Advancing sustainability of urban agriculture with plant-aquaculture systems

Abstract

Urban agriculture is gaining recognition as a crucial approach to tackling modern issues related to food security, environmental sustainability, and urban resilience. Within the rapidly urbanizing context of China, innovative agricultural systems that merge plant cultivation with aquaculture in urban and peri-urban areas show great promise. This thesis examines the potential of plant-aquaculture systems as a sustainable answer to these challenges, emphasizing their symbiotic relationships.
The research starts by offering a detailed overview of urban agriculture in China, spotlighting the integration of plant and aquaculture systems. It identifies both climatic and non-climatic challenges and draws lessons from successful practices in the Global North. Focusing on the plant-aquaculture symbiosis system, three main strategies to address food security issues in Chinese cities are introduced, encompassing traditional methods like the rice-aquaculture system and modern techniques such as aquaponics, which can be applied at various scales. These integrated systems have the potential to boost food security, promote environmental sustainability, and support urban community well-being.
Building on this foundation, the thesis explores the traditional rice-aquaculture system, recognizing it as a globally significant agricultural heritage practice. A comparative analysis between these integrated systems and conventional rice monoculture is presented, with a focus on their sustainability goals within urban agriculture. The investigation into the physiochemical properties and bacterial communities in co-culture fields in Zhejiang province reveals significant differences influenced by human activities. Total nitrogen and carbon levels in Deqing appear higher than in other fields across Zhejiang. In Tongxiang, the monoculture field showed the highest nitrogen content, while no significant differences in carbon levels were observed among the rotational and monoculture fields. Additionally, the richness and Chao1 index of bulk soil in Deqing were lower compared to other fields in the region. The bacterial communities in the five studied fields also exhibited notable differences. Specifically, the bulk soil in the concurrent field in Tongxiang was particularly distinct due to its significantly higher abundance of Firmicutes compared to the other fields. This analysis highlights the importance of localized practices and management strategies in shaping the characteristics and biodiversity of co-culture fields, providing evidence-based strategies for more scientific management of rice-aquaculture systems.
To further understand the dynamics of rice-aquaculture systems, the thesis identifies and categorizes factors influencing their performance. These factors include field conditions, management practices, feeding supplements, aquaculture techniques, and rice farming methods. By exploring the underlying mechanisms linking these factors to the systems' economic and environmental outcomes, the thesis offers future recommendations for developing comprehensive guidelines to enhance the sustainability of rice-aquaculture farming. By identifying key factors that affect both productivity and sustainability, the research can help to implement more effective management strategies that balance economic viability with environmental effects. Additionally, the insights gained could serve as a foundation for policy development, promoting practices that support both farmers and local ecosystems. Ultimately, this work aims to contribute to more resilient agricultural systems.
Additionally, the thesis investigates the impact of different fertilizer amounts on bacterial and fungal communities within rice-aquaculture systems. It explores the relationship between soil physicochemical properties and microbial dynamics in both rice monoculture and rice-crayfish co-culture fields across various rice growth stages. Before transplanting, rice-crayfish rotational fields exhibited significantly higher total nitrogen content compared to monoculture fields. Fertilization resulted in varied nitrogen and carbon levels, with the highest nitrogen observed in fields receiving 100% and 85% fertilizer. By the harvest stage, nitrogen and carbon levels were similar across all treatment groups, but heavily fertilized fields showed decreased hydrogen content. The bacterial Shannon index was initially higher in monoculture fields, while the fungal Chao1 index indicated greater richness in co-culture fields. Distinct bacterial and fungal community patterns emerged between monoculture and rotational fields, influenced by fertilizer application and soil physicochemical properties. By understanding how fertilizer use affects microbial communities, farmers can make more informed decisions that optimize soil health and enhance crop yields. Furthermore, the insights gained could contribute to the development of integrated rice-crayfish farming systems, promoting biodiversity and improving ecosystem resilience. This research not only addresses agricultural productivity but also emphasizes the importance of maintaining microbial diversity for sustainable land management.
Shifting to innovative urban agriculture techniques, the thesis examines the use of biochar in urban plant-aquaculture systems. It investigates biochar's role as a soil amendment in enhancing the yield and quality of crops like basil and lettuce in small-scale aquaponic systems. While biochar amendments did not significantly increase plant biomass, they notably enhanced the uptake of several key minerals Optimal biochar concentrations were identified as 40% v/v for manganese, iron, and calcium in basil, and 80% v/v for sulfur; for lettuce, 80% biochar was optimal for manganese, zinc, and calcium uptake. Our microbial analysis revealed that the dominant bacterial phyla in biochar-amended substrates were Proteobacteria, Bacteroidetes, and Firmicutes. These phyla are vital for nitrogen cycling and overall plant growth. Biochar treatments exceeding 60% concentration were predicted to enhance nitrogen-fixing functional groups in basil and lettuce systems. The implications of these findings are significant for both academic research and practical applications. The insights gained from this in-situ experiment can inform the design of future field studies and optimize home aquaponic systems, ultimately promoting sustainable urban agriculture.
In conclusion, this thesis presents a comprehensive approach to advancing urban agriculture through the integration of plant-aquaculture systems. By addressing challenges and exploring innovative solutions, it aims to contribute to the development of sustainable urban and peri-urban agricultural practices in China. The findings and recommendations offer valuable insights for policymakers, practitioners, and researchers dedicated to improving food security, environmental sustainability, and urban resilience.

Date of Award	Nov 2024
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Faith Chan (Supervisor), Mengxia Xu (Supervisor), Meili Feng (Supervisor) & Yongguan Zhu (Supervisor)