Identification of the Main Factors Affecting the Environmental Impact
of Passive Greenhouses
A. Anton, J.I. Montero and P. Muñoz
1
Institut de Recerca i Tecnologia
Agroalimentària. Centre de Cabrils
Ctra. de Cabrils s.n. 08348, Cabrils
Barcelona
Spain
F. Castells
Department of Chemical Engineering
ESTEQ
Universitat Rovira Virgili
43007 Tarragona
Spain
Keywords: life cycle assessment, sustainable greenhouse, cladding material
Abstract
The objective of this study was to quantitatively evaluate the environmental
impact of tomato production in passive greenhouses and to identify the most relevant
environmental issues. The LCA approach was used in this study. A tomato crop was
cultivated in a steel-framed greenhouse; plants were grown in a closed-loop irrigation
system in which the substrate was perlite bags. With the exception of the toxicity
indicators, the main sources of environmental impact were fertilizer production and
the process for manufacturing the materials used for the greenhouse structure and the
auxiliary equipment, substrate, irrigation and recirculation equipment. The relatively
short life span of plastic covered greenhouse structures and the minimal input of
external energy involved in the production process are the most important factors
related with the production process. The study compared the use of two cladding
materials: rigid PC sheet with a lifespan of 10 years and flexible LDPE film with a life
of three years. The types of cladding compared in this study (PC sheet and LDPE film)
are not particularly relevant for environmental analysis.
INTRODUCTION
Life Cycle Assessment, LCA, is a tool for assessing the potential environmental
impact of a given product or a system and considers the entire life cycle of a product from
resource extraction to waste disposal. According to ISO standardisation guidelines an
LCA study can be divided into four steps: goal and scope definition, inventory analysis,
impact assessment, and interpretation. When defining goal and scope, the aim and the
subject of the LCA study are determined and a ‘functional unit’ - for instance, yield per
square meter- is defined. In inventory analysis, all extractions of resources and emissions
of substances attributable to the studied functional unit are listed. Impact assessment
determines the magnitude of the potential impact of individual substances within each
impact category. Impact categories correspond to particular environmental problems, such
as human toxicity or ozone depletion. The final step in an LCA study involves
interpreting the results obtained from the previous three steps, drawing conclusions and
formulating recommendations (Antón et al., 2002).
When this procedure is applied to an agricultural product grown in a greenhouse,
not only are the adverse environmental effects derived from the whole of the production
process in question (these include: eutrophication, pollution associated with the use of
pesticides, and waste generation) but other aspects must also be taken into account, such
as the environmental impact associated with the manufacturing and transport of raw
materials, energy use, the production of materials used for building greenhouses, the
waste generated when the facilities are retired from use, and all of the other aspects that
form part of the life cycle of the considered product and which may produce a negative
environmental impact. All of them will have to be accounted for, by attributing a different
environmental impact to each product unit (Antón, 2004).
Previous works on the application of LCA in protected horticulture relate to
projects in northern Europe. They show that reducing heating requirements is a priority if
environmental loading is to be limited (Jolliet, 1993, Bucher et al., 1996, Nienhuis et al.,
Proc. IC on Greensys
Eds.: G. van Straten et al.
Acta Hort. 691, ISHS 2005
489
1996, Jungbluth et al., 2000, Van Woerden, 2001). Artificial lighting is a technique that
also has a major impact on the environment (Jolliet, 1993, Van Woerden, 2001). However,
most greenhouses located in the Mediterranean basin could be considered as passive
systems since they use very little external energy. As a result, factors other than heating
and lighting are the cause of the environmental burden of these passive greenhouses.
The objectives of this study were to quantitatively evaluate the environmental
impact of tomato production in passive greenhouses and to identify the most relevant
environmental issues associated with the materials used throughout their life cycles; from
their origins as raw material until their end as waste.
MATERIALS AND METHODS
The LCA approach (Audsley, 1997, Guinée et al., 2002) was used in this study
assigning Life Cycle Inventory results to the different impact categories. The following
category indicators, that are typically used in LCA, were assessed using the software
TEAM (Ecobilan, 1999): climate change; depletion of the ozone layer; photochemical
oxidant formation; air acidification; depletion of non-renewable resources; eutrophication; human toxicity; aquatic and terrestrial ecotoxicity.
Data from tomato crops cultivated in a steel-framed greenhouse were used. Plants
were grown in a closed soilless system in which the substrate was perlite bags. The study
also compared the use of two cladding materials: rigid polycarbonate, PC, sheets with a
life expectancy of 10 years and a flexible low density polyethylene, LDPE, film with a
working life of three years. This study only considers the means of production, so the
analyses were ended when the tomatoes were harvested; “at the farm gate”. Non-yield
biomass was composted and reused on other exploitations and the rest of the waste was
disposed of in landfills. The functional unit describes the primary function performed by a
product system: in this case, it provided a reference against which input and output data
were compared and standardised in the mathematical sense (ISO-14040, 1997). As the
main function of a greenhouse is to grow produce, tomato production in kg was selected
as the functional unit.
1) Tomato production
Due to its complexity and in order to facilitate study, the tomato production was
divided into five sub-systems:
1.a) Greenhouse management during tomato production
1.b) Fertilizer production
1.c) Fertilization and irrigation
1.d) Pesticide production
1.e) Pest management
2) Manufacturing
Two further subsystems were added in order to take into consideration the
different process and materials used to manufacture the greenhouse structure and the
auxiliary equipment, fertilization and irrigation system:
2.a) Greenhouse structure
2.b) Auxiliary equipment
3) Waste
A final system was analysed, which included the management of waste generated
during and at the end of greenhouse crop cultivation.
RESULTS AND DISCUSSION
Table 1 shows the overall impact of the global process of tomato greenhouse
cropping for the different impact categories and their percentage contribution to the
different subsystems considered. With relation to climate change, it is important to point
out that as a result of fixation of CO2 by the crop, there is a reduction of total CO2
releases.
490
Fertiliser production was the main stage in the cycle that contributed to climate
change, 57.2%, eutrophication, 33.9% and air acidification, 30%. During crop production,
pesticides were mainly responsible for the toxicity indicator scores, while the waste
system was the main contributer to both eutrophication and climate change: it contributed
21% to both and also 5% to aquatic toxicity. Eutrophication generated by the fertirrigation
subsystem, was low due to the fact that the crop system analysed was a closed-loop
irrigation system in which leachetes were re-circulated.
The main reason for the high rate of depletion of non-renewable resource was the
consumption of more material: substrates, collecting pipes, benches, and plastics, in
closed-loop irrigation systems. The use of perlite as a substrate, a natural resource that
consumes natural gas in its process of thermal expansion, was a particular source of
concern.
In previous work comparing closed systems with free drainage and soil cultivation
(Antón, 2004), it was shown that while eutrophication clearly improved in closed
systems, other factors, such as the depletion of non-renewable resources and the formation of photochemical oxidants, increased due to the greater quantity of material used in
these systems.
The auxiliary equipment (substrates, fertirrigation and recirculation equipment)
made the greatest contributions to the categories of air acidification, 76.6%, climate
change, 50.6%, photochemical oxidant formation, 36.3% and air acidification, 27.2%.
The greenhouse structure subsystem (steel frame and cladding) mainly contributed to the
categories of climate change, 39.5%, photochemical oxidant formation, 36.1% and air
acidification, 25.2%. The two subsystems constituted the total infrastructure of the tomato
greenhouse crop and contributed the highest source for environmental impact. These
results contrasted with those for industrial systems, where the impact of infrastructure
equipment is negligible, and concorded with those presented by Cowell (1998) for
agricultural systems. The reasons for this are to be found, on the one hand, in the
characteristics of the materials used; which have a short life span in comparison with
industrial equipment and, on the other, in the minimal consumption of fossil energy
during crop production. It should be remembered that solar energy is the main energy
source for horticulture in Southern Europe.
Comparisons between the two cladding materials; LDPE and PC sheets, reveal
similar values from an environmental point of view. The use of PC sheets increases
eutrophication and air acidification (by 6% and 5%, respectively) while it reduces damage
such as photochemical oxidant formation and climate change (by 9% and 4%
respectively).
Manufacture of polycarbonates makes greater contributions to eutrophication and
the depletion of non-renewable resources (Fig. 1a and 1b). On the other hand the shorter
life span of LDPE increases its environmental impact, particularly with respect to waste
generation that contributes to air acidification and climate change (Figs. 1c and 1d).
CONCLUSIONS
The greenhouse structure has the greatest impact in all of the environmental
categories except the toxicity indicators. This is due to the relatively short life span of
plastic covered greenhouse structures and by minimal inputs of external energy in the
production process.
The types of cladding compared in this study (PC sheet and LDPE film) are not
particularly important as regards the environmental analysis.
Further research must be oriented towards reducing the environmental impact of
the materials used in the facilities for passive greenhouse crops. Their substitution by
recycled materials with a long life span could be a possible solution. Improving fertiliser
use and looking for alternative local substrates, preferably derived from reused materials
are other important points to take into account.
491
ACKNOWLEDGEMENTS
This research was partially supported by INIA nº SC00-080-C2 and nº RTA03096-C5-2.
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492
493
0.100
0.023
0.027
81.4
2.E-05
0.170
39127
5.32
134.1
Depletion of non-renewable
resources. year-1
Air Acidification. g eq. H+
Climate change. g eq. CO2
Depletion of the ozone layer. g eq.
CFC11
Photochemical oxidant formation.
g eq. ethylen
Human Toxicity. g eq. Pb air
Aquatic toxicity. g eq. Zn water
Terrestrial toxicity. g eq. Zn air
TOTAL
Eutrophication, g eq. PO4
TOTAL
134.1
5.1
39126
0.045
2.E-05
-8.69
0.013
0.004
0.041
Greenhouse
management %
0.0
0.0
0.0
19.2
70.1
-76.3
12.7
2.8
5.9
Fertilizer
production %
0.0
0.0
0.0
5.8
7.7
57.2
30.0
15.6
33.9
Fertirrigation %
0.0
0.0
0.0
1.2
3.6
6.9
3.7
0.2
1.2
Pesticide
production %
0.0
0.0
0.0
0.1
0.6
0.4
0.2
0.0
0.1
100
95.2
100
0.2
0.5
1.1
0.6
0.0
0.2
TOTAL
0.00005
0.002
0.467
0.123
3.E-06
73.25
0.014
0.019
0.038
Greenhouse
structure %
25.2
5.4
0.0
0.0
0.0
1.1
3.3
0.0
0.0
0.0
36.1
9.9
20.6 39.5
0.3
-0.6
21.4 19.1
Auxiliary
equipment %
Manufacture
Waste
6.E-05
0.249
0.135
0.002
6.E-07
16.79
0.0001
-0.0002
0.021
TOTAL
Tomato Production
Pest
management %
Table 1. Total absolute values for tomato greenhouse crop in a closed system for each environmental category considered and percentage
contributions to the overall process for the different subsystems studied.
Tables
493
0.0
0.05
0.0
36.3
4.2
50.6
27.2
76.6
18.3
Waste %
0.025
0.020
0.015
0.010
0.005
0.000
Air acidification, g eq. H+
PC
LDPE
8.0E-05
7.0E-05
6.0E-05
5.0E-05
4.0E-05
3.0E-05
2.0E-05
1.0E-05
0.0E+00
PC
LDPE
Depletion of abiotic resources, year-1
Eutrophication, g eq. PO4
0.030
0.0018
0.0016
0.0014
0.0012
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
Climate change, g eq. CO2
Figurese
18.000
16.000
14.000
12.000
10.000
8.000
6.000
4.000
2.000
0.000
PC
LDPE
PC
LDPE
Fig. 1. Comparisons between the two cladding materials. PC sheet and LDPE film.
Contribution of the plastic manufacture subsystem to the eutrophication and
depletion of non-renewable resource categories. Contribution waste management
system to air acidification and climate change categories.
494