Bioresource Technology 102 (2011) 10286–10292

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Bioresource Technology

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Methane yield from switchgrass and reed canarygrass grown in Eastern Canada

Daniel Massé a,⇑, Yan Gilbert a, Philippe Savoie b, Gilles Bélanger b, Gaétan Parent b, Daniel Babineau c

a Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, 2000, College St., Sherbrooke, QC, Canada J1M 0C8b Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560, Hochelaga Blvd, Québec, QC, Canada G1V 2J3c Groupe EBI, 61, Montcalm St., Berthierville, QC, Canada J0K 1A0

a r t i c l e i n f o a b s t r a c t

Article history:Received 28 April 2011Received in revised form 16 August 2011Accepted 21 August 2011Available online 26 August 2011

Keywords:SwitchgrassReed canarygrassAnaerobic digestionFertilizationHarvest

0960-8524/$ - see front matter Crown Copyright � 2doi:10.1016/j.biortech.2011.08.087

⇑ Corresponding author. Tel.: +1 819 780 7128; faxE-mail addresses: daniel.masse@agr.gc.ca (D. M

(Y. Gilbert), philippe.savoie@agr.gc.ca (P. Savoi(G. Bélanger), gaetan.parent@agr.gc.ca (G. Parent),(D. Babineau).

Methane yields from silage made from switchgrass- and reed canarygrass-seeded plots with two N appli-cation rates and three harvest dates were assessed in Eastern Canada. The average specific methane yieldfrom reed canarygrass-seeded plots (0.187 NL CH4 g VS�1) was less than from switchgrass-seeded plots(0.212 NL CH4 g VS�1). Switchgrass did not establish well and made up only a small proportion of theDM yield. As a consequence, the average methane yield per hectare from reed canarygrass-seeded plots(1.37 GL CH4 ha�1) was significantly greater than switchgrass-seeded plots (0.91 GL CH4 ha�1). IncreasedN fertilization reduced specific methane yields but increased methane yield per hectare, primarilybecause of increased DM yield. Delaying harvest resulted in decreased methane yields per hectare andspecific methane yields, particularly for reed canarygrass. Further long-term research could help identifyimportant factors influencing methane yields from crops during a complete stand life cycle.

Crown Copyright � 2011 Published by Elsevier Ltd. All rights reserved.

1. Introduction

Biomass grown from numerous types of plant may become asustainable alternative to the use of fossil fuels and a more envi-ronmentally sound energy source in areas where surplus land isavailable. Various perennial grasses have been identified as prom-ising energy crops, such as Miscanthus (Miscanthus giganteus), reedcanarygrass (Phalaris arundinacea L.), and switchgrass (Panicumvirgatum L.). In general, C4 grasses have been recognized as morepromising energy crops than C3 grasses because of a more efficientphotosynthetic pathway (Lewandowski et al., 2003). The C4 cropsare well adapted to warm climates. However, the photosyntheticactivity of C4 grasses may be lower than C3 grasses under cool cli-matic conditions as found in the northeastern part of North Amer-ica. Under these conditions, some cool-season grasses (C3) mayproduce a higher yield of aerial biomass than warm-season grasses(C4) (Lewandowski et al., 2003).

Biomethanation of organic wastes and dedicated energy crops isbecoming a more common practice, mainly in Europe. Methanegenerated by anaerobic digestion of energy crops can be reportedin liters of gas either per unit of biomass (Chynoweth et al.,1993; Amon et al., 2007), or per unit of land area in the case wherethe crop is 100% of the substrate; the latter takes into account yieldvariations with plant species, cultivars, geographical location, and

011 Published by Elsevier Ltd. All r

: +1 819 564 5507.assé), yan.gilbert@agr.gc.ca

e), gilles.belanger@agr.gc.cababineaudaniel@hotmail.com

climatic conditions (Weiland, 2003; Amon et al., 2007). The harvestdate of energy crops can influence methane yield since the plantchemical composition varies with stage of development (Cherneyet al., 1986; Lehtomäki et al., 2008; Massé et al., 2010). Specificmethane yield per ton of dry matter (DM) has been observed to in-crease with delayed harvest in some grasses (Lehtomäki et al.,2008), and to decrease with other grasses and clover (Kaparajuet al., 2002; Prochnow et al., 2005; Massé et al., 2010). Fertilizationmay also influence methane yields through modification of theplant chemical composition and increased crop yield (Kline andBroersma, 1983; Lemus et al., 2008).

Some studies have investigated the methane potential of peren-nial crops produced in cool climatic areas such as Finland(Lehtomäki et al., 2008; Seppälä et al., 2009) or the northeasternpart of North America (Madakadze et al., 1999). However, littleinformation is available on the effect of harvest dates and nitrogenfertilization on methane yields of switchgrass and reed canarygrassgrown in northeastern North America. The objective of this projectwas to compare the effect of three harvest dates and two nitrogenfertilizer rates on the specific methane yield and the total methaneyield per hectare of two grass species.

2. Methods

2.1. Crop establishment, production and harvest

Switchgrass (P. virgatum L., cv. Cave-in-rock) and reed canary-grass (P. arundinacea L., cv. Bellevue) were seeded on 12th June2007 on clay soil in Lévis (46�470N, 71�070W), Québec, Canada. In

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D. Massé et al. / Bioresource Technology 102 (2011) 10286–10292 10287

the establishment year of 2007, all experimental units were treatedsimilarly. A nitrogen fertilizer was hand applied (40 kg N ha�1)prior to seeding and incorporated into the soil using a rotovator.The seed bed was compacted immediately after seeding with aBrillon™ forage crop seeder to ensure a better soil-seed contact.Atrazine (Atrex 480) was applied 2 days after seeding on theswitchgrass plots at a rate of 1.65 kg ha�1 using a hand-held porta-ble pesticide sprayer. The experimental treatments of nitrogen fer-tilization and harvest dates were applied in 2008 and 2009.Theexperimental design was a split–split plot with harvest dates asmain plots, species as sub-plots, and rates of nitrogen fertilizationas sub–sub-plots with three replicates. The two rates of nitrogenfertilization were 40 and 160 kg N ha�1 applied as calcium ammo-nium nitrate (27-0-0) at the beginning of May of both years. Theharvest dates were mid-summer (30 July 2008; 28 July 2009), latesummer (4 September 2008; 1 September 2009), and early fall (6October 2008; 15 October 2009). In 2008, accumulated growingdegree days (GDD; 5 oC) and rainfall from April 1st were respec-tively 990 GDD and 564 mm on July 30th, 1443 GDD and702 mm on September 4th, and 1670 GDD and 855 mm on October6th. In 2009, accumulated GDD and rainfall were respectively917 GDD and 494 mm on July 28th, 1406 GDD and 580 mm onSeptember 1st, and 1685 GDD and 750 mm on October 15th.

Crop yields were determined by harvesting an area of 4.55 m2

(0.91 � 5.0 m) in each plot (2 � 5 m) using a self-propelled flail for-age harvester (Carter MGF., Inc., Brookston, IN, USA) adjusted to a5 cm cutting height. A fresh sample of approximately 500 g was ta-ken from each plot, weighed, and dried at 55 �C in a forced-draftoven for 3 d for DM determination. Samples were afterwardsground using a Wiley mill (Standard model 3, Arthur H. ThomasCo., Philadelphia, PA) equipped with a 1 mm screen. Samples werestored at room temperature before further laboratory analyses.

2.2. Silage procedure

Samples of 10 kg (wet basis) were also collected from each plot,and they were air-dried in a greenhouse until they reached a DMcontent of 35%. Samples were then double-chopped (25–50 mmlength) using a stationary straw chopper prior to ensiling. A silagepreservative solution [Enersile 5™ (Lactobacillus plantarum)] wassprayed on the material at a rate of 1 g t�1 (wet basis). Approxi-mately 5 kg of chopped forage was then bagged in 6-mil plasticbags enclosed in plastic buckets. Air was vacuumed from silagebags using a shop-grade vacuum cleaner. Silage bags were thensealed using plastic zip-ties. The buckets were covered with plasticlids and airlocked with a rubber grommet and left at room temper-ature for 6 weeks prior to opening and silage characterization. Si-lage samples were then frozen at �20 �C until the beginning ofthe laboratory assay.

2.3. Laboratory assay description

Inocula for anaerobic digestion were collected at the end of thedigestion cycle from a mesophilic (35 oC) anaerobic sequentialbatch reactor fed with swine manure at an organic loading rateof 1.5 g of total chemical oxygen demand (TCOD) L�1 of initialsludge volume per day. Prior to each assay, physico-chemical char-acteristics of the inoculum were determined (Table 1). Each biore-actor (30-L barrel) was filled with 20 L of the inoculating sludgeand 500 g of thawed switchgrass or reed canarygrass silage (wetbasis). The methane yield of each sample was assessed in duplicateusing a pair of bioreactors. Sludge and silage samples were mixedthree times per day by recirculating the mixed liquor from the bot-tom to the top of the bioreactors during 1 min using a manual dia-phragm pump at a rate of 3 L min�1 (Rintoul’s Hand Pumps,Tobermory, ON, Canada). Silage samples were digested

anaerobically under mesophilic conditions (35 �C) in a temperaturecontrolled room.

2.4. Biogas measurement

Wet tip gas meters were used to monitor daily biogas produc-tion. Biogas components (CH4, H2S, CO2) were determined weeklyusing a Hach Carle 400 AGC gas chromatograph (Chandler Engi-neering, Houston, TX) at 85 �C with a helium gas flow rate of30 mL min�1. Calibration was performed weekly with a standardgas (27.3% CO2, 1.01% N2, 71.16% CH4, 0.53% H2S).

A digestion assay was considered over when less than 1%change in the total cumulative volume of biogas was observed overa week and the concentration of volatile fatty acids (VFA) de-creased to negligible levels (<100 mg L�1). Total cumulative meth-ane yield was then established at the end of the digestion assay.Specific methane yields were calculated as the ratio of total meth-ane yield over the mass of volatile solids (VS) added to the reactor.Methane production is reported in normalized liter per gram ofvolatile solids of energy crop [NL CH4 (g VS)�1], i.e. the volume ofmethane production was standardized on specific temperatureand pressure conditions (273 K; 1 atm). Methane production fromthe inoculum alone was measured (varying from 2.1% to 17.1% oftotal methane production, data not shown) and subtracted fromthe methane production as a background noise in digested cropbioreactors.

2.5. Analytical methods

Liquid samples were collected from each bioreactor and ana-lyzed weekly for pH and volatile fatty acids (VFA). Total and solu-ble chemical oxygen demand (TCOD and SCOD), and solid contentwere determined before and after each batch treatment. TCOD,SCOD, TS (total solids), VS, and pH were determined using standardmethods (APHA, 1992). The VFA concentrations were measuredusing a Perkin Elmer gas chromatograph model 8310 (Perkin El-mer, Waltham, Mass.), equipped with a DB-FFAP high resolutioncolumn.

2.6. Statistical analysis

Data were analyzed according to a split–split plot design usingthe mixed procedure with harvest dates as main plot, species assub-plot, nitrogen rate as sub–sub-plot and year as a repeatedmeasure using SAS, Release 9.0 (SAS Institute Inc., Cary, NC). Onlyfirst order interactions were then found significant for some vari-ables. Because of the important presence of weeds in switch-grass-seeded plots, a split plot analysis was also performed foreach crop with harvest date as the main plot and nitrogen rate assub-plot. Significance was set at P < 0.05.

3. Results and discussion

3.1. Chemical composition of inoculum and silages

Inocula contained low levels of VFA compared to switchgrassand reed canarygrass silages (Table 1). The inocula had an averagepH of 8.1 and a relatively low solid content (2.8% TS; 1.4% VS). Insilage samples, acetic acid was the predominant VFA over the2 years of the experiment, with concentrations ranging from 204to 12,474 mg L�1 for switchgrass-seeded plots and 304–4394 mg L�1 for reed canarygrass-seeded plots. Lower VFA concen-trations were measured in samples harvested in early fall 2008 andmid-summer 2009. Meanwhile, the pH of all silages ranged from4.0 to 4.6. The mixed liquor pH was stable at about 8.0 during

Table 1Chemical compositiona of inoculum and ensiled switchgrass and reed canarygrass used for anaerobic digestion.

Species Year Harvest date Fertilization (kg N ha�1) SCOD (g O2 L�1) TCOD (g O2 L�1) pH TS (%) VS (%) ACET (mg L�1) PROP (mg L�1) ISOB (mg L�1) BUTY (mg L�1)

Inoculum – – 5.5 (1.1) 27 (3) 8.1 (0.1) 2.8 (0.6) 1.4 (0.2) 74 (28) 55 (76) 2 (4) 8 (9)

Switchgrass 2008 Mid-summer 40 56 (14) 415 (71) NA 40 (6) 33 (7) 6348 (1382) 81 (115) 0 (0) 43 (61)160 43 (6) 442 (60) NA 35 (4) 32 (4) 5704 (1853) 72 (102) 0 (0) 27 (39)

Late summer 40 49 (1) 434 (73) 4.0 (0.1) 34 (4) 31 (5) 2410 (1072) 60 (1) 0 (0) 49 (69)160 52 (2) 440 (50) 4.1 (0.1) 37 (4) 34 (4) 2611 (1338) 0 (0) 0 (0) 31 (44)

Early fall 40 55 (7) 496 (24) 4.1 (0.0) 40 (0)c 37 (0) 204 (111) 3 (4) 0 (0) 0 (0)160 51 (7) 542 (12) 4.1 (0.0) 43 (1) 41 (0) 246 (127) 2 (3) 0 (0) 0 (0)

2009 Mid-summer 40 85 (7) 504 (14) 4.4 (0.0)c 41 (4) 36 (4) 631 (165) 11 (1) 3 (5) 5 (7)160 68 (1) 389 (29) 4.3 (0.2) 32 (0) 29 (0) 633 (224) 12 (1) 3 (5) 6 (8)

Late summer 40 93 (-)b 602 (-) 4.6 (-) 46 (-) 41 (-) 12474 (-) 115 (-) 0 (-) 217 (-)160 96 (-) 694 (-) 4.6 (-) 59 (-) 53 (-) 7892 (-) 101 (-) 0 (-) 201 (-)

Early fall 40 NAd 548 (99) 4.0 (0.1) 45 (8) 42 (8) 2863 (1061) 58 (1) 199 (20) 153 (22)160 NA 608 (15) 4.0 (0.1) 50 (2) 47 (2) 2300 (531) 53 (11) 213 (61) 125 (28)

Reed canarygrass 2008 Mid-summer 40 81 (16) 711 (110) NA 58 (8) 52 (7) 2589 (1349) 161 (51) 0 (0) 253 (55)160 73 (22) 591 (7) NA 47 (5) 42 (5) 3365 (265) 231 (98) 0 (0) 157 (59)

Late summer 40 79 (11) 500 (20) 4.1 (0.0) 42 (0) 38 (1) 1890 (187) 640 (83) 0 (0) 71 (101)160 72 (14) 484 (9) 4.1 (0.0) 40 (1) 36 (1) 3265 (943) 548 (78) 0 (0) 0 (0)

Early fall 40 75 (2) 543 (32) 4.1 (0.1) 45 (1) 41 (1) 407(109) 66 (5) 0 (0) 0 (0)160 71 (7) 530 (13) 4.0 (0.0) 44 (1) 40 (0) 385 (131) 50 (8) 0 (0) 0 (0)

2009 Mid-summer 40 86 (11) 581 (7) 4.0 (0.0) 43 (0) 42 (4) 304 (1) 13 (2) 4 (5) 5 (8)160 81 (3) 559 (1) 4.0 (0.1) 46 (0) 41 (1) 401 (76) 19 (12) 7 (10) 12 (17)

Late summer 40 108 (6) 770 (76) 4.1 (0.1) 62 (2) 55 (1) 4143 (719) 120 (53) 47 (67) 130 (127)160 105 (2) 735 (46) 4.2 (0.0) 60 (1) 53 (1) 4394 (1554) 478 (511) 27 (39) 188 (52)

Early fall 40 NA 628 (34) 4.0 (0.2) 53 (3) 47 (3) 1879 (178) 41 (5) 98 (11) 113 (38)160 NA 599 (35) 3.9 (0.2) 52 (0) 46 (0) 2726 (893) 49 (5) 188 (11) 205 (102)

a ACET: acetic acid; PROP: propionic acid; ISOB: isobutyric acid; BUTY: butyric acid. Average and standard deviation in parenthesis from 116 samples for the inocula and two samples for the ensiled material.b Only one sample was analyzed.c Standard deviations were rounded to the same number of decimals as the means.d NA: not analyzed.

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digestion for all batch assays. Average silage total solids contentranged from 32% to 59% for the switchgrass-seeded plots and40% to 62% for the reed canarygrass-seeded plots. The TS weremostly composed of VS, with proportions ranging from 86% to94% of TS for both species.

3.2. Crop yield and botanical composition

The establishment of reed canarygrass was successful with yieldsfrom 6.0 to 10.7 t DM ha�1 depending on year, harvest date and fer-tilizer level. A visual estimation of crop composition in 2009 indi-cated that reed canarygrass contributed to more than 93% of theDM yield on all three harvest dates and for both N rates. The estab-lishment of switchgrass, however, was not as successful with yieldsfrom 3.5 to 7.6 t DM ha�1. In 2009 visual observations, switchgrasscontributed only 14% of the DM yield in mid-summer and 2% in latesummer. In early fall, this contribution was 28% with 40 kg N ha�1

and 68% with 160 kg N ha�1. Weed competition, especially duringthe establishment year, is often a major impediment to the produc-tion of switchgrass (Lewandowski et al., 2003; Parrish and Fike,2005). No herbicides were used after the emergence for two reasons:(1) producing biomass at a low cost by limiting the use of inputs and(2) post-emerging applications of herbicides are not usually used forthe establishment of perennial grasses in Eastern Canada. This strat-egy worked well for reed canary grass but not for switchgrass. Be-cause of the relatively low contribution of switchgrass to DM yieldin those first two production years, crops will be more appropriatelyreferred to switchgrass-seeded plots and reed canarygrass-seededplots throughout the manuscript. Moreover, because of the possibleimpact of weeds on the statistical analysis related to

Table 2Crop yield, specific methane yield, and methane yield per hectare of switchgrass and reedanalyses.

Species Year Harvest date Fertilization(kg N ha�1)

Crop yie(t DM h

Switchgrass 2008 Mid-summer 40 4.12160 6.27

Late summer 40 4.01160 6.47

Early fall 40 3.54160 5.47

2009 Mid-summer 40 3.68160 4.18

Late summer 40 3.58160 3.54

Early fall 40 5.17160 7.57

Reed canarygrass 2008 Mid-summer 40 8.17160 10.70

Late summer 40 8.22160 9.15

Early fall 40 7.50160 8.76

2009 Mid-summer 40 6.43160 9.86

Late summer 40 6.09160 9.31

Early fall 40 6.03160 7.66

Factors F valueHarvest period 0.2Crop 75.5Nitrogen rate 35.3Harvest � Crop 2.9Harvest � N rate 0.1Crop � N rate 0.5Harvest � Crop � N rate 1.2

* The factor or combination of factors has a significant impact.

switchgrass-seeded plots, reed canarygrass was also analyzed aloneusing a split plot design with year as a repeated measure.

Nitrogen rates and crop species significantly affected crop yields,without significant interaction (P > 0.05) (Table 2). The average DMyield of the reed canarygrass-seeded plots (8.2 t DM ha�1) wasgreater than that of the switchgrass-seeded plots (4.8 t DM ha�1).The average DM yield of the reed canarygrass-seeded plots increasedfrom an average of 7.1 t DM ha�1 with 40 kg N ha�1 to 9.2 t DM ha�1

with 160 kg N ha�1. The average DM yield of switchgrass-seeded plots also responded positively to increasing N rate from4.0 t DM ha�1 with 40 kg N ha�1 to 5.6 t DM ha�1 with160 kg N ha�1.

Crop yields in 2008 and 2009 (3.5–7.6 t DM ha�1) of theswitchgrass-seeded plots established in 2007 were considerablyless than yields observed in 2007 (8.9–12.6 t DM ha�1) forswitchgrass plots established in 2002 and 2006 in anotherexperimental field in the same geographical area, with compara-ble soil and climatic conditions and without fertilizer (Masséet al., 2010). According to Di Virgilio et al. (2007), switchgrassDM yield under similar environmental conditions was found torange from less than 5 to more than 25 t DM ha�1, even inexperimental plots where plants were hand harvested and soilcharacteristics were fairly constant. The DM yields of the switch-grass-seeded plots were also generally less than those publishedin previous studies conducted under a different set of soil andclimate conditions. Heaton et al. (2004) estimated an averageswitchgrass yield of 10.3 t DM ha�1 in a meta-analysis of pub-lished yields of various varieties established for at least 3 years.Yields of 8.7–16.4 t DM ha�1 for switchgrass (Cave-in-Rock) har-vested once (early November) across five states in the uppersoutheastern USA were reported (Fike et al., 2006). Perrin et al.

canarygrass grown with two N rates and harvested on different dates and statistical

lda�1)

Specific methaneyield (NL CH4 g VS�1)

Methane yield perhectare (�106 L CH4 ha�1)

0.243 0.890.238 1.350.252 0.910.225 1.320.199 0.660.184 0.950.198 0.640.252 0.950.204 0.610.188 0.600.186 0.880.169 1.200.205 1.520.199 1.870.201 1.480.190 1.550.202 1.370.168 1.340.211 1.310.191 1.690.183 1.000.163 1.360.170 0.910.155 1.05

Pr > F F value Pr > F F value Pr > F0.83 22.2 0.007* 4.9 0.080.0001* 34.4 0.001* 46.6 0.0005*

<0.0001* 6.2 0.02* 17.8 0.0004*

0.13 3.8 0.09 3.6 0.090.89 3.4 0.05* 0.9 0.410.49 1.4 0.25 0.6 0.450.33 2.2 0.13 0.4 0.69

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(2008) obtained similar annualized yields (2.5–9.0 t DM ha�1) tothe current study in a 5-year investigation performed inMidwestern USA. McLaughlin and Kszos (2005) reported thatswitchgrass reached only 33–66% of its maximum potential yieldduring the first 2 years following seeding and that maximumpotential yield was reached in the third year because a lot ofenergy is required to develop a strong root system. Accordingto McLaughlin (1997), one of the management issues with thegreatest impact on the utilization of switchgrass as an energycrop is the establishment. The poor establishment of switchgrassin our study most likely explains the low yield compared withthose reported in other studies.

Crop yield of the reed canarygrass-seeded plots (6.0–10.7 t DM ha�1) was in the same range than those previouslypublished. Reported DM yields of reed canarygrass were up to12.6 t DM ha�1 in the upper Midwestern USA (Tahir et al., 2010),up to 8.0 t DM ha�1 in British Columbia, Canada (Kline and Bro-ersma, 1983), from 6.7 to 13.5 t DM ha�1 in Indiana, USA (Cherneyet al., 1986), and 2.9 to 13.7 t DM ha�1 in Finland under variousfertilization strategies (Seppälä et al., 2009).

3.3. Specific methane yields

All three factors (harvest dates, species and nitrogen rates) signif-icantly affected the specific methane yield (Table 2). Lower averagespecific methane yields were obtained from the reed canarygrass-seeded plots (0.187 NL CH4 g VS�1) as compared to the switch-grass-seeded plots (0.212 NL CH4 g VS�1). A lower specific methaneyield is generally due a lower digestibility. The compact arrange-ment of reed canarygrass tissues negatively affects its digestibility(Grabber and Allinson, 1992), which explains why it is usually notconsidered a good forage species (Geber, 2002). Relatively pureswitchgrass harvested in 2007 (composition was not evaluated butclose to 100%) had specific methane yields of 0.289, 0.235 and0.207 L CH4 g VS�1 in mid-summer, late summer and early fall,respectively (Massé et al., 2010). Weeds would have a reducing ef-fect on methane digestion since the switchgrass-seeded plots har-vested in 2008 and 2009 had a specific methane yield averagedover the 2 years of 0.233, 0.217 and 0.185 L CH4 g VS�1 in mid-sum-mer, late summer and early fall, respectively.

The specific methane yield decreased from mid-summer toearly fall from 0.202 to 0.174 NL CH4 g VS�1 in the reed canary-grass-seeded plots and from 0.233 to 0.185 NL CH4 g VS�1 in theswitchgrass-seeded plots. Dien et al. (2006) found that the pro-tein concentration of crops decreased with maturity while ligninconcentration increased, whereas the gross energy content deter-mined by calorimetry was not influenced. This suggests thatgross energy content is not influenced by crop maturity, but itbecomes less available for biological degradation as the plantmatures due to an increase in plant non-digestible matter. Sev-eral studies also reported decreasing specific methane yieldswith plant development for reed canarygrass (Geber, 2002;Seppälä et al., 2009) and switchgrass (Massé et al., 2010). Thedigestibility of reed canarygrass at the early stages of develop-ment is considered to be similar to fodder grasses at a similarstage of maturity, but it decreases rapidly with maturity (Geber,2002; Seppälä et al., 2009).

Increasing N fertilization decreased the specific methane yieldof reed canarygrass from 0.195 NL CH4 g VS�1 with 40 kg N ha�1

to 0.178 NL CH4 g VS�1 with 160 kg N ha�1, and of switchgrass-seeded plots from 0.214 NL CH4 g VS�1 with 40 kg N ha�1 to0.209 NL CH4 g VS�1 with 160 kg N ha�1. The lower specific meth-ane yield with increasing N rate is possibly related to changes inchemical composition. Increasing N fertilization can have a nega-tive effect on digestibility (Bélanger and McQueen, 1998) and apositive effect on lignin concentration (Cherney et al., 1986) and

nitrogen concentration (Cherney et al., 1986; Kätterer et al.,1998). Overall, if the objective is to maximize methane output byunit crop area, nitrogen fertilization has a positive effect becausespecific methane yield is decreased by 9% (Reed canarygrass-seeded plots) or 2% (Switchgrass-seeded plots) while biomass yieldis increased by 31% or 39%, respectively. Since experimental plotswere not necessarily harvested at the same developmental stages,because of higher growing rates for higher fertilization rates, it isnot clear whether the difference in composition was due to nitro-gen, plant maturity or both factors. These modifications in plantcomposition might have influenced its specific methane yield. Fur-ther analyses would help to determine the relationship betweennitrogen fertilization, crop chemical composition, and specificmethane yield. A significant interacting effect of N rate and harvestperiod on the specific methane yields was observed (Table 2),meaning that the nitrogen fertilization effect was not the samefor the various harvest periods. However, this interaction wasweak as suggested by the low F value (3.4). A split plot analysisof each crop showed that this interaction was due to switch-grass-seeded plots (F = 3.87; P = 0.05), in which the botanical com-position varied over time. No interaction was observed between Nrates and harvest periods for reed canarygrass-seeded plots(F = 0.35; P = 0.71).

Specific methane yields from switchgrass- and reed canary-grass-seeded plots ranged from 0.16 to 0.25 NL CH4 g�1 VS (Ta-ble 2). These values are within the lower range of reportedspecific methane yields of other grass species and annual fieldcrops. Chynoweth et al. (1993) found specific methane yieldsranging from 0.16 to 0.39 NL CH4 g�1 VS for various grass speciesgrown under different conditions in the United States. Seppäläet al. (2009) reported values ranging from 0.29 to0.39 NL CH4 g�1 VS for anaerobically digested field-dried cocks-foot (Dactylis glomerata L.), tall fescue (Festuca arundinaceaeSchreb.), and timothy (Phleum pratense L.) grown in Finlandand harvested at various stages of development. Higher specificmethane yields were also reported for grass silage, with valuesranging from 0.26 to 0.50 NL CH4 g�1 VS (Chynoweth et al.,1993; Seppälä et al., 2008; Koch et al., 2009). Again, the probablebias due to the presence of weeds in 2008 and 2009 for switch-grass-seeded plots must be highlighted.

In a previous study, Massé et al. (2010) obtained slightlyhigher specific methane yields from ensiled switchgrass grownin Eastern Canada, with values ranging from 0.19 to0.31 NL CH4 g�1 VS. Crop composition and yield are influencedprimarily by climatic conditions, the number of years since theestablishment, micro-environment, and soil fertility. These fac-tors can cause annual and geographical variations in forage qual-ity even when herbage is harvested at the same stage ofdevelopment (Buxton, 1996). Further research and analyses areneeded to better understand plant chemical composition vari-ability and its impact on the specific methane yield.

In the present experiment, low specific methane yields were ob-served for reed canarygrass silages (0.16–0.21 NL CH4 g�1 VS) whencompared with values reported in the literature for the same crop.Specific methane yields ranging from 0.25 to 0.42 NL CH4 g�1 VSwere reported for reed canarygrass grown in Finland and obtainedunder different fertilization and harvesting strategies (Lehtomäkiet al., 2008; Seppälä et al., 2009). This discrepancy is probablydue to different plant chemical compositions. Several factors influ-ences crop chemical composition including forage genotype, matu-rity, and growth environment, as well as interaction among thesefactors. Sahramaa and Jauhiainen (2003) reported significant dif-ferences among cultivars regarding plant development, plantheight and stem elongation, whereas it was reported that somereed canarygrass cultivars were similar in anatomical structure,digestibility, and fiber composition (Grabber and Allinson, 1992).

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3.4. Methane yield per hectare

Crop yield and specific methane yield were used to calculate thequantity of methane produced per unit area. Crop species and N ratesignificantly affected the methane yield per hectare but the harvestdate has no significant effect (Table 2). The reed canarygrass-seededplots yielded on average more methane (1.37 GL CH4 ha�1) than theswitchgrass-seeded plots (0.91 GL CH4 ha�1). However, these valuesare less than previously reported methane yields. Lehtomäki et al.(2008) found a potential volume of 3.8–4.2 GL CH4 ha�1 yr�1 for reedcanarygrass in the boreal growing conditions of Finland, with com-parable crop yield and higher specific methane yield. Preliminary re-sults reported by Katsvairo and Pillammanappallil (2007) showed aproduction of 2.3–5.4 GL CH4 ha�1 yr�1 for different switchgrasscultivars grown in Florida. Massé et al. (2010) reported methaneyields per hectare (1.8–2.8 GL CH4 ha�1 yr�1) for switchgrass grownin Eastern Canada lower than those in Florida, but still higher thanthose measured in the current study. Low methane yields in the cur-rent study were primarily due to low specific methane yields in boththe switchgrass- and reed canarygrass-seeded plots, and the lowcrop yield in the switchgrass-seeded plots.

Increasing N fertilization significantly increased the methaneyield per hectare of both species (Table 2), from an average of0.8 GL CH4 ha�1 with 40 kg N ha�1 to 1.1 GL CH4 ha�1 with160 kg N ha�1 for the switchgrass-seeded plots, and from1.3 GL CH4 ha�1 with 40 kg N ha�1 to 1.5 GL CH4 ha�1 with160 kg N ha�1 for the reed canarygrass-seeded plots. Althoughthe effect of the harvest date (P = 0.08) and the interaction betweenharvest date and species (P = 0.09) were not statistically signifi-cant, a more detailed analysis suggests that the effect of harvesttime was greater in the reed canarygrass-seeded plots than inthe switchgrass-seeded plots. The split plot analysis of reedcanarygrass alone shows a clear impact of the harvest period onthe production of methane per unit area (F = 16.94; P = 0.01), withmid-summer harvest showing the highest production(1.6 GL CH4 ha�1), averaged on both N rates. The absence of an ef-fect of harvest date in the switchgrass-seeded plots might be dueto the variable presence of weeds. Massé et al. (2010) showed,for a well established experimental plot, that switchgrass methaneyields per hectare significantly decreased with plant maturity.Long term studies are required to determine the potential formethane yield per hectare with switchgrass and reed canarygrassduring a complete stand life and for well implanted crops.

4. Conclusion

Reed canarygrass-seeded plots yielded more methane per hect-are than the weed-infested switchgrass-seeded plots. The largepresence of weeds in the experimental plots confirms the difficultyin establishing switchgrass in Eastern Canada, and precludes anyconclusion on the potential of switchgrass for methane productionin the first 2 years following establishment. More N fertilizationsignificantly increased the methane yield per hectare, whereasthe production of methane per unit area decreased when delayingharvest. Further long-term research could help identify importantfactors influencing methane yield per hectare of those two speciesover several years.

Acknowledgements

Authors are grateful to Danielle Mongrain, Mario Laterrière, andthe employees of AAFC Chapais Research Farm for theircollaboration and help in harvesting and silage making. They thankDenis Deslauriers who provided technical expertise for the anaer-obic digestion experiments. This study was funded by Agriculture

and Agri-Food Canada through a matching investment initiativeprogram.

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