Biomass production and energy balance of herbaceous and woody crops on marginal soils in the Po Valley

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1 GCB Bioenergy (2016), doi: /gc Biomss production nd energy lnce of herceous nd woody crops on mrginl soils in the Po Vlley STEFANO AMADUCCI 1, GIANNI FACCIOTTO 2,SARA BERGANTE 2, ALESSIA PEREGO 1, PAOLO SERRA 1, ANDREA FERRARINI 1 nd CARLO CHIMENTO 1 1 Deprtment of Sustinle Crop Production, Universit Cttolic del Scro Cuore, Vi Emili Prmee 84, Picenz, Itly, 2 Coiglio per l ricerc in gricoltur e l nlisi dell economi grri (CREA) Unit di ricerc per le produzioni legnose fuori forest (PFL), St. Frssineto Po, 35, Csle Monferrto (AL), Itly Astrct A welth of dt nd informtion on the cultivtion of perennil iomss crops hs een collected, ut direct compriso etween herceous nd woody crops re rre. The min ojective of this reserch ws to compre the iomss yield, the energy lnce nd the iomss qulity of six perennil ioenergy crops: Populus spp., Roini pseudocci, Slix spp., Arundo donx, Miscnthus 9 gignteus, nd Pnicum virgtum, grown in two mrginl environments. For gint reed nd switchgrss, two levels of nitrogen fertiliztion were pplied nnully (0 100 kg h 1 ). Nitrogen fertiliztion did not ffect iomss or energy production of gint reed; thus, it significntly reduced the energy return on investment (EROI) (from 73 to 27). In switchgrss, nitrogen fertiliztion significntly incresed iomss production nd the cpcity of this crop to respond to wter vilility, mking it fvorle option when only iomss production is trget. Net energy gin (NEG) ws higher for herceous crops thn for woody crops. In Csle, EROI clculted for poplr nd willow (7, on verge) ws significntly lower thn tht of the other crops (14, on verge). In Grig, the highest EROI ws clculted for miscnthus (98), followed y nonfertilized gint reed nd switchgrss (82 nd 73, respectively). Growing degree dys 10 during the cropping seson hd no effect on iomss production in ny of the studied species, lthough wter vilility from My to August ws mjor fctor ffecting iomss yield in herceous crops. Overll, herceous crops hd the highest rnking for ioenergy production due to their high iomss yield, high net energy gin (NEG), nd iomss qulity tht renders them suitle to oth iochemicl nd thermochemicl conversion. Miscnthus in prticulr hd the highest EROI in oth loctio (16 nd 98, in Csle nd Grig), while gint reed hd the highest NEG on the silty-lom soil of Grig. Keywords: Arundo donx, energy lnce, Miscnthus 9 gignteus, nitrogen, Pnicum virgtum, Populus spp., qulity, Roini pseudocci, Slix spp yield Received 30 Octoer 2015; ccepted 12 Decemer 2015 Introduction Cultivtion of perennil ioenergy crops is n importnt option in meeting future glol energy demnd (Creutzig et l., 2015). Over the lst decde, the possiility of cultivting ioenergy crops on mrginl lnd, uuitle for food production, hs een proposed (Duer et l., 2012) s possile solution to the so-clled food, energy, nd environment trilemm (Tilmn et l., 2009). A welth of dt nd informtion on the cultivtion of perennil iomss crops hs een collected in recent yers, ut direct compriso etween herceous nd woody crops re rre on mrginl soils. Field experiments designed to directly compre the cultivtion of herceous nd woody ioenergy crops enle the rnking of Correspondence: Stefno Amducci, tel , fx , e-mil: stefno.mducci@unictt.it the sme crops ccording to list of potentil gronomic, economic, nd environmentl spects (Tle 1). In the lst yers, it ws shown tht the cultivtion of perennil ioenergy crops comines the supply of iomss for renewle energy production with generl increse in the provision of multiple key ecosystem services (Milner et l., 2015). Positive impcts on the provision of ecosystem services were strictly dependent on the type of lnd use replced (Hollnd et l., 2015) nd on the sptil lloction of the crops reltive to the djcent lnd uses (Werling et l., 2013; Bourke et l., 2014). The integrtion of perennil crops into griculturl lndscpes could lso promote the mitigtion of ecosystem disservices from nnul food cropping systems, s reveled in severl studies (Powers et l., 2011; Prish et l., 2012; Meehn et l., 2013). Herceous nd woody crops re coidered promising cron-neutrl optio ecuse of their long-term 2016 The Authors. Glol Chnge Biology Bioenergy Pulished y John Wiley & So Ltd. This is n open ccess rticle under the terms of the Cretive Commo Attriution Licee, which permits use, distriution nd reproduction in ny medium, provided the originl work is properly cited. 1

2 2 S. AMADUCCI et l. Tle 1 Crop rnking sed on the min gronomic, environmentl, nd economic dvntges of the cultivtion of the herceous nd woody crops. Only review ppers tht delt with t lest one herceous nd one woody crop were coidered Herceous crops Woody crops Gint reed Switchgrss Miscnthus Poplr Willow Blck locust Genotype vilility Crop mngement* ? High yielding ? Multipurpose Nutrient use efficiency Drought resistnce + ++/+++ ++!!!! +++ Flood tolernce !!!! + Het tolernce !!!! ++ Energy lnce Soil C sequestrtion +++** +++** +++** ++** ++** ++** Biodiversity Wter qulity Invsiveness ? Economic life spn The symols +, ++, nd +++ indicte low, moderte, nd high dvntge, respectively;? stnds for not ville informtion, while!! vries on the sis of the different crops nd genotype. *The rnking is sed on the sttus of the current frming, hrvesting, nd processing technologies (Zegd-Lizrzu et l., 2010). Zegd-Lizrzu et l. (2010). Lurent et l. (2015). Quinn et l. (2015). Rettenmier et l. (2010). **Agostini et l. (2015). Duer et l. (2010) (reported only the impct t field scle). Ssegne et l. (2015). soil C storge potentil (Agostini et l., 2015; Chimento et l., 2016). Perennil herceous (Werling et l., 2013) nd woody crops (Rowe et l., 2013) cn lso sustin vriety of ecosystem functio (such s pest suppression nd pollintion), promoting the cretion of multifunctionl griculturl lndscpes. Moreover, reduced N losses (Smith et l., 2013), reduced soil erosion (Kort et l., 1998), nutrients removl from runoff (Lee et l., 2003), nd N removl from groundwter (Ssegne et l., 2015) hve een reported for herceous crops, such s Miscnthus 9 gignteus L. nd Pnicum virgtum L. In generl, sustinility of iomss production cn e chieved y cultivting high-yielding low-input crops (Ercoli et l., 1999) on mrginl soils (Powlson et l., 2011). Avilility of genetic mteril, tested in different pedoclimtic conditio, is reltively lrge for woody crops (Cunniff et l., 2015) nd ongoing reeding ctivities will further extend frmer optio (Hlling ck et l., 2015). Severl Populus spp (Dillen et l., 2013; Verlinden et l., 2013) nd Slix spp clones (Rosso et l., 2013; Amichev et l., 2014) re ville to e grown on mrginl soils in short-rottion coppice. In the cse of perennil herceous crops, reeding of Pnicum virgtum nd Miscnthus spp is ongoing (Liu et l., 2015; Tmur et l., 2015), ut the ctul selection of genotypes is limited to numer of Americn switchgrss vrieties nd to single genotype of Miscnthus 9 gignteus L. (Zegd-Lizrzu et l., 2010). No reeding hs een performed on gint reed nd ville field dt re reltive to locl clones tht hve shown very limited genetic (Ahmd et l., 2008) or phenotypic diversity (Amducci & Perego, 2015). Crop mngement is well estlished for woody crops nd switchgrss, while some djustments re need for miscnthus nd especilly for A. donx. Reduction of estlishment costs in Miscnthus 9 gignteus is pursued vi the selection of fertile genotypes tht cn e sown (Anderson et l., 2015; Xue et l., 2015), while this does not seem n option for A. donx (Pilu et l., 2013). Mechniztion nd storge of gint reed is still n open issue (Bentini & Mrtelli, 2013; Pri et l., 2015). Biomss yield is one of the most relevnt prmeters to ssess iomss crops performnce, ut it is strongly depended on environmentl conditio nd direct compriso re needed to identify the most suitle crops for specific condition. In generl, it is reported tht

3 HERBACEOUS AND WOODY CROPS ON MARGINAL SOILS 3 perennil herceous crops hve greter iomss production compred to woody crops (Nssi o Di Nsso et l., 2010; Rettenmier et l., 2010; Lurent et l., 2015). As iomss yield hs significnt impct on ioenergy yield nd on greenhouse gs (GHG) svings, herceous crops seem to hve etter environmentl impct thn woody crops (Rettenmier et l., 2010; Creutzig et l., 2015). The environmentl nd productive performnce of crop is well depicted y its efficiency in using nitrogen nd wter. It is reported nitrogen fertiliztion is necessry to support high iomss production in woody crops (Heilmn & Nory, 1998; Kuter et l., 2003), while the effect of nitrogen is limited or not significnt (Heton et l., 2004) in herceous crops. The deeper root system of perennil herceous crops compred to woody crops (Chimento & Amducci, 2015) cn explin the higher productivity of herceous crops in wterlimited conditio (Monti & Ztt, 2009). Reltively to iomss qulity, low lignin content nd high digestiility render herceous iomss crops suitle for second-genertion iofuel production (Monti et l., 2015), while energy ppliction of woody crops is generlly limited to thermochemicl conversion (Demirs, 2004). Previous work on iomss production on mrginl lnds hs een sed primrily on the lndscpe s suitility (Goplkrishnn et l., 2011; Hrvolk et l., 2014), while reserch to directly compre the performnce of herceous nd woody crops is very limited. Direct compriso re useful to relily chrcterize different iomss crops for their yield potentil (Lurent et l., 2015). More comprtive multispecies field trils nd monitoring re needed within rnge of climtic nd soil conditio to fully understnd the energy efficiency of vrious ioenergy cropping systems. Resolving the crop rnking from direct comprison of herceous nd woody crops is criticl to identify nd promote the cropping systems le to provide the gretest energy efficiency for given mrginl environment. In this study, the min ojective ws to compre the iomss yield, the energy lnce, nd the iomss qulity of six perennil ioenergy crops: three woody crops Populus spp. (poplr), Roini pseudocci (lck locust), nd Slix spp. (willow) nd three herceous crops Arundo donx (gint reed), Miscnthus 9 gignteus (miscnthus), nd Pnicum virgtum (switchgrss), grown in two mrginl environments within the griculturl lndscpe of the Po Vlley (northern Itly), where two multispecies field trils ( Csle nd Grig ) were set up. The Grig tril hs een lredy investigted for estlishing the crop rnking in soil C storge (Chimento et l., 2016) nd elowground iomss (Chimento & Amducci, 2015). Mterils nd methods Study site nd experimentl design Two field trils were estlished in April 2007 in the Po Vlley, the first t Grig di Podenzno, Itly ( N, E), on silt lom soil clssified s chromic luvisols (FAO) with low cronte content nd neutrl ph nd the second t Csle Monferrto, Itly ( N, E), on sndy soil, clssified s fluvisol. Prior to plnting, the experimentl site hd hosted mize monoculture for 30 yers in Grig, nd in Csle, the site hosted poplr stnds for out 30 yers nd set side for the lst five yers prior to the experiment. Both loctio re to e regrded s mrginl lnd for their soil qulity nd position within the griculturl lndscpe. The soil in Csle hs n extremely high content of snd (>90%) nd it is on the flood plin of the Po River; in Grig, the soil is compcted, silty with low content of orgnic cron (8 g kg 1 soil), nd the experimentl site is locted long min rod where sprinkle irrigtion is not possile. Soil chrcteristics re presented in Tle S1. At oth sites, the experimentl lyout is rndomized complete lock design with three locks nd single plot size of 450 m 2 ( m), to compre six iomss crops; three herceous, gint reed (A. donx L.), switchgrss (P. virgtum), nd miscnthus (Miscnthus 9 gignteus), nd three woody ioenergy crops, poplr (Populus spp), willow (Slix spp), nd lck locust (R. pseudocci). The plots of the woody crops were split in four suplots, ech hosting different clone, so tht for ech woody crop, the sme four clones were compred t ech loction. Dt reltive to the comprison mong clones will not e presented in this study, nd the iomss yield dt of the most productive clones for ech crop in ech loction will e used for the comprison mong crops. The most productive clones were Bldo (Populus deltoides) nd Orion (Populus x cndeis), S nd Levnte (hyrids of Slix ylonic L.), in Csle nd Grig, respectively, while Clri (ecotype from southern Itly) ws the most productive lck locust provennce t oth sites. At oth loctio, plnting ws crried out fter typicl soil preprtion (30 cm deep ploughing followed y 2 pssges of rotry tiller), using identicl plnting deities nd propgting mteril. Gint reed ws plnted using portion of rhizomes (on verge 300 g ech) from locl ecotype (the sme close t ech loction), t 1 rhizome per m 2. Miscnthus ws plnted with rhizomes (on verge 50 g ech) imported from UK (ADAS Ltd, Ely, Cmridgeshire) t 1.5 rhizomes per m 2. Switchgrss, vr Almo, ws sown with n experimentl mechnicl seed drill (Vignoli) using 0.25 g of pure live seeds (pls) per m 2. Inter-row distnce ws 1.4 m in gint reed nd miscnthus nd 0.4 m in switchgrss. Clones of poplr nd willow nd provennces of lck locust were provided y CREA-PLF (Csle Monferrto Itly). Stem cuttings (for poplr nd willow) nd 1-yer seedlings (for ck locust) were trplnted mnully in rows with n interplnt distnce of 0.6 m nd n inter-row distnce of 2.5 m (0.67 plnts m 2 ). For ll crops, iomss yield ws estimted y weighing ll the plnts hrvested on n re of pproximtely 10 m 2 in ech

4 4 S. AMADUCCI et l. plot. Dry mtter content ws estimted grvimetriclly on iomss susmple (pproximtely 1 kg) weighted t hrvest nd fter 24 h t 105 C. To ssess the effect of environmentl fctors on iomss production of the herceous crops, growing degree dys 10 nd wter input were estimted from June to Septemer of ech yer in oth loctio in greement with Trin et l. (2015), who recently found in 2-yer lysimeter experiment in centrl Itly tht gint reed nd miscnthus hd the highest wter requirements from June to Septemer. Growing degree dys 10 were clculted for ech yer y summing the dily difference etween men ir temperture nd the se temperture, which is 10 C for miscnthus nd switchgrss (Arundle et l., 2015); the sme vlue of se temperture ws ssumed for gint reed tht is regrded s mcrotherml crop (Cppelli et l., 2015). When dily men temperture ws lower thn 10 C, then growing degree dy 10 ws null. A liner regression ws performed to test the respoe of herceous iomss production to the wter input (irrigtion + rinfll) clculted from June to Septemer. As the regression ws found to e not significnt (r 2 = 0.01) for ll the crops in oth loctio, the regression ws then executed on iomss production nd the wter input clculted from My to August ecuse My rinfll vriility etween yers ws higher thn tht of Septemer (coefficient of vrition = 75% nd 49%, respectively). The liner regression ws executed etween herceous iomss production nd growing degree dys 10 from My to August. In ddition to the ovementioned common fetures of the experimentl design, there were some mngement fctors tht differed etween the two sites. These re listed s follows. In Csle, from 2007 to 2012, two irrigtio were pplied nnully to oth herceous nd woody crops from lte My to erly August ccording to the wether conditio. The nnul mount of irrigtion wter ws 70 mm (35 mm of wter per irrigtion event). In Grig, no irrigtion ws pplied. In Grig, nitrogen fertiliztion ws crried out on selection of plots t rte of 100 kg h 1 of nitrogen using mmonium nitrte. Nitrogen ws pplied (i) to the whole plot of woody crops t the eginning of growth in the spring fter the hrvest (in 2009, 2011, 2014), nd (ii) to one hlf of ech plot of gint reed nd switchgrss t the eginning of growth in the spring fter the hrvest (every yer excluding 2007, the yer of estlishment) in order to study the respoe of iomss production to nitrogen fertiliztion. In Grig, the effect of nitrogen fertiliztion ws ssessed only on gint reed nd switchgrss ecuse the plnt stnd for these crops ws uniform nd it ws possile to split the plot into two suplots to pply the nitrogen nd no-nitrogen tretment; miscnthus plnt estlishment ws not uniform enough for the sme tretment to e pplied. In Csle, nitrogen fertiliztion ws never provided to ny crop in order to simulte condition of low-input cropping. Hrvesting ws crried out every yer t the end of winter for the herceous crops, with the exception of Grig where miscnthus ws not hrvested t the end of the first yer due to the very limited iomss production (estimted <1 Mgh 1 ). In Csle, woody crops were hrvested t the end of yer 2, 4, nd 6. In Grig, woody crops were hrvested t the end of yer 2, 4, nd 7. It ws decided to postpone the third hrvesting to yer 7 for the limited plnt growth chieved s coequence of the extreme drought of In Grig, to compre qulittive chrcteristics of herceous nd woody crops, cellulose, hemicellulose, lignin, nd sh content were determined on iomss smples collected t hrvesting in The nlysis ws crried out using the AnkomII Fier Anlyzer (Ankom Technology Corportion, Firport, NY, USA) nd ws corrected for the residul sh content, following the procedure descried in Gllo et l. (2013). Energy lnce: inputs nd outputs determintion The energy lnce for iomss production ws clculted using the dt collected during the field trils in Csle. For ech crop, the energy potentilly delivered y comustion of lignocellulosic mteril (gross energy yield) ws estimted coidering the dry oveground iomss production nd its lower heting vlue, LHV (McKendry, 2002). The LHV for ech crop ws mesured y IKA C200 clorimeter t CREA-PLF of Csle Monferrto (Alessndri, northern Itly). The energy required for crop estlishment (soil preprtion nd plnting), cultivtion (control of weeds, fertiliztion nd irrigtion), nd hrvest of lignocellulosic mteril ws clculted coidering numer of opertio, time required per opertion (h h 1 ), type of mchines, reltive power (kw), nd diesel oil coumption (l h 1 ). The nlysis ccounted for direct nd indirect energy costs (H ulsergen et l., 2001): Direct costs included diesel oil coumed for ech opertion, while the coumption of luricnts ws neglected. It ws ssumed tht 1 l of diesel oil conti 35.9 MJ (Dlgrd et l., 2001). The indirect costs were relted to the mnufcture of fertilizers, pesticides nd hericides, mchines nd equipment, nd propgtion mteril for plnting. Production of fertilizers requires very high energetic cost, especilly nitrogen fertilizers: We ssumed n energetic cost of 73.3, 13.4, nd 9.2 MJ kg 1 for the production of nitrogen, phosphorus, nd potssium fertilizers, respectively (Mnzone & Clvo, 2016). The production of other chemicl compounds like pesticides nd hericides requires, respectively, 53 nd 91 MJ kg 1 (Green & McCulloch, 1976; Green et l., 1987). The energetic costs for the cotruction of mchines were derived from Fil & Bcenetti (2012): 92 MJ kg 1 in cse of trctor nd forger nd 69 MJ kg 1 in cse of other equipment (e.g., heder for hrvest). These vlues were then divided y the life spn (i.e., 800 h per yer) nd the effective nnul opertion time per hectre. In this nlysis, life spn of the mchines ws ssumed to e 10 yers. It ws coidered tht, for sprinkle irrigtion delivering out 350 m 3 h 1 of wter, n engine of 100 kw works for 6 h to pump wter from five meters deep well nd coumes 74 l of diesel fuel, corresponding to 2657 MJ (Ll, 2004). The energetic cost reltive to propgting mteril ws 0.3 MJ tree 1 (Dillen et l., 2013) for the woody crops (i.e., cutting of poplr nd willow or one-yer-old seedlings of lck

5 HERBACEOUS AND WOODY CROPS ON MARGINAL SOILS 5 locust). Energy costs for propgting mteril in herceous crops re usully coidered s negligile (Lette et l., 2003; Angelini et l., 2005); in this work, we ssumed n energy cost of 44 MJ kg 1 for producing switchgrss seeds (Schmer et l., 2008) nd n energy cost of 0.2 nd 0.15 MJ per rhizome for gint reed nd miscnthus, respectively (Ecoinvent, 2014). The totl costs of woody crops hrvesting vried ccording to nnul iomss production: An unit energy cost of 0.23 GJ t 1 of dry mtter ws ssumed for woody crops collected y self-propelled comine forger hrvester (Cls Jgur 880) equipped with the heder GBE 2 (Fil & Bcenetti, 2012). The sme cost ws ssumed for the hrvesting of miscnthus nd gint reed tht cn e crried out with forge hrvester. Switchgrss ws hrvested y shredding nd ling with direct cost of 5 l of diesel oil per hour s mesured in Csle. Time requested for hrvest vried on the sis of iomss production. Tle S2 reports energy costs of plnting, mngement, nd hrvesting (direct nd indirect costs) for ech crop in oth loctio. The estimtion of energy costs (input) nd gross energy yield (output) enle the net energy gin (input output, NEG) nd the energy return on investment (EROI) index to e clculted for oth herceous nd woody crops. NEG is n energy metric nd is defined s the gined difference in energy etween the energy content of the iomss t the frm gte nd the totl energy invested to produce it (Hill et l., 2006). EROI is dimeionless nd quntifies the efficiency of different energy technologies nd it is the rtio etween the mount of energy produced (expected return) nd the nonrenewle primry energy needed to produce it (investment) (Hll et l., 2009). Sttisticl nlysis Crops, yer, nd loction effects on iomss production were tested using repeted-mesures mixed model in rndomized complete lock design using IBM SPSS 21 (IBM Corportion, Armonk, New York, US). Crop, yer, nd loction were included in the design s fixed fctors; yer ws lso specified s the repeted-mesures term. Yer ws tken s fixed fctor s it represented the stnd ge of the perennil crops. First, the mixed model ws pplied solely to dt of herceous crops collected from nnul hrvests from 2007 to Then, the model ws run on the iomss dt collected for the woody crops t three hrvesting times: in 2008, 2010, nd 2012 in Csle nd in 2008, 2010, nd 2013 in Grig. The mixed model ws used to exmine differences in iomss production etween woody nd herceous crops. With this regrd, nnul iomss production ws estimted for ech woody crop dividing y two the production of single hrvest, with the exception of the third hrvest in Grig tht ws divided y three to estimte the verge nnul production from 2011 to As the effect of loction overwhelmed the crop effect on oth herceous nd woody crops production, the mixed model ws performed for the two loctio independently. A repeted-mesures mixed model ws pplied to the dt of gint reed nd switchgrss collected under two levels of nitrogen fertiliztion from 2008 to 2014 in Grig. As crop overwhelmed the effect of nitrogen fertiliztion, the mixed model ws performed on gint reed nd switchgrss independently. A two-wy ANOVA model ws pplied to dt of NEG nd EROI index estimted over the whole experimentl period in order to find differences etween crops nd loctio. A one-wy ANOVA ws run to ssess chnges in cellulose, hemicellulose, lignin, nd sh content etween crops using dt collected in 2013 in Grig. Comprison of me ws performed y post hoc Tukey s HSD test (Tukey, 1953) when min effects or interction of fctors were found significnt ccording to the mixed model or to the univrite ANOVA. A liner regression nlysis ws crried out to study the reltiohip etween iomss production nd environmentl fctors, nmely growing degree dys 10 nd wter input. Results In the present study, tht reports on the first eight yers ( ) fter estlishment of six perennil ioenergy crops, wide rnge of rinfll vriility ws experienced in the two field trils (Tle S3). The monthly distriution of rinfll in spring nd summer vried etween yers. In prticulr, wide rnge of rinfll ws encountered oth in Csle nd in Grig in My ( nd mm, respectively), in June (7 153 nd mm, respectively), in July (3 106 nd 0 76 mm, respectively), nd in August (8 139 mm nd 0 68 mm, respectively). The men coefficient of vrition of monthly rinfll from My to August cross yers ws 73% nd 86% in Csle nd in Grig, respectively. Annul rinfll rnged from 534 mm (2007) to 1053 mm (2014) in Csle, nd 548 mm (2012) from to 1070 mm (2010) in Grig; the men nnul rinfll ws 818 nd 757 mm in Csle nd in Grig, respectively. Biomss production When using the mixed model to exmine the effects of herceous crops, loction, nd yer, iomss production ws significntly higher in gint reed nd miscnthus (14.8 nd 13.3 Mg h 1 yr 1, respectively) thn in switchgrss (10.1 Mg h 1 yr 1 ) cross yers nd loctio (Tle 2A). As the two-wy interction etween yers nd loctio ws significnt, ech loction ws nlyzed independently. In Csle, iomss production vried significntly etween crops nd yers (Tle 2B). On verge, iomss yield mesured t the yer of estlishment ws lower thn tht chieved in susequent yers, coidering tht fter the second yer no iomss difference ws found etween yers, it cn e ssumed tht ll herceous crops reched their mxi-

6 6 S. AMADUCCI et l. Tle 2 (A) Mixed-model nlysis of vrince of the fixed effects of crop, yer, nd loction on dt of herceous dry iomss production collected in Csle nd in Grig from 2007 to (B) Mixed-model nlysis of vrince of the fixed effect of crops nd yer on dry iomss production fter splitting the dt set y loction Source Numertor df F-vlue P-vlue A Crop Yer Loction Block Yer 9 Crop Yer 9 Loction Yer 9 Crop 9 Loction B Csle Crop Yer Block Yer 9 Crop Grig Crop Yer Block Yer 9 Crop mum yield from the second yer (Fig. 1). On verge of the first eight-yer period, significnt difference in iomss production ws found etween switchgrss nd the two highest yielding crops, miscnthus nd gint reed (Fig. 1). The two-wy interction etween crops nd yer ws significnt in Grig (Tle 2B). While switchgrss nd miscnthus reched its mximum iomss yield lredy in the second yer fter estlishment, gint reed incresed its iomss yield until the third yer (Fig. 2). After hving reched their mximum yield, miscnthus nd switchgrss iomss did not vry significntly cross yers, while iomss fluctution ws oserved in gint reed (Fig. 2). The nlysis of the effect of nitrogen on iomss production showed different respoe etween gint reed nd switchgrss (Tle 3). In prticulr, nitrogen fertiliztion ffected significntly switchgrss iomss production tht incresed y 16% in the fertilized plots, from 12 to 13.9 Mg h 1 yr 1 (P < 0.001), wheres gint reed iomss production ws not significntly ffected y nitrogen fertiliztion. No significnt reltiohip ws found etween iomss production nd growing degree dys 10 clculted from My to August (r 2 = 0.01, P = 0.68) nd from June to Septemer (r 2 = 0.01, P = 0.78) in oth loction. The liner regression performed to test the respoe of herceous iomss production to the wter input (irrigtion + rinfll) clculted from June to Septemer ws found not significnt (r 2 = 0.02, P = 0.62). The reltiohip etween iomss production nd summer wter input (i.e., the sum of rinfll from June to Septemer nd irrigtion, when performed) ws significnt only for miscnthus in Csle (r 2 = 0.6, P < 0.10). A significnt reltiohip ws found etween the wter input clculted from My to August (dding irrigtion, when performed) nd iomss production of miscnthus in oth loctio, nd in gint reed in Grig with nd without nitrogen fertiliztion. The respoe to the wter input clculted from My to August ws significnt in switchgrss only in the fertilized plots (Tle 4). The nnul iomss production ws estimted for ech woody crop dividing y two the production of single hrvest, which ws collected in 2008, 2010, nd 2012 in Csle, nd in 2008 nd 2010, in Grig, for lst hrvest in Grig (2013) iomss yield ws divided y Dry mtter [Mg h 1 yr 1 ] * Gint reed Miscnthus Switchgrss Fig. 1 Biomss production of herceous crops oserved in Csle from 2007 to 2014 (left) nd men iomss production of gint reed, miscnthus, nd switchgrss cross yers (right). Letters indicte Tukey s lest men significnt difference etween yers (left) nd crops (right). *indictes the yer of full crops estlishment.

7 HERBACEOUS AND WOODY CROPS ON MARGINAL SOILS 7 Dry iomss production [Mg h 1 yr 1 ] c * * Gint reed Miscnthus Switchgrss * Dry iomss production [Mg h 1 yr 1 ] c Gint reed Miscnthus Switchgrss Yers Fig. 2 Men nnul iomss production of gint reed, miscnthus, nd switchgrss oserved in Grig from 2007 to 2014 (ove) nd men comprison etween crops within yers (elow). Letters indicte Tukey s lest men significnt difference etween yers within crops (ove) nd crops within yer (elow). *indictes the yer of full crops estlishment. n.s. =not significnt. Tle 3 Mixed-model nlysis of vrince of the fixed effect of nitrogen nd yer on dry iomss production of gint reed nd switchgrss in Grig from 2008 to 2014 Source Numertor df F-vlue P-vlue Gint reed Yer Nitrogen Block Yer 9 Nitrogen Switchgrss Yer Nitrogen Block Yer 9 Nitrogen three. The nnul iomss production of the woody crops ws significntly lower in Csle (7.1 Mg h 1 yr 1 ) thn in Grig (10 Mg h 1 yr 1, P < 0.001). When ech loction is exmined independently, the nnul production estimted from the first hrvest ws lower (4.3 Mg h 1 yr 1 ) thn tht from the second nd the third hrvests (7.7 nd 9.2 Mg h 1 yr 1, P < 0.05) in Csle; similrly, in Grig, nnul production estimted from the three hrvests ws 3.3, 12.9, nd 12.2 Mg h 1 yr 1, respectively. No significnt difference of iomss production mong crops ws found in Csle, lthough lck locust douled the nnul production of willow in the third hrvest (Fig. 3). Apprently, the high vriility etween locks in Csle overwhelmed the vriility etween Tle 4 Liner regression etween nnul herceous production nd wter input oserved in Csle (rinfll + irrigtion) nd in Grig (irrigtion) from June to August, coidering the period fter full crop estlishment (i.e., ) Crops Csle Rinfll (My August) + Irrigtion Grig Rinfll (My August) r 2 r 2 B Gint Reed * 52.7 Miscnthus 0.6* * 31.3 Switchgrss Gint Reed 100N 0.80** 74.1 Switchgrss 100N 0.94*** 20.8 is the iomss incresing rte for the unit wter input (kg mm 1 )., not significnt. *Significnt the 0.10 level. **Significnt the 0.05 level. ***Significnt the 0.01 level. crops (coefficient of vrition = 78%, 55%, 1.38%, in poplr, lck locust, nd willow, respectively). The vriility etween locks ws likely due to different content of corse snd (12%, 59%, nd 12% in lock 1, 2, nd 3, respectively) in the upper 40 cm of soil. In Grig, the significnt interction etween crops nd hrvest is explined y the lowest iomss production of lck locust tht ws oserved in 2010 (second hr-

8 8 S. AMADUCCI et l. Dry iomss production [Mg h 1 yr 1 ] Poplr Blck locust Willow vest). Thus, only the iomss production of lck locust incresed significntly from the second to the third hrvest despite the drought experienced in the summer of 2012 (Tle S3). Compring the men nnul production of herceous nd woody crops, no significnt difference ws found in Csle. In Grig, gint reed production douled tht of lck locust nd it ws 1.5 times higher thn the production of switchgrss, willow, nd poplr; miscnthus yielded significntly less thn gint reed with decrese of 26% (Fig. 4). Biomss qulity Csle Grig Csle Grig Csle Grig 1st hrvest 2nd hrvest 3rd hrvest Fig. 3 Annul iomss production of woody crops estimted dividing y two the iomss hrvested in 2008 (1st hrvest), 2010 (2nd hrvest), nd 2012 (3rd hrvest) in Csle nd in 2008 (1st hrvest), 2010 (2nd hrvest) in Grig. The nnul iomss of woody crops of the third period (3rd hrvest) ws clculted dividing y three the production hrvested in 2013 in Grig. Letters indicte Tukey s lest men significnt difference etween yers nd crops within hrvest nd loction. n.s. =not significnt. Dry mtter [Mg h 1 yr 1 ] Miscnthus Gint reed Blck locust Fig. 4 Men nnul iomss production of herceous nd woody crops in Grig from 2007 to Annul iomss production of woody crops ws estimted dividing y two the iomss hrvested in 2008 (1st hrvest), 2010 (2nd hrvest), nd y three tht hrvested in 2013 (3rd hrvest). Letters indicte Tukey s lest men significnt difference etween crops. c Poplr Switchgrss c Willow The qulittive nlysis crried out on dry smples collected in 2013 showed tht (i) the cellulose nd sh content of miscnthus ws comprle to tht of the woody crops, (ii) the hemicellulose content of switchgrss ws higher thn tht of the other crops, (iii) the lignin content ws lowest in gint reed, nd (iv) the sh content ws highest in gint reed (Tle 5). The low heting vlue (LHV) ws different etween crops (P < 0.05). Gint reed LHV ws significntly lower thn tht of the other crops (16.7 MJ kg 1 ) tht ws 17.8 MJ kg 1 for miscnthus nd switchgrss, nd on verge 18.8 MJ kg 1 for the woody crops. The differences in LHV etween herceous nd woody crops were likely due to the different iomss composition, nmely lignin content. Energy lnce A simplified energy lnce ws clculted to compre NEG nd EROI t the frm gte for the six ioenergy crops in oth loctio. Energy input nd output, nd in turn NEG nd EROI, were different etween crops nd loctio nd vried ccording to iomss production, low heting vlue (LHV), nd energy costs due to plnting, nd mngement (Tle S2). In oth loctio, the energy required for woody crops plnting ws 1.4 times higher thn tht of herceous crops ecuse of the higher fossil fuel coumption, which ws on verge 5.8 nd 4.7 GJ h 1 yr 1 for woody nd herceous crops, respectively. Among woody crops, lck locust required the lowest mngement energy input ecuse nitrogen fertiliztion ws not crried out. In Csle, the highest cost of woody crops production ws required for mngement opertio (minly irrigtion, 79%), while hrvest nd plnting required 13% nd 8% of the totl energy costs, respectively. Poplr nd willow required the highest energy input mong the six studied crops in Csle (Tle S2). Coidering the energy costs ssocited with herceous crops cultivtion, the energy required for mngement ws the highest (49.7 GJ h 1 ). Gint reed hd higher hrvest costs thn miscnthus nd switchgrss due to the higher iomss production. In Grig, the highest proportion of energy costs ws llocted to hrvesting in the unfertilized herceous crops (77%) nd to mngement (68%) in the fertilized crops due to the ppliction of nitrogen fertilizer. Among the studied crops in Grig, the highest energy costs were clculted for fertilized gint reed nd switchgrss cultivtion. Direct nd indirect energy costs of hrvesting were higher in herceous thn in woody crops (Tle S2), s coequence of the highest hrvesting frequency (every yer) nd iomss production of the herceous crops.

9 HERBACEOUS AND WOODY CROPS ON MARGINAL SOILS 9 Tle 5 Composition (%) of the studied crops iomss hrvested in 2013 fter senescence in Grig F-vlue Blck locust Poplr Willow Gint Reed Miscnthus Switchgrss Cellulose 23.5*** Hemicellulose 112.3*** 18.1 c 18.6 c 19.1 c Lignin 33.9*** c 7.2 d 11.5 cd 9.6 cd Ash 100.8*** 1.7 c 2.1 c 2.1 c c 2.9 *** is significnt of 0.01 level NEG [GJ h 1 ] Gint reed Gint reed 100N Miscnthus Switchgrss 100N Willow Poplr Switchgrss Blck locust Grig EROI c 20 0 Miscnthus Blck locust Gint reed Switchgrss Poplr Willow Miscnthus Switchgrss Gint reed Gint Reed 100N Blck locust Switchgrss 100N Willow Poplr Csle Grig Fig. 5 Net energy yield (output input, NEY) estimted for the six studied crops coidering the cumultive energy input nd output from 2007 to 2013 in Grig (ove). Energy Return On Investment (output: input, EROI) estimted for the six studied crops coidering the cumultive energy input nd output from 2007 to 2012 in Csle nd from 2007 to 2013 in Grig (elow). Letters indicte Tukey s lest men significnt difference etween crops within loctio. Vrition in NEG nd EROI ws minly driven y the lrge differences in iomss production etween crops nd loctio (Fig. 5). With regrd to energy output, miscnthus nd lck locust hd the highest vlue in Csle (Fig. 5). NEG clculted in Csle nd Grig ws higher for herceous crops (verge vlue 903 nd 1627 GJ h 1, respectively) thn for woody crops (727 nd 1244 GJ h 1 ). Although differences in NEG etween crops were not significnt in Csle, the NEG of miscnthus, gint reed, nd lck locust ws 2.3 times higher thn tht of willow. Averge NEG of crops in Csle ws 2 times lower thn tht oserved in Grig where gint reed NEG ws 1.5 times higher thn tht clculted for the other crops. In Grig, fertilized nd unfertilized gint reed hd similr energy output (1985 nd 1971 GJ h 1, respectively) nd NEG (1943 nd 1903 GJ h 1, respectively) despite the different energy input costs (82 nd 28 GJ h 1, respectively). In switchgrss, nitrogen fertiliztion induced significnt increse in energy output (from 1333 to 1506 GJ h 1, respectively) nd not significnt increse in NEG (from 1318 to 1430 GJ h 1, respectively).

10 10 S. AMADUCCI et l. As expected, the vrition of energy input due to nitrogen fertiliztion produced lrger vrition of EROI thn of NEG. In gint reed, when the input incresed y 3 times (from 28 to 82 GJ h 1 ) due to fertiliztion, NEG decresed y 2% (P = 0.99), wheres EROI y 2.7 times (P < 0.001). In switchgrss, when input incresed y 5 times (from 15 to 76 GJ h 1 ) due to fertiliztion, NEG incresed y 8% (P = 0.11), wheres EROI decresed y 3.6 times (P < 0.001). The men EROI index estimted for Csle ws 4 times lower thn tht of Grig ecuse of the lower iomss production nd the higher energy costs due to irrigtion (Tle S2). Miscnthus EROI index ws the highest oth in Csle nd in Grig. Herceous crops hd higher EROI thn woody crops in Grig, while lck locust hd similr EROI index to miscnthus in Csle. Discussion In this study, comprison of iomss production of six perennil ioenergy crops over 8 yers in two different loctio is presented, nd for the first time, direct comprison etween 3 herceous nd 3 woody iomss crops cultivted in the sme experimentl conditio is discussed. On verge, herceous crops hd higher iomss yield thn woody crops in oth loctio. This is in greement with the rnking of energy crops on the sis of met-nlysis crried out y Lurent et l. (2015) on the yield dt from 28 pulished ppers. The most nd the lest productive crops were miscnthus nd willow in Csle nd gint reed nd lck locust in Grig (Fig. 4). To compre our results with the dt reported in literture, medi of pooled iomss dt were plotted over the oxplot chrt of the dry iomss yield shown in Lurent et l. (2015). The yield levels reported in our study re coistent with those presented in the met-nlysis, with the est greement eing found for miscnthus nd switchgrss (Fig. 6), for which wide set of dt from different environments ws ville. Gint reed, while showing reltively high yield in oth loctio, flls within the 1st qurtile of literture dt (Lurent et l., 2015). This cn e explined y the mrginl nture of oth loctio in this study, nd y the fct tht most of the very high nnul yields reported for gint reed (>30 Mg h 1 yr 1 ) were otined in the optiml, often irrigted, conditio of the center nd south of Itly, where plnt growth is extended thnks to the reltively high temperture registered in utumn nd winter (Scordi et l., 2014). It is interesting to note (Fig. 6) the very different performnces of willow in Grig, where it rnked cross the 2nd nd 3rd percentiles, nd in Csle, where it equled the lowest yield reported in literture (Lurent et l., 2015). Willow is well dpted to environments with high wter vilility nd soil with high wter holding cpcity (Dimitriou et l., 2011); it therefore found suitle conditio in the silty soil of Grig, where fter slow estlishment (1st hrvest Fig. 3), it hd reltively high productivity (Arhmson et l., 2002; DEFRA, 2002). On the contrry, in the sndy soil of Csle, willow hd very low yields in the phse of estlishment (1st hrvest, Fig. 3) nd t full production (2nd nd 3rd hrvests). The mrked Dry iomss production [Mg h 1 yr 1 ] Gint reed Miscnthus Willow Switchgrss Poplr Blck locust Fig. 6 Comprison etween medin iomss production of the six crops oserved in this study cross yer ( ) nd the oxplot of the dry iomss production reported y Lurent et l. (2015) for gint reed, miscnthus, willow, switchgrss, nd poplr. White circle nd lck tringle indicte the medin production oserved cross yers in this study in Csle nd in Grig, respectively.

11 HERBACEOUS AND WOODY CROPS ON MARGINAL SOILS 11 decrese in production t the 3rd hrvest ws proly coequence of plnt mortlity (plnt deity ws 7500 plnts h 1 t estlishment nd reduced to 4500 plnts h 1 t the 3rd hrvest). Despite the sndy soil nd low wter vilility in Csle, the medin vlue of poplr iomss ws very similr to tht found in literture (Lurent et l., 2015), which confirms the tolernce of poplr genotypes elonging to the P. deltoides crops to environments with corse soils nd periods of drought (Bergnte et l., 2010). In the silty-lom soil of Grig, poplr found idel conditio, reching the highest yields found in literture (Fig. 6). Limited informtion on the productivity of lck locust s ioenergy crop is present in literture nd no direct comprison with other ioenergy crops is reported; for this reson, lck locust ws not included in the met-nlysis performed y Lurent et l. (2015). Strker et l. (2015), in recent review on lck locust s ioenergy crop, reported n verge iomss production of 10 Mg h 1 yr 1 in Itly, which is in line with the dt presented in this study (10.6 Mg h 1 yr 1 ). Interestingly, lck locust hd very similr performnce in Grig nd Csle, which denotes yield stility. Blck locust is coidered s eing prticulrly dpted to mrginl corse (light)- textured soil, while it is seitive to poorly drined or compct plstic soils (Strker et l., 2015). The lower yield of lck locust in the first period of growth, in comprison with the other woody crops, ws proly the coequence of its difficult estlishment in the compct silty-lom soil of Grig. In the 3rd period, when men summer rinfll (91 mm cumultive rinfll from June to August) ws lower thn in the previous periods (146 mm 1st period nd 120 mm 2nd period), lck locust reched the sme level of production of poplr nd willow (Fig. 3). It is pprent tht wter vilility (s function of rinfll/irrigtion nd soil wter holding cpcity) ws one of the mjor fctors ffecting iomss yield in this study nd in severl others (e.g., Heton et l., 2004; Arundle et l., 2014). However, in this study, it ws difficult to find cler reltiohip etween yield of woody crops nd wter vilility, ecuse plnts were hrvested every two yers (three in the 3rd hrvest in Grig) nd ny environmentl effect ws therefore spred over the whole growing period. Moreover, coidering tht in the 1st period iomss yield ws limited due to crop estlishment, only dt from two hrvests could e used to study the reltiohip etween environmentl prmeters nd woody crop yield. For this reson, the reltiohip etween gronomic vriles nd crop yield is only discussed for the herceous crops nd more in detil for the tril crried out in Grig where nitrogen ws pplied (on gint reed nd switchgrss). Biomss production for none of the herceous crops (in Csle or Grig) ws ffected y growing degree dys 10, s lredy shown y Heton et l. (2004) for miscnthus nd switchgrss. On the contrry, significnt reltiohip ws found etween wter input clculted from My to August nd miscnthus iomss production in oth loctio, nd in gint reed nd fertilized switchgrss in Grig (Tle 4). Coidering the period June Septemer, when gint reed nd miscnthus evpotrpirtion is highest (Trin et l., 2015), the reltiohip etween iomss production nd wter input ws significnt only for miscnthus in Csle. In the fine-textured soil of Grig, ll herceous crops were therefore ffected y wter input more in lte spring thn in Septemer, t the end of the growing seson. Miscnthus confirmed to hve stronger respoe to wter thn switchgrss s previously reported y Heton et l. (2004). Biomss production of gint reed ws ffected y wter vilility only in Grig; in this site nd on the sme experiment, the root system of the six studied crops ws chrcterized y Chimento & Amducci (2015) nd gint reed root iomss ws 2 times lower thn tht of switchgrss. It cn therefore e ssumed tht hving lower root iomss ws fctor in the higher seitivity of gint reed to wter vilility thn switchgrss. Switchgrss iomss production ws highly positively relted to wter vilility only when nitrogen fertiliztion occurred; the lck of respoe to wter vilility in the nonfertilized plots indictes tht nitrogen ws the limiting production fctor nd confirms the seitivity of switchgrss to nitrogen vilility (Tle 3) (Heton et l., 2004). The lck of significnt respoe of gint reed to nitrogen fertiliztion cn e relted to the trloction of nutrients from the leves nd the stems to the rhizomes, which tkes plce in gint reed nd miscnthus t the end of the growing seson (Heton et l., 2004; Cosentino et l., 2014). The trend of iomss production in the first 8 yers fter plnting, excluding the initil increse during estlishment, did not show ny significnt decline in either Csle or Grig for ny of the herceous crops (Figs 1 nd 2). Guder et l. (2012) lso reported miscnthus yield vriility etween yers ut did not found ny decline in 14-yer experiment in Germny. Our result is lso in greement with Lesur et l. (2013) who reported mximum yields of miscnthus reched fter 6 13 yers in long-term experiments in 16 loctio in Europe. As reported y Lesur et l. (2013), lso Clifton-Brown et l. (2007) nd Christin et l. (2008) found miscnthus yield decline fter yer 10 nd 11, respectively. Conversely, the result otined in the pre-

12 12 S. AMADUCCI et l. sent study in contrst to the dt reported y Arundle et l. (2014) for miscnthus production in the United Sttes, while it is in greement with most of the experiments crried out in Europe (Heton et l., 2004). As highlighted y Arundle et l. (2014), the yield decline of miscnthus fter the 5th - 6th yer of stnd ge might e coequence of the nutrient depletion reltive to the very high iomss yield otined in their tril, in contrst to the lower iomss yields reported in this study. To support the choice of the most suitle iomss crops for specific environment nd end use destintion, esides iomss yield, iomss qulity should lso e coidered. Dt on cellulose, hemicellulose, lignin, nd sh content presented in this study (Tle 5) re reltive to one yer (2013) nd one loction (Grig). The fct tht the composition ws nlyzed in one growing seson nd in one loction does not ffect the reliility of the results s reported y Arundle et l. (2015), who found tht there ws miniml vrition in the composition of miscnthus smples cross loction, smpling times, nd fertiliztion tretments. The composition vlues mesured in this study re in greement with those reported in literture for the herceous (Arundle et l., 2015; Mohmmed et l., 2015) nd for the woody crops (Snnigrhi et l., 2010). This study confirms tht the herceous crops hve lower quntity of lignin thn the woody crops nd higher sh content, in prticulr for gint reed nd switchgrss (Tle 5). These chrcteristics enle herceous crops to e suitle lso for iochemicl trformtio nd not only for thermochemicl conversion, s the woody crops (Monti et l., 2015). Among the herceous crops, miscnthus is the most suitle for neroic digestion nd second-genertion iofuel production due to its high cellulose nd hemicellulose content (Tle 5) (Monti et l., 2015). Energy lnce The low heting vlue (LHV) of the six crops coidered in this study vried etween crops nd it ws significntly higher in woody thn in herceous crops. This ws due to the iomss composition: Woody crops hd high lignin content tht hs higher LHV thn cellulose nd hemicellulose (Furln et l., 2013) nd lower sh content (Ciolkosz, 2010). The mesured LHV ws in line with dt reported in literture for oth herceous (Angelini et l., 2005, 2009; Mntineo et l., 2009) nd woody crops (McKendry, 2002; Nssi o Di Nsso et l., 2010; Dillen et l., 2013). In ddition, LHV of gint reed nd switchgrss ws not ffected y nitrogen fertiliztion; Ercoli et l. (1999) found the sme trend in miscnthus. The ppliction of nitrogen fertilizer represented 70% of totl energy costs in Grig, in ccordnce with results from Angelini et l. (2005) reltive to gint reed cultivtion in 6-yer experiment in centrl Itly. Similrly, irrigtion represented high percentge of totl energy costs (70%) in Csle, which is in greement with Mntineo et l. (2009) who reported tht irrigtion costs were the highest in cultivtion of gint reed, miscnthus, nd Cynr crdunculus in 5-yer experiment in southern Itly. The NEG of gint reed nd miscnthus in this study ws lower thn those reported y Angelini et l. (2009) in centrl Itly, nd the NEG of poplr ws lower thn tht reported y Nssi o Di Nsso et l. (2010) in 12- yer short-rottion coppice poplr in centrl Itly. These differences re minly due the lower iomss yields otined in our tril. For switchgrss, however, NEG vlues were similr to those found y Monti et l. (2009) who reported men nnul NEG of 200 GJ h 1 yr 1 for switchgrss fertilized with 200 kg h 1 yr 1 of nitrogen. In this study, the EROI of lck locust ws higher thn tht of the other woody crops (Fig. 5); in Grig for the lck of nitrogen fertiliztion nd the coequent lowest energy cost, in Csle, for the highest iomss yield. NEG of lck locust ws higher thn tht reported y Stolrski et l. (2015) for SRC plnttion of 4 yers in Polnd. Mnzone et l. (2015) reported NEG of 190 GJ h 1 yr 1 in lck locust 7-yer experiment in Csle, which is higher thn tht reported in this study in the sme environment (144 GJ h 1 yr 1 ), nd in Grig (167 GJ h 1 yr 1 ). This is coequence of the higher iomss production (10 Mg h 1 yr 1 ) nd higher LHV (19 MJ kg 1 ) reported y Mnzone et l. (2015) (verge iomss production 9Mgh 1 yr 1 nd LHV 18 MJ kg 1 in this study). EROI vlues clculted for Grig were in line with those found y other uthors for unfertilized gint reed (Angelini et l., 2005), fertilized gint reed nd switchgrss (Monti et l., 2009), nd woody crops (Djomo et l., 2011; Dillen et l., 2013). EROI of miscnthus (98) nd unfertilized switchgrss (82) grown in Grig ws higher thn those reported y Angelini et l. (2009) nd Monti et l. (2009), minly s coequence of different nitrogen inputs. In Csle, woody nd herceous crops hd EROI vlues lower thn those reported in literture (Angelini et l., 2009; Monti et l., 2009; Djomo et l., 2011; Dillen et l., 2013), ecuse of lower iomss production nd higher energy input due to the irrigtion. Across loctio, lck locust hd men EROI of 20 tht is in greement with tht reported y Mnzone et l. (2015). Severl uthors lso found tht lck locust hs high energy efficiency (Gonzlez-Grcı et l., 2011; Gonzlez-Grcı et l., 2012; Mnzone et l., 2015).