Quantifying the environmental impact of
production in agriculture and horticulture in
The Netherlands: which emissions do we need
to consider?
J.C. Pluimers
a,*, C. Kroeze
a, E.J. Bakker
b, H. Challa
c,
L. Hordijk
aaEnvironmental Systems Analysis Group, Wageningen University, PO Box 9101, 6700 HB Wageningen, The Netherlands
bDepartment of Mathematics, Wageningen University, Wageningen, The Netherlands
cDepartment of Agricultural Engineering and Physics, Wageningen University, Wageningen, The Netherlands
Received 18 February 1999; received in revised form 25 July 2000; accepted 25 August 2000
Abstract
This study focuses on the environmental impact of agricultural production. The aim of the study is to identify the most important sources of greenhouse gases, acidifying and eutro-phying compounds in Tomato Cultivation, Greenhouse Horticulture and Total Agriculture in The Netherlands. Within each of these three sectors we distinguish two systems. The System Agriculture (System A) includes the ®rst-order processes of the agricultural production chain and the System Industry (System I) includes some second-order processes. Results indicate that, in general, System A emissions exceed System I emissions. However, in some cases emissions from System I are relatively high compared to System A emissions, and need to be considered when quantifying the total environmental impact of agricultural production. For example, acidifying emissions from the production of electricity and rockwool (both second-order processes) contribute almost 25% to the total acidifying emissions from System
Greenhouse Horticulture A+I.#2001 Elsevier Science Ltd. All rights reserved.
Keywords:Environmental systems analysis; Agriculture; Protected cultivation
0308-521X/01/$ - see front matter#2001 Elsevier Science Ltd. All rights reserved. P I I : S 0 3 0 8 - 5 2 1 X ( 0 0 ) 0 0 0 4 6 - 9
1. Introduction
Agricultural production in The Netherlands contributes to various environ-mental problems. Well-known environenviron-mental problems due to agriculture are often related to speci®c activities and sectors. Dutch greenhouse horticulture, for exam-ple, is associated with relatively large emissions of the greenhouse gas carbon dioxide (CO2) resulting from the combustion of natural gas. At the level of the
total agricultural sector, on the other hand, the emissions of acidifying ammonia from animal waste are usually considered a major contributor to environmental problems.
Several studies have been published on the environmental impact of agricultural production in The Netherlands. These studies dier in their choice of system boundaries. Sometimes system boundaries are related to economic sectors at a national scale (e.g. RIVM, 1997). In this way, emissions from fuel combustion in farms are assigned to agriculture, while emissions from power plants are assigned to the energy sector. Other studies on the environmental impact of agriculture focus on the whole production chain of, for instance, a particular crop by using the methodology of environmental Life Cycle Assessment (LCA) (Nienhuis and de Vreede, 1994a, b; Wegener Sleeswijk et al., 1996). LCA is a tool for assessing the environmental impact of a product (Heijungs et al., 1992). Characteristic for LCA is that it aims to cover the entire life cycle from cradle to grave and to include all relevant environmental problems related to the product analysed.
Formulation of system boundaries is part of the ®rst step in environmental sys-tems analysis (Table 1) (Checkland, 1979; Wilson, 1984). Usually, environmental systems analysis deals with policymaking and aims at ®nding solutions to complex problems that arise in society by describing the system and analysing alternatives to the system. When de®ning system boundaries, one needs to take into account spatial as well as temporal aspects. The de®nition of system boundaries partly depends on the focus and purpose of the study. When studying an economic sec-tor, one may chose to de®ne sub-sectors to describe the most important aspects of a heterogeneous sector. Temporal boundaries indicate whether the analysis focuses
Table 1
The methodology of systems analysis in six steps as described by Wilson (1984) and Checkland (1979)
Step 1 In the ®rst step the problem is de®ned. The system boundaries, level of aggregation and input output relations are described
Step 2 In the second step the objectives of the analysis are clari®ed and the model demands are appointed
Step 3 During the third step the system synthesised, i.e. a model is built, system functions are listed and alternatives to the current situation are collected
Step 4 The system is analysed by using the model developed in the third step. Uncertainties are deduced and the performance is compared with the objectives
Step 5 In the ®fth step the optimum system is selected. The decision criteria are described and the consequences are evaluated
on the present situation or also includes past or future trends. In this study we focus on system boundaries within the present horticultural and agricultural production chain (Fig. 1).
When analysing the emissions of pollutants related to the agricultural sector, ide-ally, one would aim for a full LCA approach for all products of the agricultural sector. However, this is not feasible because of the complexity and heterogeneity of the agricultural sector and the amount of data and time needed for such an analysis. The question then rises what parts of the production chain have to be described to analyse a certain environmental problem related to agricultural production, without performing full LCAs for all products involved; in other words, what are the system boundaries and how can we decide which inputs, outputs and processes have to be taken into account and which can be ignored? This study aims at contributing to an answer to this question.
We focus on three sectoral aggregation levels in this study. Our primary interest is the analysis of the environmental impact of the greenhouse horticultural sector in The Netherlands, at a sectoral level resulting in recommendations to policy makers. The greenhouse horticultural sector is a relatively heterogeneous sector, both in terms of economic activities and with respect to its environmental impact. Rabbinge and Van Ittersum (1994) formulated guidelines to cope with tensions between aggregation levels. They recommend to include the next lower and next higher aggregation level
in systems analysis in order to determine the relation between the aggregation levels. In our study we therefore will analyse system boundaries for Greenhouse Horticulture (primary focus), Tomato Cultivation (a level lower) and Total Agri-culture (a level higher).
The aim of this study is to identify the most important present-day emissions of greenhouse gases, acidifying compounds and eutrophying compounds related to agricultural production in The Netherlands. For this purpose we will estimate emissions resulting from activities within the agricultural sector (i.e. ®rst-order pro-cesses) as well as answer the question whether emissions due to the production of most important inputs for the agricultural sector, such as fertilisers, biocides and electricity (second-order processes) need to be taken into account. We will include the most important greenhouse gases [carbon dioxide (CO2), methane (CH4)
and nitrous oxide (N2O)], acidifying compounds [sulphur dioxide (SO2), nitrogen
oxide (NOx) and ammonia (NH3)], and eutrophying compounds [nitrogen (N) and
phosphorus (P)].
2. Methodology
In this section we ®rst describe the dierent systems included in the analysis (sys-tem de®nition). Next, the method for calculating the emissions (calculation of emis-sions and environmental impact) is presented and we list the source of emission data or data used for the calculation of the emissions (data collection).
2.1. System de®nition: System A and System A+I
The agricultural sector is studied here at three dierent aggregation levels (Tomato Cultivation, Greenhouse Horticulture, Total Agriculture). At each of these levels two dierent systems are distinguished: System Agriculture and Sys-tem Agriculture+Industry (Table 2, Fig. 1). Basically, SysSys-tem A (Agricult-ure) includes the inputs and outputs of the agricultural production system in a strict sense (®rst-order processes). System I (Industry) includes the production of electricity, fertilisers, biocides and rockwool, which we consider second-order processes. The inputs and outputs of System A consist of direct production factors, respectively, emissions resulting from the use of these direct production fact-ors which include fossil fuels, fertilisers, biocides and rockwool. The inputs to System I include indirect production factors while the output consists of fertilisers, biocides, rockwool and electricity produced and the related emissions. Thus in total we will consider six systems: System Tomato Cultivation A and A+I, Sys-tem Greenhouse Horticulture A and A+I, and SysSys-tem Total Agriculture A and A+I (Table 2). We will also quantify indirect N2O emissions as result from
N use in agriculture. These emissions are described in the IPCC emission calcula-tion method (IPCC, 1997) and it is known that these N2O emissions account for
about one-third of the total agricultural N2O emissions worldwide (Mosier et al.,
1998).
2.2. Calculation of emissions and environmental impact
We analysed the emissions of CO2, CH4and N2O (greenhouse gases), SO2
(acid-ifying gas), NOxand NH3(acidifying gases and eutrophying gases), NO3and PO4
(eutrophying compounds). Most of the emissions are either estimated by using emission inventory data from literature or calculated as a function of agricultural activities and some emission factors (Tables 3 and 4):
EMISSIONf ACTIVITY; EMISSION FACTOR 1
Activities in System A include use of energy, biocides and fertilisers (N and P). In System A also the production of manure and processes resulting in NH3emissions
from stables are included. System I describes the production of electricity, fertilisers, biocides and rockwool.
For each of the compounds considered, the integrated impact of emissions is cal-culated as (Heijungs et al., 1992) (Table 5):
IMPACTEMISSIONCLASSIFICATION FACTOR 2
In this analysis we use as classi®cation factors the Global Warming Potentials (GWPs) de®ned by the IPCC (1997), and acidi®cation and eutrophication potentials as described by Heijungs et al. (1992) (Table 5). The GWP is an index of cumulative radiative forcing between the present and some chosen later time horizon caused by a unit mass of gas emitted now, expressed relative to the reference gas CO2(1 kg
CO2) (Houghton et al., 1995). Heijungs et al. (1992) describe classi®cation factors
for substances contributing to acidi®cation and eutrophication expressed in SO2
-equivalents and PO4-equivalents, respectively.
Table 2
Description of the systems studied: System Tomato Cultivation Agriculture (A) and Agriculture and Industry (A+I), System Greenhouse Horticulture A and A+I and System Agriculture A and A+I
Tomato Cultivation Greenhouse Horticulture Total Agriculture
System A Environmental impact
System A+I As System A but including the environmental impact of the production of electricity, fertilisers, biocides and rockwool (System Industry)
2.3. Data for Tomato Cultivation and Greenhouse Horticulture
The emissions from Tomato Cultivation and Greenhouse Horticulture are esti-mated following Eq. (1). This requires input data on activities and related emission factors. These data are listed in Tables 3 and 4, respectively.
For the production of fertilisers and biocides (both activities in System I) we dis-tinguished between energy-related and process-related emissions (Table 4). Process-related emissions are released during the chemical production process. Energy-rela-ted emissions are relaEnergy-rela-ted to the production of energy used in the chemical process. We assumed that all electricity used in the production of fertilisers and biocides is produced by a coal-®red power plant and thus we used the same emission factors as for electricity production (Table 4). This assumption can be considered a worst case scenario, because in practice electricity is produced from a mix of fuels.
For Greenhouse Horticulture we distinguished between soil and rockwool culti-vation. Based on the area of vegetables, ornamentals, soil and rockwool cultivation (CBS, 1996) on the one hand and fertiliser use in vegetables and ornamentals on the Table 3
Activity data for the calculation of the emissions from Tomato Cultivation, Greenhouse Horticulture and Total Agriculture in The Netherlands as used in Eq. (1)
Activity Value Reference
Tomato Cultivationa
Gas use 8.79108m3 KWIN, 1993
Electricity use 1.25108kWh Nienhuis and de Vreede, 1994a Fertiliser N use 1733 ton N Nienhuis and de Vreede, 1994a Fertiliser P use 409 ton P Nienhuis and de Vreede, 1994a
Rockwool use 12.8 kton Van der Berg and Lankreijer, 1994; CBS, 1996
Biocide use 11.3 ton CBS, 1996, 1997b
Greenhouse Horticultureb
Gas use 4.3109m3 Van der Velden et al., 1995
Electricity use 9.2108kWh Van der Velden et al., 1995 Fertiliser N use in soil cultivation 4259 ton N Poppe et al., 1995, CBS, 1996 Fertiliser N use in rockwool cultivation 4500 ton N Poppe et al., 1995, CBS, 1996 Fertiliser P use in soil cultivation 868.6 ton P Poppe et al., 1995, CBS, 1996 Fertiliser P use in rockwool cultivation 924.9 ton P Poppe et al., 1995, CBS, 1996
Rockwool use 25.2 kton IKC, 1995
Biocide use 704 ton Poppe et al., 1995
Total Agriculturec
Electricity use 9 PJ CBS, 1997a
Fertiliser use N 412 kton N Kroeze, 1994
Fertiliser use P 60 kton P CBS, 1997a
Biocide use 5812 ton CBS, 1997b
Rockwool use 25 200 ton IKC, 1995; CBS, 1996
a Area sector Tomato Cultivation is 1505 ha (CBS, 1996). b Area sector Greenhouse Horticulture is 10 144 ha (CBS, 1996). c Area sector Total Agriculture is 2106ha (Kroeze, 1994).
Table 4
Emission factors as used in Eq. (1) for the calculation of the emissions from Tomato Cultivation, Green-house Horticulture and Total Agriculture in The Netherlands
Activity Emission factor Reference
Emission factors related to activities in System A
Gas use
CO2 1.776 kg/m3natural gas IPCC, 1997; Boersema et al., 1986 N2O 7.2010ÿ5kg/m3natural gas IPCC, 1997; Boersema et al., 1986 NOx 1.4210ÿ3kg/m3natural gas IPCC, 1997; Boersema et al., 1986 CH4 9.510ÿ5kg/m3natural gas Berdowski et al., 1993
Fertiliser use in soil cultivation in greenhouses
N-fertiliser use
N2O 0.03 kg N2O-N/kg N All emission factors are estimated from the studies of Mosier et al. (1998), Daum and Schenk (1996),
Fertiliser use in rockwool cultivation in greenhouses
N-fertiliser use
N2O 0.01 kg N2O-N/kg N All emission factors are estimated from the studies of Mosier et al. (1998), Daum and Schenk (1996),
Emission factors related to activities in System I
Electricity production
CO2 0.834 kg/kWh IPCC, 1997; McInnes, 1996
CH4 9.010ÿ6kg/kWh IPCC, 1997; McInnes, 1996
N2O 1.2610ÿ5kg/kWh IPCC, 1997; McInnes, 1996
NOx 1.3510ÿ3kg/kWh IPCC, 1997; McInnes, 1996
SO2 3.910ÿ4kg/kWh IPCC, 1997; McInnes, 1996
Fertiliser production
N-fertiliser
Process-related emissions Kroeze and Bogdanov, 1997
N2O 2.710ÿ2kg/kg N Biewinga and Van der Bijl, 1996
NOx 1.5810ÿ3kg/kg N Biewinga and Van der Bijl, 1996
NH3 3.7210ÿ3kg/kg N
Energy-related emissionsa
CO2 2.5 kg/kg N All emission factors are estimated
other (Poppe et al., 1995), we estimated total fertiliser use in these two cultivations (soil and rockwool cultivation).
2.4. Data for Total Agriculture
The estimated emissions from the Total Agricultural sector are mainly based on studies by the National Institute for Public Health and the Environment (RIVM) (Van der Hoek, 1994; RIVM, 1996, 1997; Spakman et al., 1997). In some cases the estimated emissions are based on additional assumptions.
RIVM uses a de®nition for agriculture that is almost identical to System A described here. The only exception is indirect emissions of N2O from soils, that
RIVM assigns to agriculture (our System A) but are assigned to System A+I in the present study. The System A estimates for greenhouse gases, acidifying gases and eutrophying compounds are mostly based on RIVM studies (Kroeze, 1994; Van der Hoek, 1994; RIVM, 1996; Spakman et al., 1997). The only additional assumption Table 4 (continued)
CO2 0.705 kg/kg P All emission factors are estimated
from France and Thompson (1993),
CO2 4.77 kg/kg active ingredient All emission factors are estimated from France and Thompson (1993), IPCC (1997) and McInnes (1996) CH4 5.1510ÿ5kg/kg active ingredient
N2O 7.210ÿ5kg/kg active ingredient NOx 1.5010ÿ2kg/kg active ingredient SO2 2.1510ÿ2kg/kg active ingredient
Rockwool production
CO2 0.168 kg/kg rockwool Kaskens et al., 1992
SO2 1.9210ÿ3kg/kg rockwool Kaskens et al., 1992
NOx 0.02 kg/kg rockwool Kaskens et al., 1992
NH3 1.210ÿ3kg/kg rockwool Kaskens et al., 1992
a Energy-related emissions from N-fertiliser production are based on an energy use of 27 MJ/kg N (Melman et al.,1994).
b Energy-related emissions from P-fertiliser production are based on an energy use of 7.6 MJ/kg P (France and Thompson, 1993; Melman et al., 1994).
c Energy-related emissions from biocide production are based on an energy use of 51.5 MJ/kg active ingredient (Melman et al., 1994).
for System A is that 2.5% of the fertiliser N use is emitted as NOx, while total fer-tiliser N use in The Netherlands was 412 kt N in 1990 (Kroeze, 1994).
The emissions for System I include emissions released during the activities of the production of electricity, fertilisers, biocides and rockwool (Table 3 lists the asso-ciated activity levels). The emission factors assoasso-ciated with these activities in System I are the same as for Tomato Cultivation and Greenhouse Horticulture (Table 4).
3. Results
The estimated emissions related to speci®c activities within System A and System I for the three aggregation levels are presented in Table 6. The emissions are expressed in kg compound as well as in CO2-equivalents (CO2-eq), SO2-equivalents (SO2-eq)
and PO4-equivalents (PO4-eq).
3.1. Results for sector Tomato Cultivation
Total greenhouse gas emissions from Tomato Cultivation are mainly from System A (Figs. 2 and 3A). CO2emissions have by far the highest share in total greenhouse
gas emission of System Tomato Cultivation A+I. CO2 emissions resulting from
combustion of natural gas in System A contribute 90% to the total emission of greenhouse gases in System A+I. Production of electricity in System I results to the second highest source of greenhouse gas emissions by CO2emissions. The emissions
of NOx from System A are about half of total NO2 emissions, but are relatively
small compared to CO2emissions.
Table 5
Classi®cation factors used in Eq. (2) for emissions of greenhouse gases (in CO2-equivalents), acidifying gases (in SO2-equivalents) and eutrophying compounds (in PO4-equivalents)
Environmental theme Compounds Classi®cation factor References/notes
Global warming CO2 1 kg=1 CO2-eq Over 100 years: from IPCC, 1997
CH4 1 kg=21 CO2-eq
N2O 1 kg=310 CO2-eq
Acidi®cation SO2 1 kg=1 SO2-eq From Heijungs et al., 1992 NOxa 1 kg=0.7 SO2-eq
NH3 1 kg=1.88 SO2-eq
Eutrophication NOxa 1 kg=0.13 PO4-eq From Heijungs et al., 1992 NH3 1 kg=0.35 PO4-eq
NO3 1 kg=0.10 PO4-eq
N 1 kg=0.42 PO4-eq
PO4 1 kg=1 PO4-eq
P 1 kg=3.06 PO4-eq
a NO
Table 6
Results for Systems Tomato Cultivation, Greenhouse Horticulture and Total Agriculture A and I
Tomato Cultivation Greenhouse Horticulture Total Agriculture
System A System I System A System I System A System I
kton kton
Gas use/fuel use in agriculture 1560 1560 0 0 7672 7672 0 0 8600 8600 0 0
Electricity production 0 0 104 104 0 0 767 767 0 0 1918 1918
Fertiliser N/P production 0 0 5 5 0 0 23 23 0 0 1787 1787
Biocide production 0 0 1 1 0 0 3 3 0 0 28 28
Rockwool production 0 0 2 2 0 0 4 4 0 0 4 4
Total 1560 1560 111 111 7672 7672 797 797 8600 8600 3727 3727
CH4
Total greenhouse gas emissions 1590 134 7861 958 28 206 10 754
System A System I System A System I System A System I
Electricity production 0 0 169 118 0 0 1242 869 0 0 2.8 2
Fertiliser N/P production 0 0 18 13 0 0 92 64 0 0 0.9 0.6
Biocide production 0 0 <1 <1 0 0 11 7 0 0 0.1 0.1
Rockwool production 0 0 256 179 0 0 504 353 0 0 0.5 0.4
Total 1391 973 443 310 6854 4798 1849 1293 19 13 4.3 3.1
NH3
Total acidifying emissions 973 446 4798 1937 388 15
Table 6 (continued)
Tomato Cultivation Greenhouse Horticulture Total Agriculture
System A System I System A System I System A System I
ton N
Total eutrophying emissions 369 70 2800 281 439 4
a N
2O formation in remote soils and waters induced by agricultural N after volatilisation or leaching. b From RIVM (1996) indicated as total N and P to soil (is excluding NO
Fig. 2. Emissions of greenhouse gases (CO2, CH4 and N2O, and total CO2-equivalents), acidifying compounds (SO2, NOx and NH3 and total SO2
-equivalents) and eutrophying compounds (N and P, and total PO4-equivalents) as result of: (A) Tomato Cultivation; (B) Greenhouse Horticulture; and (C)
Total Agriculture. Units are listed in the ®gure. For Total Agriculture emissions of NH3, SO2-eq, N, P and PO4-eq are divided by 10.
Pluimers
et
al.
/
Agricultura
l
System
s
66
(2000)
167±189
Fig. 3. Emissions of greenhouse gases (CO2, CH4and N2O, and total CO2-equivalents), acidifying com-pounds (SO2, NOxand NH3and total SO2-equivalents) and eutrophying compounds (N and P, and total PO4-equivalents) per hectare as result of processes in System A and System I for: (A) Tomato Cultivation; (B) Greenhouse Horticulture; and (C) Total Agriculture in The Netherlands.
Tomato Cultivation System I has a considerable part in total acidifying emissions from System A+I (about 30%). NOx emissions contribute 90% to total acidify-ing emissions from System A+I. Most of this NOxresults from the use of natural gas in System A. Other sources of NOx emissions are rockwool production and production of electricity which are both assigned to System I and from the use of N-fertiliser which is assigned to System A (Table 6). SO2and NH3are only emitted in
System I and are relatively moderate contributors to acidifying emissions in Tomato Cultivation.
Eutrophying emissions from System A account for 84% of total eutrophying emissions from Tomato Cultivation. The use of fertiliser (N and P) in System A accounts for almost half of total eutrophying emissions in System A+I. The use of natural gas contributes about 37% to total eutrophying emissions in System A+I. Eutrophying emissions from System I can mainly be attributed to production of rockwool and electricity and only consist of N compounds.
3.2. Results for sector Greenhouse Horticulture
Total greenhouse gas emissions from Greenhouse Horticulture are mainly from CO2from System A (Figs. 2 and 3B). The most important source of these emissions
is the combustion of natural gas (Table 6). Production of electricity results in almost one-10th of total greenhouse gas emissions in System A+I. As for the System Tomato Cultivation, N2O is the second greenhouse gas of importance and is emitted
in both System A and I in equal proportions.
For acidi®cation, the use of natural gas is also an important source of emissions (about 60%). Other activities of interest contributing to acidi®cation are resulting from the production of electricity (SO2and NOx) and the production of rockwool (NOx).
Most of the emissions of eutrophying compounds to the environment are included in System A (90% of total emissions). Gas use and use of N fertilisers have about equal shares in emissions of N compounds from System A (Table 6). When expres-sed in kg N or P the emissions of P compounds are not as high as the emissions of N compounds from System A, but due to dierences in classi®cation factors (Table 5) the total impact of emissions of P is relatively high in System A (Table 6).
3.3. Results for sector Total Agriculture
For the sector Total Agriculture the greenhouse gas emissions from System I amount to about one-third of the total emissions (Figs. 2 and 3C). These Sys-tem I emissions include CO2and N2O from the production of electricity, fertiliser
and rockwool and indirect soil emissions. Fertiliser use and production are the most important source of N2O, with about equal contribution from emissions included in
System A (soils and stables mainly) and System I (industrial production of fertiliser and indirect soil emissions mainly) (Table 6).
The greenhouse gases CO2and CH4have about equal share (about 30%) in total
emissions (Fig. 2). Emissions of CO2 are mainly from fuel use within agricultural
sector (System A). Emissions of CH4are almost entirely from animal production
systems, which is also included in System A.
Most of the acidifying emissions estimated for System A+I are included in Sys-tem A (96%). In other words, electricity production and industrial production of fertilisers and rockwool are relatively small sources of acidifying compounds com-pared to the emissions from animal production systems.
Also for eutrophying emissions, System A contributes more then 95% to total emissions. These emissions are mainly from the use of fertilisers and from animal manure excretion.
3.4. Tomato Cultivation versus Greenhouse Horticulture
The results for sectors Tomato Cultivation and Greenhouse Horticulture show several similarities (Fig. 3). For instance, in both sectors gas use and related CO2
emissions are relatively high and in both sectors CO2is the most important
green-house gas. Both Tomato Cultivation and Greengreen-house Horticulture contribute to acidi®cation mainly through emissions of NOx from gas use, use of fertilisers and production of electricity and rockwool. And for both sectors it was found that SO2
and NH3are only emitted from System I.
On the other hand, the sectors Tomato Cultivation and Greenhouse Horticulture dier with respect to the use of electricity (Fig. 3). Use of electricity and related NOx emissions in Tomato Cultivation are, on an area basis, lower than the average elec-tricity use in Greenhouse Horticulture. This is caused mainly by use of supplemen-tary lighting in cut ¯ower production. Nevertheless, total NOxemissions in System A+I per hectare are higher in Tomato Cultivation, because of rockwool production for Tomato Cultivation in System I (see below).
Another dierence is related to the use of rockwool. In The Netherlands, virtually all tomatoes are cultivated on rockwool and almost none in soil. Of the total greenhouses, however, about 35% of the area is being cultivated on rockwool and about 65% in soil (CBS, 1996). These dierences are re¯ected in the relative con-tribution of System I emission due to rockwool production, as well as for System A emissions due to fertiliser use. The use of rockwool is often combined with recircu-lation of water and nutrients, which results in lower losses of N and P to the envir-onment per kg fertiliser used. However, use of N and P are relatively high for Tomato Cultivation so that, per hectare, emissions resulting from production of fertilisers are higher for the sector Tomato Cultivation than for the sector Green-house Horticulture (Fig. 3).
3.5. Tomato Cultivation and Greenhouse Horticulture versus Total Agriculture
We observed two important dierences between agricultural production in greenhouses and the total Dutch agricultural sector. The ®rst relates to the relative importance of the compound emitted form the dierent sectors. While in Tomato Cultivation and Greenhouse Horticulture CO2is by far the most important
greenhouse gas, emissions from Total Agriculture also include considerable amounts of other greenhouse gases as CH4 and N2O. These are emitted from animal
pro-duction systems and fertilised soils (Fig. 2). Secondly, we observed large dierences in areal emissions from dierent sectors. For instance, when expressed per hectare, greenhouse gas emissions from the sector Total Agriculture (Fig. 3) are considerably lower than emissions from Tomato Cultivation and Greenhouse Horticulture. Acidifying emissions in sector Total Agriculture are mainly from NH3 emissions
from animal husbandry, while in both sectors Tomato Cultivation and Greenhouse Horticulture NOx plays the most important role in acidi®cation due to use of energy. Eutrophying emissions in sector Total Agriculture are relatively high and can be fully ascribed to System A, while in Tomato Cultivation and Greenhouse Horticulture emissions of N in System I are considerable.
4. Discussion and conclusion
We investigated emissions of greenhouse gases, acidifying gases and eutrophying compounds from horticulture and agriculture in The Netherlands at three dierent aggregation levels: Tomato Cultivation, Greenhouse Horticulture and the Total Agricultural sector. We estimated emissions for these sectors with (System Agricul-ture+Industry) and without (System Agriculture) including second-order processes, which are de®ned as the production of electricity, fertilisers, biocides and rockwool (System Industry). We also addressed the question of what sources to include in an environmental systems analysis.
4.1. Discussion
To calculate emissions we used what we consider the best data available. Never-theless, calculated emissions are subject to uncertainty. In this study no sensitivity or uncertainty analysis has been carried out to analyse the sensitivity of the calculated emissions to uncertainties in assumptions and methods used. Some emission factors are commonly used and widely accepted, e.g. emission factors as described by the IPCC (1997). Other emission factors, however, were not available from the literature and have been estimated based on literature, as are the emission factors for eutro-phying and acidifying compounds related to fertiliser (N and P) use. Also the classi-®cation factors used, such as GWPs, Acidifying and Eutrophying Potentials are surrounded with uncertainties. GWPs are commonly used and accepted as classi®ca-tion factors for greenhouse gases (IPCC, 1997). The classi®caclassi®ca-tion factors for calcu-lating the PO4-equivalents of eutrophying emissions are less widely used and are
based on several assumptions (Heijungs et al., 1992). PO4-equivalents are used in
We assumed some aspects to be irrelevant for our analysis for several reasons. For instance, we did not quantify emissions from transport, such as transport of fertili-sers and rockwool from production plant to greenhouse or farm. We assumed that these emissions are relatively small because fertilisers, biocides and rockwool are produced in The Netherlands (Nienhuis and de Vreede, 1994a). For the same reason emissions during transport of natural gas were ignored. In addition, we only focused on ®rst- and second-order processes and we did not consider capital equipment, like machinery or greenhouse construction. Results of an LCA study of tomato pro-duction in The Netherlands indicate that for the environmental problems considered here (global warming, acidi®cation, eutrophication) ®rst- and second-order pro-cesses are most important contributors to the total impact (Nienhuis and de Vreede, 1994a). Further, Nienhuis and de Vreede (1994a) concluded for the LCA of Dutch tomato production that the production of capital equipment has little in¯uence on the total impact. We assume that this holds for Greenhouse Horticulture and Total Agriculture as well.
We focused our analysis on three environmental problems: climate change, acid-i®cation and eutrophication. The analysis of the eects of the choice of system boundaries and system components is most interesting for these three problems, because of the interrelation between human activities and the emissions. For instance, an activity like gas use results in the emissions of CO2, a greenhouse gas,
and NOx, a compound contributing to the problems of acidi®cation and eutrophi-cation. For the emission of toxic biocides and the production of waste this is dier-ent. For example, the environmental eect of biocides are mainly related to the direct toxic eects caused by the use of biocides (System A) (Reijnders, 1991).
In the analysis we assumed that all electricity was produced in a coal-®red power plant. In reality, part of the electricity is produced in gas- or oil-®red power plants. However, in this analysis we were searching for major contributors to environmental problems and therefore the assumption for the coal-®red power plant seems to be justi®ed. Further, the use of emission factors for a coal-®red power plant increases the possibility to compare results with many other countries where coal is the most important fuel. We ignored the possibility that electricity can be produced by co-generation at the farm. If compared to coal-®red power plants, co-co-generation may result in lower emission of CO2and higher emissions of NOx.Co-generation is only
used on 8% of the total greenhouse area and mainly in cut¯ower and potplant cul-tivation (Van der Velden et al., 1997).
(respectively, 61 vs. 52%). This may be caused by dierences in emission factors. The relative contribution of dierent processes, such as use of fertilisers, combustion of natural gas production of electricity and production of fertilisers, to eutrophica-tion dier only in the contribueutrophica-tion of emissions during the produceutrophica-tion of P-fertilisers. This dierence can be explained by dierences in emission factors (Bùck-man et al., 1990; Hoogenkamp, 1992). In other words, results of this study for the sector Tomato Cultivation are, in general, in good agreement to the results of the complete LCA of tomato cultivation for the three environmental problems.
4.2. Conclusions
For Tomato Cultivation (System Tomato Cultivation A and A+I) the emissions related to activities in System A re¯ect about 92, 69 and 84% of the System A+I emissions for the greenhouse gases and acidifying and eutrophying compounds, respectively (Table 8). Thus, including the emissions during production of electricity, fertiliser and rockwool does not in¯uence the results of the analysis to a great extent in the case of greenhouse gas emissions. However, the production of rockwool and electricity contribute to one-®fth of the total emission of acidifying compounds, a contribution that cannot be ignored. Our conclusion is therefore that a study on the impact of tomato cultivation would need to take into account: (1) CO2emissions
from gas use; (2) NOxemissions from use of gas and fertilisers, and from production of electricity and rockwool; and (3) N and P emissions from fertiliser use (Table 8). Table 7
The contribution of dierent activities to total emissions in Tomato Cultivation, a comparison of the results of this study with the results of a Life Cycle Assessment of Dutch tomato production by Nienhuis and de Vreede (1994a)
Environmental problem and activity Contribution of the activity to total emissions (in %)
Results of this study Results as described by Nienhuis and de Vreede (1994a)
Greenhouse gases
Use of natural gas 92 91
Production of electricity 6 5
Others 2 4
Acidifying compounds
Use of natural gas 61 52
Production of electricity 12 20
Others 27 28
Eutrophying compounds
Use of fertilisers 47 42
Production of P-fertiliser 1 16
Use of natural gas 37 22
Production of electricity 5 5
Table 8
Sources of emissions of greenhouse gases, acidifying gases and eutrophying compounds that contribute at least 90% of the total present-day emissions from three agricultural sectors (Tomato Cultivation, Green-house Horticulture and Total Agriculture) in The Netherlands
Environmental problem Source of emissiona Contribution to total emissions from sector (%)b
Sector Tomato Cultivation
Greenhouse gases CO2from gas use (A) 90
CO2from electricity production (I) 6
Acidifying gases NOxfrom gas use (A) 62
NOxfrom rockwool production (I) 13 NOxfrom electricity production (I) 8
NOxfrom fertiliser use (A) 7
Eutrophying gases NO3and PO4from fertiliser use (N and P) (A) 47
NOxfrom gas use (A) 37
NOx+NH3from rockwool production (I) 9 NOxfrom electricity production (I) 5
Sector Greenhouse Horticulture
Greenhouse gases CO2from gas use (A) 87
CO2from electricity production (I) 9
Acidifying gases NOxfrom gas use (A) 64
NOxfrom electricity production (I) 13
NOxfrom fertiliser use (A) 7
SO2from electricity production (I) 5 NOxfrom rockwool production (I) 5
Eutrophying gases NO3and PO4from fertiliser use (N and P) (A) 65
NOxfrom gas use (A) 26
NOxfrom electricity production (I) 5
Sector Total Agriculture
Greenhouse gases CH4from manure (A) 27
CO2from energy use (A) 22
N2O from fertilised soils (A) 16
N2O indirect emissions (I) 14
N2O from stables (I) 7
N2O in fertiliser production (I) 4
Acidifying gases NH3from fertiliser use (manure) (A) 55
NH3from stables (A) 38
Eutrophying compounds P from fertiliser use (A)c 50
N from fertiliser use (A)c 41
a Between brackets () is indicated whether the source is included in System Agricultural production (A) or System Industry (I).
b From Table 6.
c From RIVM (1996); indicated as total N and P to soil (is excluding NO
For the Greenhouse Horticulture sector (System Greenhouse Horticulture A and A+I) the emissions included in System A represent about 89% of the greenhouse gas emissions, about 71% of the acidifying emissions and about 90% of the eutro-phying emissions of System A+I (Table 8). When production of electricity is con-sidered as well as System A activities, acidifying emissions will be described for almost 90% (Table 8). Our conclusion is that a study on the impact of the Dutch greenhouse horticultural sector would need to take into account: (1) CO2from gas
use and electricity production; (2) NOx from gas use, electricity production and fertiliser use and rockwool production; and (3) N and P from fertiliser use (Table 8). For the Total Agricultural sector (System Agriculture A and A+I) the emissions included in System A re¯ect more than 90% of total (A+I) acidifying and eutro-phying emissions (Table 8). Thus, assigning emissions from production of electricity, fertiliser and rockwool does not in¯uence the results of the analysis to a great extent for acidi®cation and eutrophication. For greenhouse gas emissions, however, we estimated that the additional System A+I sources increase the System A greenhouse gas emissions by almost one-third (Table 6). This is mainly due to indirect emissions of N2O in aquatic systems and remote terrestrial systems as a result of N
volatilisa-tion or leaching, and N2O production in industrial fertiliser production. Our
con-clusion is that a study on the impact of the Dutch agricultural sector would need to take into account: (1) CH4emissions from animal waste; (2) CO2 emissions from
fuel use in the sector; (3) sources of N2O from fertilised soils, indirect emission,
fer-tilisers production and stables; (4) NH3emissions from animal production; and (5)
nitrate and phosphate inputs to soils and surface waters. Most of these sources are included in System A (Table 8).
Although this analysis has been carried out for three speci®c agricultural sectors, we may draw some more general conclusions. First, we illustrated that without per-forming a complete LCA it seems possible to identify most relevant processes that need to be taken into account when describing the environmental impact of agri-cultural production on a sectoral level. In other words, expert judgement and limited data could be used to de®ne the most important sources of emissions related to agri-cultural production. We would like to underline that the choice of system boundaries largely depend on the purpose of the study and the envisaged users of the results (e.g. policy makers or growers/farmers). Furthermore, we showed that a profound study on the de®nition of system boundaries is worthwhile and leads to more insight in the system. We found that System I emissions can be relatively high when compared to System A emissions. If we had restricted our study to System A emissions, in some cases we would have overlooked up to 30% of the total System A+I emissions. These results also imply that options to reduce the total environmental impact of an agri-cultural sector may include the application of reduction options in System I.
References
Options For Control. Proceedings of the International IPCC Workshop (RIVM report 481507003). National Institute for Public Health and the Environment, Bilthoven, The Netherlands, pp. 131±141. Biewinga, E.E., Van der Bijl, G., 1996. Sustainability of Energy Crops in Europe; A Methodology
Developed and Applied. (CLM 234-1996) Centre for Agriculture and Environment, Utrecht, The Netherlands.
Bùckman, O.C., Kaarstad, O., Lie, O.H., Richards, I., 1990. Agriculture and Fertilizers. Agricultural Group, Norsk Hydro, Oslo, Norway.
Boersema, J.J., Copius Peereboom, J.W., de Groot, W.T. (Eds.), 1986. Basisboek Milieukunde (in Dutch). BOOM, Meppel, The Netherlands.
CBS, 1996. Tuinbouwcijfers 1996 (in Dutch). Centraal Bureau voor de Statistiek, Voorburg/Heerlen, The Netherlands.
CBS, 1997. Boeren in een veranderd milieu (in Dutch). Centraal Bureau voor de Statistiek, Voorburg/ Heerlen, The Netherlands.
CBS, 1997. Gewasbescherming in de land- en tuinbouw, 1995. Chemische, mechanische en biologische bestrijding (in Dutch). Centraal Bureau voor de Statistiek, Voorburg/Heerlen, The Netherlands. Checkland, P.B., 1979. Techniques in soft systems practice. Building conceptual models. Journal of
Applied Systems Analysis 6, 41±49.
Daum, D., Schenk, M.K., 1996. Gaseous nitrogen losses from soilless culture system in the greenhouse. Plant and Soil 183, 69±78.
France, G.D., Thompson, D.C., 1993. An overview of ecient manufacturing processes. In Proceedings of The Fertiliser Society No. 337. Greenhill House, Peterborough.
Heijungs, R., Guinee, J.B., Huppes, G., Lankreijer, R.M., Udo de Haes, H.A., Wegener Sleeswijk, A., Ansems, A.M.M., Eggels, A.M.M., van Duin, R., de Goede, H.W., 1992. Environmental lifecycle assessment of products. Guidelines and backgrounds. Centre for Environmental Science, Leiden, The Netherlands.
Hoogenkamp, A.W.H.M., 1992. Productie van fosfaatmeststoen (in Dutch). SPIN (Samenwerking-sproject Projectbeschrijvingen Industrie Nederland; RIVM report 736301102). National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
Houghton, J.T., Meira Filho, L.G., Bruce, J., Lee, H., Callander, B.A., Haites, E., Harris, N., Maskell, K. (Eds.), 1995. Climate Change 1994. Radiative forcing of Climate Change and An Evaluation of the IPCC IS92 Emission Scenarios. IPCC, Cambridge University Press, Cambridge, UK.
IKC, 1995. Afvalproblematiek in de land- en tuinbouw, inventarisatie afvalproblematiek (in Dutch). Information and Knowledge Centre, Ede, The Netherlands.
IPCC, 1997. Greenhouse Gas Inventory Reference Manual, revised edition 1996. IPCC Guidelines for National Greenhouse Gas Inventories Vol. 3. IPCC, Bracknell, UK.
Kaskens, H.J.M., Verburgh, J.J., Matthijsen, A.J.C.M., 1992.Productie van Steenwol(in Dutch). SPIN (Samenwerkingsproject Projectbeschrijvingen Industrie Nederland; RIVM report 736301114). National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
Kroeze, C., 1994. Nitrous Oxide Ð Emission Inventory and Options for Control in The Netherlands (RIVM report 773001004). National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
Kroeze, C., Bogdanov, S., 1997. Application of two methods for N2O emission estimates to Bulgaria and The Netherlands. IdoÈjaÂraÂs. Quarterly Journal of the Hungarian Meteorological Service 101, 239±260.
KWIN, 1993. Kwantitatieve Informatie glastuinbouw 1993±1994 (in Dutch). Information and Knowledge Centre, Aalsmeer/Naaldwijk, The Netherlands.
McInnes, G., 1996.Atmospheric Emission Inventory Guidebook, A Joint EMEP/CORDINAIR Production, Vol. 1. European Environmental Agency, Copenhagen, Denmark.
Melman, A.G., Schiphouwer, H., Hendriksen, L.J.A.M., 1994. Energie-inhoudsnormen voor de akker- en tuinbouw- Deel 1 (hoofdrapport) (in Dutch), TNO 94-425/112325-25357. Apeldoorn, The Netherlands. Mosier, A., Kroeze, C., Nevison, C., Oenema, O., Seitzinger, S., van Cleemput, O., 1998. Closing the global atmospheric N2O budget: nitrous oxide emissions through the agricultural nitrogen cycle. Nutrient Cycling in Agroecosystems 52, 224±248.
Nienhuis, J., de Vreede, P., 1994a. Milieugerichte levenscyclusanalyse in de glastuinbouw: ronde tomaten (in Dutch). Proefstation voor de Tuinbouw onder glas, Naaldwijk, The Netherlands.
Nienhuis, J., de Vreede, P., 1994b. Milieugerichte levenscyclusanalyse in de glastuinbouw; bruikbaarheid (in Dutch). Proefstation voor de Tuinbouw onder glas, Naaldwijk, The Netherlands.
Poppe, K.J., Brouwer, F.M., Welten, J.P.P.J., Wijnands, J.H.M. (Eds.), 1995. Landbouw, milieu en economie Ð Editie 1995 (in Dutch). Landbouw Economische Instituut, Periodieke Rapportage 68-93, Den Haag, The Netherlands.
Postma, R., 1996. Stikstofverliezen door denitri®catie op praktijkbedrijven met jaarrondchrysant (in Dutch). Intern rapport, NutrieÈnten Management Instituut (NMI), Wageningen, The Netherlands. Rabbinge, R., Van Ittersum, M.K., 1994. Tension between aggregation levels. In: Fresco, L.O.,
Stroos-nijder, L., Bouma, J., Van Keulen, H. (Eds.), The Future of the Land. Mobilising and Integrating Knowledge for Land Use Options. John Wiley, New York, USA. pp. 31±40.
Reijnders, L., 1996. Bestrijdingsmiddelen (in Dutch). BOOM, Amsterdam, The Netherlands.
RIVM, 1996. Milieubalans 1996. Het Nederlandse milieu verklaard (in Dutch). National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
RIVM, 1997. Nationale milieuverkenning 4, 1997±2020 (in Dutch). National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
Spakman, J., Olivier, J.G.J., Van Loon, M.M.J., 1997. Greenhouse Gas Emissions in The Netherlands 1990±1996: Updated Methodology (RIVM Report 728001008). National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
Sonneveld, C., 1993. Mineralenbalansen bij kasteelten (in Dutch). Meststoen 1993, 44±49.
Van der Berg, N.W., Lankreijer, R.M., 1994. Milieugerichte levenscyclusanalyse van steenwol als sub-straat in de tuinbouw Ð Hoofdrapport (in Dutch) (CML rapport 113). Centre for Environmental Sci-ence Leiden, The Netherlands.
Van der Hoek, K.W., 1994. Berekeningsmethodiek ammoniakemissie in Nederland voor de jaren 1990, 1991 en 1992 (in Dutch) (RIVM Report 773004003). National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
Van der Velden, N.J.A., Van der Sluis, B.J., Verhaegh, A.P., 1995. Energie in de glastuinbouw van Nederland, Ontwikkelingen in de sector en of de bedrijven tot en met 1993 (in Dutch) (Periodieke Rapportage). LEI-DLO, Den Haag, The Netherlands.
Van der Velden, N.J.A., Van der Sluis, B.J., Verhaegh, A.P., 1997. Energie in de glastuinbouw van Nederland, Ontwikkelingen in de sector en of de bedrijven tot en met 1996 (in Dutch) (Periodieke Rapportage). LEI-DLO, Den Haag, The Netherlands.
Wegener Sleeswijk, A., Kleijn, R., Van Zeijts, H., Reus, J.A.W.A., Meeusen-van Onna, M.J.G., Leneman, H., Sengers, H.H.W.J.M., 1996. Toepassing van LCA voor agrarische produkten (in Dutch). Centre for Environmental Science, Leiden, The Netherlands.
