Delgado García, AntonioCampillo García, María del Carmen del2024-11-212024-11-212024-09-27Ayeyemi, T.T. (2024). Effectiveness of Vivianite as a Sustainable Phosphorus and Iron Fertilizer for Agricultural Crops. (Tesis Doctoral Inédita). Universidad de Sevilla, Sevilla.https://hdl.handle.net/11441/164710The continued supply of phosphorus (P) fertilizers essential for agricultural sustainability has been described as a looming crisis. This is because of the declining world reserve of phosphate rock which is the major source of raw material for P fertilizers. Hence there is a rising need for alternative sources of P for the sustenance of crop production to feed the world's rapidly growing population. The wastewater purification system presents an opportunity for the recovery and recycling of P as an alternative source of P fertilizer for crop production. Vivianite is one of the P recovery products from wastewater treatment plants (WWTPs) that has been recently gaining attention as a potential P fertilizer. Although synthetic vivianite has been promoted as an efficient iron (Fe) fertilizer for years, there is, however, little or no information about the use of vivianite as a source of P for crops. In the first chapter of this PhD thesis, a general introduction to the history of P and Fe fertilizer use and the need to close the cycle of P in agriculture through the use of recycled P products from the wastewater system, such as vivianite, is presented. The objectives of this thesis were clearly defined, focusing on the use of vivianite as a sustainable P and Fe fertilizer for agricultural crops. As a first step of this study, the efficiency of different formulations of synthetic vivianites as a source of P and Fe fertilizer was studied (Chapter 2). Magnesium (Mg) and zinc (Zn) were added to see their effects on the P use efficiency of vivianite. The effect of humic substances (HS) on the release of P from synthetic vivianites was also studied. The results confirm that the P contained in vivianite can be used by plants for growth and development and produce biomass yields that are similar to those produced by soluble P fertilizers but with a lower P uptake. However, the effect of HS on the release of P from vivianite was not positive in this study. In the next step, the effectiveness of two recycled P products from water purification, i.e., struvites and vivianites, as a source of P for plants was evaluated (Chapter 3). The result reveals that vivianite (especially synthetic and industrial process vivianite) can supply P for the production of plant development that is not too far from those obtained with superphosphate and struvite, despite having a lower P uptake. In the next phase of this study, we evaluated whether soil properties could affect the effectiveness of vivianite as a P fertilizer (Chapter 4). The results suggest that acidic soils with limited P availability status could be more responsive to the application of vivianite as a P fertilizer, with the possibility of producing more than half of the dry matter yield that could be achieved with the use of soluble P fertilizers like superphosphate. The fifth chapter of this PhD thesis was focused on testing the possibility of increasing the P use efficiency of vivianite by mixing it with more soluble P fertilizers and determining the best application method for vivianite as a P fertilizer. The study revealed that increased P use efficiency could be achieved with mixtures of slow-release and fast-release P fertilizers, i.e., vivianite and superphosphate. However, the positive contribution of vivianite in such fertilizer mix is difficult to access in short-duration crops. In the sixth chapter of this PhD thesis, the focus was placed on assessing the effectiveness of vivianite recovered from water purification as a Fe fertilizer to prevent Fe-deficiency chlorosis in calcareous soils. The result agrees with many previous studies on the use of synthetic vivianite as a source of Fe and confirms that recovered vivianite from water purification may be able to offer a sustainable, cost-effective, and circular economy approach to prevent Fe deficiency chlorosis. A general discussion of the PhD thesis result is presented in chapter seven and conclusions in chapter eight.208 p.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/info:eu-repo/semantics/doctoralThesisinfo:eu-repo/semantics/embargoedAccess