5.1. Innovation in UA
In everyday discussions and in media portrayals, UA is often addressed as something “new” and “innovative”, even though not each and every component or practice applied in UA projects is actually new. Even if the general approach of a UA project has already been applied in previous cases (such as other CSAs or rooftop farms), two important issues need to be considered when thinking about newness or innovation. The first one is that even if the approach is not new per se, there is still “a new way of doing or thinking” and a specific way of managing it for those who apply it. New practices were consequently a novelty to the interviewees and were therefore also designated as such by them. The second thing is that even if the general idea of a project may not be new (such as establishing a rooftop farm), it may still contain innovative elements. Those novelties within the project and the sum of novelties produced within a project build the core of the innovation.
As our analysis has revealed, a high number of novelties were produced within the investigated UA projects, and we even showed that some of these novelties could be characterized by a very high level of “innovativeness” (e.g., having a level of innovation characterized as an invention). This confirms the findings of Berges [49
] who concluded that UA is not an innovation in its entirety but that the different types of UA have very innovative elements. Berges et al. [41
] further described innovativeness as a direct outcome of the need to adapt to the specific spatial, economic, ecological, and social conditions in urban spaces.
Regarding innovation, we found that the conditions for the cultivation and the marketing of products in UA are so different from those in rural agriculture that the UA operators have to invent new practices. This view on innovation in UA is also in line with the findings of Pfeiffer et al. [8
] and Prain and De Zeeuw [9
], who also detected that techniques and procedures from rural agriculture cannot be simply transferred to urban environments, creating the need for innovation. Innovation in UA, therefore, includes a great deal of testing, experimenting, and failure.
Our study further illustrates that the produced novelties entail all kind of routines, behaviors, and practices throughout all three dimensions of sustainability. This follows the view of Johannesen [43
] and van der Ploeg [44
], according to whom innovation is not only technological innovation but goes far beyond that. According to Opitz et al. [40
], new products, concepts, and practices can be understood as an expression of innovation processes in UA. Confirming Biggs et al.’s [45
] theoretical considerations on innovation, our results also point to the fact that the starting point (trigger) of innovation is usually a specific problem. As Berges et al. [49
] formulated: “Space, water, energy and nutrients are precious goods in our society, especially from a sustainability perspective”. Much of the attempts of our investigated UA cases dealt with overcoming shortages, while novelties were developed to better address those needs.
5.2. Delving into the Most Common Novelties in UA
Environmental novelties are widely used in UA initiatives, which usually promote a local and green marketing identity to differentiate these novelties from conventional options. For example, aquaponics companies often claim that the nutrient recirculation for plant cultivation in their aquaponics system avoids the toxic environmental run-off that characterizes current aquaculture practices (e.g., Oko Farms, New York, USA, http://www.okofarms.com/
). The most common environmental novelties in the case studies were new ways to improve efficiency (focusing on overall resources, crop, water, or nutrient use) and new ecological practices (e.g., organic, biodiversity).
Most of the cases focused on increasing overall resource efficiency and involved introducing a local food product with a minimized supply-chain and improving the economic cost-benefit balance of the activity by enhancing the implementation and the efficiency of crop management techniques. In terms of crop efficiency, the integrated rooftop greenhouse (T6) enlarges the crop period for summer products (e.g., tomatoes), as the location of the greenhouse on the top of a building and the use of the building’s residual heat for the greenhouse ensures viable year-round temperatures for producing the crop without additional energy input [35
]. Furthermore, the integrated rooftop greenhouse (T6) employs rainwater harvested on the roof of the building to satisfy the water demand of the crop [29
]. Regarding water efficiency, the two aquaponics case studies (T3 and T4) are also an example of a novelty that boosts water efficiency by combining the water flow for two systems, i.e., crop production and aquaculture, thereby decreasing the overall water demand of the two systems [30
Increasing the nutrient use efficiency was a novelty shared by multiple cases. The combination of aquaculture and hydroponics in aquaponics (T3 and T4) leads to improved nutrient use efficiency, as wastes in the water outflow from the fish production are assimilated by the plants as nutrients. Beyond this opportunity, aquaponics offers the chance to close the water metabolism and recirculate the water outflow from hydroponics back to aquaculture. However, this circular system fully benefits the water cycle rather than the nutrient one, as water from hydroponics needs to be treated to eliminate nutrient residues before being used in the aquaculture production [35
]. Indoor farming using LED lighting (T2) also enhances nutrient use efficiency by optimizing the plant metabolism through specific red-blue light ratios [51
]. The most efficient experience assessed in this paper is the community-supported peri-urban farm (S3), which employs a crop rotation cycle leading to a 0 requirement of nutrients beyond the natural cycles. In this sense, the community-supported peri-urban farm (S3) is also one of the examples of the implementation of organic and ecological practices that build on the reciprocal interactions in the soil-plant ecosystem. To satisfy the nutrient demand of the crops, other case studies reflected the use of organic fertilizers, such as the use of manure in the peri-urban social cooperative (S2) or the peri-urban farm (S4) or the use of urban compost in the open-air rooftop garden (T5) [16
Social novelties associated with the building of capacities, know-how or knowledge were found in all the case studies except the home garden case study. In the different cases under assessment, the knowledge arising from the experience was shared with other stakeholders: this is a common output from UA initiatives [53
]. In some of the activities, such as the open-air rooftop garden (T5) or the community rooftop garden (S1), a large involvement of universities led to experimentation (new knowledge generation) and training opportunities for students. Other activities, such as the peri-urban high-tech greenhouse (T1) or the community-supported peri-urban farm (S3), offered onsite visits to citizens or specific professional groups. Finally, some experiences, such as the peri-urban farm (S4) and the peri-urban social cooperative (S2), involved an engagement with the general public in debates on the food system in cities or meet-the-farmer events.
The novelty of creating networks was already pointed out by Opitz et al. [40
], where linkages were not only considered with city-wide groups of urban agriculture activists but also with networks with a specific purpose (e.g., surplus food distribution, donations and bartering, community building and knowledge exchange). In the evaluated cases, the peri-urban farm (S4) performs direct marketing, while also participating in a local food producer network that allows them to join farmers’ markets, food fairs and meet-the-farmer events. This type of network enables the peri-urban farm to spread the knowledge of their brand and their products among citizens (i.e., potential new customers), while also enabling them to receive feedback from consumers and to exchange knowledge and experiences with other local farmers. The peri-urban social cooperative (S2) and the community-supported peri-urban farm (S3) are members of “campi aperti”(“open fields”), a network of farmers and plant growers that self-organizes farmers’ markets in capitalism-resistant spaces of the cities (e.g., squatted spaces, public areas) and that also promotes alternative values, such as fair trade and social inclusion, which are beyond those embraced by local food supply-chains. The domestic-scale aquaponics case (T3) was promoted by a local association that works to enhance the multicultural, creative and active use of the public space and that is part of a network of stakeholders involved in the decision-making around the public space of cities (e.g., local administration, architects, local farmers). The mentioned networks are comprised of not only farmers but also multiple stakeholders and citizens that are activists in urban movements. Belonging to a different type of network, other cases, such as the LED indoor farming (T2) or the peri-urban high-tech greenhouse (T1) cases that interact with other companies or researchers linked to the specific crop technology under use, are part of strictly professional networks.
Finally, another common social novelty was the generation of work and employment experiences (for both youth and adults), which is a common aspect of professionalizing UA [53
]. The peri-urban social cooperative (S2) mainly employs the population at risk of social exclusion (e.g., drug addicts and former convicts) and youth. The peri-urban farm (S4) was created by just-graduated agronomists, and the new job opportunities have also promoted the inclusion of new graduates looking for their first professional experience in the job market.
Concerning the economic dimension, most of the cases claimed to be introducing new products and practices to urban areas. Beyond the provision of food as a product, most of the UA experiences offer services as a way to differentiate their activity (e.g., equestrian services, room rental and sports activities, gastronomy services) [54
]. The peri-urban social cooperative (S2) has developed the Spazio Battirame (Battirame space), where a restaurant, a training school, meeting rooms and a handcraft workshop space are hosted. In addition, the Spazio Battirame has been used for the hosting of food-related events, such as cooking workshops, a recurring farmers’ markets and thematic dinners. The peri-urban farm (S4) was not the first UA company to offer home-delivered vegetables and fruits boxes in Bologna, but they differentiated themselves with a service that included a free-choice basket composition and a guaranteed morning-harvested and afternoon-delivered service. As an alternative to the mainstream capitalistic system, the community-supported peri-urban farm (S3) offered their members a new way of producing food in cities.
Some of the cases reflected innovation in the way the urban space was utilized. The recent development of UA has included new urban food production forms, such as the integration of agriculture in and on buildings [14
]. In Bologna, several UA experiences were deployed by the city council or developed by the citizens to regenerate urban spaces [56
]. Some of the assessed experiences take place on roofs (S1, T5, T6) and within greenhouses (T2, T3, T4). The latter systems can be designed to be performed within buildings, such as former warehouses (i.e., indoor farming). In the case of LED farming (T2), the case simulated a greenhouse in a real indoor situation (i.e., closed growing boxes that could be placed inside of buildings). The two aquaponics systems required LED lighting to perform within a building with the same efficiency, as the cases were originally developed within a greenhouse. These experiences, such as the two aquaponics systems (T3, T4) or the LED indoor farming (T2) project, are also related to the development, use and testing of new technologies.
5.3. Contrasting the Evidence of the Most Frequent Sustainability Aspects of Innovative UA
Concerning the sustainability aspects linked to the UA experiences evaluated, the literature generally supports those aspects that were also in the present study more common, i.e., taking place in six or more cases (Figure 6
). Regarding environmental benefits, an increased environmental resilience due to life-long learning was identified as a strength of the UA experiences in Bologna [56
]. Additionally, UA was indicated as a potential urban strategy for food production and self-sufficiency not only at the household level [57
] but also at the city level [58
]. In recent decades, the reuse of spaces has been highlighted in renewed UA activity where new and unused spaces of the city, such as rooftops and indoor spaces of buildings or their facades [13
], including not only residential buildings but also industrial parks [59
] or retail parks [60
], have been adapted to food growing. Previous research compared the use of rooftops for food production and photovoltaic energy production and highlighted that when producing electricity, the environmental benefits could be 6.6 times higher in terms of savings of greenhouse gas emissions [61
]. However, this study only focused on the environmental dimension, and further research including the economic and social dimensions would provide data to shed further light on this debate. In fact, some UA experiences on roofs combine food production and photovoltaic systems to satisfy the energy demand of the activity [59
]. Reduced food transportation and reduced food waste were highlighted as a benefit in studies employing life cycle assessment (LCA), where the entire supply chain of products is evaluated [61
]. Depending on the type of UA, the product and the agronomic practices, such reductions result in the decrease of the environmental impact in the LCA indicators related to carbon emissions and air pollution associated with the food product [15
]. However, the logistics of UA can lead to less efficient distribution models (e.g., smaller truck capacity, consumer transportation to the farm or to the pick-up point), and the environmental benefits depend on the logistics model implemented in each specific case [64
]. Highlighting the positive aspects of the vegetative structure, the inclusion of diverse native plants and the re-naturalization of urban areas for sustaining biodiversity and pollination ecosystem services, Lin et al. [65
] reviewed the literature regarding biodiversity and UA. Gasperi [66
] evaluated how a rooftop garden in Bologna could improve the microclimate conditions and the resulting comfort of humans. Sanyé-Mengual et al. [60
] assessed how rooftop agriculture with greenhouses can be coupled with rainwater harvesting to not only cultivate water self-sufficient crops but also to improve rainwater drainage systems. Although the employment of organic waste in UA depends on the agronomical practices, Grard et al. [34
] demonstrated that the potential use of urban organic waste as a substrate for UA could also enhance the urban circular economy. Orsini et al. [58
] highlighted the role of UA in increasing urban green areas (i.e., by transforming built rooftops into green gardens) and in implementing ecologic corridors, since new urban green spaces would be able to connect large external green areas in the outskirts with small urban parks and gardens within the city. However, the literature has not provided data on how UA improves the management of the territory. Moreover, although carbon balances were considered in the LCA studies of UA, due to the short life cycle of food and the emission of carbon when food is digested or when plant residues are managed, carbon sequestration was not included. Although the sustainability role of carbon sequestration and been demonstrated in urban parks [67
], this sustainability aspect has not yet been quantified and demonstrated for UA.
Large water consumption was the most frequently mentioned negative environmental sustainability aspect. Water requirements strongly depend on the cultivation technique implemented in UA [25
]. Although direct water consumption in the garden can be larger than that in conventional agriculture (i.e., where the economy scale allows for adopting improved technologies), the overall water use along the supply chain can result in a better water balance. In addition, rainwater harvesting can be integrated into UA systems, thereby reducing the water consumption requirements [25
]. Furthermore, compared with traditional open-field or greenhouse production systems, urban indoor growing systems may present increased water usage efficiencies. McDougall et al. [68
] also highlighted the need for UA projects to properly manage other resources beyond water (e.g., energy, chemicals) in order to be environmentally efficient activities.
Regarding the social dimension of sustainability, the existing literature reveals the contribution of UA to an increased knowledge of agri-food systems and sustainability [40
], including the role of school gardens [69
] and the associated training opportunities [53
] (e.g., community gardens [71
]). Several studies have proved that engaging in UA improves the access to healthy food as well as the consumption of fruits and vegetables [72
], while positively contributing to the mental health of the participants [75
]. Providing improved access to affordable food, UA has a positive role in low-income communities, in food deserts and in the context of economic crises [77
]. The engagement in UA experiences by citizens from different cultural backgrounds enhances the cultural exchange among individuals [79
]. The food production spaces in cities are also valued as new areas of recreation for citizens [82
]. Finally, the business potential and the professional opportunities of UA initiatives are linked to self-employment [54
Regarding the negative aspects in the social dimension, health risks can arise from soil contaminated by previous uses [85
]; however, these problems can be solved through the use of raised beds and cultivation media or through rooftop gardening [86
]. The fact that the “remediation of urban land” is one of the least common novelties may indicate that there might be low concern or knowledge of soil pollution. Even though soil contamination is generally acknowledged as one of the major health risks in UA, there seem to be minor efforts to address this specific issue in the cases displayed in this study. Furthermore, UA implementation without considering the local context was highlighted as an issue in the UA experiences in Bologna, where the low involvement of stakeholders in the design and implementation was considered as a weakness [56
The positive sustainability aspects associated with the economic dimension have been less evaluated in the literature. Due to a higher proximity between producers and consumers, the development of short food supply chains is an identity of UA. In fact, the direct marketing of short supply chain food products has been a way to differentiate UA projects from conventional food supply chain projects [54
]. UA is also related to business and employment opportunities [13
]. The enhancement of innovation has been evaluated in some studies [8
], which have highlighted how UA activities need to adapt to the urban environment and to focus on looking for alternative ways to reach consumers in order to avoid the economic competitiveness within the conventional market. Finally, reduced costs due to self-production depend on crop management and the crop species [25
]. Although no studies have evaluated the diversification of the local economy as a whole, a research study on the business models of professional UA activities has highlighted the diversification of the activities not only in terms of products but also of services [54
]. Furthermore, the role of UA in boosting the local economy, the ethical quality of UA jobs, and the cooperation (sharing production factors) between UA activities has not yet been assessed. Moreover, the literature has not yet quantified the reduced costs related to food waste prevention and the healthy food provision (i.e., the public health system’s economic benefits due to a healthier diet and the improved mental and physical health of gardeners) associated with UA.
The main negative aspect within the economic dimension was the high price of urban food products. The price strongly depends on the production costs, whose dependence on the available technologies, products, and climatic conditions [25
] may limit the viability of UA activities. The strong price pressure of the food market was indicated by Pölling et al. [54
] as a driver for adaptations in UA professional activities (e.g., specialization, diversification, differentiation) but also as a cause for a decreased number of urban farms in the last decades.
5.4. Limits and Shortcomings of the Study
Relying on 11 selected case studies, our analysis can be read as a seminal study, which may not represent the entirety of UA. The study results rely on single cases, which are influenced by specific impeding and supporting local frame conditions. The statistical assessment aimed to unveil significant differences and relationships within the analyzed sample. However, due to the limited size of the sample and the sampling method (i.e., convenient sample), no generalization of the results can be extended to UA in general or to the entire region of Western Europe. To do so, a random sampling from an extensive list of UA projects and a larger sample would be required.
Another limitation may lie within the framework employed in this study itself. First, the evaluation of the innovativeness grade of the novelties and the sustainability effects of the UA activities might be subjective evaluations based on the perspective of the representative of the activity. Further research might perform an objective evaluation, such as including an experts’ judgment, to contrast the results. Second, when setting up the risk/benefit ratio, one major weakness was that risks and benefits were not offered in an equal share, as from the beginning, the benefits outnumbered the risks. Thereby, we unintendedly created a bias leading to an expectably higher number of benefits compared to the number of risks. Third, as we applied a very broad definition of novelty (“new ways of doing or thinking”) (see Section 2.1
), many things, which in an everyday understanding may not have been labeled as a novelty, were labeled as novelties.
In this study, the applied statistical analysis allowed the formation of conclusions on significant differences and trends, although the findings based on the limited sample used for data collection should be further confirmed by use of a larger survey that would enable the application of the hereby developed methodology to a larger population of UA experiences.
Finally, further studies of different types of UA activities (e.g., business-scale rooftop farms) and in different regional areas (e.g., North America) might shed further light on the innovation and sustainability effects of UA experiences at the global scale. Moreover, the objectives targeted by UA activities in cities in the Northern part of the world vs. those targeted by UA activities in cities in the Southern part of the world [90
] may substantially alter the associated innovation potential. Consistently, the variability in the access to technologies and agricultural input in the different World regions as well as the main functions that are locally associated with UA (ranging from food production and income generation to social and environmental objectives) will call for different innovations.