Which urban agriculture conditions enable or constrain sustainable food production?

ABSTRACT

Urban agriculture (UA) has been adopted as a strategy for food security in urban areas. This study identified the conditions for development of UA through a systematic review of UA case studies. It classified the enabling and constraining conditions within the three compositional elements of UA – necessity, ability, and opportunity – and determined the primary and secondary conditions for UA design by the country income group. The following conditions are required for both high-income and low/ middle-income countries: Motivation/public awareness; labour/human resources; policy and institutional infrastructure; social capital; and arable land and resources for farming. Agricultural education/training and research and technical development are needed for low and middle-income countries as the key secondary conditions. In high-income countries, a lack of farmers’ knowledge and urban development are the main challenges to UA implementation. Therefore, the research findings could be meaningful evidence for making decisions and designing UA policies for sustainable food production.

KEYWORDS:

• Urban agriculture
• food supply
• sustainable food production
• enabling condition
• constraining condition

1. Introduction

Over half the world's population dwells in cities, and this urban population has expanded rapidly (UN Department of Economic and Social Affairs, 2018). Rapid urbanization has had unintended side effects, such as the loss of agricultural land (Ayerakwa, 2017), food shortage (Gallaher et al., 2013), higher unemployment rates (Gupta & Gangopadhyay, 2013; Karanja et al., 2010), deforestation (Gupta & Gangopadhyay, 2013; Pulliat, 2015), and environmental pollution (Chandra & Diehl, 2019). Loss of agricultural land due to urban sprawl mainly affects food security, and fragmented agricultural land reduces the sustainability of existing food systems (Chandra & Diehl, 2019; Filippini et al., 2014). Over 30% of urban dwellers worldwide reside in city slums where people cannot sustain their lives (UN Habitat, 2006), and billions of people remain in poverty (Fernandes, 2008).

Ensuring urban food security, particularly in the poorest households, is a tremendous challenge in many cities (Korth et al., 2014; Oyedele et al., 2017). Food insecurity issues have been presented in the cities of both high-income and low- and middle-income states (Bryld, 2003). Millions of urban poor cannot afford enough food to stay healthy – a situation evident in the Global North and not limited to the Global South (Gupta & Gangopadhyay, 2013; Jonas & Wilson, 2018) – which creates a growing demand for subsistence agriculture among urbanites (Filippini et al., 2018). Given that the provision of food for urban citizens is a significant problem that faces humanity in the next century (Food and Agriculture Organization, 2017), the necessity for food security has led to the vitalization of urban agriculture (UA) among city dwellers globally (Rich et al., 2018). The role of UA in food production is becoming increasingly significant in meeting rising food demands (Filippini et al., 2014). UA emphasizes the importance of stable urban and regional food production (Olsson et al., 2016).

The concept of UA that scholars use has been developed on the basis of a distinctive structure of its own (Mougeot, 2000). The basis of all definitions associates UA with food production in an urban context. Some scholars focus on inner-city areas only, others focus on agricultural activities within and around cities and towns (Mougeot, 2000). In this paper, the FAO's definition of UA is used: growing plants and raising animals within and around cities (Food and Agriculture Organization, 2019). The concept of UA has increasingly attracted environmental activists, poverty activists, and urban planners because of its ability to cope with economic and social pressures in urban areas (Henn & Henning, 2002). Its role varies according to the reason for its practice; for example, food and nutrition security, health, development of local economies (Chagomoka et al., 2017), social inclusion and gender relations (Olivier & Heinecken, 2017), and ecological and environmentally sustainable management (Gren & Andersson, 2018; Hanson et al., 2014). This study focuses on the role of food provisioning, emphasizing the importance of securing food within and around urban areas. Previous studies identified several benefits of UA, such as the strengthening of social bonds (Alaimo et al., 2010), provision of cultural spaces (Saldivar-Tanaka & Krasny, 2004), and enhancement of environmental quality with the support of ecosystem services (Barthel et al., 2010). UA has been a significant component of food systems and has provided humankind with necessary nutrition (Korth et al., 2014). Feeding a growing urban population that faces food insecurity represents a significant humanitarian challenge for the next century (Nel, 2012), and the FAO considers that UA has the potential to enhance urban food security (Redwood, 2012). Various factors influencing sustainable food production in urban areas are cited, such as land availability, climatic conditions, topography, water availability, soil quality, and city gardeners’ motivations (Ruggeri et al., 2016). Some studies that are limited to a specific city, country, or continent, and cover a particular facet, have sought to determine the elements that contribute to the successful implementation of UA (Koont, 2008; Opitz et al., 2016; Shumate, 2012). A systematic analysis of the components, overall development conditions, and factors that UA requires is needed to improve future decision making and help formulate relevant government policies and urban planning strategies (Chandra & Diehl, 2019). Therefore, this study used a systematic review methodology to examine the enabling and constraining conditions that influence the introduction, implementation, and sustainability of a range of UA activities for global food supply.

2. Materials and methods

This study employed an integrative and systematic review as an evidence-based method along with collective case studies to identify enabling and constraining conditions for UA by income level in countries. The method allows for the summarization of current conceptual thinking (Broome, 2000), the gathering of multiple cases to improve theorization from a broader context (Berg et al., 2004), and the capturing of various perspectives and the complexity of evolving phenomena (Whittemore & Knafl, 2005) to provide scientific information for policy decision making. This study found a new and comprehensive picture of knowledge through the systematic search, rigorous review, critical analysis, and comprehensive synthesis of empirical and theoretical literature (Whittemore & Knafl, 2005). It adopted the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) flow diagram (Page et al., 2021), which follows identification, screening, eligibility, and inclusion (Figure 1).

Figure 1. PRISMA flow diagram for the enabling and constraining conditions of urban agriculture, which included searches of databases and registers.

2.1. Data collection (identification), article screening, study eligibility criteria, and inclusion

Following the integrative review process of collective case studies, we searched for relevant articles published till May 2020. This study utilized two of the largest academic journal databases – Scopus and Web of Science – and used key terms related to urban agriculture and food security (Appendix Table A1). Of the 352 documents located, 76 were excluded (duplicates or inaccessible papers). Of the remaining 276, 115 were finally selected after full-screening in accordance with the following four selection criteria; (1) articles from an academic journal, (2) written in English, (3) ‘urban and peri-urban agriculture’ and ‘food security’-related terminologies included in the title (Appendix Table A1), and (4) study areas that can be identified through the title and abstract in order to distinguish case studies.

2.2. Coding strategy

To understand the context of the selected articles, each study was sorted out by the publication year, study country, and city. Countries were divided by development level (Girardet, 2005) and income level (Stewart et al., 2013), based on the World Bank’s country income-level classification: ‘low-income economies’, ‘lower-middle-income economies’, ‘upper-middle-income economies’, and ‘high-income economies’ (World Bank, 2019).

The UA conditions that are extracted from each study are preliminarily categorized on the basis of necessity, ability, and opportunity. Each ability condition was coded into the enabling and constraining conditions. Each opportunity condition was coded with five sub-categories: technical, economic, environmental, governance, and socio-cultural; following this, individual conditions were classified using enabling and constraining conditions (Table 1).

Table 1. Coding category system.

Category	Subcategory
Bibliographic data	Title, Publication year
Study site	Country, City
Necessity	Increased food prices/demand, Unemployment/Low wages, Economic/Food crisis, Need to improve food security/stability, Need to improve food safety/quality, Environmental concern, Social concern
Ability	Enabling Condition	Motivation/Awareness, Labour/Human resources, Household size, Commitment of UA participants
	Constraining Condition	Farmers/ poor health, Farmers’ ignorance, Farmers’ vulnerability/dependency, Lack of acceptance/involvement, Lack of (qualified) labour/time
Opportunity	Technical	Enabling Condition	Agricultural education/training, Research/Technical development, Farming method/system/tools
		Constraining Condition	Limited storage facilities, Poor technology, Lack of data
	Economic	Enabling Condition	Distribution channel/market, Prices/Direct selling, Collaborative arrangement in the market system, Consumer demand
		Constraining Condition	Poor distribution channels/market, Poor financial conditions, Economic crisis, Low production volumes/incomes
	Environmental	Enabling Condition	Arable land, Resources, Fertile soil, Climatic conditions, Pollination
		Constraining Condition	Limited arable land, Scarcity/Contamination of resources, Lack of fertile land, Harsh climatic conditions, Diseases/Weeds/Pests
	Governance	Enabling Condition	Policy, Governmental institution, Strong governmental will/Talented leadership, Non-Governmental institution, Collaborative partnership among stakeholders, Participatory policy-making
		Constraining Condition	Lack of institutional infrastructure, Political corruption/disputes, Incompetent system and structure, Discourse
	Socio-cultural	Enabling Condition	Social capital, Social movement, Promotion/Publicity
		Constraining Condition	Crime, Indiscriminate urban development, Limited access

2.3. Enabling and constraining conditions in UA

One of the diverse definitions of enabling conditions is ‘an imperative concept to increase the likelihood of an intended change in the governance approach, strategy, or management regime’ (Huber-Stearns et al., 2017). Research on enabling and constraining conditions is crucial for the facilitation of policy design and implementation of new strategies, that include decision making (Waite et al., 2015), policy implementation (Dawson & Robinson, 1963; Rands et al., 2010), knowledge conversion (Martin-Niemi & Greatbanks, 2010), payment for ecosystem services (Huber-Stearns et al., 2017). and knowledge organization (Choo & de Alvarenga Neto, 2010), as used in various studies.

Three coders used two guidelines to identify and log enabling/constraining conditions broadly; (1) sentences and paragraphs in the articles were recorded for the condition analysis; (2) positive (enabling) and negative (constraining) information on UA directly stated in sentences or paragraphs were recorded. The extracted information was grouped into the three principles developed by Choguill (1995) – necessity, ability, and opportunity – to demonstrate the conditions that enable or constrain UA. Several models have been applied to describe how UA advances, such as the capability approach (Sen, 1985), sustainable livelihood approach (Chambers & Conway, 1992), and urban livelihood coping model (Masvaure, 2016), but no approach unravel the UA conditions. This research utilizes the dimensions of necessity, ability, and opportunity (Choguill, 1995) among different approaches to explain UA development and existence because of its explanation power on enabling and constraining conditions for adopting UA as a food security strategy. Different studies have used this model to discuss how the introduction of UA affects food security and the reduction of urban poverty (Masvaure, 2016; Moglia, 2014).

First, necessity, or the attempt to redress such deficiencies, is an insufficient state. The conditions of necessity include unemployment and poverty, which is considered the primary initiator of UA, which reduces expenses through food cultivation, especially in developing countries (Masvaure, 2016). The vulnerable households of a city are more likely to implement UA. Second, this study’s word ‘ability’ refers to one’s capacity to perform certain functions (Sen, 1985), especially to implement UA practices. Ability conditions include worker availability, farming knowledge and skills, and cultural factors. Finally, opportunity is a set of circumstances; such as climate, political support, and access to water and land; that enable and constrain urban farming (Masvaure, 2016). All three dimensions are interlinked and essential for UA’s introduction, implementation, and maintenance (Figure 2).

Figure 2. The compositional elements of urban agriculture.

The dimensions were further classified into five sub-categories based on the factors that affect the success of UA projects mentioned in a previous study. These sub-categories included technical, economic, and socio-cultural factors (Dehnavi & Süß, 2019); two more categories, environmental and governance factors, were added by the authors (Figure 3).

Figure 3. Structure of urban agriculture conditions.

3. Results

A literature selection process was used to collect a total 130 case studies from 115 articles. Some countries dominate in terms of the number of case studies (Figure 4), especially in the North America (n = 30), such as the US (n = 20) and Canada (n = 9). Nigeria (n = 6, 19%), South Africa (n = 5, 16%), and Ghana (n = 4, 13%) account for approximately 50% of all studies in Africa (n = 31). In Asia (n = 21), China (n = 6, 29%) and India (n = 5, 24%) are the two major countries, while Brazil (n = 5, 36%) and Cuba (n = 5, 36%) lead urban farming research in Central and South America (n = 14). Among European countries (n = 30), the UK (n = 8, 28%), Italy (n = 6, 19%), and Germany (n = 4 13%) have been active in UA research.

Figure 4. Geographic distribution of the collected case studies on urban agriculture and food security. Note: The darker the colour, the greater the number of documents.

Few studies were published before 2010, during which time an uptrend in UA research was observed (Figure 5). The selected articles are almost equally distributed between low and middle, and high-income countries, indicating that agriculture practices and food security in cities are entering the spotlight worldwide. The issue of poverty gained more attention in urban studies since 2010, despite agricultural practices having been widely introduced into urban areas even earlier (Knowd et al., 2006).

Figure 5. Distribution of the number of collected publications on urban agriculture and food security by year and income level.

3.1. Necessity

This study identified the necessities that lead to the implementation of UA, which include an increase in food prices and demand, unemployment and low wages, food safety or quality concerns, economic or food crises concerns, the need for food stability and security, and environmental and social concerns (Table 2).

Table 2. Conditions of necessity in urban agriculture.

Category	Conditions (Number of case studies)
Necessity	Increased food prices/demand (31)
	Unemployment/Low wages (13)
	Economic/Food crisis (4)
	Need to improve food security/stability (22)
	Need to improve food safety/quality (15)
	Environmental concern (20)
	Social concern (17)

As the population of a city increases, so does the demand for food. Inadequate food supplies and rising prices (Increase of food price/demand, n = 31) have encouraged urban residents to participate in UA. The rapid spread of urbanization has led to increased unemployment (Masvaure, 2016) (Unemployment/low wages, n = 13) and urban poverty rates. Low wages and job insecurity are two of the most significant difficulties for urban dwellers (Okon et al., 2012). Domestic and global economic and food crises (Economic/Food crisis or War, n = 4) have led to UA implementation as urban gardens presented themselves as an appropriate means of food provision during periods of economic stress.

UA has also been implemented in response to a growing national interest in food security/stability (n = 22), increased demand for local food, and a sustainable food chain. UA has been encouraged beyond the domain of urban food production to facilitate a sustainable food supply chain (Martin & Marsden, 1999), not only in developing countries but also in developed countries, to promote a ‘local food’ movement for sustainable local food production (Nicholls et al., 2020).

Food safety issues (Food safety/quality, n = 15) are also major drivers of UA practices. Concerns about food safety and agricultural activities are increasing steadily in urban areas, where citizens desire safe and nutritious food production (White, 2011). City dwellers are increasingly considering UA an appropriate method of combating dietary-related diseases (Pettygrove & Ghose, 2018).

UA has also been implemented to improve a city's green infrastructure and increase residents’ educational, social, and recreational space (Environmental concerns, n = 20) (Saldivar-Tanaka & Krasny, 2004). People in cities have taken to UA to combat climate change and the greenhouse gas emissions that result from long-distance food supply (Broadway & Broadway, 2011). UA is also conducted for social and therapeutic purposes (Social concerns, n = 17) (Sanyé-Mengual et al., 2016).

3.2. Ability

Ability, another UA component, refers to internal and potential factors, such as innate nature (e.g. physical strength), related to UA performance. The enabling conditions of UA ability are found in the awareness and motivation of UA stakeholders, labour or human resources, household size, and commitment of UA participants (Table 3). First, personal awareness of the importance of UA and motivation (Motivation/Awareness n = 37) were identified as successful momentum factors in the UA movement, which raised awareness of the need for food (White, 2011). Second, the presence of human resources (Labour/Human resources, n = 21), such as farmers, agricultural scientists, and urban planners, is a primary condition that enables UA. The enhancement of human capacity by providing knowledge or information on food production to urban farmers is necessary for successful multifunctional agriculture (Olsson et al., 2016). Household size is essential (Household size, n = 2) as larger households have greater labour resources (Okon et al., 2012). Finally, urban gardeners’ commitment to or engagement in UA processes (Commitment of UA participants, n = 10) proved to be an enabling factor for successful UA implementation (Roth et al., 2015). In particular, a bottom-up approach to urban food production inspired more farmers to grow their food (Sartison & Artmann, 2020).

Table 3. Enabling and constraining conditions of ability in urban agriculture.

Category	Enabling condition (Number of case studies)	Constraining condition (Number of case studies)
Ability	Motivation/Awareness (37)	Farmers’ poor health (3)
	Labour/Human resources (21)	Farmers’ ignorance (13)
	Household size (2)	Farmers’ vulnerability/dependency (2)
	Commitment of UA participants (10)	Lack of acceptance/involvement (6)
		Lack of (qualified) labour/time (7)

The identified constraining conditions on UA ability are farmers’ poor health, lack of farming knowledge, urban farmers’ vulnerability or dependency, lack of acceptance and involvement of urban farmers, and lack of qualified labour or time (Table 3). Health risks (Farmers’ poor health, n = 3), especially old age, negatively affect UA activities as people lose their vigour and are can no longer cultivate agricultural products (Ampaw et al., 2017). Farmers’ ignorance of farming techniques (n = 13), poor understanding of UA (Shariful Islam 2004), and lack of training programs and farming skills (Newman, 2008) are major obstacles to the practice of UA (n = 13). Dependence on governmental support systems (Farmers’ vulnerability/dependency, n = 2) also hinders the development of sustainable UA (Amato-Lourenço et al., 2020). The lack of acceptance of and involvement in urban farming practices (n = 6) (Sanyé-Mengual et al., 2016) is another constraining condition, as is the limited time/labour available for such farming (n = 7) (Gregory et al., 2016; Newman, 2008).

3.3. Opportunity

The opportunity conditions for UA represent a series of situations that enable or obstruct UA. These were classified into five sub-categories; technical, economic, environmental, governance, and socio-cultural factors (Table 4).

Table 4. Conditions of opportunity in urban agriculture.

Category	Subcategory	Enabling condition (Number of case studies)	Constraining condition (Number of case studies)
Opportunity	Technical	Agricultural education/training (19)	Limited storage facilities (1)
		Research/Technical development (20)	Poor technology (1)
		Farming method/system/tools (8)	Lack of data (1)
	Economic	Distribution channel/market (11)	Poor distribution channels/market (10)
		Prices/Direct selling (4)	Poor financial conditions (11)
		Collaborative arrangement in the market system (5)	Economic crisis (1)
		Consumer demand (1)	Low production volumes/income (4)
	Environmental	Arable land (34)	Limited arable land (54)
		Resources (35)	Scarcity/Contamination of resources (32)
		Fertile soil (14)	Lack of fertile land (11)
		Climatic conditions (7)	Harsh climatic conditions (7)
		Pollination (1)	Diseases/Weeds/Pests (9)
	Governance	Policy (60)	Lack of institutional infrastructure (40)
		Governmental institution (20)	Political corruption/disputes (5)
		Strong governmental will/Talented leadership (10)	Incompetent system and structure (5)
		Non-Governmental institution (9)	Discourse (1)
		Collaborative partnership among stakeholders (9)	–
		Participatory policy-making (9)	–
	Socio-cultural	Social capital (28)	Crime (8)
		Social movement (3)	Indiscriminate urban development (16)
		Promotion/Publicity (2)	Limited access (1)

3.3.1. Technical conditions

Technical enabling conditions for UA include research on and technological development of UA, education and training for urban farmers, and the application of suitable farming methods, systems, and equipment (Table 4). Farmers require skills and technical advice (Agricultural education/training, n = 19) to enhance their capacity (Hosseinifarhangi et al., 2019). Place-based research and development in the agricultural sector (Research and technical development, n = 20) are fundamental for successfully implementing UA (Young, 2019). Various UA projects have been implemented with technical practices, including hydroponic, vertical farming techniques, and plant factories which provide quality food without climatic stress (Hosseinifarhangi et al., 2019). The developed technical inputs, such as improved seeds, seedling technology, eco-friendly fertilizer, and pest control, accelerate agricultural production, secure urban environment, and improve varieties in the changing climate (Pham & Turner, 2020). The development of platforms that govern agricultural education and training and empower urban farmers’ capabilities also positively affects urban crop production (Olivier & Heinecken, 2017). In addition, appropriate farming methods, systems, and tools (Farming method/system/tools, n = 8) can promote UA in different cities (Sanyé-Mengual et al., 2016; Wade, 1987); for example, Organopónicos in Cuba (Cederlöf, 2016) and container vegetable gardening in Canada (Port & Moos, 2014). However, inappropriate technical conditions, such as limited storage facilities (Ampaw et al., 2017), lack of UA technology innovations (Lynch et al., 2013), and lack of data for UA policy-making (Aubry & Kebir, 2013), hinder the vitalization of UA.

3.3.2. Economic conditions

The economic factors of UA include suitable distribution channels and markets, charging retail prices through direct selling, collaborative relationships between producers and consumers, and consumer demand (Table 4). Markets and distribution networks for agricultural products (Distribution channel/market, n = 11) directly affect the income of UA farmers (Amato-Lourenço et al., 2020). The success of UA is also dependent on direct sales to consumers at retail prices (Prices/direct selling, n = 4) (Pollard et al., 2017). Additionally, the collaboration between producers and consumers (Collaborative arrangement in market system, n = 5) is an essential factor that aids direct trade in the market system (Olsson et al., 2016). Furthermore, consumer demand for UA products (Consumer demand, n = 1) aids UA implementation (Plat et al., 2018).

Constraining conditions related to economic conditions include insufficient distribution systems for agricultural products, lack of input costs, economic crisis, and low production volumes and wages (Table 4). Poor markets and distribution channels (Poor distribution channels/market, n = 10) limit the implementation of UA (Leitgeb et al., 2016), and small farmers are especially vulnerable and suffer severe losses from poor market access (Ackerman et al., 2014). Another key barrier includes the financial constraints for new farmers about to begin UA (Poor financial conditions, n = 11) with high operational costs. In particular, initial agricultural investment costs, which include land use permits, are a significant burden and reduce people’s desire for UA (Lavallée-Picard, 2018). Economic crises (n = 1), such as the one in Zimbabwe, can undermine and restrain UA practices (Masvaure, 2016). Finally, the low agricultural production volumes (Low production volumes/income, n = 4) do not guarantee sufficient wages for urban farmers, which results in the slow implementation of UA (Leitgeb et al., 2016)

3.3.3. Environmental conditions

Environmental conditions are significant in the development of UA, such as arable land, available resources, fertile soil, suitable climatic conditions for crops, proximity to UA services, and pollination conditions (Table 4). Environmental conditions include both uncontrollable and controllable cultivation environments. UA is conducted in the outdoors, but also in the controlled indoors independently from the outside environment. This research explores the conditions from the controlled and uncontrolled environment.

The most mentioned conditions that enable UA are land for food production (Arable land, n = 34) and resources (n = 35). In this study, arable land is identified as the space where UA is performed, but beyond the confines of soil/compost-based lands. The arable lands even contain the formation without soil, including hydroponics (Hosseinifarhangi et al., 2019) and aquaponics (Pollard et al., 2017). The securement of an agricultural site in urban areas is essential in the implementation of UA, and governments have made considerable efforts to provide arable land for urban dwellers (Ayerakwa et al., 2020). In Cuba and Vietnam, for example, land reform has been implemented to secure land and food for urban farmers (Leitgeb et al., 2016; Pulliat, 2015). Additionally, to enhance crop production, urban farmers add organic manure and compost to improve poor soil quality (Fertile soil, n = 14) (Chagomoka et al., 2017). Material resources (n = 35) such as quality seeds, water, and fertilizers (compost or manure) are essential to ensure success (Gallaher et al., 2013). Climatic conditions (n = 7) are critical for agricultural production (Krul & Ho, 2017), given that the appropriate climatic conditions according to crop species can foster sustainable urban farming conditions, especially for outdoor cultivation (Lupia et al., 2017). Lastly, pollination (n = 1) affects product yields on a local or regional scale (Gren & Andersson, 2018).

Some environmental conditions, such as land issues, resource scarcity or contaminated resources, lack of fertile land, harsh climatic conditions, limited accessibility, and disease and pest, or weed problems (Table 4) make the practice of UA difficult. Limited access to high-value land (Limited arable land, n = 54) and a scarcity of arable land (Scarcity/contamination of resources, n = 32) are the most critical constraints in UA (Masvaure, 2016). Intense competition for access to land is a worldwide issue in urban farming sectors (Amato-Lourenço et al., 2020), and the poor quality of soil (Lack of fertile land, n = 11) results in low yields and limits the income of farmers (Chagomoka et al., 2017). Scarce and contaminated resources have also been identified as inhibiting factors. Additionally, adverse climatic conditions (Harsh climatic conditions, n = 7) such as heavy rains, flooding, and drought can reduce yields (Karanja et al., 2010). Finally, damage from diseases, pests, and weeds (Diseases/weeds/pests, n = 9) constrains UA (Gregory et al., 2016); in Kaduna State, Nigeria, plant diseases and pests have caused significant losses for 24% of urban farms (Saleh & Mustafa, 2018).

3.3.4. Governance conditions

The governance conditions that affect UA development are UA policies, the role of non-governmental and governmental organizations, strong governmental will, collaborative partnerships among UA stakeholders, and participatory policy-making (Table 4). For successful implementation of UA, strong governmental will and leadership (Strong governmental will/talented leadership, n = 10) are crucial in generating urban development plans while preserving agricultural land (Perrin, 2013). Further, non-governmental organizations (Non-Governmental institutions, n = 9) play an essential role in the successful implementation of UA and the informal initiation of UA projects (Bell & Cerulli, 2012; Olivier & Heinecken, 2017). Thus, frequent cooperation between non-governmental and governmental actors facilitated the rapid growth of UA (Pettygrove & Ghose, 2018). Supportive governmental institutions (Governmental institution, n = 20) are also vital in the growth of UA (Leitgeb et al., 2016). A solid participatory approach fosters UA participants’ sense of responsibility in the UA policy-making process (Participatory UA policy-making, n = 9), while open debates between internal and external stakeholders can increase awareness about the significance of UA (Perrin, 2013; Prové et al., 2019; Roth et al., 2015). Collaborative partnerships among stakeholders (n = 9) and stakeholder participation in establishing UA policies are also important enabling factors (Olsson et al., 2016; Prové et al., 2019). Lastly, the most cited governance-related enabling condition is UA policy (n = 60). UA policies, which include city planning strategies, land reform policies related to land tenure security and ownership, and economic policies such as financial incentives, tax cuts, and subsidies, assist UA and inhibit urban poverty and food insecurity (Dehnavi & Süß, 2019; Leitgeb et al., 2016; Wade, 1987; Yulida et al., 2018).

Other governance conditions, such as institutional infrastructure, political change and disputes over land use, separation of government and civil society, and existing discourse in society (Table 4) can impede UA. Insufficient support infrastructure (Lack of institutional infrastructure, n = 40) undermines ordinary citizens’ ability to participate in UA (Young, 2019) and adequate institutional support is necessary for long-term solutions to improve urban food production (Hashim, 2015). Another constraining governance condition regards wealthy elites or corrupt politicians who take advantage of their positions to exploit capital earmarked for UA development (Political corruption/disputes, n = 5), which thereby slows its development (Olivier & Heinecken, 2017). Furthermore, the political tensions involved in the construction of an international megalopolis and the securing of its food supply somewhat limit acceptance of farming in urban areas (Mcdougall et al., 2020; Pulliat, 2015), and UA practitioners have faced many barriers created by incoherent UA strategies (Incompetent system/structure, n = 5) (Hirsch et al., 2016; Olsson et al., 2016). The discourse within a society (n = 1) can indirectly and negatively affect UA development (Hasson, 2019).

3.3.5. Socio-cultural conditions

Socio-cultural conditions that improve UA include social capital, social movement, and promotion or publicity (Table 4). Community-based and grassroots actions are pivotal for long-term UA implementation (Perrin, 2013). Social capital (n = 28) – community support and community participation – provides social inclusion for urban farmers, creates a strong feeling of shared interests (Gupta & Gangopadhyay, 2013), and strengthens farmers’ networks and partnerships (Shillington, 2013). UA community, regional, national, and global movements (n = 3) are catalysts that enable its development (Hirsch et al., 2016; Mudu & Marini, 2018). Lastly, word-of-mouth recommendations, UA festivals, events, and the media (Promotion or publicity, n = 2) are also factors for successful UA projects (Hirsch et al., 2016; Sartison & Artmann, 2020).

Socio-cultural conditions that hinder UA growth include crime-related problems and reckless urban development (Table 4). Theft is an issue for urban farmers (Crime, n = 8), especially where food is scarce. This risk destroys social capital by creating mistrust and fear among city dwellers (Ayerakwa, 2017; Olivier & Heinecken, 2017). Another major challenge is indiscriminate urban development (n = 16) and encroachment on existing agricultural land in urban areas (Lynch et al., 2013; Spilková & Vágner, 2018). Lack of access (Limited access, n = 1) to resources is also identified as a constraining condition (Sanyé-Mengual et al., 2016).

4. Discussion and policy implications

4.1. Analysis by region and income level

These results provide fundamental information on UA implementation, especially with regard to enabling and constraining conditions and identification of potential challenges and opportunities for future UA practices (Huber-Stearns et al., 2017). The study also analyzed these conditions about national income level to observe possible differences in regional and income-level groups.

4.1.1. Drivers of urban agriculture

Necessity conditions are significant in the identification of UA objectives and selection of appropriate methods in the design phase. UA drivers vary distinctively by national income level (Figure 6). Increased food prices and demand are the most notable drivers in low and middle-income countries. Low-income urban communities that face poverty and high unemployment wish to produce food (or income) through UA activities (Diehl et al., 2019). Additionally, urban dwellers in developing countries promote UA to tackle urban problems like disease (Pham & Turner, 2020), food shortages during and after wars, and international economic crises (Leitgeb et al., 2016; Maxwell, 1995).

Figure 6. Urban agriculture necessity by income level and region.

Unlike low and middle-income countries, social, environmental, and cultural concerns affect the implementation of UA in high-income countries, especially in North America and Europe (Figure 6). Social integration (such as community building), cultural benefits (leisure), fresh and healthy food, and environmental concerns were the main driving forces (Bell et al., 2016). While the UA development pathways of low and middle-income countries focus primarily on food security through improving food production, high-income countries follow diverse and varied pathways with multiple purposes. Therefore, UA design should follow different pathways based on the national income level.

4.1.2. Enabling conditions and national income level

This study examined different enabling conditions by national income level and region. In Figure 7, the cell colour indicates the degree (frequency) of conditions mentioned in the literature. The darker colours indicate more frequent mentions. Several enabling conditions are independent of national income level; they include farmers’ motivation and public awareness for UA practice, labour and human resources, availability of arable land and resources (water, seed, and fertilizer) for farming, social capital, and UA policy and governmental institutions (Figure 7).

Figure 7. Enabling conditions by income level and region.

However, although the overall distribution pattern is consistent (Figure 7), there are slight differences based on the national income level. In high-income countries, the roles of governmental and non-governmental actors are emphasized. Multi-stakeholders contribute to UA formation through cooperation between urban dwellers and policy managers, farmers and officials, and voluntary and public sectors (Roth et al., 2015). Since the 1990s, governance theory worldwide has emphasized the involvement of diverse actors in policy-making. Several European countries highlight the involvement of gardeners and their neighbourhoods in the sustainable preservation of urban gardens (Perrin, 2013; Spilková & Vágner, 2018); only the roles of policy and governmental institutions are emphasized in low and middle-income countries. Although attempts have been made to distribute authority in such countries, the role of governmental organizations dominates the addressal of different agricultural reforms, and many targeted changes have been undertaken by the central authority (Wamukonya, 2003).

Technical conditions, such as the development of UA technology and agricultural education, dominated in low and middle-income countries where technological advancement and corresponding industrial development are still underway (Madu, 1989). Another interesting feature is that commitment to UA is required more in high-income countries than low and middle-income countries. Urban households in low and middle-income countries view agricultural activities as a source of income or food (Byerlee & Sain, 1986); however, urban dwellers in high-income countries also view it in terms of ancillary activities such as leisure (Deelstra & Girardet, 2000). Therefore, promoting urban farmers’ commitment to agricultural activities is an essential condition for facilitating UA in high-income countries.

4.1.3. Constraining conditions and national income level

Constraining conditions differ by region and national income level, as illustrated in Figure 8; those common to all income levels include limited arable land and scarcity or contamination of farming resources. Urban expansion makes land use for agriculture less competitive and constrains the vitalization of UA (Karanja et al., 2010; Masvaure, 2016). Poor soil fertility due to urban contamination is another common constraint (Chagomoka et al., 2017). Shortage of arable land, resources, and institutional infrastructure are also major challenges for UA at all income levels (Ayerakwa, 2017; Davies et al., 2021; Martin & Marsden, 1999; Masvaure, 2016; Sanyé-Mengual et al., 2016) and urban farming everywhere struggles without proper institutional support (Hashim, 2015). In many African countries, national governments and city administrators have tended not to support UA, and have banned farming in cities (Davies et al., 2021; Masvaure, 2016). Under such circumstances, individual citizens cannot implement UA (Hirsch et al., 2016).

Figure 8. Constraining conditions by level of income and continent.

Other constraints differ according to income level. Indiscriminate urban development plans represent a more significant challenge in high-income states. Following competition with housing or commercial developments (Hammelman, 2019), only a small proportion of arable land remains available (Mcdougall et al., 2020). Thus, urban development plans should ensure the availability of arable land in urban areas. Lack of agricultural background and knowledge was frequently mentioned as a constraint in high-income countries (Hirsch et al., 2016; Lavallée-Picard, 2018; Sanyé-Mengual et al., 2016), and time constraints make it challenging to deliver the appropriate skills to urban populations (Gregory et al., 2016; Kaiser et al., 2015; Newman, 2008). Urban gardeners in high-income countries unfamiliar with agriculture need to spend more time gathering agricultural knowledge and skills for successful UA.

4.2. Primary and secondary conditions for urban agriculture design

This study considers income levels and regions to classify UA conditions into two groups, i.e. primary and secondary. Primary conditions are prevailing conditions regardless of national income levels (Figures 7 and 8), people's motivation for taking part in urban agricultural activities, appropriate UA policies, governmental institutions in charge of UA, social networks and partnerships among different UA stakeholders, usable land and materials for farming, and human resources to carry out agricultural activities (Table 5). The results suggest that UA planners, practitioners, and policymakers should prioritize these common conditions while implementing policies and practices. The conditions include sustainable agriculture elements, mirroring the findings by McSorley and Porazinska (2001).

Table 5. The primary and secondary conditions for urban agriculture.

Type of conditions	Country by income level
	High-income Country	Low- or middle-income country
Primary conditions	Ability	Motivation/Public awareness of UA Labour/human resources
	Opportunity	UA policy and institutional infrastructure Social capital Arable land and resources for farming
Secondary conditions	Ability	Farmers’ knowledge Commitment of urban farmers	–
	Opportunity	Urban development	Agricultural education and training Research and technical development

The results identified important secondary conditions: UA food production conditions that vary based on income levels (Table 5). In low and middle-income countries, the key secondary condition is the development of UA technology. Agriculture is an essential engine for economic growth, and UA can support poor urban households in low and middle-income countries (Byerlee et al., 2009); however, increased agricultural yield and boosted profits require improved agricultural technologies (Aker, 2011) and the distribution of information on crops, fertilizers, water, and pesticide use (Shariful Islam 2004). Urban planners in underdeveloped countries should therefore prioritize innovation in agricultural technology. In high-income countries, the key secondary condition is the lack of agricultural capacity; the dearth of trained personnel and skilled urban farmers is a major UA constraint (Newman, 2008; Sanyé-Mengual et al., 2016). Each municipal government should prioritize enhancing individual farming ability and improving commitment to UA activities among urban farmers. Identifying various factors related to commitment is necessary to increase community awareness and participation. Congruence among urban farmers, decisions on a voluntary basis, self-interest, and positive feedback will improve commitment.

4.3. Limitations and directions for future research

This study attempted to include many papers to provide a robust picture of UA; still, there is a possibility of missed evidence from excluded resources, such as grey literature. We only collected documents written in English due to language barriers. Moreover, cities have their dynamics and histories in UA adoption, so the city-specific analysis of UA characteristics in individual countries should be considered. Furthermore, additional detailed and in-depth studies are required to focus on UA conditions by the farming systems and types, including backyard, tactical, and rooftop gardens, vertical farms, beekeeping, and aquaponics. In both developing and developed countries, there is a trend of increase of enterprise-based UA with controlled atmospheric conditions, such as automated vertical farming, and closed systems for aquaculture and vegetable farming (Yuan et al., 2022). Therefore, it is timely to investigate UA conditions by forms and types of UA systems with data in multiple languages for future study. However, despite these limitations, this study presents significant potential knowledge and essential results for the good implementation of UA worldwide.

5. Conclusion: alignment of urban agriculture policies with consideration of enabling and constraining conditions

This study explores the conditions for the development of urban agriculture with enabling and constraining conditions within three dimensions – necessity, ability, and opportunity – answering three questions: (1) What condition enables UA? (2) What condition constrains UA? (3) What condition should be considered first? The answer to these questions provides urban planning policymakers with meaningful evidence to help design UA focused on food production. We recommend the consideration of the following conditions for both high-income and low or middle-income countries (Table 5): Motivation/Public awareness of UA; Labour/human resources; UA policy and institutional infrastructure; Social capital; and Arable land and resources for farming. Subsequently, agricultural education/training, research, and technical development are important for low and middle-income countries as the key secondary condition. In high-income countries, the lack of farmers’ knowledge and urban development are the main challenges for UA implementation.

This comprehensive study identifies and analyses the characteristics, distribution, enabling and constraining conditions, and suggestions of UA implementation for food security. Urban policymakers can establish clear objectives for UA introduction with the necessity conditions. They can create a better environment that meets the primary conditions and then secure the secondary conditions for the development and implementation of UA following the consideration of ability and opportunity conditions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Seoul National University.

Notes on contributors

Seongeun Lee

Seongeun Lee is currently coordinating the climate change response project at Good Neighbors Ethiopia. Her research focuses on sustainable agriculture, agroforestry, and biodiversity in the food system. She holds a bachelor's degree in Plant Biotechnology and Political Science from Chonnam National University. She graduated with a master's degree in International Agricultural Technology and Regional Studies and Spatial Analytics from the Graduate School of International Agricultural Technology at Seoul National University in the Republic of Korea.

Seongmin Shin

Seongmin Shin is a research consultant with the Climate Change, Energy and Low-Carbon Development team at the Center for International Forestry Research. He holds a master's degree in International Agricultural Technology and Regional Studies and Spatial Analytics from Seoul National University, the Republic of Korea. His research interests are climate change, agroforestry, REDD+, bioenergy, and international development.

Hansol Lee

Hansol Lee is an Assistant Program Officer at the Asian Forest Cooperation Organization. She earned her master's degree in International Agricultural Development Cooperation and Regional Studies and Spatial Analytics from the Graduate School of International Agricultural Technology at Seoul National University in the Republic of Korea. Her research interests encompass International Forest/ Environment Policy, Social Conflicts, REDD+, Natural Resource Management, and International Development.

Mi Sun Park

Mi Sun Park is an Associate Professor in international forest policy from the Graduate School of International Agricultural Technology at Seoul National University in the Republic of Korea. She studied forest science (bachelor's degree) and environmental education (master's degree) at the Seoul National University in the Republic of Korea. She earned a forest policy Ph.D. from the University of Göttingen in Germany. Her research interests include governance, discourse, policy integration, international cooperation, and traditional knowledge in forest policy. Currently, she is a coordinator of Research Group 9.03.04 Traditional Forest Knowledge and a deputy coordinator of Research Group 9.01.07 Forests and the Media from IUFRO (International Union on Forest Research Organizations).

Appendix

Table A1. Key concepts and keywords for document collection.

Key component	Keyword	Reference
Urban	Urban, City, Peri-urban, Periurban, Metropol*, Town, City adj*	(Clucas et al., 2018; Korth et al., 2014; Warren et al., 2015)
Agriculture	Agriculture, Farm*, Crop*, Food production, Commun* garden*, Private garden*, Allotment garden*, Semisubsisten* farm, Home garden*, Food process*, Agricultural park*, Livestock
Food security	food adj* insecur*, food adj* secur*, nutrit* adj* secur*, nutrit* adj* insecur*, food suffic*, food insuffic*, nutri* suffic*, nutri* insuffic*, hunger, food distribut*, food procurement, food insecurity, food security, food poverty, food availability, food utilization, food access, diet, food by-product*, food demand, food price*, food process*, food product*, food quality, food safety, food sovereignty, food supply, food supply chain, food system*, food transfer, food	(Abu Hatab et al., 2019; Holley & Mason, 2019; McKay et al., 2019; Warren et al., 2015)
Search query	TITLE (((‘urban’) OR (‘city’) OR (‘peri-urban’) OR (‘periurban’) OR (‘metropol*’) OR (‘town’) OR (‘city adj*’)) AND ((‘agriculture’) OR (‘farm*’) OR (‘crop*’) OR (‘food production’) OR (‘commun* garden*’) OR (‘private garden*’) OR (‘allotment garden*’) OR (‘semisubsisten* farm*’) OR (‘home garden*’) OR (‘food process*’) OR (‘agricultural park*’) OR (‘livestock’))) AND TITLE ((‘food adj* insecur*’) OR (‘food adj* secur*’) OR (‘nutrit* adj* secur*’) OR (‘nutrit* adj* insecur*’) OR (‘food suffic*’) OR (‘food insuffic*’) OR (‘nutri* suffic*’) OR (‘nutri* insuffic*’) OR (‘hunger’) OR (‘food distribut*’) OR (‘food procurement’) OR (‘food insecurity’) OR (‘food security’) OR (‘food poverty’) OR (‘food availability’) OR (‘food utilization’) OR (‘food access’) OR (‘diet’) OR (‘food by-product*’) OR (‘food demand’) OR (‘food price*’) OR (‘food process*’) OR (‘food product*’) OR (‘food quality’) OR (‘food safety’) OR (‘food sovereignty’) OR (‘food supply’) OR (‘food supply chain’) OR (‘food system*’) OR (‘food transfer’) OR (‘food’))