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From Release Kinetics to Field Performance: A Critical Review of Slow- and Controlled-Release Fertilizers, Nutrient-Use Efficiency, Environmental Benefits, and Scale-Up Challenges
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This review of 130 studies finds that slow-release fertilizers work best when they match how fast crops actually need nutrients, not simply when they release nutrients slowly. It also flags a hidden downside: some coatings can leave behind microplastics or persist in soil, so environmental benefits must be weighed against these risks.
Slow- and controlled-release fertilizers (SRFs and CRFs) are increasingly used to improve nutrient-use efficiency and reduce nutrient losses, yet slower release does not inherently translate into superior field performance. This critical review synthesizes 130 priority studies published from 2020 to 2026 using a performance-first framework that links material architecture, release mechanism, soil interaction, nutrient availability, plant uptake, yield, nutrient loss, environmental impact, cost, and industrial readiness. The evidence shows that dissolution, diffusion, osmotic transport, swelling, coating degradation, ion exchange, mineral reactions, and biological processes can dominate under different conditions. Nitrogen systems have the largest evidence base, while phosphorus and potassium technologies require nutrient-specific criteria. A crop–release synchronization concept and a five-level technology-readiness scale for slow- and controlled-release fertilizers (TRL-SRF) are proposed to distinguish laboratory novelty from field and industrial readiness. Environmental gains must also be weighed against coating persistence, microplastics, embodied inputs, and cost. The optimum fertilizer is therefore the one whose nutrient-delivery profile best matches crop demand under realistic soil and climatic conditions, rather than the formulation with the longest release duration.
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Controlled-Release Fertilizers: Innovations, Challenges, and Practical Applications
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This review paper looks at "slow-release" fertilizers designed to feed crops more efficiently while cutting down on runoff that pollutes water supplies. The catch: many of these fertilizers are coated in plastic to control how nutrients release, and that coating can break down into microplastics that end up in soil, water, and potentially our food. The researchers highlight promising plant-based and biodegradable alternatives being developed, but note more work is needed before these safer options are ready for widespread farm use.
Techniques for encapsulating slow-release fertilizers using smart polymers: Towards controlled and sustainable release of plant nutrients: A review
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This review paper looks at "smart" fertilizer coatings that release plant nutrients slowly and only when crops need them, instead of dumping it all at once, a shift that could cut down on chemical runoff into rivers and groundwater. One catch worth noting: many of these coatings are made from plastic, which can break down into microplastics in soil, so the researchers highlight the need to switch to plant-based, biodegradable alternatives (like cellulose or chitosan) to keep this "smart farming" approach truly environmentally and food-chain safe.
Advancements and challenges in controlled-release fertilisers: An approach to integrate biopolymer-based strategies
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This review examines controlled-release fertilizers, which are designed to deliver nutrients to plants gradually, and finds that many use synthetic polymer coatings that can leave microplastic residues in soil. The authors highlight biopolymers made from natural materials like chitosan, cellulose, and starch as promising alternatives that can biodegrade without contributing to plastic pollution. The shift toward biodegradable fertilizer coatings could help reduce a significant but often overlooked source of agricultural microplastic contamination.
Analysis of Slow-Released Fertilisers as a Source of Microplastics
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Analysis of slow-release fertilisers coated with polymer shells found that these products can release microplastics into agricultural soils as the coatings degrade. Two major manufacturers' products showed varying polymer compositions and differing abilities to adsorb soil contaminants, raising concerns about MP accumulation from fertiliser use.
Mechanisms of microplastic generation from polymer-coated controlled-release fertilizers (PC-CRFs)
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This study investigated how the plastic coatings on slow-release fertilizers break down and release microplastics into soil. Significantly more microplastic particles were released in soil conditions than in water alone, and wet-dry cycles accelerated the breakdown, meaning agricultural soils receiving these fertilizers may be accumulating substantial amounts of microplastic pollution.
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