Quantifying the environmental impact of production in agriculture and horticulture in The Netherlands: which emissions do we need to consider?

Agricultural Systems 66 (2000) 167±189

www.elsevier.com/locate/agsy

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 a a

Environmental Systems Analysis Group, Wageningen University, PO Box 9101, 6700 HB Wageningen, The Netherlands b Department of Mathematics, Wageningen University, Wageningen, The Netherlands c Department 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 eutrophying 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 secondorder 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

* Corresponding author. 0308-521X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0308-521X(00)00046-9

168

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

1. Introduction Agricultural production in The Netherlands contributes to various environmental problems. Well-known environmental problems due to agriculture are often related to speci®c activities and sectors. Dutch greenhouse horticulture, for example, 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 di€er 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 systems 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 sector, 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 Step 6 During the last step the whole analysis and its conclusions are described

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

169

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, ideally, 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

Fig. 1. Overview of System A(gricultural production) and System A+I(ndustry) and the three aggregation levels: sector Tomato Cultivation, sector Greenhouse Horticulture and sector Total Agriculture.

170

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

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 Agriculture (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 processes) 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 di€erent systems included in the analysis (system de®nition). Next, the method for calculating the emissions (calculation of emissions 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 di€erent aggregation levels (Tomato Cultivation, Greenhouse Horticulture, Total Agriculture). At each of these levels two di€erent systems are distinguished: System Agriculture and System Agriculture+Industry (Table 2, Fig. 1). Basically, System A (Agriculture) 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 factors 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, System Greenhouse Horticulture A and A+I, and System 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 calculation 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).

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

171

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

System A

Tomato Cultivation

Greenhouse Horticulture Total Agriculture

Environmental impact from use of gas, fertilisers, biocides and rockwool

As Tomato Cultivation, but Greenhouse Horticulture includes both soil and rockwool cultivation

System A+I As System A but including As Tomato Cultivation the environmental impact of the production of electricity, fertilisers, biocides and rockwool (System Industry)

Environmental impact from fuel use and co-generation in farms, soils and stables

As System A but including the environmental impact of the production of electricity, fertilisers, biocides and rockwool (System Industry)

2.2. Calculation of emissions and environmental impact We analysed the emissions of CO2, CH4 and N2O (greenhouse gases), SO2 (acidifying gas), NOx and NH3 (acidifying gases and eutrophying gases), NO3 and 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): EMISSION ˆ f …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 NH3 emissions 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 calculated as (Heijungs et al., 1992) (Table 5): IMPACT ˆ EMISSION  CLASSIFICATION 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 SO2equivalents and PO4-equivalents, respectively.

172

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

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 Cultivation Gas use Electricity use Fertiliser N use Fertiliser P use Rockwool use Biocide use

8.79108 m3 1.25108 kWh 1733 ton N 409 ton P 12.8 kton 11.3 ton

KWIN, 1993 Nienhuis and de Vreede, 1994a Nienhuis and de Vreede, 1994a Nienhuis and de Vreede, 1994a Van der Berg and Lankreijer, 1994; CBS, 1996 CBS, 1996, 1997b

Greenhouse Horticultureb Gas use Electricity use Fertiliser N use in soil cultivation Fertiliser N use in rockwool cultivation Fertiliser P use in soil cultivation Fertiliser P use in rockwool cultivation Rockwool use Biocide use

4.3109 m3 9.2108 kWh 4259 ton N 4500 ton N 868.6 ton P 924.9 ton P 25.2 kton 704 ton

Van der Velden et al., 1995 Van der Velden et al., 1995 Poppe et al., 1995, CBS, 1996 Poppe et al., 1995, CBS, 1996 Poppe et al., 1995, CBS, 1996 Poppe et al., 1995, CBS, 1996 IKC, 1995 Poppe et al., 1995

Total Agriculturec Electricity use Fertiliser use N Fertiliser use P Biocide use Rockwool use

9 PJ 412 kton N 60 kton P 5812 ton 25 200 ton

CBS, 1997a Kroeze, 1994 CBS, 1997a CBS, 1997b IKC, 1995; CBS, 1996

a

a b c

Area sector Tomato Cultivation is 1505 ha (CBS, 1996). Area sector Greenhouse Horticulture is 10 144 ha (CBS, 1996). Area sector Total Agriculture is 2106 ha (Kroeze, 1994).

2.3. Data for Tomato Cultivation and Greenhouse Horticulture The emissions from Tomato Cultivation and Greenhouse Horticulture are estimated 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 distinguished between energy-related and process-related emissions (Table 4). Processrelated emissions are released during the chemical production process. Energy-related emissions are related 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 cultivation. 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

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

173

Table 4 Emission factors as used in Eq. (1) for the calculation of the emissions from Tomato Cultivation, Greenhouse Horticulture and Total Agriculture in The Netherlands Activity

Emission factor

Emission factors related to activities in System A Gas use CO2 1.776 kg/m3 natural gas N2O 7.2010ÿ5 kg/m3 natural gas NOx 1.4210ÿ3 kg/m3 natural gas 9.510ÿ5 kg/m3 natural gas CH4 Fertiliser use in soil cultivation in greenhouses N-fertiliser use N2O 0.03 kg N2O-N/kg N NOx 0.025 kg NOx-N/kg N 0.35 kg NO3-N/kg N NO3 P-fertiliser use PO4

All emission factors are estimated from the studies of Mosier et al. (1998), Daum and Schenk (1996), Sonneveld (1993) and Postma (1996)

All emission factors are estimated from the studies of Mosier et al. (1998), Daum and Schenk (1996), Sonneveld (1993) and Postma (1996)

0.1 kg PO4-P/kgP

Emission factors related to activities in System I Electricity production CO2 0.834 kg/kWh CH4 9.010ÿ6 kg/kWh N2O 1.2610ÿ5 kg/kWh NOx 1.3510ÿ3 kg/kWh 3.910ÿ4 kg/kWh SO2 Fertiliser production N-fertiliser Process-related emissions N2O NOx NH3 Energy-related emissionsa CO2 CH4 N2O NOx SO2

IPCC, 1997; Boersema et al., 1986 IPCC, 1997; Boersema et al., 1986 IPCC, 1997; Boersema et al., 1986 Berdowski et al., 1993

0.2 kg PO4-P/kgP

Fertiliser use in rockwool cultivation in greenhouses N-fertiliser use N2O 0.01 kg N2O-N/kg N NOx 0.025 kg NOx-N/kg N 0.1 kg NO3-N/kg N NO3 P-fertiliser use PO4

Reference

2.710ÿ2 kg/kg N 1.5810ÿ3 kg/kg N 3.7210ÿ3 kg/kg N 2.5 kg/kg N 2.710ÿ5 kg/kg N 3.7810ÿ5 kg/kg N 8.110ÿ3 kg/kg N 1.1310ÿ2 kg/kg N

IPCC, 1997; McInnes, 1996 IPCC, 1997; McInnes, 1996 IPCC, 1997; McInnes, 1996 IPCC, 1997; McInnes, 1996 IPCC, 1997; McInnes, 1996

Kroeze and Bogdanov, 1997 Biewinga and Van der Bijl, 1996 Biewinga and Van der Bijl, 1996 All emission factors are estimated from France and Thompson (1993), IPCC (1997) and McInnes (1996)

(Table continued on next page)

174

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

Table 4 (continued) Activity

Value

Reference

P-fertiliser Process-related emissions NOx P Energy-related emissionsb CO2 CH4 N2O NOx SO2

1.5310ÿ3 kg/kg P 4.010ÿ3 kg/kg P

Hoogenkamp, 1992 Bùckman et al., 1990

0.705 kg/kg P 7.610ÿ6 kg/kg P 1.0610ÿ5 kg/kg P 2.2810ÿ3 kg/kg P 3.1810ÿ3 kg/kg P

All emission factors are estimated from France and Thompson (1993), IPCC (1997) and McInnes (1996)

Biocide production Energy-related emissionsc CO2 CH4 N2O NOx SO2

4.77 kg/kg active ingredient 5.1510ÿ5 kg/kg active ingredient 7.210ÿ5 kg/kg active ingredient 1.5010ÿ2 kg/kg active ingredient 2.1510ÿ2 kg/kg active ingredient

All emission factors are estimated from France and Thompson (1993), IPCC (1997) and McInnes (1996)

Rockwool production CO2 SO2 NOx NH3

0.168 kg/kg rockwool 1.9210ÿ3 kg/kg rockwool 0.02 kg/kg rockwool 1.210ÿ3 kg/kg rockwool

Kaskens et al., Kaskens et al., Kaskens et al., Kaskens et al.,

1992 1992 1992 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).

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

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

175

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 CH4 N2O

1 kg=1 CO2-eq 1 kg=21 CO2-eq 1 kg=310 CO2-eq

Over 100 years: from IPCC, 1997

Acidi®cation

SO2 NOxa NH3

1 kg=1 SO2-eq 1 kg=0.7 SO2-eq 1 kg=1.88 SO2-eq

From Heijungs et al., 1992

Eutrophication

NOxa NH3 NO3 N PO4 P

1 1 1 1 1 1

From Heijungs et al., 1992

a

kg=0.13 PO4-eq kg=0.35 PO4-eq kg=0.10 PO4-eq kg=0.42 PO4-eq kg=1 PO4-eq kg=3.06 PO4-eq

NOx=mainly/average NO2.

for System A is that 2.5% of the fertiliser N use is emitted as NOx, while total fertiliser 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 associated activity levels). The emission factors associated 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). CO2 emissions 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 CO2 emissions. The emissions of NOx from System A are about half of total NO2 emissions, but are relatively small compared to CO2 emissions.

176

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

kton

kton CO2-eq

kton

kton CO2-eq

kton

kton CO2-eq

kton

kton CO2-eq

Greenhouse gases CO2 Gas use/fuel use in agriculture Electricity production Fertiliser N/P production Biocide production Rockwool production Total

1560 0 0 0 0 1560

1560 0 0 0 0 1560

0 104 5 1 2 111

0 104 5 1 2 111

7672 0 0 0 0 7672

7672 0 0 0 0 7672

0 767 23 3 4 797

0 767 23 3 4 797

8600 0 0 0 0 8600

8600 0 0 0 0 8600

0 1918 1787 28 4 3727

0 1918 1787 28 4 3727

CH4 Gas use/energy use Manure Electricity production Fertiliser N/P production Biocide production Total

<1 0 0 0 0 <1

1.8 0 0 0 0 1.8

0 0 1 1 1 1

0 0 1 1 1 1

<1 0 0 0 0 <1

8.6 0 0 0 0 8.6

0 0 1 1 1 1

0 0 <1 1 1 <1

2 505 0 0 0 507

42 10 505 0 0 0 10 647

0 0 <1 <1 <1 <1

0 0 <1 <1 <1 <1

N2O Gas use/energy use Fertiliser use Stables Electricity production Fertiliser N/P production Indirect soil emissionsa Biocide production Total

1 1 0 0 0 0 0 1

20 8 0 0 0 0 0 28

0 0 0 1 1 1 1 1

0 0 0 <1 15 8 1 23

<1 <1 0 0 0 0 0 <1

96 84 0 0 0 0 0 180

0 0 0 <1 <1 <1 1 <1

0 0 0 4 73 84 1 161

<1 20 8 0 0 0 0 28

93 6293 2573 0 0 0 0 8959

0 0 0 <1 6 <1 17 23

0 0 0 9 1705 <1 5301 7015

1590

134

7861

958

kton CO2-eq

28 206

kton

kton CO2-eq

10 754

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

Total greenhouse gas emissions

kton

System I

Table 6 (continued) Tomato Cultivation

Greenhouse Horticulture

Total Agriculture

System A

System A

System A

System I

System I

System I

ton SO2-eq

ton

ton SO2-eq

ton

ton SO2-eq

ton

ton SO2-eq

kton

kton SO2-eq

kton

kton SO2-eq

Acidifying gases SO2 Gas use/energy use Electricity production Fertiliser N/P production Biocide production Rockwool production Total

0 0 0 0 0 0

0 0 0 0 0 0

0 49 21 <1 25 95

0 49 21 <1 25 95

0 0 0 0 0 0

0 0 0 0 0 0

0 358 105 15 48 526

0 358 105 15 48 526

0 0 0 0 0 0

0 0 0 0 0 0

0 0.9 0.7 0.1 0.1 1.8

0 0.9 0.7 0.1 0.1 1.8

NOx Gas use/energy use Fertiliser use Electricity production Fertiliser N/P production Biocide production Rockwool production Total

1248 143 0 0 0 0 1391

873 100 0 0 0 0 973

0 0 169 18 <1 256 443

0 0 118 13 <1 179 310

6134 720 0 0 0 0 6854

4294 504 0 0 0 0 4798

0 0 1242 92 11 504 1849

0 0 869 64 7 353 1293

9 10 0 0 0 0 19

6 7 0 0 0 0 13

0 0 2.8 0.9 0.1 0.5 4.3

0 0 2 0.6 0.1 0.4 3.1

NH3 Fertiliser use Stables Fertiliser N/P production Rockwool production Total

0 0 0 0 0

0 0 0 0 0

0 0 7 15 22

0 0 12 29 41

0 0 0 0 0

0 0 0 0 0

0 0 33 30 63

0 0 61 57 118

118 82 0 0 200

222 153 0 0 375

0 0 5.1 0.3 5.4

0 0 9.6 0.6 10.2

Total acidifying emissions

973

446

4798

1937

388

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

ton

15

177

(Table continued on next page)

178

Table 6 (continued)

P Fertiliser use (PO4) Fertiliser P production Total Total eutrophying emissions a b

Greenhouse Horticulture

Total Agriculture

System A

System I

System A

System I

System A

ton N or P

ton PO4-eq

ton N or P

ton PO4-eq

ton N or P

ton PO4-eq

ton N or P

ton PO4-eq

kton N or P

kton PO4-eq

kton N or P

kton PO4-eq

374 43 0 173 0

162 19 0 73 0

0 0 0 0 51

0 0 0 0 22

1840 216 0 1941 0

793 94 0 815 0

0 0 0 0 373

0 0 0 0 161

3 3 97 426b 0

1 1 41 179b 0

0 0 0 0 <1

0 0 0 0 <1

0 0 0 590

0 0 0 254

11 <1 89 151

5 <1 39 65

0 0 0 3997

0 0 0 1702

54 3 176 606

23 1 74 259

0 0 0 529

0 0 0 222

8 <1 <1 8

3 <1 <1 3

38 0 38

115 0 115

0 2 2

0 5 5

359 0 359

1098 0 1098

0 7 7

0 22 22

71b 0 71

217b 0 217

0 <1 0

0 1 1

369

70

2800

N2O formation in remote soils and waters induced by agricultural N after volatilisation or leaching. From RIVM (1996) indicated as total N and P to soil (is excluding NOx and NH3 emissions).

281

System I

439

4

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

Eutrophying emissions N Gas use/energy use (NOx) Fertiliser use (NOx) Fertiliser use (NH3) Fertiliser use (NO3) Electricity production (NOx) Fertiliser N/P production(NOx+NH3) Biocide production (NOx) Rockwool production (NOx+NH3) Total

Tomato Cultivation

Fig. 2. Emissions of greenhouse gases (CO2, CH4 and N2O, and total CO2-equivalents), acidifying compounds (SO2, NOx and NH3 and total SO2equivalents) 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.

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189 179

180

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

Fig. 3. 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) 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.

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

181

Tomato Cultivation System I has a considerable part in total acidifying emissions from System A+I (about 30%). NOx emissions contribute 90% to total acidifying emissions from System A+I. Most of this NOx results 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 Nfertiliser which is assigned to System A (Table 6). SO2 and NH3 are 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 CO2 from 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 (SO2 and 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 expressed 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 di€erences 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 System I emissions include CO2 and 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 CO2 and CH4 have about equal share (about 30%) in total emissions from System A+I, while N2O contributes 40% to total greenhouse gas

182

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

emissions (Fig. 2). Emissions of CO2 are mainly from fuel use within agricultural sector (System A). Emissions of CH4 are 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 System A (96%). In other words, electricity production and industrial production of fertilisers and rockwool are relatively small sources of acidifying compounds compared 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 CO2 is the most important greenhouse gas. Both Tomato Cultivation and Greenhouse 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 NH3 are only emitted from System I. On the other hand, the sectors Tomato Cultivation and Greenhouse Horticulture di€er 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 electricity use in Greenhouse Horticulture. This is caused mainly by use of supplementary lighting in cut ¯ower production. Nevertheless, total NOx emissions in System A+I per hectare are higher in Tomato Cultivation, because of rockwool production for Tomato Cultivation in System I (see below). Another di€erence 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 di€erences are re¯ected in the relative contribution 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 recirculation of water and nutrients, which results in lower losses of N and P to the environment 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 Greenhouse Horticulture (Fig. 3). 3.5. Tomato Cultivation and Greenhouse Horticulture versus Total Agriculture We observed two important di€erences between agricultural production in greenhouses and the total Dutch agricultural sector. The ®rst relates to the relative importance of the compound emitted form the di€erent sectors. While in Tomato Cultivation and Greenhouse Horticulture CO2 is by far the most important

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

183

greenhouse gas, emissions from Total Agriculture also include considerable amounts of other greenhouse gases as CH4 and N2O. These are emitted from animal production systems and fertilised soils (Fig. 2). Secondly, we observed large di€erences in areal emissions from di€erent 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 di€erent aggregation levels: Tomato Cultivation, Greenhouse Horticulture and the Total Agricultural sector. We estimated emissions for these sectors with (System Agriculture+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. Nevertheless, 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 eutrophying 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®cation factors for greenhouse gases (IPCC, 1997). The classi®cation factors for calculating 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 LCA studies to indicate the gross e€ect of eutrophication irrespective of the location of the emissions. However, eutrophication is an environmental problem with typically local e€ects. The eutrophication potentials for di€erent compounds may change when considering eutrophication as a local scale problem. Despite these limitations the data presented here may be the best presently available and serve the purpose of the study.

184

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

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 fertilisers 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 production in The Netherlands indicate that for the environmental problems considered here (global warming, acidi®cation, eutrophication) ®rst- and second-order processes 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, acidi®cation and eutrophication. The analysis of the e€ects 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 eutrophication. For the emission of toxic biocides and the production of waste this is di€erent. For example, the environmental e€ect of biocides are mainly related to the direct toxic e€ects 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 cogeneration at the farm. If compared to coal-®red power plants, co-generation may result in lower emission of CO2 and higher emissions of NOx. Co-generation is only used on 8% of the total greenhouse area and mainly in cut¯ower and potplant cultivation (Van der Velden et al., 1997). We compared our results for Tomato Cultivation to results of the LCA of Dutch tomato production executed by Nienhuis and de Vreede (1994a). Table 7 shows that there is a good agreement between our estimated greenhouse gas emissions related to System A and those calculated by Nienhuis and de Vreede (1994a). Our estimates of the contribution of natural gas and electricity to total greenhouse gas emissions largely agree with the estimates of Nienhuis and de Vreede. For acidi®cation there is a reasonable agreement between our estimated emissions and those described by Nienhuis and de Vreede. The total contribution of emissions from natural gas and electricity to total acidi®cation agree well (73 v.s 72%). However, the contribution of natural gas in our study is higher than in the study by Nienhuis and de Vreede

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

185

Table 7 The contribution of di€erent 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 Production of electricity Others

92 6 2

91 5 4

Acidifying compounds Use of natural gas Production of electricity Others

61 12 27

52 20 28

Eutrophying compounds Use of fertilisers Production of P-fertiliser Use of natural gas Production of electricity Others

47 1 37 5 10

42 16 22 5 15

(respectively, 61 vs. 52%). This may be caused by di€erences in emission factors. The relative contribution of di€erent processes, such as use of fertilisers, combustion of natural gas production of electricity and production of fertilisers, to eutrophication di€er only in the contribution of P-emissions during the production of Pfertilisers. This di€erence can be explained by di€erences in emission factors (Bùckman 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) CO2 emissions from gas use; (2) NOx emissions from use of gas and fertilisers, and from production of electricity and rockwool; and (3) N and P emissions from fertiliser use (Table 8).

186

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

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, Greenhouse Horticulture and Total Agriculture) in The Netherlands Environmental problem

Source of emissiona

Contribution to total emissions from sector (%)b

Sector Tomato Cultivation Greenhouse gases CO2 from gas use (A) CO2 from electricity production (I)

90 6

Acidifying gases

NOx from gas use (A) NOx from rockwool production (I) NOx from electricity production (I) NOx from fertiliser use (A)

62 13 8 7

Eutrophying gases

NO3 and PO4 from fertiliser use (N and P) (A) NOx from gas use (A) NOx+NH3 from rockwool production (I) NOx from electricity production (I)

47 37 9 5

Sector Greenhouse Horticulture Greenhouse gases CO2 from gas use (A) CO2 from electricity production (I)

87 9

Acidifying gases

NOx from gas use (A) NOx from electricity production (I) NOx from fertiliser use (A) SO2 from electricity production (I) NOx from rockwool production (I)

64 13 7 5 5

Eutrophying gases

NO3 and PO4 from fertiliser use (N and P) (A) NOx from gas use (A) NOx from electricity production (I)

65 26 5

CH4 from manure (A) CO2 from energy use (A) N2O from fertilised soils (A) N2O indirect emissions (I) N2O from stables (I) N2O in fertiliser production (I)

27 22 16 14 7 4

Acidifying gases

NH3 from fertiliser use (manure) (A) NH3 from stables (A)

55 38

Eutrophying compounds

P from fertiliser use (A)c N from fertiliser use (A)c

50 41

Sector Total Agriculture Greenhouse gases

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 NOx and NH3 emissions).

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

187

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 eutrophying emissions of System A+I (Table 8). When production of electricity is considered 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) CO2 from 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 eutrophying 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 volatilisation or leaching, and N2O production in industrial fertiliser production. Our conclusion is that a study on the impact of the Dutch agricultural sector would need to take into account: (1) CH4 emissions from animal waste; (2) CO2 emissions from fuel use in the sector; (3) sources of N2O from fertilised soils, indirect emission, fertilisers production and stables; (4) NH3 emissions 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 performing a complete LCA it seems possible to identify most relevant processes that need to be taken into account when describing the environmental impact of agricultural 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 agricultural 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 agricultural sector may include the application of reduction options in System I.

References Berdowski, J., Olivier, J., Veldt, C., 1993. Methane from fuel combustion and industrial processes. In van Amstel, A.R. (Ed.), Methane and Nitrous Oxide, Methods in National Emissions Inventories and

188

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

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 ecient 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 fosfaatmeststo€en (in Dutch). SPIN (Samenwerkingsproject 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.

J.C. Pluimers et al. / Agricultural Systems 66 (2000) 167±189

189

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., Stroosnijder, 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). Meststo€en 1993, 44±49. Van der Berg, N.W., Lankreijer, R.M., 1994. Milieugerichte levenscyclusanalyse van steenwol als substraat in de tuinbouw Ð Hoofdrapport (in Dutch) (CML rapport 113). Centre for Environmental Science 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. Wilson, B., 1984. Systems: Concepts, Methodologies and Applications, 2nd Edition. John Wiley, Chichester, UK.