Energetic and economic evaluation of a poplar cultivation for
the biomass production in Italy

Marco Manzone

*

, Gianfranco Airoldi, Paolo Balsari

University of Turin, Department of Agricultural Forest and Environmental Economics and Engineering, Section of Mechanics, Via Leonardo da
Vinci, 44, Grugliasco 10095 (TO), Italy

a r t i c l e

i n f o

Article history:

Received 16 January 2008
Accepted 6 May 2009
Published online 21 June 2009

Keywords:

Short rotation forestry
Biomass production
Economic evaluation
Energetic evaluation

a b s t r a c t

The cultivation of crops for biomass production on good soils allows to reduce surplus
production of food crops and increase the sustainability of energy production from the
environmental point of view. The short rotation forestry (SRF), is only at a preliminary
study level in Italy but, is already a reality in North Europe where was already developed an
high planting density (6000–8000 cuttings ha

-1

) technique and a whole mechanization of

plantation and biomass harvest.
On the basis of this cultivation technique, it was realized as an energetic and economic
evaluation of a poplar SRF in Northern Italy. In detail, they were considered data of poplar
growth in a plantation for the production of two-year whips in Western Po Valley
considering SRF duration of 8 years and a biomass (20 t ha

1

D.M.) harvest every 2 years.

Indeed it was assumed to operate on a plantation in production (12.5% of the surface
replanted every year) with a spacing 3.00 0.4 m (6700 cutting per hectare) that allows the
use of conventional tractors.
In this computing system it was pointed out a ratio between output and input energy of 13
and a cost of 80 V t

1

of D.M. Nevertheless a positive energetic balance, the economic

sustainability of poplar SRF depends, due to the present monopolistic energy management
in the same countries, on political choices of chip price or public subventions to the
producers.

ª

2009 Elsevier Ltd. All rights reserved.

1.

Introduction

The cultivation of crops for biomass production on good
arable soils allows to increase the energy production and it’s
really beneficial from the environmental point of view.

This solution increases the farmer’s revenues and leads to

advantages for the environment

[1–5]

.

The short rotation forestry (SRF) is only at a preliminary

study level in Italy, whereas it already is a real production in
Northern Europe

[6–10]

.

The technique developed in Scandinavian countries with

a high planting density (10,000–12,000 cuttings ha

1

) and the

total mechanization of both plantation and biomass harvests
seems to be very interesting also for the North Italian situation

[11]

. In order to evaluate from the energetic and economic

point of view a poplar SRF in the Po Valley an ad hoc study was
made and a specific model has been developed.

2.

Materials and methods

A series of data was collected both in the nursery and in the
poplar SRF plantation nearby the experimental farm ‘‘MEZZI’’
close to Casale Monferrato (AL) during 2006 season. The

* Corresponding author. Tel.: þ39 011 670 8608; fax: þ39 011 670 8591.

E-mail address:

[e-mail]

(M. Manzone).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / b i o m b i o e

0961-9534/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biombioe.2009.05.024

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 1 2 5 8 – 1 2 6 4

nursery resulted to be the necessary cultivation phase for SRF
cuttings production. All the cultural operations both for
nursery and poplar plantation were analysed: the working
time and both machines and manpower requirements were

recorded on the field, following the CIOSTA (Comite´ Interna-
tional d’Organisation Scientificue du Travail en Agricolture)
methodology, on at least 5.000 m

2

surface areas and for

periods not shorter than 2 h

[12]

.

Fig. 1 – Operation required in the different cycles of the considered poplar SRF plantation.

Table 1 – Cultural operation and amounts of production factors considered in the model.

Operation (n

)

Type of operation

Material utilized

Yearly nursery cultural operation

1

Top dressing

Urea (218 kg ha

1

)

1

Pre-emergence chemical weed control

Metaclor (1700 g ha

1

)

Linuron (500 g ha

1

)

Pendimethalin (800 g ha

1

)

2

Post-emergence chemical weed control

Piridate (1125 g ha

1

)

Fluzifop-p-butile (665 g ha

1

)

2

Insecticide treatment

Chloropyrifos-metyl (120 g ha

1

)

Cypermethrin (12 g ha

1

)

Fenitrothion (285 g ha

1

)

SRF cultural operation at the first years

after biomass harvest

1

Top dressing

Urea (218 kg ha

1

)

1

Seed bed fertilization

8.24.24-N.P.K. (500 kg ha

1

)

1

Pre-emergence chemical weed control

Metaclor (1700 g ha

1

)

Linuron (500 g ha

1

)

Pendimethalin (800 g ha

1

)

2

Post-emergence chemical weed control

Glufosinate-ammonium
(500 g ha

1

)

White oil (2000 g ha

1

)

4

Lane mechanical weed control

–

2

Irrigations

–

SRF cultural operation at the second

years after biomass harvest

1

Top dressing

Urea (218 kg ha

1

)

2

Post-emergence chemical weed control

Glufosinate-ammonium
(500 g ha

1

)

White oil (2000 g ha

1

)

4

Lane mechanical weed control

–

1

Biomass harvest

–

1

Stumps removed (only at the end of the cycle)

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 1 2 5 8 – 1 2 6 4

1259

The developed model allowed the determination of

manpower and energy requirement as well as the costs
analysis considering different crop density and biomass
production. The model considers a continuous poplar SRF
plantation: the whole acreage is divided into different
‘‘modules’’ each corresponding to 1 year of the crop cycle ,
allowing to refer all costs to annuity. As regards to the
economic and energetic evaluation, an 8-year rotation with
harvesting carried out every 2 years and with a starting poplar
plants density of 6700 for ha was considered (

Fig. 1

) with

a 3.00 0.5 m spacing and a production of 10 t ha

1

D.M. year

1

[13,14]

. In this evaluation it was considered to use the same

machines in both the nursery and the poplar SRF plantation.
For all post-emergence treatment it was supposed to use
traditional tractors with 4 RM with a maximum width of 2.2 m.
In detail, for the nursery and the poplar SRF plantation it has
been assumed to prepare the soil with ploughing at 40 cm
depth after seed bed fertilization – 500 kg ha

1

of 8.24.24

(N,P,K).

Secondary tillage was carried out by two harrowing inter-

ventions, while for the plantations, a traditional transplanter
with different spacing was considered. The cultural opera-
tions assumed for the SRF cultivation and nursery were
fertilization and weed control necessary to allow high

production biomass

[15,16]

. In the nursery, an insecticide

treatment was also considered to allow a high quality of the
propagation material. Finally, it was assumed to use a heavy
cultivator for stumps removal (

Tables 1 and 2

).

For biomass harvesting a self-propelled harvester CLASS

850 (purchase cost 300,000V) was utilized with a cutting head
for little trees (purchase cost 60,000V). The working capacity of
the self-propelled harvester is about 30 t ha

1

[17]

. For the

transport of the biomass in the farm (about 400 m), two trac-
tors with trailers were used. The average cost of the CLASS 850
was

determined

considering

contractors

costs.

The

manpower requirement was determined considering the
number of operators and the working time to carry out every
cultural operation. The economic evaluation was determined
for every cultural operation considering both the cost of the
machine and the cost of the production factors (fertilizers,
plant protection products) (

Table 3

).

The hourly cost rate of each machine was evaluated using

the method proposed by Ribaudo

[18]

, with prices updated to

2007. An annual utilisation of at last 500 h (tractor used also
for other operation) was assumed for tractors, and the power
requirement was calculated by taking into consideration the
data recorded during experimentation and the drawbar pull
and power requirement in the different operating conditions.
A cost for manpower of 12.5V h

1

was considered

[19]

. The

tractor hourly cost was determined with the methodology
proposed by the Mechanic Section of –DEIAFA – Turin
University

[20]

.

For the evaluation of economic sustainability it was

determined the Net Present Value (NPV) that indicates the
difference between the total income and the total costs
determined considering a biomass value of 80V t

1

D.M. This

determination was done for different costs of land and water
use

[21]

.

The energetic costs were determined considering both

direct costs – fuel and lubrificant consumption – and indirect
costs – machine, equipment and mineral fertilizer energetic
contents (

Table 4

). The human work was expressed in

manpower hour requirement for every cultural operation but
it was not considered from the energetic point of view

[22]

.

Table 2 – Machines considered in the biomass cultivation.

Machine

N

Power

(kW)

Mass

(kg)

Working

width (m)

Load

capacity (m

3

)

Harvester

1

303

12,600

1.5

–

Tractor

2

88

4350

–

–

Tractor

1

125

5900

–

–

Trailer

2

–

3700

–

22.0

Gangplough

1

–

1160

1.6

–

Harrow

1

–

1500

4.0

–

Transplanter 1

–

750

6.0

–

Spreader

1

–

300

8.0

0.5

Boom

sprayer

1

–

200

12.0

0.6

Orchair

sprayer

1

–

550

3.0

1.0

Stump

redder

1

–

450

1,5

–

Table 3 – Material, machines and manpower cost
considered in the economic evaluation.

Material

Unitary cost

(V kg

1

)

Diesel fuel

0.6

Motor oil

5.5

Mineral fertilizer

0.3

Fertilizer (top dressing)

0.3

Herbicides

15.1

Plant protection products

16.2

Machine

Cost (V)

Tractor

52,000

Trailer

18,500

Harvester (class 850)

300,000

Cutting head

60,000

Manpower

12.5 (V h

1

)

Table 4 – Primary energy content of production factor
considered in the model [22].

Material

Primary

energy

content (MJ kg

1

)

Bulk density

to 15

C

(kg dm

3

)

Diesel fuel

51.5

0.88

Motor oil

83.7

0.93

Tractor and self

propelled

92.0

–

Implements

69.0

–

N

73.3

–

P

13.4

–

K

9.2

–

Herbicide

81.5

–

Biomass

18.8

a

–

a Refered to M.D.

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 1 2 5 8 – 1 2 6 4

1260

3.

Result

3.1.

Required manpower

Nearly 22 h a year

1

of manpower were required for the

cultivation of one SRF hectare and of its necessary nursery
surface.

The cultural operations that required the highest

manpower resulted to be the cuttings preparation (cut rods

in the nursery, transport of rods in the farm and cut rods
in cutting) and the plantation of both the SRF and nursery.

The weed control required more than 32% of the total

time. Whereas the production and transport of the cuttings
the 27.4%. The biomass harvesting required less than 15%
(

Fig. 2

).

Besides, it is to highlight that the cutting plantation pres-

ents a difficulty in operation management due to the reduced
available time (March and April).

Fig. 2 – Manpower requirement for the different operation necessary to cultivate the poplar SRF (nursery included).

Fig. 3 – Incidence (%) of the different operations on the whole energetic costs.

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 1 2 5 8 – 1 2 6 4

1261

3.2.

Energetic evaluation

The energetic cost for the cultivation and management of
100 ha of poplar irrigated SRF is of 14.2 GJ ha

1

per year and

represents about 7% of the biomass energy production (about
188 GJ ha

1

for years). The input/output ratio is close to 13. The

largest part of energetic input (47%) is linked to cultural
operations, in particular at the top dressing (37 % of the total
energy requirement). Harvesting and biomass transport to the
farm storage represents about 16% of the total energy
requirements; the flood irrigation does not require any energy
input (

Fig. 3

).

In conclusion, for arable surfaces between 50 and 200 ha,

the total energy cost resulted between 7.4 and 7.8% of
produced energy.

In the total balance, the direct energetic cost results to be

1.9% and the indirect energetic cost the 5.8% for a 50 ha SRF
cultivation and 5.5% for a 200 ha SRF cultivation.

3.3.

Economic evaluation

The production cost of the SRF resulted closely connected to
both the cultivated surfaces and to the production level.
Considering a biomass production of 20 t ha

1

D.M. per cycle,

equivalent to a 50 t ha

1

W.B., the production cost is close to

90V t

1

D.M. and to 75V t

1

D.M. for SRF surfaces of 50 and

200 ha respectively (

Fig. 4

), values that are higher than the

market price ones.

The nursery cultivation weights upon the total cost for 8%

and the cutting production cost is of 10 Eurocents. The oper-
ations that weight upon the total production cost are the
cultural operation (near 35.9%) (

Fig. 5

). Those with high value

are the weed control for post-emergence treatment and the
irrigation intervention but, these operations are indispensable
to get high biomass yield. Besides, very important are water
and land use costs. For example, considering a 100 ha SRF
surface with 20 ha

1

D.M. biomass production for every cycle

Fig. 4 – Price of the biomass to compensate production costs (NPV [ 0) for different production levels and different surface
dimensions.

Fig. 5 – Incidence of different operations on the whole cost of a 100 ha poplar SRF.

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 1 2 5 8 – 1 2 6 4

1262

and zero cost for irrigation, the biomass cost production is
66V t

1

D.M. with land use cost of 100V ha

1

year

1

. In the

case of a land use cost of 400V ha

1

year

1

the biomass

production cost is of 96V t

1

D.M. The land rent cost weights

upon total production cost for the 15 and 41% respectively.
Considering zero the cost rate of land, the biomass production
cost fluctuates from 56V t

1

D.M. to 76V t

1

D.M. with 50 and

200V ha

1

irrigation costs respectively (

Fig 6

).

Nevertheless, it has to be considered the influence of the

transport and storage costs in terms of biomass losses on the
total biomass production cost.

The transport cost weights upon total cost for the 5 and

20% for distances of 5 and 50 km respectively. The storage
losses, for a 12 months storage period resulted of 40% and
increased the biomass production cost of 60% (

Fig. 7

)

[23]

.

4.

Summary and conclusion

The poplar SRF plantation, in the considered condition, an 8
years rotations with harvesting carried out every 2 years and
a production of 10 t ha

1

DM year

1

, is very interesting under

the energetic point of view since the output/input ratio results
to be higher than 13. The largest part of energetic input (47%) is
linked to cultural operations, in particular at the top dressing
(37% of the total energy requirement). In the total balance the
direct energetic cost results to be 1.9% and the indirect

energetic cost the 5.8%. The poplar SRF is not the same from
economic point of view. In order to get economic SRF
sustainability, the biomass price shall be at least 77V t

1

D.M.

A large biomass diffusion will be possible only with an
increase of the biomass market value or with economic
support for the production. It is to underline that SRF culti-
vation can contribute to solve the problem of the exceeding
traditional cultivations and that it is able to improve the
relations between agriculture and environment. It’s getting
more important to find low environmental impact cultural
solutions able to maximize the biomass yield by using the
poplar auxometric curve.

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