3.1. Comparison of the farms
3.1.1. Main input and output flows
The main input and output flows were expressed per ha of land occupied per year (Table 3). SP had the highest N fertiliser input (362 kg N/ha/yr), mainly from solid (90%) and liquid (10%) commercial fertilisers made with raw materials such as livestock manure, castor bean meal, bone meal, phosphate, or plant-based compost and waste. MF applied 141 kg N/ha/yr, which was provided mainly by slow-release N fertilisers: composted cow manure (40% of N input), shredded green waste (30%), and compost of green waste (25%). OP had the lowest N input, with 96 kg N/ha/yr from livestock manure. The direct energy used by SP (74 GJ/ha/yr) was composed mainly of electricity (72%), mainly for irrigation. The direct energy used by MF (48 GJ/ha/yr) was composed entirely of diesel, also mainly for irrigation. The direct energy used by OP (16 GJ/ha/yr) was composed of diesel for tractors (64%) and electricity for a storage refrigerator (33%). SP had the highest yield (109 t/ha/yr), followed by MF (43 t/ha/yr) and OP (11 t/ha/yr). MF had the highest mean vegetable price (2.83 €/kg), followed by SP (2.20 €/kg) and OP (1.90 €/kg).
Direct emissions of NO, NO3, and N2O were nearly proportional to fertiliser N input. NH3 was also emitted after application of N fertiliser, but because fertiliser types varied, emissions were not proportional the quantities applied. CO2 emissions were caused by lime used to whitewash tunnels.
Table 3
Main annual inputs and output flows of the three farms expressed per ha of total cultivated land
Type | Item | Unit | Open-field production | Microfarm | Sheltered production |
|---|
Inputs | Fertiliser | kg N/ha/yr | 96 | 141 | 362 |
| | Electricity | GJ/ha/yr | 5.1 | 0 | 53.4 |
| | Diesel | GJ/ha/yr | 10.0 | 48.4 | 20.3 |
| | Natural gas | GJ/ha/yr | 0.4 | 0 | 0 |
| | Irrigation water | m3/ha/yr | 0 | 4622 | 4111 |
| | Plastic | kg/ha/yr | 1 | 363 | 1821 |
| | Seedlings | no./ha/yr | Cabbage: 3903 Onion: 2857 Leek: 1029 Swiss chard: 263 Squash: 143 Potato: 286 kg/ha/yr + self-production of seedlings and direct sowing | 0 (self-production of seedlings and direct sowing) Potting soil: 5357 kg/ha/yr | Tomato: 3355 Cucumber: 3097 Lettuce: 119 323 Strawberry: 4788 Celery: 3327 Fennel: 6397 |
| | Chemicals | - | - | Copper sulphate: 0.47 kg/ha/yr Iron phosphate: 36 kg/ha/yr | Wettable sulphur: 0.6 kg/ha/yr Neem oil: 1.8 L/ha/yr Plant-based biostimulant: 0.8 L/ha/yr Sex pheromone: 180 doses/ha/yr Horn silica (501): 20 g/ha/yr Prepared horn manure (500P): 140 g/ha/yr |
| | Purchased insects | no./ha/yr | - | - | Macrolophus spp. (box of 1000 insects): 6 Chrysoperla carnea (box of 10 000 insects): 28 Bumblebee hives: 17 |
| | Shading paint | kg/ha/yr | 0 | 0 | 590 |
| | Plastic tunnel | ha/ha/yr | 0 | 0.43 | 1 |
Output | Vegetables | t/ha/yr | 11 | 43 | 109 |
| | Price | €/kg | 1.90 | 2.83 | 2.20 |
Emissions | N2O | kg/ha/yr | 1.73 | 2.75 | 7.30 |
| | NH3 | kg/ha/yr | 9.39 | 7.22 | 16.90 |
| | NO | kg/ha/yr | 3.54 | 5.69 | 13.92 |
| | NO3 | kg/ha/yr | 131 | 214 | 531 |
| | CO2 | kg/ha/yr | 0 | 0 | 259 |
3.1.2. Assessment of farm impacts
Environmental impacts of the three farms differed among impact categories and FUs (Fig. 5). Per ha of land occupied, OP had the lowest CC impact (1.3 t CO2 eq./ha) and CED (29 GJ/ha), due to its low input use. Conversely, SP had the highest CC impact (13.3 t CO2 eq./ha) and CED (387 GJ/ha) per ha because it produced 2–3 crops per year, which led to higher input use. MF had an intermediate CC impact (7.5 t CO2 eq./ha) and CED (157 GJ/ha). Part of this farm had one crop per year (open field), and the other part had two crops per year (tunnel). The CC impact of SP per ha was 10.6 times as high as that of OP.
Per kg of vegetables, MF and SP had a similar CC impact (215 and 198 g CO2 eq./kg, respectively), while that of MF was 1.6 times as high as that of OP (134 g CO2 eq./kg). This difference was much smaller than for the CC impact per ha because OP had a lower total yield than MF. The higher productivity of SP gave it a similar or slightly lower CC impact per kg despite using more inputs per ha; however, for CED, SP had higher impact than MF per kg (5.7 and 4.5 MJ/kg, respectively). SP relied more on direct (diesel and electricity) and indirect (plastic and seedlings) energy than MF and OP (CED of 3.1 MJ/kg).
Per €, the highest CC impact (SP; 90 g CO2 eq./€) was 1.3 times as high as the lowest CC impact (OP ; 71 g CO2 eq./€). MF (76 g CO2 eq./€) practiced direct selling of several vegetables, including those with high value (e.g. tomatoes, mixed greens), for a mean price of 2.83 €/kg. SP sold in a long supply chain, which dilutes the value among more stakeholders. Nevertheless, SP’s high-value vegetables (e.g. tomatoes, strawberries, lettuces) under a biodynamic label sold for a mean price of 2.20 €/kg. OP produced mainly less valuable vegetables (e.g. potatoes, cabbages, turnips, carrots) that were sold in a short supply chain for a mean price of 1.90 €/kg.
For CC impact and CED, the contribution of system components varied among farms. Major contributors to CC impact and CED included the use of diesel (MF) and electric (SP) pumps for irrigation, the tunnel structure (MF and SP), the use of plastic water pipes and mulch (SP), and seedling production in heated greenhouses (SP); these inputs were not used by OP.
For OP, diesel (mainly used by tractors) and field emissions were the two main contributors (54% and 34%, respectively) to CC. For MF, diesel (mainly used by the pumps for irrigation) was the main contributor (49%), followed by tunnels (27%), fertilisers (10%), and field emissions (9%). For SP, tunnels were the main contributor (34%), followed by seedlings (15%, mainly for greenhouse heating), fertilisers (16%), field emissions (11%), and plastic (10%) mainly for plastic water pipes and mulch. Impacts of tunnels were due mainly to their galvanized steel structures, which was assumed to last 20 years, and plastic covers, which were assumed to last 4–8 years, depending on the farm. Using the same tunnel longer would reduce impacts.
For CED, the contributions were generally similar to those to CC, except that field emissions did not contribute; instead, seedlings (due to the use of peat) contributed more, particularly for MF (2% of CC vs. 23% of CED), as did electricity, particularly for SP, where it was used for irrigation (4% of CC vs. 33% of CED). Irrigation was a major source of energy demand both for MF and SP.
Land competition impacts of the three farms differed among FUs. Per ha of land occupied, OP, MF and SP had similar impacts (10 178, 10 684, and 12 018 m²a/ha, respectively), close to 10 000 m²a/ha due to limited use of indirect land. Direct use of land was the main contributor for all farms. Per kg of vegetables and per €, OP had the highest land competition, followed by MF and SP (1.09, 0.31, and 0.18 m²a/kg, respectively, and 0.57, 0.11, and 0.08 m²a/€, respectively). CC and CED impacts were the opposite of land competition per kg and per €, which illustrates that land and energy inputs are substitutable (Martin et al., 2023).
For ME, the ranking of the farms also depended on the FU, with OP having the lowest impact per ha (7.17 kg N eq./ha against 12.07 and 23.35 kg N eq./ha for MF and SP, respectively) but the highest impact per kg (0.77 g N eq./kg against 0.35 and 0.35 g N eq./kg for MF and SP, respectively) and € (0.40 g N eq./kg against 0.12 and 0.16 g N eq./kg for MF and SP, respectively). Field emissions dominated ME for OP, MF, and SP and OP (96%, 98% and 96%, respectively), followed by a modest contribution of fertilisers (2% for SP) and seedlings (4% for OP). NO3 leaching, which is the main contributor to ME, was estimated using proportions of fertiliser and crop residue N (IPCC, 2019b) and ignoring N output. The farms’ yields differed greatly, which suggests that their levels of crop N output did as well. The type of fertilisers also differed among the farms, because some mineralise faster (e.g. commercial fertilisers used by SP, poultry manure used by OP) than others (e.g. shredded green waste used by MF), which results in differing rates of N release in the soil. According to Qasim et al. (2021), incorporating straw into a greenhouse soil tended to reduce NO3 leaching by stimulating denitrification. The Agence de l’eau Seine Normandie (2018) found low NO3 leaching under vegetable crops grown with “market gardening on living soil” principles, as on MF. The high C:N ratio of the fertilisers used by MF enhances the activity of soil microbes and immobilises NO3 (Kirchmann et al., 2002), and these fertilisers increase water retention (Zemánek, 2014), which decreases leaching. Furthermore, soil sequestration of N decreases NO3 leaching (Knudsen et al., 2019) and depends on fertiliser properties. NO3 leaching may also depend on whether fertiliser is applied in a greenhouse (i.e. a controlled water supply) or an open field (i.e. rainfall) (Koch and Salou, 2020). The IPCC Tier 1 emission factor we used to estimate NO3 leaching is rudimentary and easy to apply in a farming-system LCA, but it seems too coarse given the variety of the farms’ fertilisation strategies. Consequently, estimated ME impacts had high uncertainty, which calls for considering fertiliser properties and soil sequestration to improve estimates of NO3 leaching.
3.1.3. Biodiversity
Differences in the biodiversity score among the farms were smaller when considering cultivated land alone (7.2, 7.7, and 6.0 for OP, MF, and SP, respectively) than when considering the entire farm, for which SP had the highest score (20.8), with a contribution of 82% from semi-natural habitats (especially ruderal areas (76% of the total)) and 18% from tunnels (Fig. 6). MF had a score of 16.4, with relatively equal contributions from cultivated land (40%) and semi-natural habitats (60%). OP had a score of 14.6, with cultivated land contributing 43% and semi-natural habitats contributing 57%, of which 40% of the total was due to hedges.
Assessing biodiversity on the cultivated land alone or on the entire farm gave contrasting results, which highlighted the importance of a farm’s semi-natural habitats for biodiversity (Chiron et al., 2010; Jeanneret et al., 2021; Rischen et al., 2021). On SP, the cultivated land had a low biodiversity score, which was offset by the high proportion of ruderal area (i.e. spaces between tunnels that are left to ruderal organisms). On OP, most fields were surrounded by a ruderal strip or hedge. As OP had large fields, its proportion of semi-natural habitats was smaller, which resulted in a lower biodiversity score for the entire farm. On MF, the cultivated land had a biodiversity score similar to those of the other systems. Out of a maximum score of 45 in SALCA-BD, semi-natural habitats (e.g. hedges, biodiversity-friendly managed grasslands) can reach a score of 25 (Lüscher et al., 2017), which was the case for the grassland on OP. These scores were much higher than those of the vegetable fields on the farms (3–8).
Consequently, for all farms, semi-natural habitats obviously contributed more to the biodiversity score than cultivated land. This result is consistent with ecological studies that concluded that semi-natural habitats were important for spiders (e.g. Šálek et al., 2018), carabid beetles (e.g. Knapp and Řezáč, 2015), butterflies (e.g. Dover et al., 2000), birds (e.g. Billeter et al., 2007), and vascular plants (e.g. Billeter et al., 2007). The benefits of small farms for biodiversity were also acknowledged by Ricciardi et al. (2021), as the fields of smaller farms have a higher perimeter:area ratio than those of larger farms. Smaller farms are also more likely to create heterogeneous landscapes.
SALCA-BD analysed impacts of land-use type, farmer practices, and elements of spatial organisation of the farms. Other biodiversity assessment methods (Chaudhary and Brooks, 2018; Knudsen et al., 2017; Koellner and Scholz, 2008; Mueller et al., 2014) quantify impacts on biodiversity based on land-use classes and the distinction between organic and conventional farming. These methods are not adapted for assessing organic farms that have the same land use (arable land) but different farming practices.
3.1.4. Plastic use
Depending on the FU, SP used 2–4 times as much plastic as MF (1129 and 299 kg/ha, 16.8 and 8.5 kg/t of vegetables, and 7.6 and 3.0 kg/k€ of vegetables, respectively), whereas OP used little plastic (2 kg/ha, 0.2 kg/t of vegetables, and 0.1 kg/k€ of vegetables) (Fig. 7). Plastic was used mainly in tunnels (60% of plastic use for MF and SP). For MF, insect-proof netting and pots and trays represented 17% and 12% of plastic use, respectively. For SP, plastic mulch in tunnels and disposable water pipes represented 28% and 9% of plastic use, respectively.
SP used the most plastic, particularly to cover its 33 tunnels. MF also covered its tunnel in plastic, but used less, for two reasons: 1) only some of the cultivated land was under shelter, whereas all was under shelter on SP, and 2) the plastic lifetime was 8 years for MF and 4 for SP. The smaller tunnel area of MF allowed the farmer to repair plastic when damaged. In south-eastern France, where SP was located, plastic on small farms similar to MF had a lifetime of 6–7 years (Oriane Mertz, Agribio 84, pers. comm.); thus, the climate may influence this practice, along with the effect of the farming system. SP also used more plastic for mulching than MF and OP. On SP, all crops were mulched with single-use plastic, whereas on MF, straw mulch, manual weed control, and reusable plastic mulch were combined.
Plastic use is not an LCA indicator, and to our knowledge it has not been included before in an environmental assessment of vegetable production. In our study, it revealed major differences among systems. Plastic use in agriculture is a growing concern (United Nations Environment Programme, 2021b). Plastic mulch is a major source of microplastics (Bläsing and Amelung, 2018; Campanale et al., 2022) as it is thin and hard to remove from the soil (Qi et al., 2020). Microplastics may have detrimental effects on plant growth (Liu et al., 2021), soil properties (Zhang et al., 2020), and the fitness of soil bacteria and earthworms (Jiang et al., 2020), and can be found in fruit and vegetables at worrying concentrations (Oliveri Conti et al., 2020). An alternative to single-use plastic mulch that SP used the year after the survey is biodegradable plastic mulch, which is a common substitution approach (Hill and MacRae, 1995). Its benefits remain uncertain, as some studies conclude that it has no noxious effects on soil organisms (Sforzini et al., 2016), while others state that single-use and biodegradable plastic mulch have the same effects on earthworms (Ding et al., 2021; Kumar et al., 2020).
Plastic use included all types of items, from thin single-use items (e.g. mulch, drip tape) to long-lasting items (e.g. hard pipes). All types of plastic, regardless of their life span, can generate microplastics because the breakdown process starts on the surface. However, plastic used on the soil is more likely to be a source of soil microplastics (United Nations Environment Programme, 2021b). We included on-farm plastic but excluded up-stream plastic and products unintentionally contaminated with plastic (e.g. compost). Considering these sources of plastic would improve the indicator.
Persson et al. (2022) considered the quantities of plastic produced as a control variable (i.e. an indicator equivalent to that developed in the present study) of planetary boundaries, while recognizing its inability to represent impacts of plastic pollution. To this end, they considered the quantities of plastic released into the environment as another control variable, which represents impacts more closely but still lacks methods to estimate it. This strengthens the case for developing an LCA indicator that reflects contamination of the environment (e.g. fresh and marine water, soil) by plastics. Several recent studies have developed a new impact category for marine pollution by plastic waste that uses an emission factor specific to each type of plastic (Boone et al., 2023; Lavoie et al., 2021; Saling et al., 2020; Woods et al., 2021).
3.1.5. Effects of farm area on impacts per ha
In the sensitivity analysis of farm area, the cultivated area of 0.28 ha represented 25%, 39%, 61%, and 82% of the farm area when farm area equalled 1.10, 0.71, 0.46 and 0.34 ha, respectively. These four areas resulted in CC impacts of 2.3, 3.6, 5.6, and 7.5 t CO2 eq./ha, respectively (Fig. 8A), while biodiversity scores were 28.8, 24.3, 20.0, and 16.4, respectively (Fig. 8B).
In a product LCA, the area of the field or greenhouse is usually used for an area-based FU. In a farming-system LCA, the farm area is used, but farms often have uncultivated semi-natural areas. On microfarms, farmers may leave land uncultivated due to a lack of time or labour, or to enhance biodiversity and/or regulating ecosystem services (Morel et al., 2019). On farms with tunnels, areas between tunnels are rarely considered in yields or for an area-based FU. Microfarms and small farms that specialise in sheltered production have small areas; thus, uncultivated land may represent a much higher proportion of the area than that on a larger farm. The sensitivity analysis of farm area showed large differences in CC per ha and yielded a different ranking of the farms for biodiversity, depending on the area considered for MF. It is therefore important to establish clear rules for defining farm area, in particular when comparing farms of different types and sizes. Consequently, results with area-based FUs must be interpreted cautiously. It is reasonable to consider semi-natural areas as part of the farming system, as they provide regulating ecosystem services.
3.2. Ranking and farm-specific effects
Considering the different impacts and FUs, a clear ranking of the farms did not emerge. OP had the lowest impacts, except for CED per € and for ME per kg and per €, and it was not best for biodiversity. However, OP had a much lower yield than MF and SP (75% and 90% lower, respectively), which required more land to produce the same quantity of vegetables. Although the three farms are typical of the variety of such farming systems, farm-specific effects cannot be ignored. For example, MF used a diesel pump for irrigation, which contributed strongly to its CC impact. MF tried to limit input use, whereas some microfarms inspired by “bio-intensive” practices may use commercial fertilisers or plastic mulch intensively. On MF, the tunnel had large impacts, but some microfarms, particularly in southern France, do not use tunnels. On SP, ruderal areas between tunnels occupied a large proportion of the farm, but farms similar to SP use glasshouses or multispan greenhouses rather than tunnels, without inter-tunnel areas. Microfarms, often inspired by permaculture design methods, include semi-natural areas (e.g. hedges, ponds, woodland) (Morel et al., 2019) that would increase their biodiversity score. OP reduced its use of plastic close to zero, but some farms that grow vegetables on large open fields such as OP use plastic mulch or small plastic “caterpillar” tunnels.
Pépin et al. (2021) developed a biotechnical index that quantifies the biotechnical functioning of a farm. It ranges from 0 (i.e. external-input-based system) to 1 (i.e. biodiversity-based system) and is thus inversely proportional to the level of external input use. According to Pépin et al. (2021), the index was highest for MF (0.73), intermediate for OP (0.47), and lowest for SP (0.07). Per ha, SP had the highest CC and ME impacts, and the highest CED and plastic use, which is consistent with having the lowest index (i.e. highest level of input use). However, MF (highest index) did not have lower impacts per ha than OP (intermediate index). For MF, the tunnel and diesel, used mainly used for irrigation, contributed 75% of CC and 60% of CED, but tunnels and irrigation were not included in the index, which was a methodological oversight. Consequently, whereas Pépin et al. (2021) ranked the level of input use lowest for MF and intermediate for OP, we now conclude that it was lowest for OP and intermediate for MF.
The heterogeneity of input use influenced the environmental impacts, with lower impacts per ha for low input use for all impact categories. Intensification in input use led to a decrease in eutrophication and land competition when expressed per kg or per €, but had no clear effect on other impacts. Similar results were found by Salou et al. (2017) who analysed environmental impacts of dairy system intensification.
Microfarming is often promoted as a solution to produce food with lower environmental impacts, but the LCA results in this case study suggest that this benefit is not obvious. However, microfarms may be a good compromise by having higher yields than large open-field farms and lower impacts per ha, and promoting biodiversity by having a high ratio of semi-natural habitats to cultivated land and diversified crops.
3.3. Comparison to similar studies
CC impacts of the farms studied are consistent with those estimated by the few studies of similar systems (Table 4). CC impacts of a small-scale organic farm in Washington, USA (Adewale et al., 2016), were 1.7–2.7 t CO2 eq./ha/yr and 45–623 g CO2 eq./kg, depending on the vegetable. Irrigation contributed strongly to CED, like for MF and SP. The greenhouse contributed 7–10% to the CC impact of vegetables produced under shelter. When assessing a small and a large organic farm, Adewale et al. (2019) estimated a CC impact of 7.1 and 3.4 t CO2 eq./ha/yr, respectively. For onion and winter squash, they estimated 188 and 276 g CO2 eq./kg, respectively, for the small farm and 50 and 68 g CO2 eq./kg, respectively, for the large farm. Jensen et al. (2024) estimated CC impacts of 0.20–0.28 kg CO2 eq./kg and 5.0-10.3 t CO2 eq./ha/yr for summer-grown vegetables. Their CC impacts per ha were 4–8 times as high as those for OP, due mainly to high input levels, in particular for pointed cabbage and cos lettuce, which produce two crops per year, and their CC impacts per kg of vegetable were 1.5–2.1 times as high as those for OP.
For the community-supported vegetable farms that Christensen et al. (2018) studied in California, USA, estimated CC impacts were 1.72–6.69 kg CO2 eq./kg and 1.4–6.3 t CO2 eq./ha/yr. These farms had very low yields (534–949 kg/ha/yr), which explains their very high CC impact per kg. Cellura et al. (2012) estimated a CC impact of 740 g CO2 eq./kg for conventional tomatoes produced in an unheated tunnel in Italy. These impacts are higher than those for SP, partly because of a wider scope that included packaging and transport, and a shorter tunnel life span. He et al. (2016) estimated a CC impact for organic tomatoes in China of 208 g CO2 eq./kg, and Martinez-Blanco et al. (2011) estimated 182 and 289 g CO2 eq./kg for conventional tomatoes produced in tunnels and on open fields, respectively, both with compost and mineral fertilisers. Tomatoes produced in a heated greenhouse had CC impacts 10–50 times as high as those of vegetables produced in unheated tunnels, and heating and lighting contributed 97% of the impact (Williams et al., 2006). In open-field production in Oregon, USA, which is likely similar to OP, Venkat (2012) estimated a CC impact of 409 and 268 g CO2 eq./kg for organic broccoli and lettuce, respectively. As a comparison to other organic crops, Nitschelm et al. (2021) estimated a mean CC impact for 106 cereals and legumes (e.g. spring and winter barley, spring and winter wheat, winter pea, fava bean) of 0.8 ± 0.2 t CO2 eq./ha and 255 ± 112 g CO2 eq./kg, respectively.
Table 4
Literature results for climate change impact (100-year horizon) per ha during 1 year and per kg of vegetables
Type of farm | Vegetable | Country | t CO2 eq./ha/yr | g CO2 eq./kg | Greenhouse (GH)/open-field (OF) | Organic (Yes/No) | Source |
|---|
Open-field production (OP) | Various | France | 1.3 | 134 | OF | Yes | Present study |
Microfarm (MF) | Various | France | 7.5 | 215 | GH + OF | Yes |
Sheltered production (SP) | Various | France | 13.3 | 198 | GH | Yes |
Small vegetable farm | Winter squash | USA | 1.9 | 101 | OF | Yes | Adewale et al. (2016) |
Potato | 2.7 | 45 | OF | Yes |
Dry bush beans | 1.7 | 623 | OF | Yes |
Chard | 1.7 | 101 | OF | Yes |
Summer squash | 2.1 | 62 | OF | Yes |
Peppers | 2.6 | 65 | OF | Yes |
Onion | 2.1 | 79 | OF | Yes |
Cauliflower | 2.7 | 155 | OF | Yes |
Small vegetable farm | Various | USA | 7.1 | - | OF | Yes | Adewale et al. (2019) |
Onion | - | 188 | OF | Yes |
Winter squash | - | 276 | OF | Yes |
Large organic vegetable farm | Various | USA | 3.4 | - | OF | Yes |
Onion | - | 50 | OF | Yes |
Winter squash | - | 68 | OF | Yes |
Large organic vegetable farm | Pointed cabbage | Denmark | 8.4 | 198 | OF | Yes | Jensen et al. (2024) |
Cos lettuce | 10.3 | 278 | OF | Yes |
Onion | 5.0 | 252 | OF | Yes |
Community-supported agriculture | Various | USA | 2.9 | 3290 | GH + OF | Yes | Christensen et al. (2018) |
Various | 1.3 | 1720 | OF | Not certified |
Various | 6.4 | 6690 | GH + OF | Yes |
Various | 2.0 | 3720 | GH + OF | Not certified |
Various | 3.7 | 3980 | GH + OF | Not certified |
Mediterranean greenhouse | Tomato | Italy | - | 740 | GH | No | Cellura et al. (2012) |
Mediterranean greenhouse | Tomato | Spain | - | 182 | GH | No | Martinez-Blanco et al. (2011) |
Open field | Tomato | Spain | - | 289 | OF | No |
Heated greenhouse | Tomato | UK | - | 9400 | Heated GH | No | Williams et al. (2006) |
Mediterranean greenhouse | Tomato | Morocco | - | 220 | GH | No | Payen et al. (2015) |
Heated greenhouse | Tomato | France | - | 1750 | Heated GH | No |
Urban greenhouses | Tomato | China | - | 208 | GH | Yes | He et al. (2016) |
Urban greenhouses | Tomato | China | - | 261 | GH | No |
National data base (practices considered typical) | Broccoli | USA | - | 409 | OF | Yes | Venkat (2012) |
Broccoli | - | 353 | OF | No |
Lettuce | - | 268 | OF | Yes |
Lettuce | - | 192 | OF | No |
3.4. Advantages and disadvantages of the farming-system approach
The farming-system LCA approach was able to estimate several environmental impacts of complex farms by considering the system as a whole, without modelling every single crop. It also compared farms and identified hotspots (i.e. the main contributors to impacts). For example, in unheated greenhouse production, we found fertilisers (including compost), the greenhouse structure, and heated seedling production to be major contributors to CC, which confirms other results in the literature (Boulard et al., 2011; Cellura et al., 2012; Martinez-Blanco et al., 2011). The FUs identified differences in environmental impacts and eco-efficiency. Expressing impacts per kg and per unit of economic value are two ways to relate impacts to products. The mass-based FU considered production but introduced a bias when comparing farms that produced vegetables with different characteristics and value. In contrast, the value-based FU can compare any vegetables.
The farming-system approach followed the rationale of agroecology, in which inputs are farm-oriented rather than crop-oriented (e.g. fertilising the soil rather than the crop (Gliessman, 2021)). On MF, the goal of fertilisation was to have a fertile soil that was rich in organic matter and soil organisms. In a product LCA approach, MF’s tunnel would be allocated to the vegetables grown in tunnels and not to those grown on open fields. However, it is difficult for a microfarm in this region to earn a sufficient turnover with only open fields, which means that the farm needed to have a tunnel. On OP, rye production in the crop rotation had the main functions of producing rye and reducing pest and disease pressure. Because the latter function influences the (non-)use of inputs for vegetable production, it would make sense to include rye impacts in vegetable LCAs, with the challenge of allocating impacts between the two functions.
Some vegetables may have higher impacts than others due to specific needs (e.g. seedlings, fertiliser, water, pest control), lower yields, and/or longer cropping periods, but the farming-system approach cannot identify such “hotspot” vegetables. Identifying specific operations that have high impact requires detailed information about farmer practices. For example, knowing total diesel consumption does not provide information about how it was used for individual operations.
3.5. Methodological concerns when assessing organic vegetable farms
Estimates of NO3 leaching influence the ME impact greatly. On agroecological farms that use organic fertilisers with high stability and slow mineralisation, the IPCC Tier 1 equation for NO3 leaching (IPCC, 2019b) we used seems inappropriate, although it was easy to use. This calls for improving modelling of NO3 leaching in a farming-system approach for systems that use organic fertilisers.
N added to the soil by crop residues was estimated using a generic coefficient for all vegetables, although the N content of residues differs among vegetables. N2O emissions from crop residues and cover crops represented 5–12% of farm N2O emissions and 1–2% of CC impacts. Crop residues and cover crops caused 18–28% of NO3 leaching and 17–27% of ME impacts. These results suggest that improving estimates of crop residues is a priority for estimating ME impacts but not CC impacts, which agrees with Akkal-Corfini et al. (2021), who observed a large contribution of crop residues to NO3 leaching from artichoke and cauliflower.
Biocontrol, particularly using macro-organisms against pests or for pollination, is commonly used in organic vegetable production. Producing them requires infrastructure, feed, heat, and rapid transportation, but to our knowledge, their impacts are not known or no data are available. Studies that mention the use of insects for pest control or pollination excluded their impacts (Cellura et al., 2012). Estimating impacts of these insects would improve estimates of impacts of organic vegetable production (Montemayor et al., 2022), as the biocontrol market is growing rapidly.