willow (Salix spp.) and provenances of Robinia pseudoacacia L. in Central and Northern Europe [8,9,16e21], as well as clones of Eucalyptus spp. in Southern Europe [22,23]. Some studies highlighted that the biomass yield of willow clones can be higher than that of poplar [8,11,17]; nevertheless, SRC based on poplar clones is the main solution performed at the commercial level.
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With regard to clones, many genotypes of poplars and willows are in study and evaluation at CREA-PLF and in other private farms and public Institutes. Some new genotypes have been selected for biomass production at SRC plantations: They show resistance to principal poplar diseases, good rooting, and re-sprouting ability and rusticity. The most important and commercialized clones are P. canadensis as “Orion” and “Imola” or “AF2,” while others are P. deltoides, such as “Baldo.” Between willows, the new clones selected for biomass purposes are S. babylonica (previus S. matsudana) hybrids, such as “Drago” and “Levante.” SRC plantations can be managed with different cutting cycles: plantations with short cutting frequency (1 or 2 years) and plantations with medium cutting frequency (>5 years). Two- and fiveyear cutting cycles are the most widespread in Italy; the annual one, which initially foresaw extremely high planting density, although originally used (mainly due to issues related to harvesting mechanization) [24], has not been adopted more due to low coppice survival, low material quality (high ash content), and high planting costs [18e20]. Planting systems for different SRC models are different, too, with highly variable plant density: 10,000e14,000 plants ha1 (annual SRCs), 5000e10,000 plants ha1 (biennial SRCs) and 1000e1800 plants ha1 (5-year SRCs). In SRC with short cutting frequency, regarding planting layout, a single-row or twin-row plantation can be realized. The single-row layout is currently the most widespread, but twin rows can be an alternative solution [8,17]. The cultivation practice is quite different in the two principal models. In SRCs with medium cutting time, the crop cultivation requires low inputs, and it is most similar to traditional poplar plantations. On the contrary, in annual and biennial SRCs, fertilization and weed control are more frequently carried out [13,14,17]. However, among SRCs with short and medium cutting times, the main differences are related to the harvest. The harvesting operations include the felling, chipping, and transporting of the chips to the collecting point where the biomass is temporarily stored before being sold or used. With medium cutting time, at the end of 4e6 years of growth, felling and chipping are performed separately because the stem basal diameters (0.20e0.25 m) are too big for foragers [24]. On the contrary, for annual and biennial SRCs, at the harvest time, the basal diameters are lower (<0.12e0.14 m) and can be felled and chipped simultaneously. For this purpose, different harvesting units are available: the tractor-based method or foragerbased method [24e27]. The foragers are equipped with specific headers developed for harvesting SRC plantations [24,25]. In Italy, although better economic performances and a better quality of the biomass are related to SRC with medium cutting time, the SRCs with a 2-year cutting cycle are predominant (about 75% of the total area dedicated to SRC plantations) [16,28,29]. However, besides the economic aspects, the environmental ones also must be carefully evaluated to improve the environmental sustainability of this renewable energy source. In this regard, some studies were carried out at the end of the 1990s and at the beginning of new century, but most of them focused on the evaluation of a few environmental issues. They usually limited the analysis to energy and GHG or energy balance [13,15,16,30]. The most recently carried-out studies [6,22,23,32e36] only rarely used primary data regarding biomass yield and cultivation practice [6,22,32,33]. There is a lack of information about the environmental performance (benefits and/or impacts) of SRC carried out using different species and clones as well as considering different plant layouts. In this context, the aim of this paper is to analyze the environmental performances of SRC plantations with 2-year cutting cycles, realized with different planting layouts (single and twin rows) using 20 clones of poplar and of willow. For this purpose, primary inventory data were collected by means of a 12-year experimental
field test carried out in Piedmont (Northern Italy) with 14 poplar clones and 6 willow clones. In addition, to assess the environmental performances of SRC plantations, the environmental hotspots (processes most responsible for the environmental impact) were highlighted, and the impact of low water availability was evaluated using the life-cycle assessment (LCA) method. LCA is a holistic methodology that aims to analyze products, processes, or services from an environmental perspective (ISO 14040, 2006) [37]. Although originally developed for industrial processes, in the past few decades, it has increasingly become employed to analyze agricultural systems as well. 2. Materials and methods 2.1. Goal and scope definition The goal of this study is to assess the environmental impact of SRC plantations characterized by poplar and willow clones, a short (2e3 years) cutting cycle, and different planting layouts. For this purpose, primary data regarding the biomass yield as well as all of the field operations carried out were collected over 12 years of experimental field tests. The two genera, the cutting cycle, and the planting layouts evaluated are the most widespread for SRCs in Europe. In more detail, the research questions can be summarized as follows: 1) What is the environmental impact of SRC plantations performed with different poplar and willow clones? 2) What are the main environmental hotspots associated with SRC cultivation? 3) Between the single- and twin-row layouts, which solution has the lower environmental load? The study outcomes can be useful for farmers and farmer associations involved in SRC plantation, for stakeholders involved in the woody biomass market and in energy generation from wood chips, and for local politicians involved in the woody-bioenergy process. Regarding the latter, the achieved results are important in view of the development of the new Rural Development Program; willow and poplar clones with better environmental performances should be favored inside the subsidy framework. 2.2. Functional unit The functional unit provides the reference to which all other data in the assessment are normalized. With LCA's application to agricultural processes, different functional units (FUs) can be selected. In many LCA studies of agricultural production systems, the FU is the area (e.g., 1 ha) [36,38,39], in others, it is the energy produced [40e43]. Nevertheless, the mass-based functional unit is prevalent in LCA studies of agricultural systems [44e46]. Therefore, in this study, 1 t (tons) of dry-matter chipped biomass was considered as FU. However, considering that, although slightly, the lower heating value (LHV) of poplar and willow wood is different, the energy content of the biomass was taken into consideration (using the LHV of the two biomass) as additional FU for comparison among the most productive clones. 2.3. System description The SRC trial was grown in Piedmont (Po Valley e Northern Italy) at the experimental farm “Mezzi” of Research Unity for Intensive Wood Production (CREA-PLF) at Casale Monferrato in the district of Alessandria. The climate of the Po Valley is a climate of
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transition between the Mediterranean climate, dominated by anticyclonic patterns, and the Central European climate (Koeppen's Cfb), dominated by the oceanic influence of westerlies. The annual mean temperature is about 13 C. The precipitation regime has two minima (in the summer and winter) and two maxima (in the spring and fall); the average annual rain is 600e800 mm (with high variations in the past few years), with almost 350e400 mm distributed during the vegetative period (April-October); and a dry period occurs in June-July. The experimental trial was planted in spring 2002 in a sandy soil in a field covering a surface of about 1.2 ha [17]. In more detail, in the field, a split-plot design with 16 replications (8 for the singlerow layout and 8 for the twin-row layout) was utilized. The layout disposition was assigned to the plot and the different clones to the different sub-plots, with a total of 320 sub-plots of 25 m2 (224 with poplar and 96 with willow). The field operations involved in the cultivation practice are the same for all of the clones evaluated (14 for poplar and 6 for willow) and can be divided into the following: 1) Pre-planting and planting: Pre-planting operations involve soil tillage performed with ploughing and a harrowing, organic fertilization carried out with a manure spreader and 50 t ha1 of cow manure. The planting, carried out with a transplanting machine, is followed by a chemical weed control (Metolachlor, 1 kg ha1 þ Pendimethalin 4 kg ha1). During planting, 0.20e0.22 m long cuttings, obtained from 1-year-old sets, are inserted into the soil in a vertical position. For all of the poplar and willow clones, two different plant layouts were realized: a single row (spacing: 1.90 0.52 m) and a twin row (spacing: 0.75 þ 0.75 1.90 m). The plantation density was about 10,000 trees ha1 in both layouts. 2) Crop management: This section involves irrigation and weeds as well as pest control. The irrigation has been variable over the years; for example, during the first year, the trial received only 42 mm of water because the growing season was rainy (1051 mm of total annual rainfall and 645 during the growing season). In the first biennial cycle, the SRC plantations were drip irrigated; however, this irrigation system was destroyed during the first harvesting. Therefore, starting from the 3rd year, the trial was sprinkle irrigated each time with 30 mm of water only when necessary: three irrigations in the third year, and one in the 4th and 5th years. In the other years, no irrigations were performed. Globally, in the 12 years, 5800 m3 of water were applied. 3) Weed and pest control were performed with different intensities during the crop cycle. Weed control was performed with the application of herbicides and by means of mechanical interventions. Comprehensively, 13 interventions with a disc harrow were carried out, mainly performed during the first rotation cycle, in the first growing season (4 interventions) and, to improve the stumps' resprouting, in the years after each harvest. chemical weed control was performed 3 times with Ammonium Glufosinate (7 kg ha1), Metholachlor (4 kg ha1), and Pendimethalin (1 kg ha1) at years 1, 3, and 8. Pest control was performed 5 times (Clorpyriphos þ Cipermetrina 600 ml ha1), 4 treatments were done to control Chrysomela populi (year 1; year 2, 2 times; and year 5), and was done for Chryptorrhinchus lapathy (year 1). 4) Harvesting operations, felling, and chipping are performed simultaneously by means of a self-propelled combine forage harvester equipped with a specific header. The chipped wood is loaded through an outlet pipe inside farm trailers and is transported to the storage point located in the farmyard (transport distance of 1.15 km).
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2.4. System boundary The system boundary is shown in Fig. 1. Regarding system boundaries, the assessment was carried out considering a cradle-to-farm-gate approach. Therefore, raw material extraction (e.g., fossil fuels and minerals), manufacture (e.g., pesticides, tractors, foragers, and agricultural machines), use (diesel fuel consumption and derived combustion, tyre abrasion emissions, and emissions related to pesticide and organic fertilizer application), maintenance, and the final disposal of machines were considered. 2.5. Life cycle inventory All of the inventory data concerning the SRC were directly collected over a 12-year experimental field trial performed at the experimental farm “Mezzi” of Research Unity for Intensive Wood Production (CREA-PLF) at Casale Monferrato. There were 14 poplar clones and 6 willow clones. During the field test, the following data were collected (for more details, see Refs. [8,17]): rooting (%) at the end of the planting year, survival (%) at the end of every year, number of living shoots with height > 150 cm per tree/stump, diameter (mm) at breast height of stem on a sample of trees/stumps, total height (H), wet and dry weights of stems and branches of a sample per clone. To obtain the dry weights, the samples (stems and branches) were dried to a constant weight in an oven at 103 ± 1 C. In addition, information about the cultivation practices (e.g., the field operations carried out as well as the consumed production factors) was collected via survey forms. Table 1 reports the main inventory data for the cultivation practice of SRC. Considering that the trial was performed in a sandy soil and that soil characteristics deeply affect the environmental impact of field operations, all of the Ecoinvent processes were modified. In more detail, the directly measured diesel fuel consumption was used and the related emission accordingly adapted; the number of machines (tractors, foragers, and equipment) consumed for each operation was modified considering their mass, economical and physical life spans, annual use, and effective work capacity. In more detail, economical and physical life spans were taken from Bodria et al. [47], while the annual working time (h year1) for the different pieces of equipment was obtained by a direct measure.1 Background data for the production of diesel fuel, tractors, equipment, and self-propelled foragers were obtained from the Ecoinvent database v.3 [49e53]. Table 2 shows the biomass yield (expressed as dry matter) measured during the experimental field tests. The average stump survival was, for poplar, equal to 81.4%; 71.6%; 55.7%; and 49.0%, respectively, at the end of the 1st, 2nd, 3rd, and 4th cutting cycles; for willow, it was higher (95.1%; 82.8%; 74.5%; 66.3%). Table 3 reports the LHV for the most productive poplar and willow clones. LHV was achieved by means of a Calorimeter IKA C200 (ISO/DIS 18125:2015) [54]. 2.6. Life cycle impact assessment (LCIA) Twelve impact potentials were evaluated: climate change (CC), ozone depletion (OD), human toxicity, cancer effects (HTc), noncancer effects (HT), particulate matter (PM), photochemical ozone
1 According to Bacenetti et al. [48], for a self-propelled forager, the annual working time (h year1) was accounted for considering its use in harvesting cereal for silage production (maize 450 h year1 and winter cereals, such as triticale, wheat barley, and oat 250; h year1) and in the harvesting of 400 ha of SRC.
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Fig. 1. System boundary of SRC. (M ¼ manure, C ¼ cuttings, H ¼ herbicides, P ¼ pesticides, W ¼ water).
Table 1 Main data for SRC cultivation practice over the 12-years. Operations
Year of the crop cycle 1
Pre-seeding organic fertilization
1
Ploughing
1
Harrowing
1
Planting
1
2 3
Chemical weeding (pre-emergence) 1a c
Irrigation Mechanical weeding
4
Insects and diseases control
2f
4
5
Tractor
6 7 8
1b d 3e 1 2
2f
9 10 11 12 Mass Power
1b 1e 1e 1 1 1 1 1 2f
1
1
Harvesting
1
1
1
1
1
Transport
1
1
1
1
1
a b c d e f
Operative machine Type Size - Mass
Note Time Diesel cons. (h ha1) (kg ha1)
2620 kg 70 kW 6000 kg 95 kW 2620 kg 70 kW 2460 kg 48 kW 2620 kg 48 kW
Manure spreader 1.00 20 m3 - 2000 kg 1.6 m - 2000 kg 1.5
10.4
Cow manure 50 t ha1
Rotary Harrow 3,0 m - 1580 kg Rotor 1 line 200 kg Sprayer 300 kg
1.00
17.6
e
6.00
11.2
Cuttings: 10,000 trees ha1
0.33
3.3
2460 kg 55 kW 2620 kg 70 kW 11450 kg 480 kW 3000 kg 70 kW
Disch Harrow 2,0 m - 750 kg Sprayer 610 kg Biomass header, 2000 kg 3 Farm trailer 25 m3 - 1860 kg
1.5
10.1e 8.9
0.5
3.4
5
37.6
21.3
6.9
35 mm per intervention
Distance 0.7 km
1 kg ha1 Metholachlor þ 4 kg ha1 Pendimethalin. Ammonium Glufosinate 7 kg ha1 þ 1 kg ha1 þ 1 kg ha1 Metholachlor þ 4 kg ha1 Pendimethalin. 42 mm carried out with a drip irrigation system. 366 mm carried out with a drip irrigation system. 35 mm for each intervention. Clorpiriphos þ Cipermetrina 600 ml ha1.
formation (POF), acidification (TA), freshwater eutrophication (FE), terrestrial eutrophication (TE), marine eutrophication (ME), freshwater ecotoxicity (FEx), and mineral, fossil, and renewableresource depletion (MFRD). The characterization factors were reported by ILCD [55]. 3. Results 3.1. Hotspot identification for SRC The environmental hotspots for poplar and willow SRC are reported in Fig. 2. The hotspots are the same for both of the crops because the crop cultivation technique is the same. The
mechanization of field operations is the main one responsible for CC (75.8%); OD (90.9%), PM (43.5%), POF (89.3%), and MFRD (99.2%). The cutting production cannot be neglected for CC (4.3%), POF (8.8%), and ME (4.2%). Agro-chemical production has a negligible impact (<2%) except than for CC (5.6%), OD (8.2%), and PM (5.3%), while their related emissions in the environment are the main responsible of FEx. The emissions related to fertilizer application (ammonia volatilization, nitrate leaching, dinitrogen oxide production, and phosphorous runoff) cause 14.2% for CC, 50.2% for PM, 76.5% for TA, 78.2% for TE, 83.4% for FE, and 59.6% for ME. Among the different field operations (Fig. 3), harvesting, irrigation, and mechanical weed control are the ones with the highest impact for all of the evaluated impact categories.
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Table 2 Biomass production (expressed as mass of dry matter per hectare and per year) during the field test for poplar and willow clones. Unit
Poplar
Planting layout Clone
Willow
Average yield Planting layout Clone
Twin row Single row OGLIO ORION 83.148.020 83.039.009 80e020 84e078 85e037 BALDO ITA-098 83.039.018 I-214 DVINA LENA LAMBRO Twin row Single row S78-003 SI64-017 SE65-066/131-25 S76-008 LEVANTE DRAGO
Average yield
t t t t t t t t t t t t t t t t t t t t t t t t t t
1
ha ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1
Year of the crop cycle
1
y y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1
Cumulative yield
1 -2
3 -4
5 -7
8 -9
10e12
1 -12
12 13 14.1 16.9 12.7 10.2 10.8 13.9 16.1 17.4 8.8 10.3 8.3 11.8 14.2 9.5 12.50 12.2 13.6 14.8 9.8 7.7 11 14.8 19.2 12.87
6.9 8.1 9.9 8.7 6.5 5.2 8.8 9 9.7 11.6 3 5.7 2.4 8.2 9.2 7 7.49 10.7 10.8 15.1 6.8 4.8 8.2 12.4 17.3 10.75
7 6.2 11.9 10.1 8.3 3.7 9.2 4.6 7.4 13.8 1.2 4.3 0.7 4.5 9.4 3.6 6.62 10.5 12 13 7.7 7.2 11.9 14 14.2 11.25
7.8 7.4 11.3 11.4 8.8 3.3 11.8 4.2 10.7 15.3 0.6 5.5 0.3 5.1 12.2 4.1 7.61 12.1 16.9 18.7 8.9 6.5 14.3 18.7 19.8 14.49
8.425 8.675 6.00 13.28 10.45 5.36 12.15 2.93 7.86 9.09 1.34 6.41 1.01 2.71 11.22 4.38 8.67 11.38 13.33 13.27 6.91 5.28 9.20 8.94 15.57 12.38
99.68 101.63 124.30 144.13 112.24 64.59 126.84 76.80 118.79 157.27 32.42 75.12 27.14 71.82 133.05 65.14 101.07 135.63 158.58 176.02 94.84 75.44 130.30 160.63 201.92 147.43
Table 3 Lower Heating Value (LHV) of the most productive poplar and willow clones. Specie
Clone
LHV (MJ/kg of dry matter)
Populus deltoides Bartr € nch Populus canadensis Mo Populus deltoides Populus canadensis Salix babilonica L (ex S. matsudana Koidz.) hybrid Salix babylonica (ex S. matsudana) hybrid
Baldo Orion Oglio 83.148.020 Drago Levante
18.95 19.01 18.98 19.16 19.03 18.50
± ± ± ± ± ±
1.16 0.19 0.16 0.05 0.19 0.32
Fig. 2. Hotspot identification for SRC. [Note: CC ¼ climate change, OD ¼ ozone depletion, HTc ¼ Human toxicity, cancer effects, HT ¼ Human toxicity, non-cancer effects, PM ¼ particulate matter, POF ¼ photochemical ozone formation, TA ¼ acidification, FE ¼ freshwater eutrophication, TE ¼ terrestrial eutrophication, ME ¼ marine eutrophication, FEx ¼ freshwater ecotoxicity, MFRD ¼ mineral, fossil and renewable resource depletion].
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Fig. 3. Impact of mechanization: Environmental contribution of the different field operations [For impacts nomenclature see Fig. 2].
The impact of mechanization is mainly related to diesel fuel consumption and exhaust gas emissions due to its combustion in tractors and forager engines (data not shown). In more detail, in the different field operations, the share of environmental load due to diesel fuel production is predominant for OD, while for CC and POF, the diesel fuel emissions are the major contributor. The number of machines virtually consumed during the operation plays a minor role for most of the impact categories but cannot be neglected for HT, FE, and MFRD (data not shown). 3.2. Poplar and willow clones Fig. 4 shows the comparison among the environmental performances of the different poplar clones, while in Fig. 5, the results for
the willow clones are reported. The differences among the environmental impacts of the different poplar and willow clones are mainly related to their biomass yields. For the poplar, the clone with the higher yield (Baldo) presents a considerably lower environmental impact (from 80% to 82% for the different impact categories) with respect to the less productive clone (I-214). For the willow, the variability among the different clones is lower; however, with respect to the clone with a lower biomass yield (SE65-66/132-25), the best clone (Drago) shows a reduction of the environmental impact ranging from 61% to 63%. Both for poplar and willow, the impact categories less affected by the yield differences are HT and MFRD (namely the ones where the impact of biomass transport is higher).
Fig. 4. Environmental impact of the different poplar clones [For impacts nomenclature see Fig. 2].
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Fig. 5. Environmental impact of the different willow clones [For impacts nomenclature see Fig. 2].
3.3. Single-row and twin-row planting layout Fig. 6 reports the comparison between SRC plantations of poplar and willows considering the two different planting layouts (single row and twin rows) and the average biomass yield recorded during the experimental field tests. Both for poplar and willow SRC, the twin rows show higher environmental impacts for all of the evaluated impact categories. This difference is almost completely due to the different biomass yield. With respect to poplar, where the differences between the two planting layouts are small (about 2%), for willow, the single row achieves considerably better environmental performances (about 15%) with respect to twin rows. 3.4. Comparison between poplar and willow For 1 ton of chipped biomass, Table 4 reports a comparison of the environmental performances of poplar and willow SRC considering: 1) the average biomass yield; 2) the biomass yield of the two most productive clones. Respect to poplar, the willow SRC achieve better environmental performances for all of the evaluated impact categories considering both the average biomass yield and the most productive clone. Both for poplar and willow, the most productive clone (Baldo for poplar and Drago for willow) achieves an environmental impact reduction rate ranging from 34% to e 37% for the 12 evaluated impact categories. With respect to the biomass produced by the Drago willow clone, the average results for poplar clones shows a twice environmental impact. Similar results are achieved when the energy content of the dry biomass is considered as FU (Fig. 7). 4. Discussion The outcomes of this study arise from an experimental trial of 1.2 ha realized at one site of Northern Italy (Po Valley area).
Therefore, they should not be generalized for other cultivation areas characterized by different climatic and soil conditions. Nevertheless, for what concerns the environmental results of SRC, the achieved results are in agreement with those of previous studies in which poplar [23,30,32,35,56e58] and willow [6,32,33,35,59] clones were considered. Although a direct comparison among the absolute values for the different environmental impacts2 cannot be drafted due to different system boundaries, functional units, and LCIA methods, it is interesting to underline that: 1) All of the studies highlighted the biomass yield as the main parameter affecting the environmental performance above all when the system boundary is limited to the biomass production; 2) When poplar and willow clones are compared, the environmental performances of willow are slightly better; 3) Among the field operations carried out over the whole crop cycle, the harvest is the one with the higher environmental impact [14,23,29,31]. This impact is mainly due to the fuel consumption [48]. Therefore, to deepen the knowledge regarding the environmental sustainability of SRC, particular
2 With regard to the CC, the results of this study (31.58 and 49.62 kg CO2eq t1 for the most productive poplar clone and for the poplar on average, respectively, and 33.66 and 24.69 kg CO2eq t1 for the most productive willow clone and for the willow on average, respectively) are similar to the ones found by:
- San Miguel et al. [23] (2.33 kg CO2eq GJ1, which, considering an LHV for poplar equal to 18.5 GJ t1 of dry matter, correspond to 43.11 kg CO2eq t1); - Gonzalez-Garcia et al. [14] (35.46 kg CO2 eq t1 for poplar); - Roedl [35] (38.4 kg CO2 eq t1 for poplar); - Bacenetti et al. [13] (33.59 kg CO2eq t1 for poplar); - Fiala et al. [10] (40 kg CO2 eq t1 for poplar); - Gonzalez-Garcia et al. [57] (26.44 kg CO2 eq t1 for willow);
but lower respect to Rugani et al. [32] (66.94 kg CO2 eq t1 for mixed-woody-cropdwillows clones and local speciesdSRC in Belgium).
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Fig. 6. Comparison between single row and twin rows for poplar (top) and willow (bottom) SRC [For impacts nomenclature see Fig. 2].
attention must be paid to the evaluation of harvesting operations.
4.1. Water availability and environmental impact Biomass yields recorded during field tests have been affected by irrigation and, in particular, by the destruction of the drip irrigation
system at the end of the first biennial cutting time. For SRC plantations growing with good water availability, previous experiences have highlighted [17,30,56e58,63e65] that, with respect to the biomass yield achieved in the first two years, the yields of the second and third cutting cycles is higher (about þ30/þ50%). Due to the progressive reduction of stump survival, no yield increases have been considered for the fourth and fifth cutting cycles. In fact, differently from the second and third harvests, for these cutting
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Table 4 Environmental performances for poplar and willow (average biomass production among the all tested clones and most productive clone) expressed for 1 t of dry matter. Impact category Climate change Ozone depletion Human toxicity, cancer effects Human toxicity, non-cancer effects Particulate matter Photochemical ozone formation Acidification Terrestrial eutrophication Freshwater eutrophication Marine eutrophication Freshwater ecotoxicity Mineral, fossil & ren resource depletion
CC OD HTc HT PM POF TA TE FE ME FEx MFRD
Unit
Poplar average yield
Willow average yield
Poplar best clone (Baldo)
Willow - best clone (Drago)
kg CO2 eq kg CFC-11 eq CTUh CTUh kg PM2.5 eq kg NMVOC eq molc Hþ eq molc N eq g P eq kg N eq CTUe g Sb eq
49.618 4.87$1006 3.44$1006 3.85$1005 0.047 0.379 1.408 6.141 4.963 0.301 4560 1.139
33.660 3.30$1006 2.33$1006 2.64$1005 0.032 0.257 0.952 4.153 3.357 0.203 3081 0.777
31.581 3.10$1006 2.19$1006 2.48$1005 0.030 0.241 0.893 3.894 3.147 0.191 2888 0.729
24.693 2.43$1006 1.72$1006 1.96$1005 0.023 0.189 0.696 3.036 2.454 0.149 2249 0.573
Fig. 7. Environmental results for the most productive poplar and willow clones considering 1 MJ of the LHV as FU [For impacts nomenclature see Fig. 2].
cycles, the death of stumps is not offset more by an increase of the stem diameters produced by the surviving plants [8,17]. The impact of the irrigation issue on the environmental performances of SRC was evaluated considering the yield reported in Fig. 8, where an increase of the biomass yield equal to 30% has been considered for the second and third cutting cycles. When this yield increase is considered, the impact reduction ranges from 31.0% to 32.6% and from 15.2 to e 16.0% for poplar and willow biomass, respectively. Therefore, the impact reduction is higher for poplar where the biomass yield has been more deeply affected by the low water availability in the second and third cutting cycles. 5. Conclusions SRC can be a suitable solution for the production of biomass, mainly thanks to the good-quality feedstock. Besides the technical, social, and economic aspects, environmental issues are important to consider when developing SRC as well as when further development is foreseen. Although some studies focusing on the environmental sustainability of SRC have been carried out, only a few research studies compare different arboreous species by using primary data. In this study, the environmental impact of SRC plantations carried out by 14 poplar and 6 willow clones was evaluated using data
collected during an experimental test lasting 12 years. Among the different clones, for both poplar and willow, the environmental performances greatly vary mainly due to yield variation. However, willow SRC involves lower environmental burdens with respect to poplar SRC considering both the average biomass yield and the most productive clones. For both poplar and willow, the choice of the most productive clones involves a reduction of the environmental impact of about 35%. Concerning the two planting layouts, with respect to the twin rows, the single row presents a lower environmental impact for both poplar (about 2% for all of the evaluated impact categories) and willow (about 15%). Biomass yield is the main driver of environmental results. For this purpose, it should be considered that, with respect to the productivity recorded during experimental trials, commercial plantations can suffer considerable yield reductions [60e62]. In Italy, commercial poplar SRCs, established in fertile soil with good water availability, show yields similar to the ones [10,13,14,14,27] achieved in the experimental field considered in this study. Nevertheless, if the plantation was carried out in less fertile soils without irrigation, it is reasonable to expect a yield reduction with a consequent effect on environmental outcomes as well. This study can be useful for operators and stakeholders involved in SRC cultivation, in particular regarding the choice of the best
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Fig. 8. Average biomass yield for poplar (in green on the left) and willow (in blues on the right) considering a yield increase in the second and third cutting cycle (þ30% respect to the first cutting cycle). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
clones from both a productive and an environmental point of view. Furthermore, the achieved results can be upscaled to SRC plantations performed in other countries (e.g., Spain, Portugal, Greece) characterized by low water availability as well. References [1] European Commission, COM/2014/015 Final, a Policy Framework for Climate and Energy in the Period from 2020 to 2030, 2014, pp. 1e18. [2] M. Negri, J. Bacenetti, M. Brambilla, A. Manfredini, C. Cantore, S. Bocchi, Biomethane production from different crop systems of cereals in Northern Italy, Biomass Bioenergy 63 (2014) 321e329. [3] S. Caserini, S. Livio, M. Giugliano, M. Grosso, L. Rigamonti, LCA of domestic and centralized biomass combustion: the case of Lombardy (Italy), Biomass Bioenergy 34 (2010) 474e482. [4] F. Cherubini, N.D. Bird, A. Cowie, G. Jungmeier, Energy-and greenhouse gasbased LCA of biofuel and bioenergy systems: key issues, ranges and recommendations, Resour. Conserv. Recycl. 53 (8) (2009) 434e447. [5] C.M. Gasol, X. Gabarrell, A. Anton, M. Rigola, J. Carrasco, P. Ciria, J. Rieradevall, LCA of poplar bioenergy system compared with Brassica carinata energy crop and natural gas in regional scenario, Biomass Bioenergy 33 (1) (2009) 119e129. [6] S. Gonz alez-García, D. Iribarren, A. Susmozas, J. Dufour, Life cycle assessment of two alternative bioenergy systems involving Salix spp. biomass: bioethanol production and power generation, Appl. Energy 95 (2012) 111e122. [7] G. Facciotto, G. Minotta, P. Paris, F. Pelleri, Tree farming, agroforestry and the new green revolution. A necessary alliance, in: Proceedings of the Second International Congress of Silviculture, Florence, Italy, November 26th - 29th, 2014, p. 7. [8] S. Bergante, G. Facciotto, Nine years of measurements in Italian SRC trial with 14 poplar and six willow clones, in: Proceedings of the 19th European Biomass Conference and Exhibition, Berlin, Germany, ETA, 6e10 June 2011, pp. 178e182. [9] S. Bergante, G. Facciotto, G. Minotta, Identification of the main site factors and management intensity affecting the establishment of short-rotation coppices (SRC) in Northern Italy through stepwise regression analysis, Cent. Eur. J. Biol. 5 (2012) 522e530. [10] M. Fiala, J. Bacenetti, A. Scaravonati, A. Bergonzi, Short rotation coppice in Northern Italy: comprehensive sustainability, in: 18th European Biomass Conference and Exhibition, 2010. Lyon, France. [11] S.N. Djomo, Q. El Kasmioui, R. Ceulemans, Energy and greenhouse gas balance of bioenergy production from poplar and willow: a review, GCB Bioenergy 3 (3) (2011) 181e197. [12] M. Manzone, P. Balsari, R. Spinelli, Small-scale storage techniques for fuel chips from short rotation forestry, Fuel 109 (2013) 687e692. lez-García, A. Mena, M. Fiala, Life cycle assessment: an [13] J. Bacenetti, S. Gonza application to poplar for energy cultivated in Italy, J. Agric. Eng. 43 (2012) 72e78.
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Research paper
Woody biofuel production from short rotation coppice in Italy: Environmental-impact assessment of different species and crop management Jacopo Bacenetti a, *, Sara Bergante b, Gianni Facciotto b, Marco Fiala a degli Studi di Milano, Via AgriFood LCA LAB, Department of Agricultural and Environmental Sciences, Production, Landscape, Agroenergy, Universita Giovanni Celoria 2, 20133, Milano, Italy b di ricerca per le Produzioni Legnose fuori Foresta (PLF), Strada Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria (CREA), Unita Frassineto 35, 15033, Casale Monferrato, AL, Italy a
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 January 2016 Received in revised form 16 July 2016 Accepted 5 September 2016
Short Rotation Coppices (SRC) can be a suitable solution for the production of biomass, mainly due to the easy-to-harvest good-quality feedstock. Besides technical, social and economic aspects, environmental issues are important to be taken into account when developing SRC. Although some studies focused on environmental sustainability of SRC were carried out only few compare different arboreous species using primary data. In this study, the environmental evaluation of SRC plantations carried out with 14 poplar and 6 willow clones was performed using primary data collected during experimental field tests over 12 years. Twelve impact potentials were evaluated using the characterization factors reported by the ILCD method: climate change (CC), ozone depletion (OD), Human toxicity, cancer effects (HTc), Human toxicity, non-cancer effects (HT), particulate matter (PM), photochemical ozone formation (POF), acidification (TA), freshwater eutrophication (FE), terrestrial eutrophication (TE), marine eutrophication (ME), freshwater ecotoxicity (FEx) and mineral, fossil and renewable resource depletion (MFRD). Both for poplar and for willow, among the different clones the environmental performance greatly vary mainly due to the yield. The choice of the most productive clones involves a reduction of the environmental impact of the produced biomass of about 35% (respect to the average results both for poplar and willow). However, biofuel production from willow SRC achieves lower environmental burdens respect to poplar SRC considering both the average biomass yield and the most productive clones. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Chips wood Poplar Willow Woody biomass Renewable energy Experimental trials
1. Introduction In Europe, energy policies are increasingly promoting the generation of energy from renewable sources (i.e., the European Union [EU] target of 27% renewable energy by 2030 and 40% of greenhouse gas [GHG] emission reduction) [1]. Among the different renewable sources, woody biomass is an interesting solution for energy generation in rural areas for both electricity [2] and heat production [3,4]. Woody biomass can be produced from forestry management but also from dedicated plantations in which woody species are grown for energy purposes [5e7]. In more detail, regarding the latter, the Short Rotation Coppice (SRC) plantations
* Corresponding author. E-mail address: [email protected] (J. Bacenetti). http://dx.doi.org/10.1016/j.biombioe.2016.09.002 0961-9534/© 2016 Elsevier Ltd. All rights reserved.
are cultivations of woody crops (poplar, willow, black locust, and other fast-growth species) characterized by short cutting cycles (1, 2, or 5e6 years), high plant density (from 1000 to 12,000 trees per hectare), and a crop cycle ranging from 10 to 15 years, over which several harvests take place [7e11]. Over the years, thanks to public subsidy frameworks, in Italy, about 10,000 ha of SRC were realized mainly in northern regions (Lombardy and Veneto) [7,8,12e16]. Poplar clones (Populus spp.) are the most used for SRC, but experiences were also carried out with new clones of willow (Salix spp.) and provenances of Robinia pseudoacacia L. in Central and Northern Europe [8,9,16e21], as well as clones of Eucalyptus spp. in Southern Europe [22,23]. Some studies highlighted that the biomass yield of willow clones can be higher than that of poplar [8,11,17]; nevertheless, SRC based on poplar clones is the main solution performed at the commercial level.
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With regard to clones, many genotypes of poplars and willows are in study and evaluation at CREA-PLF and in other private farms and public Institutes. Some new genotypes have been selected for biomass production at SRC plantations: They show resistance to principal poplar diseases, good rooting, and re-sprouting ability and rusticity. The most important and commercialized clones are P. canadensis as “Orion” and “Imola” or “AF2,” while others are P. deltoides, such as “Baldo.” Between willows, the new clones selected for biomass purposes are S. babylonica (previus S. matsudana) hybrids, such as “Drago” and “Levante.” SRC plantations can be managed with different cutting cycles: plantations with short cutting frequency (1 or 2 years) and plantations with medium cutting frequency (>5 years). Two- and fiveyear cutting cycles are the most widespread in Italy; the annual one, which initially foresaw extremely high planting density, although originally used (mainly due to issues related to harvesting mechanization) [24], has not been adopted more due to low coppice survival, low material quality (high ash content), and high planting costs [18e20]. Planting systems for different SRC models are different, too, with highly variable plant density: 10,000e14,000 plants ha1 (annual SRCs), 5000e10,000 plants ha1 (biennial SRCs) and 1000e1800 plants ha1 (5-year SRCs). In SRC with short cutting frequency, regarding planting layout, a single-row or twin-row plantation can be realized. The single-row layout is currently the most widespread, but twin rows can be an alternative solution [8,17]. The cultivation practice is quite different in the two principal models. In SRCs with medium cutting time, the crop cultivation requires low inputs, and it is most similar to traditional poplar plantations. On the contrary, in annual and biennial SRCs, fertilization and weed control are more frequently carried out [13,14,17]. However, among SRCs with short and medium cutting times, the main differences are related to the harvest. The harvesting operations include the felling, chipping, and transporting of the chips to the collecting point where the biomass is temporarily stored before being sold or used. With medium cutting time, at the end of 4e6 years of growth, felling and chipping are performed separately because the stem basal diameters (0.20e0.25 m) are too big for foragers [24]. On the contrary, for annual and biennial SRCs, at the harvest time, the basal diameters are lower (<0.12e0.14 m) and can be felled and chipped simultaneously. For this purpose, different harvesting units are available: the tractor-based method or foragerbased method [24e27]. The foragers are equipped with specific headers developed for harvesting SRC plantations [24,25]. In Italy, although better economic performances and a better quality of the biomass are related to SRC with medium cutting time, the SRCs with a 2-year cutting cycle are predominant (about 75% of the total area dedicated to SRC plantations) [16,28,29]. However, besides the economic aspects, the environmental ones also must be carefully evaluated to improve the environmental sustainability of this renewable energy source. In this regard, some studies were carried out at the end of the 1990s and at the beginning of new century, but most of them focused on the evaluation of a few environmental issues. They usually limited the analysis to energy and GHG or energy balance [13,15,16,30]. The most recently carried-out studies [6,22,23,32e36] only rarely used primary data regarding biomass yield and cultivation practice [6,22,32,33]. There is a lack of information about the environmental performance (benefits and/or impacts) of SRC carried out using different species and clones as well as considering different plant layouts. In this context, the aim of this paper is to analyze the environmental performances of SRC plantations with 2-year cutting cycles, realized with different planting layouts (single and twin rows) using 20 clones of poplar and of willow. For this purpose, primary inventory data were collected by means of a 12-year experimental
field test carried out in Piedmont (Northern Italy) with 14 poplar clones and 6 willow clones. In addition, to assess the environmental performances of SRC plantations, the environmental hotspots (processes most responsible for the environmental impact) were highlighted, and the impact of low water availability was evaluated using the life-cycle assessment (LCA) method. LCA is a holistic methodology that aims to analyze products, processes, or services from an environmental perspective (ISO 14040, 2006) [37]. Although originally developed for industrial processes, in the past few decades, it has increasingly become employed to analyze agricultural systems as well. 2. Materials and methods 2.1. Goal and scope definition The goal of this study is to assess the environmental impact of SRC plantations characterized by poplar and willow clones, a short (2e3 years) cutting cycle, and different planting layouts. For this purpose, primary data regarding the biomass yield as well as all of the field operations carried out were collected over 12 years of experimental field tests. The two genera, the cutting cycle, and the planting layouts evaluated are the most widespread for SRCs in Europe. In more detail, the research questions can be summarized as follows: 1) What is the environmental impact of SRC plantations performed with different poplar and willow clones? 2) What are the main environmental hotspots associated with SRC cultivation? 3) Between the single- and twin-row layouts, which solution has the lower environmental load? The study outcomes can be useful for farmers and farmer associations involved in SRC plantation, for stakeholders involved in the woody biomass market and in energy generation from wood chips, and for local politicians involved in the woody-bioenergy process. Regarding the latter, the achieved results are important in view of the development of the new Rural Development Program; willow and poplar clones with better environmental performances should be favored inside the subsidy framework. 2.2. Functional unit The functional unit provides the reference to which all other data in the assessment are normalized. With LCA's application to agricultural processes, different functional units (FUs) can be selected. In many LCA studies of agricultural production systems, the FU is the area (e.g., 1 ha) [36,38,39], in others, it is the energy produced [40e43]. Nevertheless, the mass-based functional unit is prevalent in LCA studies of agricultural systems [44e46]. Therefore, in this study, 1 t (tons) of dry-matter chipped biomass was considered as FU. However, considering that, although slightly, the lower heating value (LHV) of poplar and willow wood is different, the energy content of the biomass was taken into consideration (using the LHV of the two biomass) as additional FU for comparison among the most productive clones. 2.3. System description The SRC trial was grown in Piedmont (Po Valley e Northern Italy) at the experimental farm “Mezzi” of Research Unity for Intensive Wood Production (CREA-PLF) at Casale Monferrato in the district of Alessandria. The climate of the Po Valley is a climate of
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transition between the Mediterranean climate, dominated by anticyclonic patterns, and the Central European climate (Koeppen's Cfb), dominated by the oceanic influence of westerlies. The annual mean temperature is about 13 C. The precipitation regime has two minima (in the summer and winter) and two maxima (in the spring and fall); the average annual rain is 600e800 mm (with high variations in the past few years), with almost 350e400 mm distributed during the vegetative period (April-October); and a dry period occurs in June-July. The experimental trial was planted in spring 2002 in a sandy soil in a field covering a surface of about 1.2 ha [17]. In more detail, in the field, a split-plot design with 16 replications (8 for the singlerow layout and 8 for the twin-row layout) was utilized. The layout disposition was assigned to the plot and the different clones to the different sub-plots, with a total of 320 sub-plots of 25 m2 (224 with poplar and 96 with willow). The field operations involved in the cultivation practice are the same for all of the clones evaluated (14 for poplar and 6 for willow) and can be divided into the following: 1) Pre-planting and planting: Pre-planting operations involve soil tillage performed with ploughing and a harrowing, organic fertilization carried out with a manure spreader and 50 t ha1 of cow manure. The planting, carried out with a transplanting machine, is followed by a chemical weed control (Metolachlor, 1 kg ha1 þ Pendimethalin 4 kg ha1). During planting, 0.20e0.22 m long cuttings, obtained from 1-year-old sets, are inserted into the soil in a vertical position. For all of the poplar and willow clones, two different plant layouts were realized: a single row (spacing: 1.90 0.52 m) and a twin row (spacing: 0.75 þ 0.75 1.90 m). The plantation density was about 10,000 trees ha1 in both layouts. 2) Crop management: This section involves irrigation and weeds as well as pest control. The irrigation has been variable over the years; for example, during the first year, the trial received only 42 mm of water because the growing season was rainy (1051 mm of total annual rainfall and 645 during the growing season). In the first biennial cycle, the SRC plantations were drip irrigated; however, this irrigation system was destroyed during the first harvesting. Therefore, starting from the 3rd year, the trial was sprinkle irrigated each time with 30 mm of water only when necessary: three irrigations in the third year, and one in the 4th and 5th years. In the other years, no irrigations were performed. Globally, in the 12 years, 5800 m3 of water were applied. 3) Weed and pest control were performed with different intensities during the crop cycle. Weed control was performed with the application of herbicides and by means of mechanical interventions. Comprehensively, 13 interventions with a disc harrow were carried out, mainly performed during the first rotation cycle, in the first growing season (4 interventions) and, to improve the stumps' resprouting, in the years after each harvest. chemical weed control was performed 3 times with Ammonium Glufosinate (7 kg ha1), Metholachlor (4 kg ha1), and Pendimethalin (1 kg ha1) at years 1, 3, and 8. Pest control was performed 5 times (Clorpyriphos þ Cipermetrina 600 ml ha1), 4 treatments were done to control Chrysomela populi (year 1; year 2, 2 times; and year 5), and was done for Chryptorrhinchus lapathy (year 1). 4) Harvesting operations, felling, and chipping are performed simultaneously by means of a self-propelled combine forage harvester equipped with a specific header. The chipped wood is loaded through an outlet pipe inside farm trailers and is transported to the storage point located in the farmyard (transport distance of 1.15 km).
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2.4. System boundary The system boundary is shown in Fig. 1. Regarding system boundaries, the assessment was carried out considering a cradle-to-farm-gate approach. Therefore, raw material extraction (e.g., fossil fuels and minerals), manufacture (e.g., pesticides, tractors, foragers, and agricultural machines), use (diesel fuel consumption and derived combustion, tyre abrasion emissions, and emissions related to pesticide and organic fertilizer application), maintenance, and the final disposal of machines were considered. 2.5. Life cycle inventory All of the inventory data concerning the SRC were directly collected over a 12-year experimental field trial performed at the experimental farm “Mezzi” of Research Unity for Intensive Wood Production (CREA-PLF) at Casale Monferrato. There were 14 poplar clones and 6 willow clones. During the field test, the following data were collected (for more details, see Refs. [8,17]): rooting (%) at the end of the planting year, survival (%) at the end of every year, number of living shoots with height > 150 cm per tree/stump, diameter (mm) at breast height of stem on a sample of trees/stumps, total height (H), wet and dry weights of stems and branches of a sample per clone. To obtain the dry weights, the samples (stems and branches) were dried to a constant weight in an oven at 103 ± 1 C. In addition, information about the cultivation practices (e.g., the field operations carried out as well as the consumed production factors) was collected via survey forms. Table 1 reports the main inventory data for the cultivation practice of SRC. Considering that the trial was performed in a sandy soil and that soil characteristics deeply affect the environmental impact of field operations, all of the Ecoinvent processes were modified. In more detail, the directly measured diesel fuel consumption was used and the related emission accordingly adapted; the number of machines (tractors, foragers, and equipment) consumed for each operation was modified considering their mass, economical and physical life spans, annual use, and effective work capacity. In more detail, economical and physical life spans were taken from Bodria et al. [47], while the annual working time (h year1) for the different pieces of equipment was obtained by a direct measure.1 Background data for the production of diesel fuel, tractors, equipment, and self-propelled foragers were obtained from the Ecoinvent database v.3 [49e53]. Table 2 shows the biomass yield (expressed as dry matter) measured during the experimental field tests. The average stump survival was, for poplar, equal to 81.4%; 71.6%; 55.7%; and 49.0%, respectively, at the end of the 1st, 2nd, 3rd, and 4th cutting cycles; for willow, it was higher (95.1%; 82.8%; 74.5%; 66.3%). Table 3 reports the LHV for the most productive poplar and willow clones. LHV was achieved by means of a Calorimeter IKA C200 (ISO/DIS 18125:2015) [54]. 2.6. Life cycle impact assessment (LCIA) Twelve impact potentials were evaluated: climate change (CC), ozone depletion (OD), human toxicity, cancer effects (HTc), noncancer effects (HT), particulate matter (PM), photochemical ozone
1 According to Bacenetti et al. [48], for a self-propelled forager, the annual working time (h year1) was accounted for considering its use in harvesting cereal for silage production (maize 450 h year1 and winter cereals, such as triticale, wheat barley, and oat 250; h year1) and in the harvesting of 400 ha of SRC.
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Fig. 1. System boundary of SRC. (M ¼ manure, C ¼ cuttings, H ¼ herbicides, P ¼ pesticides, W ¼ water).
Table 1 Main data for SRC cultivation practice over the 12-years. Operations
Year of the crop cycle 1
Pre-seeding organic fertilization
1
Ploughing
1
Harrowing
1
Planting
1
2 3
Chemical weeding (pre-emergence) 1a c
Irrigation Mechanical weeding
4
Insects and diseases control
2f
4
5
Tractor
6 7 8
1b d 3e 1 2
2f
9 10 11 12 Mass Power
1b 1e 1e 1 1 1 1 1 2f
1
1
Harvesting
1
1
1
1
1
Transport
1
1
1
1
1
a b c d e f
Operative machine Type Size - Mass
Note Time Diesel cons. (h ha1) (kg ha1)
2620 kg 70 kW 6000 kg 95 kW 2620 kg 70 kW 2460 kg 48 kW 2620 kg 48 kW
Manure spreader 1.00 20 m3 - 2000 kg 1.6 m - 2000 kg 1.5
10.4
Cow manure 50 t ha1
Rotary Harrow 3,0 m - 1580 kg Rotor 1 line 200 kg Sprayer 300 kg
1.00
17.6
e
6.00
11.2
Cuttings: 10,000 trees ha1
0.33
3.3
2460 kg 55 kW 2620 kg 70 kW 11450 kg 480 kW 3000 kg 70 kW
Disch Harrow 2,0 m - 750 kg Sprayer 610 kg Biomass header, 2000 kg 3 Farm trailer 25 m3 - 1860 kg
1.5
10.1e 8.9
0.5
3.4
5
37.6
21.3
6.9
35 mm per intervention
Distance 0.7 km
1 kg ha1 Metholachlor þ 4 kg ha1 Pendimethalin. Ammonium Glufosinate 7 kg ha1 þ 1 kg ha1 þ 1 kg ha1 Metholachlor þ 4 kg ha1 Pendimethalin. 42 mm carried out with a drip irrigation system. 366 mm carried out with a drip irrigation system. 35 mm for each intervention. Clorpiriphos þ Cipermetrina 600 ml ha1.
formation (POF), acidification (TA), freshwater eutrophication (FE), terrestrial eutrophication (TE), marine eutrophication (ME), freshwater ecotoxicity (FEx), and mineral, fossil, and renewableresource depletion (MFRD). The characterization factors were reported by ILCD [55]. 3. Results 3.1. Hotspot identification for SRC The environmental hotspots for poplar and willow SRC are reported in Fig. 2. The hotspots are the same for both of the crops because the crop cultivation technique is the same. The
mechanization of field operations is the main one responsible for CC (75.8%); OD (90.9%), PM (43.5%), POF (89.3%), and MFRD (99.2%). The cutting production cannot be neglected for CC (4.3%), POF (8.8%), and ME (4.2%). Agro-chemical production has a negligible impact (<2%) except than for CC (5.6%), OD (8.2%), and PM (5.3%), while their related emissions in the environment are the main responsible of FEx. The emissions related to fertilizer application (ammonia volatilization, nitrate leaching, dinitrogen oxide production, and phosphorous runoff) cause 14.2% for CC, 50.2% for PM, 76.5% for TA, 78.2% for TE, 83.4% for FE, and 59.6% for ME. Among the different field operations (Fig. 3), harvesting, irrigation, and mechanical weed control are the ones with the highest impact for all of the evaluated impact categories.
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Table 2 Biomass production (expressed as mass of dry matter per hectare and per year) during the field test for poplar and willow clones. Unit
Poplar
Planting layout Clone
Willow
Average yield Planting layout Clone
Twin row Single row OGLIO ORION 83.148.020 83.039.009 80e020 84e078 85e037 BALDO ITA-098 83.039.018 I-214 DVINA LENA LAMBRO Twin row Single row S78-003 SI64-017 SE65-066/131-25 S76-008 LEVANTE DRAGO
Average yield
t t t t t t t t t t t t t t t t t t t t t t t t t t
1
ha ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1 ha1
Year of the crop cycle
1
y y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1 y1
Cumulative yield
1 -2
3 -4
5 -7
8 -9
10e12
1 -12
12 13 14.1 16.9 12.7 10.2 10.8 13.9 16.1 17.4 8.8 10.3 8.3 11.8 14.2 9.5 12.50 12.2 13.6 14.8 9.8 7.7 11 14.8 19.2 12.87
6.9 8.1 9.9 8.7 6.5 5.2 8.8 9 9.7 11.6 3 5.7 2.4 8.2 9.2 7 7.49 10.7 10.8 15.1 6.8 4.8 8.2 12.4 17.3 10.75
7 6.2 11.9 10.1 8.3 3.7 9.2 4.6 7.4 13.8 1.2 4.3 0.7 4.5 9.4 3.6 6.62 10.5 12 13 7.7 7.2 11.9 14 14.2 11.25
7.8 7.4 11.3 11.4 8.8 3.3 11.8 4.2 10.7 15.3 0.6 5.5 0.3 5.1 12.2 4.1 7.61 12.1 16.9 18.7 8.9 6.5 14.3 18.7 19.8 14.49
8.425 8.675 6.00 13.28 10.45 5.36 12.15 2.93 7.86 9.09 1.34 6.41 1.01 2.71 11.22 4.38 8.67 11.38 13.33 13.27 6.91 5.28 9.20 8.94 15.57 12.38
99.68 101.63 124.30 144.13 112.24 64.59 126.84 76.80 118.79 157.27 32.42 75.12 27.14 71.82 133.05 65.14 101.07 135.63 158.58 176.02 94.84 75.44 130.30 160.63 201.92 147.43
Table 3 Lower Heating Value (LHV) of the most productive poplar and willow clones. Specie
Clone
LHV (MJ/kg of dry matter)
Populus deltoides Bartr € nch Populus canadensis Mo Populus deltoides Populus canadensis Salix babilonica L (ex S. matsudana Koidz.) hybrid Salix babylonica (ex S. matsudana) hybrid
Baldo Orion Oglio 83.148.020 Drago Levante
18.95 19.01 18.98 19.16 19.03 18.50
± ± ± ± ± ±
1.16 0.19 0.16 0.05 0.19 0.32
Fig. 2. Hotspot identification for SRC. [Note: CC ¼ climate change, OD ¼ ozone depletion, HTc ¼ Human toxicity, cancer effects, HT ¼ Human toxicity, non-cancer effects, PM ¼ particulate matter, POF ¼ photochemical ozone formation, TA ¼ acidification, FE ¼ freshwater eutrophication, TE ¼ terrestrial eutrophication, ME ¼ marine eutrophication, FEx ¼ freshwater ecotoxicity, MFRD ¼ mineral, fossil and renewable resource depletion].
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Fig. 3. Impact of mechanization: Environmental contribution of the different field operations [For impacts nomenclature see Fig. 2].
The impact of mechanization is mainly related to diesel fuel consumption and exhaust gas emissions due to its combustion in tractors and forager engines (data not shown). In more detail, in the different field operations, the share of environmental load due to diesel fuel production is predominant for OD, while for CC and POF, the diesel fuel emissions are the major contributor. The number of machines virtually consumed during the operation plays a minor role for most of the impact categories but cannot be neglected for HT, FE, and MFRD (data not shown). 3.2. Poplar and willow clones Fig. 4 shows the comparison among the environmental performances of the different poplar clones, while in Fig. 5, the results for
the willow clones are reported. The differences among the environmental impacts of the different poplar and willow clones are mainly related to their biomass yields. For the poplar, the clone with the higher yield (Baldo) presents a considerably lower environmental impact (from 80% to 82% for the different impact categories) with respect to the less productive clone (I-214). For the willow, the variability among the different clones is lower; however, with respect to the clone with a lower biomass yield (SE65-66/132-25), the best clone (Drago) shows a reduction of the environmental impact ranging from 61% to 63%. Both for poplar and willow, the impact categories less affected by the yield differences are HT and MFRD (namely the ones where the impact of biomass transport is higher).
Fig. 4. Environmental impact of the different poplar clones [For impacts nomenclature see Fig. 2].
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Fig. 5. Environmental impact of the different willow clones [For impacts nomenclature see Fig. 2].
3.3. Single-row and twin-row planting layout Fig. 6 reports the comparison between SRC plantations of poplar and willows considering the two different planting layouts (single row and twin rows) and the average biomass yield recorded during the experimental field tests. Both for poplar and willow SRC, the twin rows show higher environmental impacts for all of the evaluated impact categories. This difference is almost completely due to the different biomass yield. With respect to poplar, where the differences between the two planting layouts are small (about 2%), for willow, the single row achieves considerably better environmental performances (about 15%) with respect to twin rows. 3.4. Comparison between poplar and willow For 1 ton of chipped biomass, Table 4 reports a comparison of the environmental performances of poplar and willow SRC considering: 1) the average biomass yield; 2) the biomass yield of the two most productive clones. Respect to poplar, the willow SRC achieve better environmental performances for all of the evaluated impact categories considering both the average biomass yield and the most productive clone. Both for poplar and willow, the most productive clone (Baldo for poplar and Drago for willow) achieves an environmental impact reduction rate ranging from 34% to e 37% for the 12 evaluated impact categories. With respect to the biomass produced by the Drago willow clone, the average results for poplar clones shows a twice environmental impact. Similar results are achieved when the energy content of the dry biomass is considered as FU (Fig. 7). 4. Discussion The outcomes of this study arise from an experimental trial of 1.2 ha realized at one site of Northern Italy (Po Valley area).
Therefore, they should not be generalized for other cultivation areas characterized by different climatic and soil conditions. Nevertheless, for what concerns the environmental results of SRC, the achieved results are in agreement with those of previous studies in which poplar [23,30,32,35,56e58] and willow [6,32,33,35,59] clones were considered. Although a direct comparison among the absolute values for the different environmental impacts2 cannot be drafted due to different system boundaries, functional units, and LCIA methods, it is interesting to underline that: 1) All of the studies highlighted the biomass yield as the main parameter affecting the environmental performance above all when the system boundary is limited to the biomass production; 2) When poplar and willow clones are compared, the environmental performances of willow are slightly better; 3) Among the field operations carried out over the whole crop cycle, the harvest is the one with the higher environmental impact [14,23,29,31]. This impact is mainly due to the fuel consumption [48]. Therefore, to deepen the knowledge regarding the environmental sustainability of SRC, particular
2 With regard to the CC, the results of this study (31.58 and 49.62 kg CO2eq t1 for the most productive poplar clone and for the poplar on average, respectively, and 33.66 and 24.69 kg CO2eq t1 for the most productive willow clone and for the willow on average, respectively) are similar to the ones found by:
- San Miguel et al. [23] (2.33 kg CO2eq GJ1, which, considering an LHV for poplar equal to 18.5 GJ t1 of dry matter, correspond to 43.11 kg CO2eq t1); - Gonzalez-Garcia et al. [14] (35.46 kg CO2 eq t1 for poplar); - Roedl [35] (38.4 kg CO2 eq t1 for poplar); - Bacenetti et al. [13] (33.59 kg CO2eq t1 for poplar); - Fiala et al. [10] (40 kg CO2 eq t1 for poplar); - Gonzalez-Garcia et al. [57] (26.44 kg CO2 eq t1 for willow);
but lower respect to Rugani et al. [32] (66.94 kg CO2 eq t1 for mixed-woody-cropdwillows clones and local speciesdSRC in Belgium).
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Fig. 6. Comparison between single row and twin rows for poplar (top) and willow (bottom) SRC [For impacts nomenclature see Fig. 2].
attention must be paid to the evaluation of harvesting operations.
4.1. Water availability and environmental impact Biomass yields recorded during field tests have been affected by irrigation and, in particular, by the destruction of the drip irrigation
system at the end of the first biennial cutting time. For SRC plantations growing with good water availability, previous experiences have highlighted [17,30,56e58,63e65] that, with respect to the biomass yield achieved in the first two years, the yields of the second and third cutting cycles is higher (about þ30/þ50%). Due to the progressive reduction of stump survival, no yield increases have been considered for the fourth and fifth cutting cycles. In fact, differently from the second and third harvests, for these cutting
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Table 4 Environmental performances for poplar and willow (average biomass production among the all tested clones and most productive clone) expressed for 1 t of dry matter. Impact category Climate change Ozone depletion Human toxicity, cancer effects Human toxicity, non-cancer effects Particulate matter Photochemical ozone formation Acidification Terrestrial eutrophication Freshwater eutrophication Marine eutrophication Freshwater ecotoxicity Mineral, fossil & ren resource depletion
CC OD HTc HT PM POF TA TE FE ME FEx MFRD
Unit
Poplar average yield
Willow average yield
Poplar best clone (Baldo)
Willow - best clone (Drago)
kg CO2 eq kg CFC-11 eq CTUh CTUh kg PM2.5 eq kg NMVOC eq molc Hþ eq molc N eq g P eq kg N eq CTUe g Sb eq
49.618 4.87$1006 3.44$1006 3.85$1005 0.047 0.379 1.408 6.141 4.963 0.301 4560 1.139
33.660 3.30$1006 2.33$1006 2.64$1005 0.032 0.257 0.952 4.153 3.357 0.203 3081 0.777
31.581 3.10$1006 2.19$1006 2.48$1005 0.030 0.241 0.893 3.894 3.147 0.191 2888 0.729
24.693 2.43$1006 1.72$1006 1.96$1005 0.023 0.189 0.696 3.036 2.454 0.149 2249 0.573
Fig. 7. Environmental results for the most productive poplar and willow clones considering 1 MJ of the LHV as FU [For impacts nomenclature see Fig. 2].
cycles, the death of stumps is not offset more by an increase of the stem diameters produced by the surviving plants [8,17]. The impact of the irrigation issue on the environmental performances of SRC was evaluated considering the yield reported in Fig. 8, where an increase of the biomass yield equal to 30% has been considered for the second and third cutting cycles. When this yield increase is considered, the impact reduction ranges from 31.0% to 32.6% and from 15.2 to e 16.0% for poplar and willow biomass, respectively. Therefore, the impact reduction is higher for poplar where the biomass yield has been more deeply affected by the low water availability in the second and third cutting cycles. 5. Conclusions SRC can be a suitable solution for the production of biomass, mainly thanks to the good-quality feedstock. Besides the technical, social, and economic aspects, environmental issues are important to consider when developing SRC as well as when further development is foreseen. Although some studies focusing on the environmental sustainability of SRC have been carried out, only a few research studies compare different arboreous species by using primary data. In this study, the environmental impact of SRC plantations carried out by 14 poplar and 6 willow clones was evaluated using data
collected during an experimental test lasting 12 years. Among the different clones, for both poplar and willow, the environmental performances greatly vary mainly due to yield variation. However, willow SRC involves lower environmental burdens with respect to poplar SRC considering both the average biomass yield and the most productive clones. For both poplar and willow, the choice of the most productive clones involves a reduction of the environmental impact of about 35%. Concerning the two planting layouts, with respect to the twin rows, the single row presents a lower environmental impact for both poplar (about 2% for all of the evaluated impact categories) and willow (about 15%). Biomass yield is the main driver of environmental results. For this purpose, it should be considered that, with respect to the productivity recorded during experimental trials, commercial plantations can suffer considerable yield reductions [60e62]. In Italy, commercial poplar SRCs, established in fertile soil with good water availability, show yields similar to the ones [10,13,14,14,27] achieved in the experimental field considered in this study. Nevertheless, if the plantation was carried out in less fertile soils without irrigation, it is reasonable to expect a yield reduction with a consequent effect on environmental outcomes as well. This study can be useful for operators and stakeholders involved in SRC cultivation, in particular regarding the choice of the best
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Fig. 8. Average biomass yield for poplar (in green on the left) and willow (in blues on the right) considering a yield increase in the second and third cutting cycle (þ30% respect to the first cutting cycle). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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