Non-human actants such as soil, water, and organic certification, are not included in this diagram. Further, it only accounts for actors that were encountered during fieldwork and is not meant to be exhaustive. Instead, it hopes to provide a snapshot of the ever-changing networks of actors and actants that were involved during the research period . The practice of mapping out the flows allowed us to identify key nodes of power among the urban agriculture networks in San Diego County, which are indicated on the diagram by use of a darker hue of the parent shade used for each network. For example, Leichtag Foundation is a key node of power in the Coastal Roots Farm actor-network. These actors marshall considerable power in comparison to the other actors enrolled in the networks, whether through the possession of crucial resources such as land and capital, political power, and/or consensus-building. In what follows, we discuss the discoveries we made through examining the vignettes and the network relationships. This discussion provides the results we drew from analyzing the vignettes and the network diagram.The microgeographies of these local commodity circuits had considerable influence on the discursive and material relations present at these sites. Narratives around place drove and legitimatized sites’ growing practices and their approaches to justice, whether based on donations or democratic participation. Further, the characteristics of place drove production, distribution, and consumption practices, which had important implications for justice. Every place in this research had different needs and populations, which drove their place-specific emphases and practices. For example, a mission focused on food sovereignty might be inappropriate in an affluent,plastic plants pots primarily white community like Encinitas . However, this mission is apt in a low-income, minority neighborhood like Southeastern San Diego, which has experienced considerable disinvestment and structural oppression.
These missions at our sites were fitting and reflected what was going on in those places and within their communities. This drove not only production practices, but also distribution and consumption – the lack of substantial need in Encinitas led to distribution in “less fortunate” communities outside of the neighborhood in order to fully realize their mission. This distribution pattern resulted in a more geographically dispersed network that engaged multiple communities with disparate experiences in a single commodity circuit. The characteristics of place and the narratives around production and distribution drove the actors and actants that enrolled in these networks. The most successful and stable networks in our cases, Solutions Farms and Coastal Roots Farms, successfully enrolled actors with substantial capital resources such as Leichtag Foundation and Alliance Healthcare. Indeed, Daftary-Steel, Herrera, and Porter convincingly argue that urban agriculture projects can only truly sustain themselves and produce public goods like nutritious food, education, and job readiness with external investment in the absence of “major shifts in our national wage structure” . Three factors, we argue, contribute to this successful enrolment of funders: proximity, measurable outcomes, and narrative content. Powerful actors, especially those with sustaining capital resources, are often not located in areas of the most need like Southeastern San Diego and therefore may have few, if any, ties to the neighborhood. Measurable outcomes also play a role in enrolling actants with capital resources – as we illustrated in Chapter 3, sites that practice distributive justice, which produces more readily quantifiable outcomes, attract more funding because they can illustrate the efficacy of investment. Although Mt. Hope Community Garden is still successful at enrolling philanthropic foundations into its network, investments are relatively small because of the difficulty of quantifying outcomes like participation and social cohesion. The final aspect is the content of narratives associated with each urban agriculture site, which are part of what makes them unique places. These narratives are both produced by the actor-networks and at the same time powerful actants that shape these networks – an important contribution of Actor-Network Theory. Mainstream neoliberal and reformist narratives that focus on social enterprising and food security may be more successful at attracting funding, as opposed to narratives that focus on food sovereignty. Indeed, funders are often less connected to the histories of structural oppression that drive grassroots urban agriculture projects like Mt. Hope Community Garden. This trend results in a situation in which the most disenfranchised find it difficult to enroll actors with crucial financial resources, giving support to the hypothesis that those with significant resources are more successful at attracting funding .
It also reinforces race- and class-based inequalities because projects run by disenfranchised groups, which more often have progressive or radical agendas , struggle to obtain the support necessary to sustain themselves financially. We saw this in our analysis of Mt. Hope Community Garden. The food justice narratives that surround the garden and its parent organization do successfully enroll actors with knowledge and skills to support its activities. However, the garden received considerably less funding from its network members, leaving it at the helm of the City of San Diego and its decision to sell their property. Actants like soil, water, technology, produce, and the narratives attached to them also drive action and enroll actors into the networks supporting urban agriculture commodity circuits. For instance, the produce grown at the sites determines the extent to which the organizations can generate revenue, feed people, and drive their mission. The use of soil and narratives around its ability to foster community are particularly salient at sites like Coastal Roots Farm. Technology and narratives around innovation similarly enroll actors that value modernization and novelty – technology played an important role in Solutions Farms enrollment of Alliance Healthcare and its $1 million-dollar Innovation grant. These actants, as Bosco describes them, allow our case sites to “become what they are” and explain why some networks and the justice activities embedded within them are more sustainable than others . Tracing the many connections and relations across our commodity circuits illustrates that the story is more complicated than the presence or absence of soil. Watercress is a semi-aquatic plant that grows in f lowing shallow freshwater and is found across Europe, Asia, the Americas, the Caribbean, New Zealand and Australia. Watercress is placed within the Brassicaceae family together with several other important food crops including broccoli, kale, cabbage, and mustard. A significant amount of commercial aquatic watercress cultivation is centred in a few locations including Florida in the USA, southern Spain and Portugal, France and the south of England, with 90% of production occurring in Dorset, Hampshire and Wiltshire. These chalky areas provide nutrient-rich spring water and boreholes that directly supply the watercress beds. Phosphate-rich fertiliser is used to boost crop yield; however,blueberry pot this presents a major challenge in watercress production since it results in direct leakage of phosphate into the waterways which have high conservation value.
Excess phosphate results in eutrophication of aquatic ecosystems, a process where nutrient enrichment of water sources results in excessive algal and plant growth, and subsequent disruption of ecosystem community dynamic. Approximately 90% of watercress farms in the UK are on, or upstream of, a Site of Special Scientific Interest , increasing the pressure to minimise phosphate release.Phosphate is vital for plant survival; it forms the phosphodiester bonds that link nucleotides in nucleic acids and is critical for the structure of proteins and carbohydrate polymers, for powering cells through the release of phosphate from ATP and for regulating several metabolic pathways Symptoms of P deficiency are retarded growth, increased root:shoot biomass, decreased leaf area and often dark green or purplered colouration in severely deficient plants due to anthocyanin production. Ninety percent of the global demand for phosphorus is used for food production, however, rock phosphate is a limited resource with estimates that reserves could be exhausted in the next 50–100 years . In addition, most of the remaining rock phosphate reserves areunder the control of only a few countries, with Morocco and the Western Sahara holding over 70% of the total reserves, making it sensitive to political instability. This, combined with increasing costs of extraction and issues of eutrophication,make reducing fertiliser use an important global driver. The high reactivity and low solubility of phosphates make them commonly the growth-limiting nutrient for plants. Accounting for fertiliser application, approximately 30% of global cropland area exhibits soil P deficits although global P imbalances in water sources have not been investigated to any significant extent.Like soil, P in aquatic systems is also divided into different fractions based on solubility and reactivity in aquatic systems, with dissolved orthophosphate the most bio-available. P in water adsorbs to oxides and tightly binds with carbonates in the same manner as when in soil. However, the P inputs to natural water systems and the interaction with P in bed sediments is altered. This creates a dynamic source of phosphorus that transfers between particulate and dissolved forms, between bed sediments and the water column, and between dead and living material . In a watercress bed, the sediment is shallow gravel and thus P uptake from water likely represents the major P source. This is ref lected in a study by Cumbus and Robinson who found that a greater proportion of P was absorbed by the adventitious roots of watercress , compared to basal roots. However, some organic detritus held within the sediment should still be considered. Phosphate dynamics in hydroponic agricultural systems such as watercress beds have not been studied, representing a knowledge gap, but P is likely uniformly distributed due to f lowing water and regular maintenance of P concentrations. Since P retention in sediments is high, P delivery into freshwater systems is largely governed by release from point sources such as sewage treatment works , leaking septic tanks, and from excess fertiliser application. Globally, domestic sources contribute 54% to total P inputs into freshwater systems, 38% from agriculture and 8% from industry. Although substantial steps towards P reduction in fresh waters have been made over the last 50 years there is still much to be done, with only 40% of European surface waters currently in good ecological status.
Eutrophication of watercourses is also prevalent across the UK: in the most recent analysis, 55% of river water bodies in England failed to meet the revised P standards for good ecological status. Eutrophication is both an economic as well as environmental issue. In the US, the economic damage of eutrophication equates to $2.2 billion annually, due to losses in recreational water use, waterfront real estate, recovery of endangered species and drinking water. Naturally, phosphate levels in chalk aquifers are less than 20 μg/l, however, inputs of phosphate rapidly increase these concentrations above P targets downstream of watercress farms. In the river Itchen where several watercress farms are located, total SRP load comes predominantly from sewage treatment works but watercress beds can be responsible for up to 62% of the total reactive phosphate in some chalk streams, suggesting room for improvement in P management. Casey and Smith found watercress beds increased mean P concentrations which may cause undesirable growth of algae and disruption of community dynamics. One important strategy to tackle this problem of eutrophication is through plant breeding. By breeding watercress varieties with improved phosphorus use efficiency , the impact of watercress farming on eutrophication could be minimised. To date, no breeding for nutrient use has been conducted in watercress even though P release represents a clear issue in watercress production.Phosphate use efficiency is defined as the capacity for biomass production using the P absorbed . Here PUE is used as a broader term that also encompasses phosphate acquisition efficiency, defined as the ability to take up P, as has been used in several studies. Plant traits underpinning PUE can be observed at the macroscopic, microscopic, and molecular levels and we consider their relevance to future breeding for enhanced PUE. To date, knowledge on P acquisition by aquatic plants only covers the effectiveness of plants for phytoremediation , rather than breeding for PUE in aquatic crops such as water chestnut , water spinach , lotus and watercress. Present information does not cover morphological or genetic components to improve PUE in aquatic species, and with new plant species emerging as suggested model organisms, watercress is offered as a model crop for aquatic systems.