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Le, Nguyen Quang Tu (2025) Preparation of controlled release phosphorus fertilisers via advanced flow technologies for enhancing crop yields in degraded soils. PhD thesis, University of Nottingham.

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Abstract

Conventional phosphorus (P) fertilisers are widely used in agriculture, yet their low nutrient use efficiency and significant contribution to environmental pollution through leaching and soil fixation present critical challenges. This doctoral research addresses these issues by developing novel controlled-release P fertilisers, specifically chitosan-apatite-citrate (CAC) formulations, leveraging the inherent advantages of continuous flow chemistry technologies for enhanced precision and scalability.

The thesis systematically investigated and compared the phased development of CAC fertilisers. Initially, a CAC formulation prepared via a coiled flow inverter (CFI) was assessed for its viability against batch preparation and commercial fertilisers. Subsequently, a water/oil sheath flow system was introduced to refine the CAC fertiliser production, focusing on improved morphology and controlled nutrient release in response to the change in pH (i.e. simulated rainwater pH). Finally, a comprehensive comparison of four distinct continuous manufacturing strategies: the aforementioned CFI and sheath flow systems, a StoliChem Scalable Agitated Baffle Reactor (SABRe), and a pilot-scale spray dryer was conducted. Each approach was rigorously evaluated for its influence on fertiliser composition, morphology, and, critically, its performance in promoting crop growth and remediating diverse soil types. Cherry Belle radish (Raphanus sativus L.) served as the demonstrator crop, with extensive evaluations conducted across multiple model growing seasons in both acidic and calcareous soil conditions. Key performance indicators included germination rates, early growth dynamics, fresh and dried biomass yields (leaves and roots), P distribution within the plant, and residual soil-available P levels.

Among the developed formulations, the core-shell CAC fertiliser prepared via the sheath flow system (Sheath_CAC) consistently demonstrated superior efficacy and robustness. It promoted the fastest germination and early growth, leading to a significant increase in dried root yield (up to 60% compared to control pots in season two) and a maximum of 46.9% increase in radish P uptake. Despite observed increases in overall plant biomass, the total P uptake remained stable, indicating highly efficient nutrient utilisation. While commercial fertilisers typically exhibited high immediate P availability, Sheath_CAC demonstrated a stable and controlled nutrient release profile over time, effectively minimising the risk of P leaching, a major environmental concern in agricultural systems. Notably, soil column leaching experiments showed that the leaching loss of Sheath_CAC was approximately 1.2% of the initial applied dosage, dramatically lower than the commercial fertiliser's 65%. This research highlights the transformative potential of flow-manufactured controlled-release P fertilisers for fostering more sustainable agricultural practices and contributing to enhanced global food security.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Hessel, Volker Tran, Nam Nghiep Marschner, Petra Fisk, Ian Robertson, Karen Williams, Phil
Keywords:	Flow Chemistry; Microfluidics; Fertiliser; Soil remediation; Controlled-release
Subjects:	S Agriculture > S Agriculture (General)
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	82437
Depositing User:	Le, Tu
Date Deposited:	12 Dec 2025 04:40
Last Modified:	12 Dec 2025 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/82437

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