Carbon dynamics_Switchgrass

Carbon dynamics in a biochar-amended loamy
soil under switchgrass
Suzanne E. Allaire1
, Benjamin Baril1
, Anne Vanasse2
, Se´bastien F. Lange3
,
John MacKay4
, and Donald L. Smith5
1
Centre de Recherche sur les Mate´riaux Renouvelables, Pavillon 2480 Hochelaga, Universite´ Laval, Que´bec,
Canada G1V 0A6 (e-mail: suzanne.allaire@fsaa.ulaval.ca); 2
De´partement de phytologie, Pavillon Comtois, 2425,
rue de l’Agriculture, Universite´ Laval, Que´bec, Canada G1V 0A6; 3
Centre de Recherche en Horticulture, 2480
Hochelaga, Universite´ Laval, Que´bec, Canada G1V 0A6; 4
Centre d’e´tude de la foreˆt, De´partement des sciences
du bois et de la foreˆt, 1030 rue de la Me´decine, Universite´ Laval, Que´bec, Canada G1V 0A6; and 5
Department
of Plant Science, McGill University, Macdonald Campus, 21111 Lakeshore Road, Ste-Anne-de-Bellevue,
Que´bec, Canada H9X 3V9.
Received 7 May 2014, accepted 22 November 2014. Published on the web 28 November 2014.
Allaire, S. E., Baril, B., Vanasse, A., Lange, S. F., MacKay, J. and Smith, D. L. 2015. Carbon dynamics in a biochar-amended
loamy soil under switchgrass. Can. J. Soil Sci. 95: 1Á13. The environmental impacts of switchgrass production for
bioenergy could be reduced through the use of biofertilizers rather than mineral fertilizers and through soil amendment with
biochar. The objectives of this study were: (1) to assess the impact of biochar and biofertilizer on switchgrass (Panicum
virgatum L.) yield and parameters related to carbon dynamics, (2) to correlate carbon parameters with soil physico-chemical
properties over the first two growing seasons, and (3) to develop a C budget. A complete randomized block design was
installed in a sandy loam with split plot treatment design, the main plots receiving 0 or 10 t ha(1
of biochar and the sub(
plots receiving no fertilization, mineral N fertilization, or biofertilizers. Biofertilizers had no significant impact on plant and
soil. Biochar increased yield relative to the control treatment by about 10% during the first year and root biomass by up to
50% after 2 yr (P0.1). Mineral N fertilization also increased yield resulting in higher plant C sequestration after 2 yr.
Biochar increased CO2 soil concentration (CO2-soil) by up to 50% but its impact on CO2 emission flux (CO2-flux) changed
over time. The impact of mineral fertilization on CO2-flux also varied with time. Soil CO2 dynamics was mostly influenced by
temperature, N and water content. Biochar and fertilization treatments showed interactions on some plant and soil
parameters. The highest C sequestration budget was obtained with a combination of biochar and mineral N fertilization.
The equivalent of about one-third of the increase in soil C content associated with biochar treatments was respired away by
soil microorganisms. Nearly one-fourth of C sequestered by plants remained in or at the soil surface (root and crop
residues).
Key words: Panicum virgatum L., carbon sequestration, CO2 emissions, soil carbon, soil gas concentration
Allaire, S. E., Baril, B., Vanasse, A., Lange, S. F., MacKay, J. et Smith, D. L. 2015. Dynamique du carbone dans une production
de panic e´ rige´ amende´ e de biochar sur sol loameux. Can. J. Soil Sci. 95: 1Á13. Le biochar et les bioengrais pourraient aider a`
re´ duire les impacts environnementaux associe´ s a` la production de panic e´ rige´ pour la bioe´ nergie. Cette e´ tude vise a` (1)
quantifier l’impact du biochar et d’un bioengrais sur le rendement du panic e´ rige´ (Panicum virgatum L.), la se´ questration
de carbone, le CO2 dans le sol (CO2-soil) et son e´ mission (CO2-flux); (2) corre´ ler les parame` tres de carbone avec les proprie´ te´ s du
sol et (3) e´ valuer le budget de carbone. Un plan expe´ rimental en tiroirs a e´ te´ instaure´ sur un loam. Les parcelles principales ont
rec¸ u 0 ou 10 t ha(1
de biochar, les parcelles secondaires ont rec¸ u diffe´ rents traitements d’engrais. Les bioengrais n’ont pas
influence´ les plantes et le sol. Le biochar a favorise´ une augmentation de rendement de 10% a` la premie` re saison et la biomasse
racinaire de 50% apre` s deux saisons. La fertilisation mine´ rale a augmente´ les rendements apre` s deux saisons. Le CO2-soil e´ tait
jusqu’a` 50% plus e´ leve´ sous le biochar. Le CO2-flux n’e´ tait pas toujours influence´ par le biochar, mais a augmente´ avec la
fertilisation mine´ rale. La tempe´ rature, la teneur en azote et l’eau du sol ont influence´ la dynamique du carbone. Le meilleur
budget de carbone a e´ te´ obtenu avec l’utilisation combine´ e du biochar et de la fertilisation azote´ e mine´ rale. L’e´ quivalent du
tiers de l’augmentation de la teneur en carbone du sol associe´ e au biochar a e´ te´ re´ e´ mis par le sol. Environ le ¼ du carbone
se´ questre´ par les plantes est reste´ dans le sol (plantes et sol).
Mots cle´s: Panicum virgatum L., se´ questration du carbone, e´ missions de CO2, carbone du sol,
concentration de gaz du sol
The general goal of producing biomass for energy is to
decrease overall greenhouse gas (GHG) emissions from
fossil fuel consumption without additional deleterious
effects on the environment. The major biofuel produced
in the United States and Canada has been starch-based
Abbreviations: B, biochar treatment; C-soil, carbon content in
soil; CO2-soil, carbon dioxide concentration in soil; CO2-flux, carbon
dioxide surface emission fluxes; CV, coefficient of variation; GHG,
greenhouse gas; NB, treatment without biochar; N-Bacteria,
bacterial fertilization treatment; N-Full, mineral N fertilization
treatment representing the full recommended dosage;
uv, volumetric water content
Can. J. Soil Sci. (2015) 95: 1Á13 doi:10.4141/CJSS-2014-042 1
Can.J.Soil.Sci.Downloadedfrompubs.aic.cabyUniversityofLavalon04/20/15
Forpersonaluseonly.

ethanol. About 30% of the entire corn production is
sold for ethanol production in the United States com-
pared with about 10% in Quebec (Fe´ de´ ration des
producteurs de cultures commerciales du Que´ bec
2014). Switchgrass (Panicum virgatum L.) has been
proposed as a biofuel crop for mitigating climate change
(Zan et al. 1997). It has a good potential for C
sequestration with its deep root system, efficient water-
use (Ma et al. 2000), relatively low nutrient requirement
and good biomass production (Bransby et al. 1998).
Davis et al. (2011) showed that the amount of fuel per
land area would be greater with switchgrass than with
corn. Switchgrass is a C4 perennial grass species native
to North America. It offers the advantage of being
highly efficient in capturing sunlight energy as it gives
up to 160 GJ ha(1
compared with 110 GJ ha(1
for corn
and 45 GJ ha(1
for soybean (Samson et al. 2008).
However, it has been pointed out that energy produc-
tion and C budgets are inefficient for bioenergy crop
production when considering the entire production
cycle including: GHG emissions, the loss of soil carbon,
the energy for producing fertilizer, and the energy for
transporting the crop to the power plant and for
discarding the residues. For switchgrass to become a
valuable source of bioenergy, energy consumption and
GHG emissions related to its production must be re-
duced, and along with overall environmental impacts.
Biochar application to soil has been suggested for
plant production to improve overall environmental
impact of agriculture and to sequester C (Lehmann
et al. 2006; Sohi et al. 2010; Jeffrey et al. 2011). Biochar
is a product of pyrolysis of any matter containing C
(e.g., organic matter, tires, plastics) under temperature
ranging from 350 to 8008C without or with very low
oxygen concentration (Laird et al. 2009; Allaire and
Lange 2013). It can be used as a soil amendment and has
the advantage of recycling crop residues. Biochar can
increase soil C content, including a large portion that
remains in the soil for hundreds of years (Woolf 2008) as
well as soluble and slowly degradable pools (Lehmann
et al. 2006). It also has the potential to reduce soil
density and protect against compaction (Sohi et al. 2010;
Verheijen et al. 2010), both of which decrease energy
needs for crop production. It has been reported to
improve water budget, crop yield, N and C cycles, and
reduce overall GHG emissions (Woolf 2008), all of
which reduce its environmental impact. Biochar is
viewed as a good soil amendment not only because of
its ability to improve soil physico-chemical properties,
but also because it seems to favor root and microbial
activities (Lehmann et al. 2006). Researchers reported
that biochar had larger impacts on soil and plants under
poor soil conditions and in dry climates, than in well-
structured soils under sufficient rainfall (Verheijen et al.
2010). The importance of biochar varies with soils,
climate, and crops (Sohi et al. 2010; Jeffrey et al. 2011),
but its impact on soil under switchgrass production in
Quebec, a cold humid climate, is not well known.
Since biochars typically contain a low level of N,
they cannot be used as a source of N for plants. Besides
mineral fertilization, biofertilizers such as atmospheric
N fixing rhizobacteria (Fuentes-Ramirez et al. 2006)
may offer an interesting environmental alternative.
They seem to improve plant productivity (Lal and
Tabacchioni 2009), favor C sequestration (Sohi et al.
2010), and require little energy for their production or
for their application since they are usually applied by seed
inoculation. Their use does not release as much GHG
as N fertilizers and they do not pollute surface waters.
However, their efficiency for switchgrass production is
unknown.
Because the aim of producing switchgrass for energy
is to reduce GHG emissions and improve the C budget,
a better understanding and quantification is needed for
CO2 emissions and C dynamics under standard and
alternative switchgrass production systems. In addition
to microbial and plant activities, soil surface CO2
emission fluxes (CO2-flux) are influenced by parameters
related to: (1) soil physical properties such as tempera-
ture, moisture, texture, density, and gas diffusion (Smith
et al. 2003; Allaire et al. 2012), (2) soil biochemical pro-
perties such as organic matter content, N and C cycles
(Sainju et al. 2008), (3) environmental conditions such as
rain, temperature, and field morphology (Allaire et al.
2012), and (4) crop management such as fertilization,
tillage, and amendment (Kiss et al. 2009). However,
these factors vary in the field and interact in a complex
manner so that it is very difficult to predict their relative
and combined effects on CO2-flux and C dynamic in soil.
As a result, gas and C dynamics in soils under switch-
grass production with or without biochar or biofertilizer
is poorly understood.
The objectives of this study were: (1) to assess and
compare the impacts of biochar, N fertilizer and biofer-
tilizers switchgrass biomass above and below ground and
plant C sequestration and on CO2 soil concentration
(CO2-soil) and CO2-flux, (2) to correlate C components
with physico-chemical soil properties, and (3) to evaluate
a C budget over two growing seasons in a sandy loam soil.
It was expected that biochar will increase plant biomass,
soil microbial activity, water content and favour overall
more C sequestration budget.
MATERIAL AND METHODS
Experimental Site and Design
This study was carried out at the experimental farm of
Laval University at St-Augustin-de-Desmaures (lat.
46845?00??N, long 71827?00??W) near Quebec City on the
St-Lawrence plain with 2300 UTM (22). The site was used
for soybean production in 2005, for corn from 2006 to
2008 and oat in 2009. The climate is humid temperate;
data from an on-site weather station gave a 30-year
(1970Á2000) average air temperature of 16, 19, 18, and
13 8C with monthly precipitation of 110, 119, 120, 124 mm
for June, July, August and September, respectively.
2 CANADIAN JOURNAL OF SOIL SCIENCE
Forpersonaluseonly.

The sandy loam soil (Gasser and Collin 2004) at this site is
classified as a Gleyic Podzol (Soil Survey Staff 1999)
formed from alluvial deposits. Plowing was completed
during fall 2009.
A complete randomized block design was used for
this experiment. An experiment with a split plot treat-
ment layout was set up in a sandy loam with biochar (0 to
10 t ha(1
) as the main plots and fertilizer types as the sub-
plots. Fertilizer treatments included: (1) without fertiliza-
tion (Control), (2) with calcium ammonium nitrate at a
rate of 50 kg N ha(1
corresponding to 100% of the
recommended dose as the mineral fertilizer (N-full); and
(3) with N fixing rhizobacteria (N-bacteria) as the
biofertilizer. The plots were 6 m long)1.62 m wide and
included nine rows spaced at 0.18-m interval. The main
plots include an amendment with (B) or without biochar
(NB). This biochar application rate was selected based on
previous researches in Quebec climate (Husk and Major
2010) and economic considerations. The biochar was
produced by Pyrovac Inc. (Que´ bec, Canada) through
slow pyrolysis of coniferous wood at about 5008C. Bio-
char was manually applied and incorporated into the first
0.05 m of the soil. Biochar characteristics were analyzed
following standard methods as listed in Table 1. Based on
the biochar C concentration of 0.636 kg kg(1
, 10 Mg dry
matter ha(1
biochar rate added 6.36 Mg C ha(1
was
added to the soil.
Mineral fertilizers were applied by hand right after
biochar incorporation and during the following spring
after biomass harvest. For this paper, only the main
plots with the following subplots were considered:
Control, N-Full, and N-Bacteria from only three blocks,
resulting in 18 plots used in this paper (3 blocks)2
main plots (B vs. NB))3 treatments).
N-fixing bacteria were a mixture of Paenibacillus
polymyxa, Rahnella sp., Serratia sp. and Pseudomonas
sp. with peat moss and seeds. Peat was mixed with the
seeds in order to improve adherence. About 24 h prior
to application, bacteria inoculum was mixed to 10 kg of
mixture (seed-peat) at a rate of about 107
Á108
CFU
mL(1
in an aseptic environment. These mixtures were
then kept at 20918C in plastic tubes. These plastic tubes
containing the mixture were open to let the seeds dry
about three hours prior to seeding. Bacteria were not re-
applied during the experiment and we did not attempt to
measure their presence in soil, their survival or their
activities during the experiment.
The switchgrass (Panicum virgatum sp.) variety ‘up-
land Cave in Rock’ was selected for its good perfor-
mance in Quebec (Samson 2007). It was seeded at a rate
of 10 kg ha(1
on 2010 Jun. 11 (Wintersteiger seeder)
after secondary tillage with spacing between rows of
0.18 m. Atrazine was applied before emergence in 2010
for control of broad-leaf weeds.
Yield and Biomass Carbon Content
Above-ground biomass was manually sampled during
fall 2010 and fall 2011 on rows 2 and 8 over a row
segment of 1.5 m in length with the biomass cut 7 cm
above ground, while it was harvested in spring 2011 with
a harvester (model PH554 OHV, Hobbs) over the entire
plots. Biomass left over in each plot after harvesting (the
lowest first 7 cm) was evaluated following hand clipping
using two quadrats of 0.50 m in length)0.50 m wide.
Root biomass was sampled with a 0.08-m-diameter
auger 0.3 m long. Only the center of the cores at the se-
lected depths was kept to avoid contamination. Compo-
site samples of eight cores from each plot were taken from
both row and interrow samples at 0Á0.15 m and 0.15Á
0.3 m depths in November 2011. Weeds were removed
prior to sampling. The samples were soaked during 16 h
in 500 mL of sodium hexametaphosphate (100 g L(1
).
They were then washed with a hydropneumatic elutriation
Table 1. Initial physico-chemical properties of biochar
Property Units Average CV (%) Reference
Physical properties
Ash g g(1
0.10 10 Centre d’expertise en analyse environnementale du Que´ bec (2003)
Mean weight diameter mm 1.38 0.5 International Biochar Initiative (2011)
Uniformity index g g(1
)100 2.65 0.5 Allaire and Parent (2004)
Bulk density kg m(3
270 3.6 Grossman and Reinsch (2002)
Solid density kg m(3
1547 5.1 Flint and Flint (2002)
Total porosity m3
m(3
0.83 5.1 Flint and Flint (2002)
Water retention at saturation g g(1
)100 250 20 Allaire and Parent (2004)
Specific surface area m2
g(1
5.3 14 ASTM D6556-10
Chemical properties
pH-H2
O Á 7.3 1.9 Conseil des productions ve´ ge´ tales du Que´ bec (CPVQ) (1997)
Electrical conductivity mHoms 123 6.2 CPVQ (1997)
Ctotal g g(1
)100 63.6 1.4 CPVQ (1997)
Csoluble mg g(1
0.04 62 Amacher et al. (1990)
Ntotal g g(1
)100 0.42 2.4 ASTM E1941
Psoluble cmol'
kg(1
1.42 1.8 Amacher et al. (1990)
Nasoluble cmol'
kg(1
5.46 3.7 Amacher et al. (1990)
CEC cmol'
kg(1
60.1 2.7 CPVQ (1997)
ALLAIRE ET AL. * C DYNAMICS IN A BIOCHAR-AMENDED LOAMY SOIL 3
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instrument using 760- and 250-mm sieves (Boehm 1981).
Root cleaning was completed by hand.
A representative subsample of 300 g of the above-
ground and root biomass was weighed, oven dried at 708C
for 3 d to determine dry matter content in each plot. Root
biomass density was estimated using a method slightly
adapted from Ma et al. (2000). For C content, above-
ground biomass subsamples were ground and passed
through a 1-mm sieve and then dried prior to combus-
tion for C content. Roots were ground with a laboratory
mill and analyzed with a CNS analyzer (Carlo-Erba,
model NA 1500) for total C. Concentration values were
multiplied by dry yield to calculate C sequestration.
CO2 Emission Fluxes and Soil C Concentration
Gas emissions were measured near the edge of each
plot where the soil received the same treatment, but
where switchgrass above-ground biomass was removed.
Switchgrass roots were allowed to grow into this space,
but not the weeds.
Carbon dioxide emissions from the soil to the atmos-
phere (CO2-flux) were measured several times during
2010 and 2011using acrylic closed chambers (Rochette
and McGinn 2005) that were 1.22 m long, 0.76 m wide
and 0.115 m high. All chambers had a reflective surface
on their top to decrease greenhouse effect within the
chamber. Soil disturbance in the chamber was reduced
to a minimum, and atmospheric pressure was main-
tained with a small hole without significant loss of gases.
CO2-flux measurements were performed as rapidly as
possible to minimize the impact of microclimate changes
caused by the chamber. Gas samples were taken during
18 min at 3-min interval. There was no significant
change in soil temperature during measurement. Six
chambers were simultaneously used on six plots and
the chambers were rotated to complete the 18 plots within
2 h. This precaution minimizes the effect of varying sun
intensity and temperature during measurement events
on CO2-flux.
Gas samples (10 mL) were withdrawn through septa
with hypodermic gastight syringes (10 mL, Becton-
Dickinson 309643, Franklin Lakes, NJ) and were
immediately inserted into gastight vials (10 mL model
5182-0838, Agilent, Wilmington, DE) that were pre-
viously vacuumed and capped with aluminium seal
(20 mm, 224178-01, Wheaton, Milleville, NJ) and rubber
butyl septa (Wheaton cat. 224 100Á202, Millville, NJ)
specifically chosen for CO2 (Lange et al. 2008).
Access tubes of 5 mm diameter were installed at 0.15
and 0.3 m depth about 5 cm apart from the flux
chambers. The access tubes were purged 2 h prior to
gas sampling. A 10-mL gas sample was withdrawn in
each plot to obtain CO2-soil at each depth using the same
syringes as for CO2-flux. Access tubes and thermocouples
remained in the field for two growing seasons.
CO2 concentration in the vials (emissions and soil
concentration) was measured within 48 h using a gas
chromatograph (6890 N Agilent, Wilmington, DE) with
a 30-m HP-PLOT-Q column (19095P-QO4PT) and a
TCD detector. Helium (UH-T 5.0, Praxair, Darbury,
CT) was the carrier gas. Soil CO2-flux were calculated
with the linear portion of the curve representing
temporal change in concentration that occurred within
the chamber (Rochette and McGinn 2005).
A 0.02-m-diameter auger 0.3 m long was used for
extracting composite soil samples at 0.1 m depth in
order to evaluate soil C content during both growing
seasons. The auger was used to directly reach depth
greater than the desired one to prevent surface soil from
falling into the hole and contaminate the soil at the
depth of interest. The soil was dried at 708C for 3 d and
sieved through a 250-mm sieve. Soil C content was
obtained with the instant combustion method (CN
Eager 1112) and reported on a per-hectare basis using
the equations of Ellert and Bettany (1995).
Other Soil Properties
Prior to planting and incorporating biochar at the
beginning of the experiment, composite soil samples
were randomly extracted from each block at 0.05Á0.15
and 0.15Á0.3 m depth. These samples were used for
chemical analyses. The soil contained 216, 293, 5472,
and 291 kg ha(1
of total P, K, Ca, and Mg. Texture
analysis, using the hydrometer method (Gee and Bauder
1986) indicated a sandy loam soil containing 55% of
sand, 25% of silt and 20% of clay. Intact soil cores were
also extracted from the same depths for measuring bulk
density (Grossman and Reinsch 2002) varying between
1.4 g cm(3
at 0.15 m and 1.6 g cm(3
at 0.30 m depth. Sur-
face bulk density was not measured. This soil is con-
sidered well structured (stable sub-angular aggregates)
relatively rich soil (Gasser and Collin 2004).
In addition, 0.15-m-long TDR probes were vertically
inserted into the soil at a depth of 0Á0.15 m for measuring
the volumetric water content (uv, m3
m(3
) through a
connection to a TDR100 (Campbell Scientific) and using
the Topp et al. equation (Topp et al. 1980). Type T
thermocouples (copper-constantan) were installed at
0.15-m and 0.3-m depths immediately after seedling.
Soil water content and temperature were measured with
a datalogger (CR23X Micrologger, Campbell Scientific,
Logan, UT) at the same time as CO2-soil and CO2-flux
measurements. They were measured nine times during
2010 and five times during 2011.
Statistical Analyses
Descriptive statistics for yield, biomass C content,
CO2-flux, and soil physico-chemical properties were ob-
tained with SAS 9.2 (SAS Institute Inc. 2008). Data were
first submitted to a BoxÁCox transformation (Box and
Cox 1964) when required, to improve the normality of
their distribution. The generalized MIXED linear proce-
dure (SAS Institute Inc. 2008) provided the main
analyses. Since some soil properties such as CO2-soil
and CO2-flux were repeated in time, the procedure
MIXED included a repeated procedure with multivariate
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unstructured covariance model. Given the large natural
variability in soil parameters such as CO2-soil, CO2-flux and
the variability in soil C content due to manual applica-
tion, the effects were considered significant at the P00.1
level and we considered a strong effect at P00.05. The
means were separated with the LSD test. Since the
statistical distribution and transformation were different
between years, they were separately analyzed. In addi-
tion, root biomass from 0Á0.15 m and 0.15Á0.3 m depths
were pooled to improve statistical analyses.
RESULTS AND DISCUSSION
Plant C Sequestration
The average switchgrass yield was close to 6 Mg ha(1
in
fall 2010 and ranged from 11 to 14 Mg ha(1
in fall 2011
(Table 2). The yields represent an efficient establishment
during the first year (Kiss et al. 2009) relative to an
expected yield of 8Á12 Mg ha(1
as measured in other
experimental sites with a mature crop in Quebec (Centre
de Re´ fe´ rence en Agriculture et Agroalimentaire du
Que´ bec 2008). The yield of the second year was higher
than those obtained from established crops under si-
milar climatic conditions [5.5 Mg ha(1
and 6.9 Mg ha(1
in Bolinder et al. (2002)]. Other studies have reported 3.2
to 35 Mg ha(1
in different sites across the United States
with lower yields in North Dakota and the highest
obtained in southwestern states (Liebig et al. 2008).
Follett et al. (2012) also measured yields ranging from
3.5 to 11 Mg ha(1
for the same cultivar as in this study.
This high yield was explained in part with its well-
developed root system (Ma et al. 2000). The soil at this
site was a loam from a fluvial deposit, with a good
texture, which represents suitable soil properties for
switchgrass production (Best and Campbell 1971).
Root biomass was about half that of the above-ground
biomass ranging from 4.3 to 7.8 Mg ha(1
(Table 2). The
root biomass was similar to those of 5.3 Mg ha(1
found
by Bolinder et al. (2002) and those of 4.6 to 8.4 Mg ha(1
for several cultivars including those of 4.7 Mg ha(1
for
‘Cave in Rock’ measured by several authors (Bransby
et al. 1998; Frank et al. 2004; Follet et al. 2012). The high
variability observed in root biomass was due to collars
near soil surface.
Biochar improved yield (above-ground biomass) by
about 10% and root biomass by 40% during the
establishment year (Table 2). The high water reten-
tion of the biochar (Table 1) may have helped plant
growth during the driest part of the summer in a dry
year (Table 3) since water content (uv) was slightly
higher with the biochar treatment that in the control
treatment (Fig. 1). Indeed, it is usually assumed that
biochar increases soil water content (Sohi et al. 2010).
Comparatively, the second growing season received
frequent rainfalls during the entire summer, resulting
in a moist soil throughout 2011 (Fig. 1, Table 3). The
biochar had no effect on plant growth during the second
year probably because water content was not limiting
during this year. In addition, seed germination may have
been more influenced by biochar during the first year
Table 2. Effect of treatments on yield (above-ground biomass as exportable for bioenergy) and root biomass, carbon content in biomass, and change in soil
carbon content (DC) during the experiment
Biomass C content DC
Above-ground Roots Above-ground Roots Soil
Fall-10 Spring-11 Fall-11 Fall-11y
Fall-10 Spring-11 Fall-11 Fall-11 Fall-11 Á Spring-10
Treatmentsz
(Mg dry matter ha(1
) (Mg C ha(1
) (DMg C ha(1
)
Main plots, biochar treatments
B 6.53ax
2.48 12.55 7.44a 3.00a 1.21 5.87 3.49a 8.65a
NB 5.90b 2.51 11.66 4.90b 2.70b 1.22 5.50 2.25b 0.19b
Subplots, fertilization
Control 6.45 2.45 11.04b 6.63 2.92 1.20 5.16b 3.02 3.59b
N-Bacteria 5.95 2.47 11.45b NA 2.78 1.20 5.41b NA 4.87a
N-Full 6.23 2.55 13.82a 5.71 2.85 1.24 6.49a 2.72 4.80a
Interactions between treatments
B'Control 6.76 2.47 11.27b 7.78 3.05 1.22 5.26 3.61 6.63b
B'N-Bacteria 6.59 2.42 12.27b NA 3.11 1.18 5.80 NA 9.72a
B'N-Full 6.24 2.55 14.13a 7.10 2.83 1.25 6.56 3.38 9.52a
NB'Control 6.15 2.43 10.81c 5.48 2.79 1.19 5.06 2.43 0.54c
NB'N-Bacteria 5.32 2.52 10.64c NA 2.46 1.23 5.02 NA 0.009d
NB'N-Full 6.22 2.55 13.52a 4.32 2.86 1.24 6.43 2.06 0.007d
z
B, biochar; NB, no biochar; N-Control, control treatment without fertilization; N-Bacteria, biofertilizer treatment; N-Full, full dosage of mineral
fertilization.
y
Combined samples from 0Á0.15 m and 0.15Á0.3 m for improving statistical analysis.
x
Bold numbers indicate significant effect at P00.1; bold and underlined numbers indicate significant effect at P00.05 resulting in groups identified
by letters. The mean separation letters apply to means in columns.
Forpersonaluseonly.

because it was applied in the first 0.05 m where seed
germination occurred. The reason for the greater effect
of biochar on root biomass than above-ground biomass
is not clear. It may be in part due to the very high
variability of root biomass estimate (which includes the
collars sometimes present and sometimes not present in
the samples).
Switchgrass typically responds to N fertilization after
at least 1 yr of growth (Martel and Perron 2008) and
above a certain level of fertilization. Martel and Perron
(2008) suggested that at least 50Á60 kg N ha(1
should
be applied for switchgrass production in Quebec. Vogel
et al. (2002) observed increased yield when more than
75 kg N ha(1
was applied in Nebraska and Iowa. The
same trends were observed in this study with no yield
response during the establishment and an increase
during the second year (Table 2).
N-fixing bacteria did not influence plant growth, yield
and C content (Table 2). Since bacterial survival and
activities were not determined, this treatment will not be
further discussed.
The C content of the above-ground biomass was
within the expected range with a minimum of 36% and
a maximum of 51% of C content on a dry biomass
basis in 2011. The sequestration resulted in 2.7 to 3.1 Mg
C ha(1
in 2010 and to 5.0 to 6.6 Mg C ha(1
in 2011.
Comparatively, Liebig et al. (2008) obtained between
3 to 5 Mg C ha(1
in Iowa for several cultivars, Bolinder
et al. (2002) about 3 Mg C ha(1
in Quebec, while Zan
et al. (1997) reported 5.5 Mg C ha(1
for the same
cultivar in a warmer region of Quebec.
Biochar and mineral N fertilization increased the
above-ground C sequestration (Table 2) mainly because
of a higher yield since plant C contents were not affected
Table 3. Descriptive statistics of soil properties during both years
C-soil CO2-soil CO2-flux N uv Temperature
0Á0.15 0Á0.15 0.15 0.3 Surface 0Á0.15 0Á0.15 Surface 0.15 0.3
Depth (m) (g g(1
)100) (Mg C ha(1
) (mg mL(1
) (mg m(2
s(1
) (g g(1
)100) (m3
m(3
) (8C)
2010
n eventsz
2 2 9 9 9 2 9 9 9 9
n obs.z
168 168 155 154 161 168 162 161 155 162
Mean 1.84 28.20 11.55 16.86 44.91 0.27 0.18 26.40 21.16 20.98
Min 1.47 23.61 0.60 2.11 (7.48 0.20 0.07 16.07 9.17 11.84
Max 2.84 42.49 27.59 34.83 156.40 0.36 0.34 36.08 25.93 25.89
CVz
29.1 28.8 59.7 53.8 70.0 27.4 46.6 35.8 37.5 33.7
2011
n events 2 2 5 5 8 2 5 5 5 5
Mean 1.99 30.60 53.28 73.21 34.54 0.27 0.27 22.65 17.44 17.13
Min 1.29 20.29 14.68 14.42 (8.68 0.15 0.18 11.14 7.28 9.31
Max 2.76 42.55 123.67 141.47 160.89 0.38 0.33 31.35 23.64 23.08
CV 37.9 38.2 57.6 52.7 96.5 37.5 18.9 23.4 37.4 22.7
n, number of events or number of observations; CV, coefficient of variation (%).
Fig. 1. Soil water content and temperature in 2010 and 2011 as inﬂuenced by biochar treatment (B, biochar, NB, without biochar).
Vertical error bars are standard errors.
Forpersonaluseonly.

by treatments (data not shown). Variation in harvested
C (Table 2) was thus largely due to variation in biomass
yield. Liebig et al. (2008) also reported no difference in
plant C content for a large range of fields during 5 yr of
production.
Soil C Content and Soil CO2 Concentration
Soil C content and CO2 emissions are important for
establishing C budget. CO2 soil concentration may help
in understanding C dynamics in soil. In the present
study, the initial soil C content was low, with an average
of 1.5 to 2.8%. Differences in soil C content ranged
from nearly 0 to 9.7 Mg C ha(1
(Table 2) over the 2-yr
period. The large variability observed in soil C content
(CV in Table 3) was due to the abundance of very fine
roots (B250 mm) that could not be removed from the
soil samples, biochar movement by runoff at the soil
surface observed after intense rainfalls, and potentially
to movement of soluble C in the soil profile since both
biochar (Table 1) and fresh organic matter contained
soluble C.
Differences in C content (DC) between the beginning
and the end of the study was about nine times higher
with biochar than without biochar (Table 2). Of course,
this change was largely associated with the biochar
itself, but N fertilization also had an impact. Full-N
fertilization favored higher increases in soil C content as
it probably activated microbial activity and root devel-
opment, both increasing biomass turnover (Halvorson
and Wienbold 2002). A significant interaction between
biochar and fertilization indicated a synergy between
both treatments (Table 2). The treatment without
biochar and with full-N resulted in no or a very small
change in soil C content. The higher increase in C
content with full-N treatment and biochar (Table 3) may
indicate that biochar may improve nutrient use by roots
and bacteria resulting in increased C addition to soil.
The capacity of perennial grasses to affect soil proper-
ties over time and the importance of soil properties for
plant growth are well documented (Follett 2001). It is
generally accepted that changes in soil C content only
slowly respond to changes in management. However,
other studies also reported differences in soil C content
after the first year of switchgrass production (Woolf
2008) without biochar application. Davis et al. (2011)
indicated that switchgrass almost always increased soil C
content by, on average, 27 Mg C ha(1
, representing
about a 1.9% yearly change. Zan et al. (1997) observed
about a 45% increase in soil C content near the soil
surface (the 0 to 0.15 m depth) after replacing annual
crops by switchgrass. Also, Garten and Wullschleger
(1999) reported that 19Á31% of the soil C content
changed after several years of root growth and senescence
of switchgrass. Follet et al. (2012) observed up to 50%
increase in C content in the 0Á1.5 m depth corresponding
to about 2 Mg C ha(1
yr(1
. Schmer et al. (2011) reported
a change of 0.1 to 1.2 Mg C ha(1
yr(1
at a 0Á0.3 m depth
over several years. However, Follet et al. (2012) observed
that half of the total increase in soil C content was below
0.3 m depth. Schmer et al. (2011) reported a change of
up to 3.3 Mg C ha(1
yr(1
at 1.2 m depth. Deeper soil
measurements in this study may have increased the
estimated changes in soil C content under switchgrass.
Average CO2-soil and its coefficient of variation (Table 3)
were similar to ranges observed for other crops in
Canadian studies (Allaire et al. 2012). The maximum
values in 2010 were lower than in 2011 (Table 3). They
indicate either good exchange, lateral diffusion, or a
slower respiration than in 2011, in part because plant
roots were much less developed and the soil was dryer
in 2010. As usual for agricultural soils, the CO2-soil
concentration at 0.3 m depth was 20 to 50% higher
than at 0.15 m (Fig. 2, Table 3) because the exchange
with the atmosphere decreases its concentration near the
soil surface (Allaire et al. 2012). The concentration in
2011 nearly reached 141 mg mL(1
during the hottest
days of the growing season, in what was a particularly
wet summer (Table 3). The high concentration indicates
either low exchange with the atmosphere or high soil
respiration or both. Low gas exchange occurs in a wet
Fig. 2. CO2 soil concentration (CO2-soil) (average of all fertilization treatments and replicates) with (B) and without biochar (NB) for
both depths (0.15 and 0.30 m) during 2010 and 2011. Vertical error bars are standard errors.
Forpersonaluseonly.

soil because of its low air-filled porosity, which con-
siderably reduced gas movement in soil. Soil water
content was one of the sources of CO2-soil variation
(Fig. 3). In addition, the rainwater of 2011 infiltrated
into the soil during the hottest days of the summer,
which likely activated microbial and root activities
(Rochette and Angers 1999) resulting in higher concen-
trations of CO2-soil.
Biochar significantly influenced CO2-soil (Table 4). It
increased CO2-soil concentration during both years and at
both depths (Fig. 2). This was probably due to the
soluble C in biochar (Table 1) and in microelements
(Verheijen et al. 2010), as well as its impact on soil water
content and specific surface area (Table 1). The influence
of biochar at 0.3 m remained significant during the
2-yr period (Fig. 2). This is probably due to the down-
ward movement of soluble C released from the biochar
(Table 1) in the soil profile that fed microorganisms, and
roots extending deeper in the soil profile over time.
Therefore, biochar has a very short-term effect on soil
properties as observed in this study in addition to a long-
term effect as observed in other studies (Lehmann et al.
2012; Sohi et al. 2010).
Comparatively, N fertilization influenced CO2-soil, but
differently between depths (Table 4). Forward multiple
regressions indicated a linear correlation between soil N
content and fertilization (data not shown, P00.02) and
between N content with CO2-soil (P00.04). It is known
that N and C cycles are intricate. In this case, mineral
fertilization, by influencing N content may have indi-
rectly influenced CO2-soil by stimulating microbial and
root activity.
CO2 Fluxes
TheCO2-flux rangedfrom (8 to160 mgm(2
s(1
(Table 3).
Sequestration rather than emissions occurred during
coldest conditions measured in this study such as dur-
ing early spring and late fall 2011 (Fig. 4). Similar
observations were reported for switchgrass by Skinner
et al. (2010). Schmer et al. (2012) also showed a simi-
lar trend during switchgrass production with increasing
rate from 15 (ex: late spring, day 160) to 69 mg m(2
s(1
in the warmest months (ex: day 180) and going down to
15 mg m(2
s(1
toward the end of the growing season.
As observed for most agricultural soils (Allaire et al.
2012), the coefficient of variation nearly reached 100%
(Table 3).
The average flux for 2011 was about 20% higher than
in 2010 (Table 3) probably because July and August
emitted significantly more in 2011 than in 2010 (Fig. 4).
Although the seasonal average CO2-soil was almost four
times higher in 2011 than in 2010 (Table 3, Fig. 2), the
emissions were in the same order of magnitude between
years (Table 3, Fig. 4). Either, more accumulation in the
soil, sporadic high emissions, more reabsorption, or
more lateral movement may have occurred during 2011
because of a wetter soil, in addition to change and
movement of soluble C (not measured), change in root
growth and depth compared with 2010.
The cumulative flux was calculated with a linear
interpolation between measuring events. It ranged
between 1.2 and 5 Mg C ha(1
for both growing seasons
combined with an average of 3.3 Mg C ha(1
for all
treatments combined (data not shown but used in the
calculation of soil CO2 emissions in Table 5). Roughly,
the C lost by CO2-flux represents more than one-third of
that added to the soil through biochar amendment, or
about 25% of total plant C captured over the establish-
ment period (Table 5). Comparatively, Frank et al.
(2004) estimated that C loss by CO2-flux was about 44%
of the total plant sequestration, a higher loss, although
similar methods and instrumentation were used in both
studies and over about the same period of the year but
in a different region.
A strong interaction was observed between biochar
treatment and time (Table 4, Fig. 4). The addition of
biochar did not influence CO2-flux right after its applica-
tion in 2010, but had a positive effect later on toward the
end of the growing season (Fig. 4). In 2011, CO2-flux
under biochar treatment was lower than under no
biochar throughout most of the season (Fig. 4). Min-
eral N fertilization not only increased CO2-soil but also
CO2-flux (Table 4) by almost doubling the emission rate,
but only when the soil was warmer (Fig. 4). It was
probably limiting only when microbes and roots were
the most active. Mineral fertilization tended to promote
higher respiration throughout most of the year in 2010,
but it was not significant during 2011 (Fig. 4). The
impact of fertilization was also probably indirect since
CO2-soil in 2011 and CO2-flux of both years were cor-
related with soil N contents (data not shown, P00.001).
Lee et al. (2006) observed similar results with switch-
grass under mineral fertilization, and an increase in
CO2-flux with manure application.
Stepwise multiple regressions linear relationship be-
tween soil properties, mainly CO2-soil and CO2-flux as
Fig. 3. Relationship between CO2 soil concentration (CO2-soil)
and volumetric water content at 0.15 m depth in 2010 and
2011.
Forpersonaluseonly.

dependant variables. As expected, stepwise multiple
regressions indicated that CO2-soil (P00.02) was highly
related to soil water content (Fig. 3) but weakly correlated
to CO2-flux (Fig. 5). The fact that CO2-soil and CO2-flux did
not follow the same trends all the time, although they
were correlated, may be due to several factors. Some
processes occurred near the soil surface in part because of
biochar application, which cannot be captured by mea-
suring soil properties at 0.15 and 0.30 m depth as was
done for CO2-soil. CO2 may have formed at the surface
where biochar was applied, or transformed (Sohi et al.
2010), captured or laterally deviated near the soil surface.
In addition, small pressure gradients caused by wind
and water infiltration (e.g., during rainfall) create high
Table 4. Significance of treatment (PF value), depth and time on soil properties measured several times during each growing seasons
C-soil CO2-soil CO2-flux uv Temperature
Treatment 2010 2011 2010 2011 2010 2011 2010 2011 2010 2011
Biochar 0.0009z
0.02 0.03 0.037 0.41 0.56 0.09 0.02 0.85 0.42
Fertilization 0.0001 0.71 0.69 0.35 0.11 0.12 0.59 0.31 0.24 0.015
Depth Á Á 0.0001 0.001 Á Á Á Á 0.14 0.11
Time y
0.0001y
0.0001 0.0001 0.013 0.0015 0.0001 0.0003 0.0001 0.0001
Biochar'fertilization 0.02 0.02 0.33 0.3 0.40 0.82 0.5 0.31 0.68 0.02
Biochar'Depth Á Á 0.0027 0.6 Á Á Á Á 0.22 0.84
Fertilization'depth Á Á 0.0074 0.89 Á Á Á Á 0.72 0.29
Biochar'time Á Á 0.0092 0.033 0.09 0.10 0.0012 0.31 0.0003 0.30
Fertilization'time 0.0001 0.093 0.68 0.53 0.016 0.02 0.99 0.16 0.78 0.14
Depth'time Á Á 0.0001 0.20 Á Á Á Á 0.0001 0.005
Biochar'fertilization'depth Á Á 0.26 0.45 Á Á Á Á 0.93 0.71
Biochar'fertilization'time 0.52 0.27 0.07 0.87 0.13 0.35 0.32 0.73 0.19 0.84
Biochar'depth'time Á Á 0.63 0.48 Á Á Á Á 0.46 0.90
Fertilization'depth'time Á Á 0.17 0.74 Á Á Á Á 0.64 0.61
Biochar'fertiliz'depth'time Á Á 0.93 0.80 Á Á Á Á 0.98 0.92
z
Bold and underlined numbers indicate significant effect at P00.05; bold numbers indicate significant effect at P00.1.
y
Csoil was measured only twice. In this case, the time effect corresponds to the difference between Spring 2010 and Fall 2011.
Fig. 4. CO2 emission fluxes (CO2-flux) influenced by biochar treatments (average of all fertilizer treatments and replicates) and by
fertilization treatments (average of all biochar treatments and replicates) during both growing seasons 2010 and 2011. Vertical error
bars are standard errors.
Forpersonaluseonly.

temporarily convective fluxes than cannot be detected by
the flux chamber method or by soil gas concentration in
depth.
Soil temperature at different depths (P00.01) and N
content (P00.01) measured at 0.15 m depth also
explained some of CO2-flux variability. The warmer soil
of July and August (between days 175 and 225) corre-
sponded to higher emission fluxes (Figs. 1 and 5). Frank
et al. (2004) and Lee et al. (2006) also observed values of
CO2-flux that coincided with changes in soil temperature
under switchgrass production with higher emissions
during the warmest months. Further studies are needed
to assess current outcome related to the relationship with
N content.
Carbon Budget
The C budget (Table 5) was obtained by combining
plant, soil and management budgets. The plant and soil
budgets were calculated from data obtained in this study
while the management budget was calculated using data
Table 5. Estimated carbon budget in switchgrass production during the first 2 yr of establishment
Control B N-Full B' N-Full
(Mg C ha(1
)
Plant sequestrationz
11.47 13.14 12.59 14.02
Plant exportsy
(7.85 (8.31 (9.29 (9.39
Soil sequestrationx
0.54 6.63 0.007 9.52
Soil CO2 emissionsw
(2.58 (2.56 (3.99 (3.18
Emissions for fertilizer and biochar manufacturingv
0 0 (0.02 (0.02
Emissions from equipmentu
(0.060 0.062 (0.062 (0.063
Plant budgett
3.22 4.83 3.30 4.63
Soil budget 2.04 4.07 (3.98 6.34
Management budget (0.06 (0.06 (0.08 (0.08
Net C budget 1.52 8.84 (0.76 10.87
z
Summation of all plants parts over two seasons (above-ground for fall 2010, Spring 2011, and fall 2011, roots for fall 2011).
y
Summation of harvested biomass for energy production (above-ground for fall 2010 and 2011).
x
Difference between soil C concentration at the beginning of the experiment and in fall 2011.
w
Total emissions of both growing seasons assuming (1) no emissions before Julian day 145 (May 25), (2) no emissions after Julian day 264 (Sep. 22),
and (3) linear interpolations between measurement events.
v
From Davis et al. (2011).
u
Emissions related to machinery used in this type of production, such as plowing, disk, seedbed preparation, application of fertilizer and biochar,
mowing and baling (different from seedling year and established year), values from Adler et al. (2007).
t
Equivalent to leftover from spring harvest and root biomass of 2011.
Fig. 5. Correlation between CO2 emission fluxes (CO2-flux) at 0.15 m and 0.30 m depths with CO2 soil concentration (CO2-soil) and
temperature at the same depths.
Forpersonaluseonly.

from the literature. The use of plants after harvesting
(e.g., biochar for sequestration vs. for energy) was not
considered. The plant C budget was most likely under-
estimated since switchgrass roots grow to 3 m deep
(Liebig et al. 2008), whereas we only measured to 0.3 m
deep. It was partly compensated by an underestimation
of CO2-flux because winter and spring were not included
in the budget. In addition, industrial biochar produc-
tion, such as used for this biochar, tends toward zero
emissions because pyrolysers reuse and recirculate en-
ergy and gases within the process (Allaire and Lange
2013). We therefore consider zero emissions for manu-
facturing biochar in this budget.
Based on a C budget, the greatest C sequestration by
plant was obtained with biochar irrespective of fertiliza-
tion (Table 5). This result is in agreement with several
authors who also considered biochar as a good way of
improving the C budget (Lehmann et al. 2006; Woolf
2008). The relative importance of soil C sequestration
on the net C budget was about the same as that of the
plants. In practice, the impact of biochar on the C
budget relative to that of plants will tend to be lower
over time because long intervals are likely to occur
between biochar applications. The equivalent of about
one-third of the increase in soil C content in the biochar
treatments was respired away by the soil. Most of the
biochar remained in the soil. Nearly one-fourth of C
sequestered by plants remained in or at the soil surface
(root and crop residues) to be degraded into soil organic
matter or lost through CO2-flux at later times. The C lost
by management represented a small portion of the C
budget. This is true for the first years of establishment,
but loss of C from management is expected to gain in
relative importance over time as biochar addition will
likely be rare. The best overall C budget occurred with
the biochar treatment combined with the mineral N
fertilization followed by biochar alone, then by fertiliza-
tion alone (Table 5). Based on these results, improved
biomass production with mineral N fertilization does
not have a negative impact on the C budget as long as it
is combined with biochar amendment.
Implications for Energy Biomass Production
Several implications could be listed from these findings:
(1) Switchgrass can grow fast and lead to high yields,
even as early as the second year of growth. (2) Switch-
grass slightly responded to biochar amendment at a rate
of 10 Mg ha(1
in a loamy sand. Considering switch-
grass as not demanding in terms of environmental
conditions and fertilization, the soil of this study to be
relatively favorable to plant growth, and the low level of
biochar addition to soil, we expect a stronger influence
of biochar with more-sensitive plants or under poorer
soil conditions in short- and long-term periods and,
thus, more valuable financial return of biochar applica-
tion. (3) Because biochar influenced soil properties at a
rate of 10 Mg ha(1
in a cold humid climate in a loamy
soil (e.g., humidity and temperature), we expect that it
will help germination during springtime and plant
growth during dry summers not only in loamy soils,
but also in sandy soils. (4) Because biochar influen-
ced CO2-soil, and biochar and fertilization treatments
showed interactions on some plant and soil parameters,
potential benefits associated with changes in soil proper-
ties should be considered when evaluating its application
irrespective of yield effects. (5) The best C budgets were
obtained with biochar application with or without min-
eral N fertilization, but the long-term impact of biochar
on the C budget will highly decrease depending upon
the frequency of biochar application. (6) Averaged over
the first 2 yr of establishment, switchgrass, produced for
bioenergy, can immediately start sequestering C as long
it is accompanied with an amendment high in C such as
biochar.
CONCLUSIONS
Switchgrass may be produced for bioenergy, but to be
efficient in terms of energy and environment, one should
consider decreasing input energy and matter for its
production. In addition, its global environmental impact
should be as low as possible. In this study, switchgrass
was produced with biochar and/or with N-fixing bacteria
hoping to sequester C and reduce input materials.
Swithgrass produced up to 14 Mg dry matter ha(1
over the first 2 yr of establishment, which is efficient
compared with other perennial plants. Biochar slightly
increased yield, by about 10%, during the first year
and root biomass by up to 50% after 2 yr, increasing
C sequestration. Biochar had the highest influence on
CO2-soil at 0.15 and 0.3 m depths with up to 50% increase,
while its influence on CO2-flux varied over time. Mineral
N fertilization tended to increase CO2-soil and CO2-flux.
Variations in CO2-flux were mostly explained by CO2-soil
followed by temperature, and soil N content. The
interaction between CO2-soil and CO2-flux with soil pro-
perties changed during the growing seasons. Biochar and
fertilization treatments showed interactions on some
aspects of plant and soil. Using plant C, soil C content,
C losses through emissions, we found that the best C
budget was obtained with a combination of biochar and
mineral N fertilization. The equivalent of about one-third
of the increase in soil C content in biochar treatments
was respired away by the soil. Nearly one-fourth of C
sequestered by plants remained in or at the soil surface
(root and crop residues) to be degraded into soil organic
matter or lost through CO2-flux at later times. Since
switchgrass, which is a non-exigent plant, responded to
biochar in a good soil with a low application level of
biochar, we expect that more-sensitive plants, poorer
soils and higher application of biochar should result in
much stronger impact of biochar on C budget. Also, it is
often pointed out that biomass production for energy is
not efficient in terms of C budget; these results indicate
that short-term biomass production with biochar appli-
cation has the potential to have an efficient C budget.
Forpersonaluseonly.

ACKNOWLEDGMENTS
The authors thank the FQRNT and NSERC for their
financial support. They are grateful for the technical
support of Vale´ rie Be´ langer and Franç ois Marquis, who
provided aid in plant and biochar analyses, respectively.
The team also thanks Benjamin Dufils, Marie-Pier
Amyot, Samuel Richard, Claudia Sylvain and Jennifer
Granja for field measurement, sampling and data
collection. They also thank the managers of the experi-
mental farm of Laval University for their collaboration.
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