Biomass productivity of different energy crops under French conditions

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Biomass productivity of different energy crops under French conditions

S. Cadoux, Hubert Boizard, S. Marsac, F. Labalette, S. Briand, Matthieu Preudhomme, I. Félix, Brigitte Chabbert, A. Besnard, M.L Savouré

To cite this version:

S. Cadoux, Hubert Boizard, S. Marsac, F. Labalette, S. Briand, et al.. Biomass productivity of

different energy crops under French conditions. 18. European Biomass Conference & Exhibition, May

2010, Lyon, France. �hal-02755975�

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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. Cadoux^1*, 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 S^t 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

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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.

0 5 10 15 20 25

Miscanthus February

Sw itchgrass February

Fescue Alfalfa Fiber sorghum Triticale

Biomass production (tDM.ha-1)

Q1 min. median max. Q3

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.

0 5 10 15 20 25

Miscanthus February

Fescue Alfalfa Fiber

sorghum Triticale

0 5 10 15 20 25

Miscanthus February

Fescue Alfalfa Fiber sorghum

Triticale

0 5 10 15 20 25

Miscanthus February

Fescue Alfalfa Fiber sorghum

Triticale

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

a)

b)

c)

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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].

0 50 100 150 200 250 300 350 400 450 500

Miscanthus (February)

Sw itchgrass (February)

Fescue Alfalfa Fiber

sorghum Triticale

Primary Energy Yield (GJ.ha-1)

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.

0 1 2 3 4 5

Ethanol Yield (tEhanol.ha-1)

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.

0 50 100 150 200 250 300 350 400 450 500

Nitrogen removed at harvest (kgN.ha-1)

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

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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