Assessment of Improvements of Polyculture Against Monoculture in An

Assessment of improvements of polyculture against monoculture in an

urban farming hydroponic system

Leonardo Pablo Nicolás Parra Almonacid

Advisors: Xavier Gabarrell (Universitat Autònoma de Barcelona)

Verónica Arcas-Pilz (Universitat Autònoma de Barcelona)

Felipe Parada (Universitat Autònoma de Barcelona)

Official Master’s Degree in Interdisciplinary Studies in

Environmental, Economic and Social Sustainability

Science and Management of Global Change

Journal of the Agriculture, Food and Human Values Society

October 30th, 2020

How this project fits within the lines the research of SosteniPra: This literature review has been carried out for supporting the work of SOSTENIPRA Research Group from ICTA-Universidad Autònoma de Barcelona. The mentioned research group is mainly focused on the development of urban agriculture as one of the possible solutions against climate change. As per the past activities of the group, these have been focused on the design of vegetable production systems that imply the minimum environmental impact while increasing resilience in the aspect of Food Security. This article fits with the research objectives of SOSTENIPRA by providing possible combinations of vegetables for their production in intercropping, in order to find ways for the achievement of Agricultural Efficiency, which is one of the issues pointed out in the development of sustainable urban agriculture. The main findings of this article are the proposal of the associations ‘tomato-cucumber’, ‘tomato- cabbage’ and ‘tomato-basil’ for their production testing in even conditions (hydroponic-based rooftop greenhouse in the city of Barcelona). Also, it is suggested to consider tomato as one of the members of the possible dual associations, considering the special features such as: phytoremediation of the cultivation medium, efficiency in the use of resources during production, among others. It is key to mention that all of the assessed vegetables for their consideration for possible association options are considered as ‘highly demanded’, not only as a result of consulting market information, but also because the species are considered to be part of the Mediterranean diet.

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4 Assessment of improvements of polyculture against monoculture in an urban farming hydroponic systems

Leonardo Pablo Parra Almonacid a, Veronica Arcas a, Felipe Parada a, Xavier Gabarrell ab*. a Sostenipra Research Group (SGR 1683), Institute of Environmental Sciences and Technology (ICTA) of the Universitat Autònoma de Barcelona (UAB), Carrer de les Columnes S/N, Building Z,), Campus UAB, 08193 Bellaterra, Barcelona, Spain. b Department of Chemical Engineering, Biological and Environmental, School of Engineering, Building Q, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain. *Corresponding author: [email protected]

Abstract Food security is one of the most critical impacts of climate change. Climatic phenomena such as flooding, soil acidification, changes in the use of land and water scarcity and other non-climatic impacts of climate change, such as forced migration and urban concentration, are compromising the supply of food. Scholars have proposed Urban Agriculture (UA), especially rooftop greenhouses, for producing vegetables in a more organic manner, applying production techniques to increase yield and the efficiency in the use of resources, while decreasing the environmental impact of the activity and causing positive social impacts. However, Sanyé-Mengual et al. (2015) described that rooftop agriculture requires ‘agronomic efficiency’ for being a better option than conventional production. Agronomic efficiency can be achieved, for example, through intercropping vegetables, which became the objective of this article as a literature review was carried out for finding and suggesting the best associations of vegetables that show positive interactions in intercropping, for their production in a hydroponics-based system, in the city of Barcelona. The results show that ‘tomato-cucumber’, ‘tomato-cabbage’ and ‘tomato-basil’ stand as the associations with the most documented overall benefits for their production in intercropping settings. Furthermore, tomato is recommended as a species to consider in the associations to produce, due to its benefits in production cycles and pest control. An important research opportunity is proposed, as the associations studied were not tested in even conditions for an accurate comparison.

Keywords: Urban agriculture, greenhouse, intercrop, polyculture, food security

5 1. Introduction Climate change is possibly one of the most controversial issues that society has been facing, mainly because of the eroding implications that the phenomenon has on environmental, social and economic aspects. The severity of the effects of climate change has driven some intellectuals to develop drastic proposals for a change in the pillars of modern society, such as the change in the understanding of economic growth. This change in the concept of economic growth is conceived as the ultimate policy goal, given that it has been demonstrated that this focus has led to the carbonization of the global energy matrix and the economic activities, which cause CO2 emissions, the main trigger of climate change (Kallis et al., 2018). The effects of climate change are several, but one reason for its significant relevance for society is that food security is compromised. The term “food security” has been defined by the FAO's Committee on World Food Security (2017) as a situation “that exists when all people, at all times, have physical, social and economic access to sufficient, safe, and nutritious food that meets their dietary needs and food preferences for an active and healthy life”. According to the World Bank (2020), in the past 10 years, the world population has been growing at a constant annual rate ranging from 1.1 to 1.2%, reaching to an approximate of 7.6 billion individuals. Furthermore, not only is this a relevant fact, but also the way in which the population and its activities and impacts are distributed. According to Almusaed & Almssad (2016) the sustainable design of cities is imperative, as more than 50% of world population is concentrated in urban centers, comprising nearly 80% of the global GDP; producing more than 70% of GHG emissions and consumed almost 80% of overall energy consumption. In terms of comprehensive solutions to the problem described, Urban Agriculture, defined broadly as the development of spaces for food production in urban spaces, was appointed as a potential field that addresses the problems mentioned so far. As described by Specht et al. (2014), Urban Agriculture provides several positive features with environmental benefits such as the reduction of environmental impact; the reduction of the logistics in the supply chain (from producer to consumer) and the improvement of energy and resources efficiency and, in social terms, the increase of food security for communities; the linkage of consumers and food production through education and so on. In other words, Urban Agriculture becomes part of a major set of solutions for improving the eroded resilience that society is experiencing. A possible option to perform Urban Agriculture is not only directly on the soil but also the implementation of Rooftop Greenhouses (RTG’s) on top of buildings. Sanyé-Mengual et al. (2015) carried out a comprehensive environmental and economic life cycle assessment and concluded that RTGs, in the case of the Mediterranean city of Barcelona, provide a potential solution to food security, however, their viability and credibility strongly rely on the environmental impacts, economic costs and the yield of the project. It is pointed out that the Agronomic Efficiency determines whether the RTG stands as an option against conventional production systems. Agronomic Efficiency is mainly determined by aspects such as yield, disease, and pest control, culture medium/soil quality, among other factors. In this line, existing literature proposes polyculture and intercropping as ways to achieve synergetic dynamics between species, characterized by the positive effect that one species may have on one or more issues that a secondary species may develop during its production. The benefits of polyculture and intercropping, as a measure to ensure food security, over monoculture, include the possibility of increasing yield and diversity of the species being produced; the reduction of disease and pest incidence; chemical and nutrient stabilization of the culture medium; efficient use of growing area; increased energy and water use efficiency, among others (Ahmad et al., 2013; Debra & Misheck, 2014; Zhou et al., 2011). From another perspective, whereas Soares et al. (2019) explained that climate change compromises the nutritional quality of vegetables; Zhen et al. (2020) concluded that organic greenhouses cause lower environmental impacts compared to conventional productions; Pérez-Neira & Grollmus-Venegas (2018) found out that it is possible to consume less non-renewable energies as observed in an organic community- managed urban agriculture context and Yu et al. (2015) also found out that diversified crops production may be xºa useful measure for sustainable food production, as intercropping systems may have 22% higher yields, in average, compared to sole crops This information leads to the idea that urban agriculture has to be feasible in order to tackle climate change and one of the ways to achieve it is through the identification of vegetable species that show positive synergies when grown together. This work's main objective is to provide groups of vegetable species for which intercropping enhances positive synergies to seek its viability in hydroponic-based polyculture in RTGs. This will be done through different case studies identified in a literature review and applied to the context of the city of Barcelona in order to supply the demand for vegetables in this Mediterranean city.

Ultimately, the associations recommended are highlighted, being close to achieve the requirements for Agronomic Efficiency to produce vegetables in a sustainable manner, which are described in the following sections. In this sense, regarding the concept of Agronomic Efficiency, the expected positive synergies from the recommended associations may be characterized, but not limited to, decreased consumption of resources during the production phase (energy, water, nutrients, etc.); increased yield; cultivation medium remediation; pest & disease control, among others. All in all, the effects of producing the recommended associations are expected to aim to production and economic efficiencies, in line with the logic of circularity and sustainability within the context of Urban Agriculture.

2. Material and Methods: Research Method and Analytical Framework 2.1. Identification of Species A critical consideration is that the species that are to be used in association, must be part of the Mediterranean diet and be demanded consistently in Barcelona. For this matter, Mercabarna (2020), which is a data base that delivers food statistics in Barcelona, was consulted in order to obtain a dataset that comprised the list of vegetable species, along with total weight [kg] and average price [€/kg] for any timespan consulted. The timeframe was set to 10 years, as it was estimated that a decade may reflect properly the recent trends of the demand. The dataset that was obtained by default from Mercabarna required to be adapted to avoid misinterpretation, as the “total weight” column comprises the commercialized total weight for each species in the past decade, while not specifying if a certain commercial unit is, weight-wise, greater or smaller than the rest. This implies the plausibility of scenarios in which high-demanded species may be discarded for the analysis compared to low-demanded species. Considering the economic component of the demand, the average price was incorporated for the development of the Selection Ratio, in order to reflect the preference of the demand side, regardless of the associated price. This ratio was used to make the data comparable. The Selection Ratio (SR) was computed as follows for each species:

푆푒푙푒푐푡푖표푛 푅푎푡푖표 (푆푅) = 푇표푡푎푙 푊푒𝑖𝑔ℎ푡 [푘𝑔] × 10−6 (1) 퐴푣푒푟푎𝑔푒 푃푟𝑖푐푒 [€/푘𝑔]

Then, the dataset was arranged by the SR in a descending order. Two criterions were applied simultaneously to the dataset to estimate and rank the relevance of each of the species listed. Selection Criteria Nº1: The first criterion was applied as a first filter to identify the species that were considered part of the constant demand for vegetables. In this part, the average of all of the SRs was computed and it was declared that the species considered for the study would be the ones that had a SR higher than the averaged SR of the Mercabarna dataset, as explained in formula Nº2:

푆푅푆푒푙푒푐푡푒푑 푠푝푒푐𝑖푒푠 > 퐴푣푒푟푎푔푒푑 푆푅퐷푎푡푎푠푒푡 (2) Selection Criteria Nº2: The second criterion was applied to include species that are part of the Mediterranean diet that may have been excluded. The criterion consisted in the inclusion of the species that would add up at most 95% of the Accumulated Historical Weight (AHW) of the complete Mercabarna (2020) dataset.

The resulting information is shown in Table 1.

7 Table 1: Selected Vegetables from MercaBarna Data Base. Period SRa AHWc Selection Selection price Vegetable Products Total [kg] DAb: Criteria Criteria (%) [€/kg] 143.46 Nº1 Nº2

Tomato Ripe 549,040,330 0.74 741.95 37 ✓ ✓ Lettuce (Unspecified) 101,378,249 0.56 181.03 58 ✓ ✓ Tomato Green 146,270,365 0.89 164.35 62 ✓ ✓ Onion Spring 71,983,460 0.61 118.01 70 ✕ ✓ Lettuce Long-Leaf 52,580,945 0.46 114.31 71 ✕ ✓

Cucumber 80,224,349 0.72 111.42 73 ✕ ✓ Cabbage 34,664,395 0.66 52.52 89 ✕ ✓ Garlic Fresh 17,889,224 0.59 30.32 94 ✕ ✓ Total Database

Historical Weight [kg] 3,919,371,681 a: Selection Ratio; b: Database Average; c: Averaged Historical Weight. Source: Mercabarna (2020). Complete table in Supplementary Information section. 2.2. Intercropping Options The resulting list of species was used to create a double axis matrix. According to existing literature, this exercise was carried out to generate the different combinations to perform a literature review to find out the positive and negative effects of intercropping the different alternatives. Considering that the selection of species from Mercabarna may have filtered species that are highly important from a cultural perspective, experts from ICTA at Universitat Autònoma de Barcelona and other entities were consulted to provide their opinion on the species and/or associations that should be included, in order to increase the number of possible associations for research, which resulted in the inclusion of the ‘tomato-basil’ association. 2.3. Evaluation of Intercropping Options A set of eight criteria has been developed, which were designed to be in line with the concept of Agronomic Efficiency. From the perspective of each criterion, the associations were scored according to the results of the positive and negative effects, that one species had on another, for every combination. Points were added in the case that the effects were positive, otherwise, points were discounted. The scoring ranges from -2 to 2. Score “0” represents that there is no information available for the evaluation or that the association has no relevant implications from the perspective of the criterion that is being evaluated. It is important to highlight that positive results imply higher chances of achieving Agronomic Efficiency. This scoring process was carried out for both the species included in the associations, since this work's interest is to propose associations in which both the species demonstrate a mutual positive synergetic effect on each other. For each association, in an A-B association, the effects of “B” on “A” were assessed, and also the case of “A” to “B”. In order to get the final score for the association under evaluation, both numbers for each criterion were averaged and rounded to the closest discrete number. Since every study has been carried out in different conditions, the scoring has been applied based on each paper, e.g.: if there is an association for which its yield performance is being scored, the final score that the association obtains in this criterion is based in the comparison against the other associations tested in the study. In the case of studies in which a certain association has been only compared to the monocrop of one of the species, the scoring that is applied is either “-2”, “0” or “2”, given that in case of positive or negative synergy, there is no other option to score as best performer, but the association itself. The criteria and the parameterization scoring methodology that was applied for evaluating each association is described as follows in Tables 2 and 3:

8 Table 2: Criteria for the evaluation of the associations Criterion Description Production obtained from a polyculture, measured as the total weight of Yield (Y) each of the species produced per unit of surface. Stands for the capacity of an association to overcome difficult adverse Resilience (R) climatic/weather conditions, which are determined by the different seasons of a year. Analyzes the impact that a particular association has on the cultivation Cultivation Medium medium, in terms of the emissions to the soil. Cases such as Quality (CMQ) phytoremediation are considered at this point. Economic implications of the production of an association. In this Economic Aspects (EA) criterion, impacts on income and/or costs are considered. Pest & Disease Control Incidence that the association of species has on pest and disease control. (P&DC) Resources Consumption Influences the overall consumption of resources, namely: energy, water, (RC) nutrients, etc., during a production cycle. Evaluation of environmental burdens of the lifecycle of the production of Environmental Impact the association. This factor considers Global Warming Index, Carbon (EI) Footprint and the criteria/factors considered in Life Cycle Assessments. Index indicates the land area required to produce a group of species, in Land Equivalent Ratio monocultures, an equivalent output compared to the intercrop (LER) polyculture of the same species in one hectare.

It is important to highlight that some of these indicators may be related or, at least, one may have an influence on the another. For example, the case of the indicators of ‘Resources Consumption’ and ‘Environmental Impact’, for which it is known that both are directly proportional. However, since the point of this study is to identify the associations of vegetables that show positive synergies, if documented, it would be valuable to track the cases in which the use of resources is reduced due to the performance of the association itself (specifically for the cases in which carbon sequestration features are enhanced), leaving factors that may be non-strictly related to the production process, such as related logistics, traceable through the indicator ‘Environmental Impacts’.

9 Table 3: Parameterization Scoring Score Rationale The association presents negative results for the criterion under evaluation. Both species have -2 negative influence on each other. Also, this score is assigned if the association is the worst performer in cited studies. The association presents negative results for the criterion under evaluation. One of the species has negative influence on the other. This score is assigned if the association has negative -1 results on the criterion under assessment in the cited literature, while not being the worst performer. No information available or no changes in the development of the association, compared to 0 monocrop production of the species. The association presents positive results for the criterion under evaluation. One of the species has positive influence on the other. This score is assigned if the association has positive 1 results on the criterion under assessment in the cited literature, while not being the worst performer. The association presents positive results for the criterion under evaluation. Both species have 2 positive influence on each other. Also, this score is assigned if the association is the best performer in cited studies. The complete description of the Parameterization Scoring can be found in the Supplementary Information section.

In the Supplementary Information section, a figure that explains the graphical manner in which the results are presented for comparison, is presented.

Ultimately, the scores obtained by every association are to be averaged to compute the “Overall Score”. The association that results to have an “Overall Score” over or equal to “1” is to be considered as recommended for production testing in a hydroponic-based system for best possible performance in a rooftop greenhouse in the urban area of Barcelona.

3. Results In the following section, the results of the literature review are presented in figures, analyzed, and compared against each other according to the evaluation criteria that was described in the previous sections. The order in which the names of the species are presented does not represent which is the main one and the intercrop, since what has been studied is the impact that one species has on the other. The “Overall Score” for each association is presented in Table 4.

3.1. Tomato-Garlic The association, according to the existing literature, offers great potential to be produced in intercrop, especially considering that the association, in Figure 1 has scored with the maximum of points, in key criteria such as ‘Cultivation Medium Quality’, ‘Environmental Impact’ and ‘Land Equivalent Ratio’ with maximum score. Minimum score was given in the aspect of ‘Pest & Disease Control’. Information regarding the incidence of tomato on garlic (as main crop) was not available or has not been studied. However, the impact that garlic has on tomato has been documented by Liu et al. (2014), who found that before the harvesting of garlic, the growth of spring tomato was decreased, coinciding with the case of the photosynthetic rate of tomato, which also decreased whereas the content of chlorophyll in the leaves were increased. Another aspect to take into account from the results of Liu et al. (2014), is that the quality of tomato was enhanced due to intercropping, as the dry matter, tritratable acid and vitamin C concentrations increased when compared to the monocrop, whereas other aspects such as soluble protein and sugar, along with solid matter contents did not vary drastically among intercrop and monocrop. The possibility of increasing the number of cycles in the use of the substrate bags in hydroponics, takes relevance as Liu et al. (2014) concluded that the intercropping of tomato with garlic has a direct incidence in the enzyme activity and microorganism populations of the cultivation medium. The authors state that both effects ease the continuous production cycles of tomato. Similarly, An et al. (2011) suggested , in the

10 context of their study, that tomato production may take a relevant role in phytoremediation of the cultivation medium, as it performed successfully in terms of heavy metal absorption. These results stand as an argument in favor of the first two mentioned criteria in which the association scored with maximum points. There is also an impact on the criterion ‘Economic Aspects’ of the association, given that even though on the one hand Liu et al. (2014) concluded that higher net income was increased, on the other, the reuse and use efficiency of resources may decrease the total production costs, which in theory, may provide the producer with a positive net profit in the case that the cultivation is being carried out for profit-oriented business. Regarding the ‘Resources Consumption’ criterion, no information was found. However the facts exposed in the previous paragraph, along with the results of Nassef & El-gaid (2012), that concluded that intercropping garlic with tomato may result in a LER of 12%, a priori, these are fair arguments to expect that producing the tomato-garlic association may imply an efficient use and consumption of resources. Nevertheless, this aspect is still a research gap to be covered in future research. One of the negative aspects of intercropping tomato with garlic is increasing the presence of pests. Azouz (2016) determined in a 2-year experiment that the mentioned association caused an increase of two to three times the presence of spider mite and thrips, compared to the control monocrop. However, in the case of tuta absoluta, its presence increased in the first year, but the results were the opposite in the next year.

3.2. Tomato-Onion As it can be concluded from Figure 1, regarding the criterion of ‘Yield’, the combination causes a decrease in this aspect due to a reduction in the fruit weight of tomato (marketeable yield), while not implying a significant difference compared to the control monocrop. Furthermore, according to the study carried out by Ramkat et al. (2008), it did not influence the ‘Land Equivalent Ratio’ of the production. In the case of how tomato affects onion, the marketable yield is affected negatively, becoming the worst performer of the experiment. In terms of ‘Pest Control’, Ramkat et al. (2008) also found out that the association may not be convenient as per this criteria, given that high disease incidence was observed as onion is an alternate host of the ‘tomato spotted wilt virus’ (TSWV). The effects that have been explained for the tomato-onion association contrast with the economic aspects. According to the study carried out by Son et al. (2018), in which the tomato-onion association was compared against tomato-basil and tomato-garlic, which are also covered in this thesis, tomato-onion association provided the highest sales value, profit, total yield and marketable yield. Also, it is convenient to consider that Rufí-Salís, Petit-Boix, et al. (2020) concluded that tomato is a good option for resilience to winter season, which is a result to be tested in intercrop with onion. In combination with the economic results, the association still stands as a convenient one economic-wise. However, these results would only be possible cultivation options if the objective of producing this tomato-onion association is profit-oriented. Otherwise, the association has a negative performance in key criteria, namely, yield and pest control management, which are important for achieving agronomic efficiency. Mohammadzadeh et al. (2018) in a study based on the experience of 110 farmers, determined that the production of onion, as a sole crop, was the most energy-intensive and recorded the highest GHG emissions, however, along with tomato (also as a sole crop), both recorded high efficiency in terms of the use of land, nitrogen, phosphorous and potassium. In the same study, onion production had the highest net return in the economic analysis, but having the highest cost of production. In this sense, economic benefits of the production of tomato may be seized by intercropping it with tomato, in order to increase the efficiency in the use of energy and to decrease the overall GHG emissions of the production cycles. In the study by Mohammadzadeh et al. (2018), the onion production resulted to be the crop with the lowest irrigation water productivity. At this point, according to the results by Rufí-Salís, Petit-Boix, et al. (2020), the spring tomato cycles, in terms of water consumption, were the most efficient and productive, offering the opportunity of acting as a buffer of the environmental impacts and resources consumption of onion. Even though these results were obtained for the species separately, testing the tomato-onion association in the urban context in Barcelona seeking to estimate the environmental impact and resources consumption through a Life Cycle Assessment becomes an interesting research gap as the ‘Land Equivalent Ratio’, along with the economic results from previous mentioned literature may potentially become aspects that may cover the pest and disease management negative experiences. However, a priori, the tomato-onion combination does not have enough positive features to qualify it as a convenient association to grow in an hydroponic-based greenhouse in Barcelona.

3.3. Tomato-Cucumber Even though information regarding the impact of cucumber on the yield of tomato was not found, a priori, as it can be observed in Figure 1, the association is highlighted because of the previous studies that support the idea of achieving efficiency in terms of ‘Land Equivalent Ratio’, which in the study by Schultz et al. (1982), it is stated that their experiment achieved an averaged 14%. Also, according to Al-Musa (1982), cucumber has a high performance in terms of protecting tomato from the ‘tomato yellow leaf curl virus’ (TYLCV) by delaying its incidence and the same study explains that it may be due to cucumbers, for whiteflies which is a vector for ‘TYLCV’, are better hosts than tomato. In terms of ‘Environmental Impacts’, these have been studied through the Life Cycle Assessment (LCA) methodology for the sole crops (Khoshnevisan et al., 2014). The analysis considered aspects such as: abiotic and ozone layer depletion; the potential of acidification, eutrophication and global warming; and freshwater, marine and terrestrial ecotoxicity, to name the most relevant for this work. The authors determined that the greenhouse production of tomato had lower environmental impacts compared to cucumber. However, when compared to the environmental impacts of an average European citizen in one year, Khoshnevisan et al. (2014) show that the production of one tonne of both species have a significant lower impact. Furthermore, even though emissions related to fertilizers, pesticides and other on-farm categories are not included, the authors estimated that, as per the emissions to the water, measured in grams per tonne of crop, the highlighted emissions were ammonia, lead and nickel. The maximum value was achieved by cucumber production with 55.9 [g] of lead. On top of the result, considering that the environmental impact of the production of cucumber, in this particular case, was compromised by the use of nylon and energy consumption, the authors demonstrate that production of both species produce less emissions into the air, top soil, groundwater and surface water, compared to one average european citizen during one year. Testing this association in the equality of conditions with the rest of the proposed options, becomes a relevant research gap, considering that the existing literature has not covered comprehensively the implications of the tomato-cucumber association. Furthermore, part of the literature reviewed for this case is focused on the species' individual features, providing reasons to test the association, instead of discarding it.

3.4. Tomato-Cabbage The effects of intercropping tomato with cabbage have not been studied comprehensively. However, existing literature points out the benefits that tomato has on cabbage (Figure 1). Asare-Bediako et al. (2010) commented that tomato plays a relevant role for the pest control and yield as it can substitute chlorpyrifos spray for Diamondback Moth (Plutella Xylostella), causing better production results when compared to cabbage monocrop. Also, in the same study it is highlighted that head and lower leaf damage was decreased due to the intercropping with tomato. The tomato-cabbage association is presented with positive scores, whereas the data for ‘Economic Aspects’, ‘Resources Consumption’ and ‘Land Equivalent Ratio’ was not found. With the same logic applied to the tomato-cucumber association, there are chances that the ‘Land Equivalent Ratio’ may be positive as tomato enhances the yield of cucumber, which was scored with the maximum points. On the other hand, the fact that tomato has a positive incidence in the factor of ‘Pest Control’, sheds light on the possibility that the ‘Land Equivalent Ratio’, once calculated, may be positive. However, the fact that the data on ‘Economic Aspects’ was not found, generates doubts on the convenience of the production of the tomato-cabbage association in terms of income and/or costs. In this sense, positive scores in ‘Pest & Disease Control’ may not ensure economic viability, leading to the requirement of the ‘Land Equivalent Ratio’ to estimate the convenience of producing this association. However, the mentioned positive scores in ‘Pest & Disease Control’, ‘Yield’ and ‘Cultivation Medium Quality’ may act as arguments in favor of agronomic convenience.

3.5. Tomato-Lettuce Regarding the performance of this association, as shown in Figure 1, Jett et al. (2015) and Tringovska et al. (2015), in their respective experiences, found that the incidence that tomato has on lettuce and vice versa, is negative in terms of yield. However, Jett et al. (2015) pointed out that the yield of lettuce in intercropping is also determined by whether it is carried out in a concurrent manner or in relay intercropping, being the

12 latter the setting in which the yield of lettuce was not decreased, as opposed to concurrently. However, the average fruit weight was decreased through relay intercropping, therefore it is estimated that either fashion undermines the yield of tomato either in total weight per plant or the average fruit weight. Both studies concluded that the quality of tomato fruits was increased in intercropping. In terms of ‘Pest & Disease Control’, intercropping tomato with lettuce was positive by causing lower incidence of root-knot nematodes (Meloidogyne spp.) (Tringovska et al., 2015), but these results may be affected by the results obtained by Son et al. (2018) who concluded that, against basil, garlic and onion as intercrops, lettuce was the worst performer in terms of pest avoidance, since the insect diversity was higher in this association under analysis. Against the other proposed associations, in the same situation of the tomato-onion association, the tomato- lettuce association has negative scores for ‘Yield’ and ‘Pest Control’, therefore making the other associations more attractive. As these both associations seem to be risky in terms of viability and food security. In terms of the ‘Economic Aspects’ of intercropping both species, Filho et al. (2010) determined that for both species, gross income and the operational profit are increased although the total operational costs are also higher when compared to the monocrops of both species. Also, as another positive aspect, Jett et al. (2015), also concluded that in terms of the ‘Land Equivalent Ratio’, intercropping both species increased by 40%, an aspect that, pendant on the respective experiment, a priori one may state that the criteria of ‘Resources Consumption’ may be positive, especially taking into account the results by Tringovska et al. (2015) as the research team found out that when intercropping tomato and lettuce, the energy use efficiency is increased, only surpassed by the association tomato-basil, however, not statictically significant. In other words, either intercropping tomato with basil or lettuce, the efficiency in energy use is increased. In the aspect of ‘Environmental Impact’, and in line with the results by Rufí-Salís et al., (2020), even though they stated that tomato has a positive environmental impact performance, therefore there are hints that the overall environmental impact of the tomato-lettuce association may be positive as ‘Land Equivalent Ratio’ is positive, as well as energy is consumed more efficiently as mentioned in the past paragraph.

3.6. Onion-Cabbage Figure 1 shows that net yield implication of the association is zero. However, when cabbage is produced as a main crop, with onion as an intercrop, yield scored with maximum points (Asare-Bediako et al., 2010; Leong & Lee, 1993), however, Yildirim & Guvenc (2016) determined that the onion yield, when intercropped with cabbage, was significantly decreased, when compared to the sole onion cropped. Debra & Misheck (2014) suggested that in terms of ‘Pest Control’, onion may play a very positive role when used as an intercrop for cabbage, supporting the same results obtained by Asare-Bediako et al. (2010). Liu et al. (2014) noticed that when onion is intercropped with cabbage between the planted rows instead of within them, the repellent effect is even higher than garlic's potential. From the opposite view, cabbage may also play a role in pest control as Zereabruk et al. (2019) found that Thrips tabaci (Thysanoptera: thripdae), which is a type of onion thrip, may be decreased due to the intercrop with cabbage. These results shed light on the possibility of crossed protection between the species. From the perspective of the criterion of ‘Economic Aspects’, there could be savings in the production because a minor dependance on insecticides and other chemical compounds used precisely for ‘Pest Control’. However, in terms of the expected net income of producing this association, Yildirim & Guvenc (2016) also state that expected earnings for cabbage production may be higher when intercropped with onion in comparison with the cabbage monocrop production. In terms of the ‘Land Equivalent Ratio’, Leong & Lee (1993) determined that when cabbage is intercropped onion, a ‘Land Equivalent Ratio’ of 2.12 may be achieved in total, whereas the results for individual crops in intercrop may be of 1.19 for cabbage and 0.93 for onion.

3.7. Tomato-Basil The association of tomato-basil has been pointed as a positive intercrop in existing literature. In fact, as per the available information that was found, the association (tomato as a main crop) scored positively at basically all of the criteria in this review, as shown in Figure 1. However, information regarding the incidence that tomato has on basil has not been found.

13 As per the criterion of ‘Yield’, de Carvalho et al. (2009) experimented determining whether rue, peppermint, fennel and basil, had a positive impact on the production of tomato, concluding that it was in the third place of productivity. Passing to the next criteria, ‘Cultivation Medium Quality’, even though this association was not tested, Rufí-Salís et al. (2020) suggested that tomato, among other species, information was not found. However, as mentioned in the analysis of the association tomato-garlic, An et al. (2011) commented on the properties that tomato has in intercrops for absorbing heavy metals, becoming a suitable member for intercrops for phytoremediation. Considering the positive effects that basil has on tomato yield, as mentioned before, Rufí-Salís et al. (2020) commented that tomato may show resilience in winter seasons. A priori, these facts are positive, considering that both results are tested in an experiment. Also, it is convenient to add that Tringovska et al. (2015) confirmed that intercropping tomato with basil, reduces appearance of root-knot nematodes (Meloidogyne spp.), which is a pest that affects tomato. In terms of ‘Economic Aspects’, (2018) found that both species' commercial production in intercrop may result in positive profit. This may partly be due to the explanation of Tringovska et al., (2015), as they stated that from the perspective of energy consumption, savings and efficiency in the use of resources may be achieved. Furthermore, M. K. Bomford (2009) explained that the association may achieve a ‘Land Equivalent Ratio’ higher than 1.

3.8. Cabbage-Lettuce Throughout the literature review, not much information regarding cabbage-lettuce's association on the incidence that one species has on the other has been found. Key criteria such as ‘Cultivation Medium Quality’, ‘Resources Consumption’ and ‘Environmental Impact’ could not be assessed because of the lack of published literature analyzing this association. As seen in Figure 1, in the case of the rest of the evaluation criteria, in the same scenario as the onion-cabbage association, ‘Yield’ was scored with zero as, in one experience, cabbage is benefitted by lettuce (Leong & Lee, 1993); in other, yield was not affected significantly (Yildirim & Guvenc, 2016) , and regarding the incidence that cabbage has on lettuce, the yield decreased significantly (Yildirim & Guvenc, 2016). The production of the association, according to Yildirim, E., & Guvenc, I. (2016), may cause outstanding performance on the ‘Economic Aspects’ and ‘Land Equivalent Ratio’ criteria, as the authors found out in their study that the association cabbage-lettuce surpassed the rest of the associations under analysis. As per ‘Pest Control’, Leong & Lee, (1993) determined that the performance that lettuce has on preventing Hellula webworm activity on cabbage is significant.

14 Comparison Chart Nº1 Comparison Chart Nº2 Comparison Chart Nº3

Y Y Y 2 2 2 LER 1 CMQ LER 1 CMQ LER 1 CMQ 0 0 0 -1 -1 -1 EI -2 R EI -2 R EI -2 R

RC EA RC EA RC EA

P&DC P&DC P&DC

Tomato-Garlic Tomato-Onion Tomato-Cabbage Tomato-Lettuce Tomato-Basil Cabbage-Lettuce

Tomato-Cucumber Onion-Cabbage

Figure 1. Comparison charts of the associations assessed. Y: Yield; CMQ; Cultivation Medium Quality; R: Resilience; EA: Economic Aspects; P&DC: Pest and Disease Control; RC: Resources Consumption; EI: Environmental Impact; LER: Land Equivalent Ratio

15 Table 4: Overall Scores and data summary Overall Score Association Y CMQ R EA P&DC RC EI LER (average) Tomato-Garlic -1 2 1 1 -2 0 2 2 0.63 Tomato-Onion -2 2 1 2 -1 0 0 2 0.50 Tomato-Cucumber 2 2 1 0 2 0 2 2 1.38 Tomato-Cabbage 2 2 1 0 1 0 2 0 1.00 Tomato-Lettuce -2 2 1 2 -1 1 2 2 0.88 Onion-Cabbage 0 0 2 1 2 0 0 2 0.88 Tomato-Basil 1 2 1 1 1 1 0 1 1.00 Cabbage-Lettuce 0 0 1 2 1 0 0 2 0.75 The associations with an Overall Score equal or higher than ‘1’ are highlighted. Y: Yield; CMQ; Cultivation Medium Quality; R: Resilience; EA: Economic Aspects; P&DC: Pest and Disease Control; RC: Resource Consumption; EI: Environmental Impact; LER: Land Equivalent Ratio.

16 4. Discussion

The majority of the studied associations include tomato as a main crop, not only because it plays an important role in the Mediterranean diet, but also because, in hydroponics, tomato has a high performance in terms of efficient consumption of resources, as suggested by Yang & Kim (2020), . It was also concluded that tomato production presents high nitrogen and phosphorus use efficiency (24% and 14%, respectively), compared to basil (15% and 13%) and lettuce (14% and 10%), adding up to the results by Rufí-Salís, Petit- Boix, et al. (2020), that had as one of their conclusions that the cycles of spring tomato are efficient and productive in terms of water usage. The possibility of carrying out a triple species intercrop results to be an interesting research opportunity, as tomato shows positive responses when intercropped with cucumber, cabbage and basil. However, after research, information regarding experiments oriented towards crossed-intercropping cucumber, cabbage and/or basil has not been found, in order to propose a third participant in the association. It has to be kept in mind that these associations cannot be compared against each other because the experiments were not carried out in even conditions. Namely, a number of studies were carried out in different cultivation settings, such as: plastic tunnels, open plantations, closed greenhouses, etc. Therefore, it is recommended for future analysis to compare the production and environmental performance of the proposed associations in even conditions. However, the potential of the suggested associations reflects on the experience of Abasolo & Zamora (2019), in which they concluded that organic multicrop vegetable production systems in a region in Philippines, was the option that had the lowest overall life cycle environmental impact, against its competitors. Motavalli et al. (2008) concluded that despite nitrogen fertilizers are essential for food production, the efficiency in their use has to be increased, in order to diminish the environmental impacts of the agricultural activities. In this sense, the lack of research on the production of the associations assessed in this study sheds light on the need of testing the associations, in even conditions, for determining if the efficiency in the consumption of resources may effectively be increased under the scenario proposed in this literature review. In terms of the planification of the production cycles, it is highly recommended to take also into consideration the benefits of monocrop settings, in intermitted manner, as Fu et al. (2017) concluded that tomato monoculture enables soil microbial properties and enzyme activities an aspect that may be positive for the next production cycle of vegetables and for decreasing the environmental impact of the greenhouse activity as, potentially, the lifespan of the cultivation medium could increase, which also could become a research gap. Existing literature highlights the importance of ensuring that every aspect of urban agriculture adds up to become a realistic alternative to conventional agriculture to tackle the effects of climate change on food security. Therefore, even though soilless culture, in the manner of substrate bags for vegetable production, has benefits, as named by Fernández et al. (2018) such as the decrease in the chances of existence of soil- borne pathogens; environmentally friendly in terms of nutrient, disinfection and water issues, especially the latter, as according to Gruda (2019), soilless culture can help overcoming local water shortages. Besides, the benefits of seizing the free spaces in Barcelona's urban area, it is imperative to carry out Life Cycle Assessments of the production of intercropped vegetable species, the advantages of this culture methodology have already been demonstrated. From another perspective, the convenience of intercropping different highly demanded vegetable species, in a sustainable manner, may potentially drive consumers to change their purchasing habits, leading to a potential reduction of GHG emissions related to the traditional supply channels, as studied by Yoshikawa et al. (2016). Information on ‘Resource Consumption’ was only obtained for the associations ‘tomato-lettuce’ and ‘tomato-basil’. However, Rufí-Salís, Petit-Boix, et al. (2020) concluded that, in terms of water usage, spring tomato was the most efficient and productive option in their study that was oriented on carrying out a Life Cycle Assessment of a sustainable rooftop greenhouse. However, the authors did not study the implications of intercropping tomato with other vegetable species. Therefore, this result only suggests that tomato potentially is an appropriate candidate for intercropping oriented to achieve efficiency in using resources during cultivation. Overall, the association that out-performed in this study is tomato-cucumber, which only surpasses the second best one, tomato-cabbage in terms of 'Pest & Disease Control' and 'Land Equivalent Ratio'.

17 This occurred due to information regarding the effects of the tomato-cabbage association on 'Land Equivalent Ratio' could not be found, in contrast with rest of the associations studied. However, the fact that tomato increases cabbage yield may shed some light on the chance that both mentioned associations may be as convenient to grow, at least from an agronomic-wise perspective. Since the relevance of the Economic Aspects is high when it comes to its implications on developing an 'urban agriculture' related project, best performers were clearly: tomato-onion; tomato-lettuce and cabbage- lettuce. Perhaps the criterion of 'Economic Aspects' is not as relevant as ones related to the agronomic performance of the associations, however, this criterion may suggest that the association 'tomato-lettuce- cabbage' may be an intercrop to test, to determine if it may offer not only economic benefits, but also agronomic as well. As for the criterion of 'Cultivation Medium Quality', the most outstanding association is 'tomato-garlic' as the 'crossed-benefitting' stands as an idea to consider. It is important to take into account that, on one side, "(The association)...can improve both the microorganism populations and the enzyme activity of the medium, which together reduce the obstacles of continuous tomato production." (Liu et al., 2014), and from another side, tomato has been pointed as a vegetable species that has a good performance in terms of heavy metal absorption (An et al., 2011), becoming the association a very good candidate to consider growing, which pendant to be analyzed through a proper Life Cycle Assessment, seems to be the option that might potentially imply lower environmental impacts. Except for the 'onion-cabbage' association, which outperformed in the criterion of 'Resilience', for all of the associations listed in this study there is literature supporting the existence of the feature of 'Resilience' in association. Understanding the word 'Resilience', as previously defined as “(…) the capacity of an association to overcome difficult adverse climatic/weather conditions, which are determined by the different seasons of a year”. This feature becomes relevant as the possibility of ensuring food security is increased, in a context of climate change. In case of limited production resources, another criterion to consider, covered in this study, is 'Pest & Disease Control'. If associations are to be chosen through the optics of the defensive performance against pests and diseases, only the tomato-cucumber' and 'onion-cabbage' associations outperformed. The relevance of this criterion is related to the expectations put on the production yield and quality. From another perspective, these species may be considered as essentials, at least in the Barcelona market, considering that, according to the MercaBarna database, the tomato, cucumber, onion and cabbage, historically, account for 30% of the total commercialized vegetables in the last decade. Pending the estimating the possible 'Land Equivalent Ratio' and 'Resource Consumption' numbers that may be obtained for the case of the tomato-cabbage association, if eventual results are positive and synergetic, the association might the top 3 recommended associations in this literature review.

5. Conclusions Finally, this study highlights the associations that, according to existing literature, may offer the best results for their application for urban agriculture purposes, adding up to the benefits of soilless production and urban greenhouses. The associations that show best results are ‘tomato-cucumber’, ‘tomato-cabbage’ and ‘tomato-basil’. After computing the average score that all of the associations obtained in the evaluation criteria, these four associations outperformed by scoring equal to or higher than “1”. It is worth to mention that some of the associations scored ‘zero’ in some criteria, due to the lack of available information. An interesting research opportunity becomes producing these associations in equal production conditions to confirm this literature review's findings.

Ultimately, finding associations that include tomato for its hydroponic-based urban greenhouse production is highly recommended since several important features were highlighted by a number of authors. An et al. (2011) determined that tomato may play an important role in the phytoremediation of soil, due to heavy metal absorption. In terms of resilience to difficult weather conditions, Rufí-Salís et al. (2020) found out that tomato is resilient to winter season. When it comes to the efficient use of resources, Mohammadzadeh et al. (2018) and Tringovska et al. (2015) defended tomato, especially the latter, demonstrating that even in intercrop with lettuce, tomato production was still efficient in use of resources. This statement may resonate on the findings of Khoshnevisan et al. (2014) who determined that one ton of tomato greenhouse production may have a lower environmental impact than an average European citizen in a year. Finally, tomato

18 demonstrated to be able to play a relevant role in terms of pest control when it is intercropped with cabbage (Asare-Bediako et al., 2010) and with lettuce (Tringovska et al., 2015).

6. Declarations 6.1. Funding The authors did not receive support from any organization for the submitted work.

6.2. Conflict of Interest/Competing Interest The authors declare that they have no conflict of interest.

All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.

6.3. Author’s contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Leonardo Parra, Felipe Parada and Verónica Arcas. The first draft of the manuscript was written by Leonardo Parra and all authors commented on previous versions of the manuscript. All authors read and Xavier Gabarrell approved the final manuscript.

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22 8. Supplementary Information Table 1: Mercabarna Database

Period Selection Ratio (SR) Accumulated Selection Selection Nº Product Total [kg] price DB: 143.46* Historical Weight (%) Criteria #1 Criteria #2

1 POTATO MONA LISA QUALITY WHITE VEGETABLES 787,741,143 0.39 2019.85 20 ✓ ✓ 2 SHALLOT VEGETABLES 129,759,469 0.1 1297.59 23 ✓ ✓ 3 TOMATO RIPE VEGETABLES 549,040,330 0.74 741.95 37 ✓ ✓ 4 ONION DRY VEGETABLES 230,887,311 0.36 641.35 43 ✓ ✓ 5 LETTUCE ICEBERG VEGETABLES 213,018,314 0.47 453.23 49 ✓ ✓ 6 CARROT VEGETABLES 157,338,936 0.43 365.90 53 ✓ ✓ 7 POTATO RED VEGETABLES 102,520,872 0.37 277.08 55 ✓ ✓ 8 LETTUCE UNSPECIFIED VEGETABLES 101,378,249 0.56 181.03 58 ✓ ✓ 9 TOMATO GREEN VEGETABLES 146,270,365 0.89 164.35 62 ✓ ✓ 10 COURGETTE VEGETABLES 125,915,385 0.87 144.73 65 ✓ ✓ 11 AUBERGINE LONG VEGETABLES 115,660,562 0.87 132.94 68 ✕ ✓ 12 ONION SPRING VEGETABLES 71,983,460 0.61 118.01 70 ✕ ✓ 13 LETTUCE LONG-LEAF VEGETABLES 52,580,945 0.46 114.31 71 ✕ ✓ 14 CUCUMBER VEGETABLES 80,224,349 0.72 111.42 73 ✕ ✓ 15 ONION DRY FIGUERAS VEGETABLES 74,355,607 0.67 110.98 75 ✕ ✓ 16 PEPPER GREEN ITALIEN VEGETABLES 97,800,997 1.08 90.56 77 ✕ ✓ 17 PEPPER RED VEGETABLES 92,805,962 1.19 77.99 80 ✕ ✓ 18 VEGETABLES OTHER VEGETABLES 50,549,887 0.7 72.21 81 ✕ ✓ 19 CELERY VEGETABLES 36,506,006 0.57 64.05 82 ✕ ✓ 20 PARSLEY VEGETABLES 27,798,358 0.44 63.18 83 ✕ ✓ 21 ARTICHOKE VEGETABLES 74,155,213 1.26 58.85 85 ✕ ✓ 22 RADISHES VEGETABLES 23,270,340 0.4 58.18 85 ✕ ✓ 23 CHARD VEGETABLES 30,658,544 0.57 53.79 86 ✕ ✓ 24 LAMUYO PEPPER VEGETABLES 64,720,199 1.21 53.49 88 ✕ ✓ 25 CABBAGE VEGETABLES 34,664,395 0.66 52.52 89 ✕ ✓ 26 SPAGHETTI VEGETABLES 27,774,578 0.56 49.60 89 ✕ ✓

23 Period Selection Ratio (SR) Accumulated Selection Selection Nº Product Total [kg] price DB: 143.46* Historical Weight (%) Criteria #1 Criteria #2 27 POTATO EARLY VEGETABLES 16,119,393 0.35 46.06 90 ✕ ✓ 28 CAULIFLOWER VEGETABLES 38,828,943 0.98 39.62 91 ✕ ✓ 29 ESCAROLE VEGETABLES 25,991,994 0.68 38.22 91 ✕ ✓ 30 SWEET POTATO VEGETABLES 27,243,227 0.73 37.32 92 ✕ ✓ 31 LEEK VEGETABLES 29,461,026 0.83 35.50 93 ✕ ✓ 32 SPINACH VEGETABLES 24,499,725 0.73 33.56 93 ✕ ✓ 33 GARLIC FRESCH VEGETABLES 17,889,224 0.59 30.32 94 ✕ ✓ 34 BROCCOLI VEGETABLES 26,217,646 0.87 30.14 95 ✕ ✓ 35 BELGIAN ENDIVE VEGETABLES 21,082,602 0.79 26.69 95 ✕ ✓ 36 ASPARAGUS GREEN VEGETABLES 35,103,370 1.88 18.67 96 ✕ ✕ 37 TURNIP VEGETABLES 11,961,903 0.7 17.09 96 ✕ ✕ 38 BEETROT VEGETABLES 10,603,747 0.67 15.83 97 ✕ ✕ 39 CAULIFLOWER VEGETABLES 14,418,266 1.08 13.35 97 ✕ ✕ 40 CABBAGE CHINESE VEGETABLES 9,093,206 0.75 12.12 97 ✕ ✕ 41 GREEN BEAN PERONA VEGETABLES 31,813,969 2.76 11.53 98 ✕ ✕ 42 BROAD SEAN VEGETABLES 12,806,011 1.26 10.16 98 ✕ ✕ 43 CABBAGE RED VEGETABLES 5,153,764 0.59 8.74 98 ✕ ✕ 44 GARLIC DRY VEGETABLES 19,062,882 2.24 8.51 99 ✕ ✕ 45 PARSNIP VEGETABLES 6,146,213 0.8 7.68 99 ✕ ✕ 46 FENNEL VEGETABLES 3,290,745 0.78 4.22 99 ✕ ✕ 47 GREEN BEAN BOBI VEGETABLES 9,191,411 2.39 3.85 99 ✕ ✕ 48 CARDOON VEGETABLES 2,377,436 0.73 3.26 99 ✕ ✕ 49 BEAN UNSPECIFIED VEGETABLES 6,777,037 2.4 2.82 100 ✕ ✕ 50 BRUSSELS SPROUT VEGETABLES 1,720,140 0.85 2.02 100 ✕ ✕ 51 SNOWPEA VEGETABLES 4,427,954 2.34 1.89 100 ✕ ✕ 52 AUBERGINE ROUND VEGETABLES 1,569,698 0.9 1.74 100 ✕ ✕ 53 GREEN BEAN FINE VEGETABLES 4,035,923 2.85 1.42 100 ✕ ✕ 54 BORAGE VEGETABLES 862,883 0.84 1.03 100 ✕ ✕ 55 WATERCRESS VEGETABLES 745,584 0.86 0.87 100 ✕ ✕

24 Period Selection Ratio (SR) Accumulated Selection Selection Nº Product Total [kg] price DB: 143.46* Historical Weight (%) Criteria #1 Criteria #2 56 ASPARAGUS WHITE VEGETABLES 1.495,983 3.29 0.45 100 ✕ ✕

Total 3,919,371,681

Table 3: Parameterization Scoring

Score Description

Yield (Y)

-2 The worst performer according to the cited literature. Yield is decreased for both the species involved, compared to monocrops.

-1 Causes the decrease in the yield of one of the species involved.

0 No data/No change

1 Causes the increase in the yield of one of the species involved.

2 Results to increase the yield for both the species involved. Also, the intercrop is the best performer of cited literature.

Resilience (R)

-2 Worsens the impact of adverse climatic/weather conditions for both of the species intercropped. Also, the association is the worst performer of the cited literature.

-1 Worsens the impact of adverse climatic/weather conditions of one of the intercropped species.

0 No data/No change

1 Increases the tolerance to climatic/weather conditions of one of the intercropped species.

2 Enhances the tolerance of both the intercropped species to climatic/weather conditions. Also, the association is the best performer of the cited literature.

Cultivation Medium Quality (CMQ)

-2 Worst performer by cited literature, as the intercrop decreases soil/cultivation medium quality.

-1 In intercropping, one of the species decreases soil/cultivation medium quality.

0 No data / No change

1 In intercropping, one of the species improves soil/cultivation medium quality.

2 Best performer by improving soil/cultivation medium quality, according to cited literature. Both species have a positive impact.

25 Economic Aspects (EA)

-2 Worst performer in economic aspects for both intercropped species. Lowest RR, OP, PI and/or highest production costs. Also is considered the worst performer of the cited literature.

-1 Negative RR, OP, PI, and/or increased production costs. Intercropping worsened the economic aspects for one of the species involved.

0 No data/No change.

1 Positive RR, OP, PI, and/or decreased production costs. Intercropping improved the economic aspects for one of the species involved.

2 Best performer in economic aspects for both intercropped species. Highest RR, OP, PI and/or lowest production costs. Also is considered the best performer of the cited literature.

Pest & Disease Control (P&DC)

-2 Worst performer by resulting in a decrease of tolerance of both species produced to pests and diseases.

-1 Intercropping causes that the tolerance of one of the species to pests and/or diseases is decreased. The other species shows no significant change.

0 No data/No change. This score is applied when one species is affected by intercropped and the other is benefitted.

1 Intercropping causes that the tolerance of one of the species to pests and/or diseases is increased. The other species shows no significant change.

2 Best performer by resulting in an increase of tolerance of both species produced to pests and diseases.

Resources Consumption (RC)

-2 Worst performer in resource consumption/efficiency in the cited literature. The intercropping of both species causes an increase in the consumption of resources.

-1 One of the species in the intercrop causes an increase in the consumption of resources. The other species causes no change. No data/No change. In an association, one of the species causes an increase in consumption of resources, and the other one, causes a decrease, leading to a zero net change in resource 0 consumption, compared against monocrops. 1 One of the species in the intercrop causes a decrease in the consumption of resources. The other species causes no change.

2 Best performer in resource consumption/efficiency in the cited literature. The intercropping of both species causes a decrease in the consumption of resources.

26 Environmental Impact (EI) Worst performer in terms of environmental impact throughout the lifecycle, according to the cited literature. The production of both intercropped species causes an increase in either -2 Global Warming Index and/or carbon footprint. -1 The association presents an increase in environmental impact, either in the Global Warming Index and/or carbon footprint, caused by one of the species. The other species has no impact.

0 No data/No change.

1 Presents a decrease in environmental impact, either in the Global Warming Index and/or carbon footprint, caused by one of the species. The other species has no impact. Best performer in terms of environmental impact throughout the lifecycle, according to the cited literature. The production of both intercropped species causes a decrease in either Global 2 Warming Index and/or carbon footprint. Land Equivalent Ratio (LER)

-2 Presents the lowest LER of the results of the experiment in cited literature. The overall decreased LER is caused by the performance of both the species.

-1 The association presents a LER lower than 100%, whereas it is not the worst performer in the cited literature. Only one species causes the reduction in the LER.

0 No data, not applicable, no change.

1 The association presents a LER higher than 100%, whereas it is not the best performer in the cited literature. Only one species causes the increase in the LER.

2 Presents the highest LER of the results of the experiment in cited literature. The overall increased LER is caused by the performance of both the species.

Scoring Y 2 LER 1 R 0 -1 EI -2 CMQ

RC EA

P&DC A/B…

Figure 1. Example of the graphical representation of the results. Evaluation criteria on the spider web diagram. Y (Yield); R (Resilience); CMQ (Cultivation Medium Quality); EA (Economic Aspects); P&DC (Pest & Disease Control); RC (Resource Consumption); EI (Environmental Impact); LER (Land Equivalent Ratio)