biomass productivity of different energy crops under french conditions. results of the “regix” experimental network. cadoux s, boizard h

Biomass productivity of different energy crops under French
conditions.
Results of the “REGIX” experimental network.
Cadoux S, Boizard H, Marsac S, Labalette F, Briand S, Preudhomme M,
Félix I, Besnard A, Savouré ML, Chabbert B.
S. Cadoux1*, S. Briand2, B. Chabbert3, A. Besnard4, I. Félix5, M.L.
Savouré2, S. Marsac2, M. Preudhomme1, F. Labalette2, H. Boizard1
1INRA, US 1158 Agro-Impact Laon/Mons, 2 Chaussée Brunehaut, 80200
Péronne, France
2GIE ARVALIS/ONIDOL, 12 Avenue George V, 75008 Paris, France
3INRA, UMR 614 FARE, 2 Esplanade Rolland Garros, 51000 Reims, France
4ARVALIS – Institut du végétal, La Jaillière, 44370 La Chapelle St
Sauveur, France
5ARVALIS – Institut du végétal, 18570 Le Subdray, France
*Corresponding author: [email protected], tel. +33 3 22 85
75 15, fax. +33 3 22 85 69 96
ABSTRACT: The climatic, energetic and political context promotes the
development of bioenergies. However we have a lack of knowledge to
find out the best energy crops, depending on the soil, the climate and
the end-use. This work aimed at studying the adaptation and the
biomass and biofuel yield, of several energy crops grown in France in
different soil and climate conditions. The biomass yields were very
variable between the different experimental sites and no differences
were observed on the median biomass yield between crops. Moreover,
there was no evidence of a highly productive crop in all the
conditions of soil and climate. Because of little differences of the
lower heating value between crops, no differences were observed on the
primary energy yield. The ethanol yield per hectare was higher for
miscanthus, switchgrass and fiber sorghum because of higher cellulose
content in these crops. The nitrogen removed at harvest by miscanthus
and switchgrass were significantly lower than the other crops witch
could lead to reduced fertilizer-N requirements. Further research are
needed to clarify the effect of limiting factors on the biomass yield
of the different energy crops and to consider other parameters such as
the environmental impacts to give rules to choose the most suitable
crop in a given region.
Keywords: energy crops, yield, energetic value, ethanol
1 INTRODUCTION
The development of bioenergies is currently encouraged in the EU for
its contribution to reduce global warming and fossil fuel dependence.
Thanks to processes able to convert the lignocellulose of whole plants
into bioenergy (e.g. combustion, second generation biodiesel or
bioethanol) a wide choice of energy crop is available. The suitable
energy crops will have to meet several requirements such as a high
biomass and biofuel productivity per hectare in order to limit the
competition with food productions, low environmental impacts at global
and local scale, ability to be inserted in existing farming systems,
etc. However few studies compared a panel of crops in different
conditions of soil and climate with regard to these criteria. Vogel et
al. [1], Richter et al. [2], Riche et al. [3] have studied the yield
variability across sites but only for one species. Boehmel et al. [4]
compared different energy crops but only in one site and did not take
into account the biomass quality.
An experimental network was set up in the frame of the French project
“REGIX” to compare the biomass production and composition of different
energy crops in different soil and climate conditions. In this paper
we focused on the biomass production, the energy and ethanol yield per
hectare and the nitrogen removal at harvest, used as an indicator for
fertilizer-N requirements and potential N-related environmental
impacts (N2O emissions, NO3 leaching, soil N changes with time).
2 MATERIAL AND METHODS
In 2006, an experimental network of fifty sites was set up to cover
different soil and climate conditions over the France. Six
lignocellulosic energy crops, from annual to perennial systems, were
mainly grown: triticale (Triticosecale Wittmack), fiber sorghum (Sorghum
bicolor (L.) Moench), fescue (Festuca Arundicea), alfalfa (Medicago
sativa), switchgrass (Panicum virgatum, var. kanlow) and miscanthus (Miscanthus
x giganteus). Each crop was grown in small plots of about 200m² with a
low input management. The rate of fertiliser-N depended on the crop
and the soil potential (Table I).
Table I: Minimum, median and maximum fertilizer-N rate (kgN.ha-1)
Crop Mini. Median Maxi.
miscanthus 0 60 120
switchgrass 0 60 120
fescue 60 140 240
alfalfa 0 0 0
fiber sorghum 60 100 220
triticale 80 140 200
For this study a selection of ten sites, based on three criteria, were
done: 1) sites with almost all the crops, 2) sites with a satisfactory
stand establishment of the perennial crops and 3) keeping a balance in
the number of experiments in Northern (three sites), Central (four
sites) and Southern France (three sites). The soil and climate
characteristics for the three regions are summarized in Table II.
Table II: Minimum and maximum soil available water capacity (AWC),
mean annual rainfall (Rf) and temperature (Tp)
Region AWC (mm) Rf (mm) Tp (°C)
North 135-300 633-819 10.5-11.3
Center 75-160 599-1075 11.0-12.0
South 160-216 383-1242 12.7-13.2
In 2007 and 2008, the biomass yield was measured at harvest by using
conventional manual sample methods. The biomass was then dried until
constant weight to allow the calculation of dry matter yield. The
biomass composition, i.e. nitrogen content, higher heating value
(HHV)and sugar content, was analysed on the whole network. We used the
median composition as reference parameters (1) to make different
calculations:
*
Lower Heating Value (LHV; MJ.kg-1) =
((HHV*1000)-((H/C*72*18*2257)/ (144*(1+(H/C)+(O/C)))))/1000
*
Primary Energy Yield (PEY; GJ.ha-1) = Dry matter yield*LHV (after
Boehmel et al. [4])
*
Ethanol yield (t ethanol.ha-1) = Dry matter yield*Cellulose
content*saccharification yield*fermentation yield
The cellulose content calculation was based on the sugar composition
in the biomass. The saccharification and fermentation yields used were
respectively 90% and 48%. We assumed no differences between crops
implying an optimum process adaptation for each biomass.
The data are presented with minimum, first quartile, median, third
quartile and maximum value. Statistical analyses were done by using
Kruskal & Wallis non parametric test. The comparison of median values
were done for p<0.05.
3 RESULTS AND DISCUSSION
The biomass production of all the crops was very variable (Figure 1).
The variation ranged between 5 and 20 tDM.ha-1 for most crops. The
median biomass yields were 14.6 tDM.ha-1, 14.3 tDM.ha-1, 10.8 tDM.ha-1,
14.0 tDM.ha-1, 14.3 tDM.ha-1, 12.8 tDM.ha-1, respectively for
miscanthus, switchgrass, fescue, alfalfa, fiber sorghum and triticale.
Despite no statistical difference on the median biomass production
between crops we noticed a trend to a slightly higher yield of C4
crops. The new crops Miscanthus, switchgrass and fiber sorghum were
thus particularly well adapted to French conditions.

Figure 1: Biomass production of the different energy crops
The crop yields were high and the variability was low in Northern
France (Figure 2a). There were significant differences between crops
with higher biomass yield of miscanthus and switchgrass. The yield of
fiber sorghum was limited by temperatures and intercepted radiations
(not shown). The crop yields were low in Central France because of
shallow soils, with no significant differences between crops (Figure
2b). There was a very high variability in crop yield in Southern
France (Figure 2c). It was partly explained by very different rainfall
conditions (cf. Table II). There were no significant differences
between crops but the yield of fiber sorghum was slightly higher and
never below 15 tDM.ha-1.

a)
b)
c)

Figure 2: Biomass production of the different energy crops in Northern
(a), Central (b) and Southern (c) France
The huge variability in crop yield thus depended i) on the interaction
between crop and soil and climate conditions, but probably also ii) on
other parameters such as sample methods, quality of the stand
establishment of perennial crops, etc.
Due to small differences of LHV between crops, there were no
statistical differences on the median PEY between crops (Figure 3).
The variation was still very high, between 50 and 350 GJ.ha-1 for most
crops. That gives indications on the potential heat, electricity or
second generation biodiesel production. However other criteria should
influence the conversion efficiency such as alkali metal content or
ash quality [5].

Figure 3: PEY of the different energy crops
The cellulose content varied a lot between crops which led to
significant differences of the ethanol yield between crops (Figure 4).
The median ethanol yields were 2.9 t ethanol.ha-1, 2.4 t ethanol.ha-1,
1.4 t ethanol.ha-1, 1.5 t ethanol.ha-1, 2.0 t ethanol.ha-1, 1.3 t
ethanol.ha-1, respectively for miscanthus, switchgrass, fescue,
alfalfa, fiber sorghum and triticale. In this calculation, we assumed
the same conversion rate for all crops. However, recalcitrance of
lignocellulose to biological or chemical degradation can differ
between crops, notably because of variations in lignin and phenolic
acid esters that render the cellulose less accessible through
cross-linkage [5]. These differences should have a significant
influence on the bioethanol yield. We also assumed that only the
cellulose should be converted into ethanol but part of the
hemicellulose is likely to be converted through improved conversion
technologies.

Figure 4: Ethanol yield of the different energy crops
The differences between crops in nitrogen removal at harvest were very
high (Figure 5). The nitrogen removals of miscanthus and switchgrass,
respectively 29 kgN.ha-1 and 50 kgN.ha-1, were significantly lower
than those of fescue, alfalfa, fiber sorghum and triticale,
respectively 143 kgN.ha-1, 398 kgN.ha-1, 139 kgN.ha-1 and 143 kgN.ha-1.
The nitrogen removals of alfalfa were the most variable and the
highest. However, part of this nitrogen originated from symbiotic
fixation and no fertilizer-N was applied to the crop.

Figure 5: Nitrogen removed at harvest for the different energy crops
4 CONCLUSION AND PROSPECTS
The variability of biomass yields of all energy crops were very high
and led to huge differences in the conversion to energy and thus on
bioenergy yields. There was no evidence for a highly productive crop
in all the conditions of soil and climate; the choice for the best
suited crop regarding biomass yields must depend on the soil and
climate conditions. Crop modeling should be an interesting tool to
better take into account the variability in crop yield depending on
the conditions of soil and climate. However, for the new crops
miscanthus and switchgrass, further research is needed to clarify and
quantify the limiting factors of the production.
Furthermore, other parameters than production have to be taken into
account to give rules to choose the most suited crop. The global and
local environmental impacts are of particular interest. In this study,
we used the nitrogen removed at harvest as an indicator for
fertilizer-N requirements and potential N-related environmental
impacts such as N2O emissions, NO3 leaching or soil N changes with
time. With this indicator, the perennial C4 crops miscanthus and
switchgrass were more interesting than the other crops. However, there
is a need to better quantify the potential N-related environmental
impacts due to their importance [6] and to integrate other criteria
such as the impact on water resources, soil carbon changes with time,
biodiversity, etc.
5 NOTES
(1) The reference parameters for the different biomass compositions
are presented in this conference by D. Dasilva Perez et. al. and
Labalette et al.
6 REFERENCES
[1] Casler M.D., Vogel K.P., Taliaferro C.M., Ehlke N. J., Berdahl J.
D., Brummer E. C., Kallenbach R. L., West C. P. and Mitchell R. B,
2007. Latitudinal and longitudinal adaptation of switchgrass
populations. Crop Science, 47-6, pp 2249-2260.
[2] Richter G. M., Riche A. B., Dailey A. G., Gezan S. A., Powlson D.
S., 2008. Is UK biofuel supply from Miscanthus water-limited? Soil Use
and Management, 24-3, pp 235-245.
[3] Riche A. B., Gezan S. A., Yates N.E., 2008. An empirical model for
switchgrass to predict yield from site and climatic variables. Aspects
of Applied Biology, 90, pp 213-218.
[4] Boehmel C., Lewandowski I., Claupein W., 2008. Comparing annual
and perennial energy cropping systems with different management
intensities. Agricultural Systems, 96, pp 224–236.
[5] Karp A. and I. Shield. 2008. Bioenergy from plants and the
sustainable yield challenge. New Phytologist, 179, pp 15-32.
[6] Crutzen P. J., Mosier A. R., Smith K. A., Winiwarter W., 2008. N2O
release from agro-biofuel production negates global warming reduction
by replacing fossil fuels. Atmos. Chem. Phys, 8, pp 389–395.
7 ACKNOWLEDGEMENTS
*
This work was done in the frame of the French “REGIX” project
funded by the French National Research Agency (ANR, 0501c0136) and
supported by ADEME
*
We thank all the experimenters who provided the data through the
experimental network

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