Chitosan can play a key role in modern agriculture production and could be a valuable source promoting agricultural ecosystem sustainability. Future suggestions will be based on current achievements and also notable gaps. In addition, chitosan has a huge contribution to reducing fertilizers pollution, managing agricultural pests and pathogens in modern-day agriculture.
The overwhelming demand for food in line with the ever-increasing global population has given rise to additional exploration to produce sufficient food with sustainable agriculture to satisfy consumers’ current nutritional needs. Fertilizers are crucially important for delivering nutrients to plants to produce high-quality crops for food security. Similarly, pesticides are chemicals used to eliminate pests and pathogens . At the same time, fertilizers and pesticides are also identified as agricultural pollutants . Whereas, contamination became a considerable challenge in advanced industrial countries compared to undeveloped countries. Freshwater availability is affected due to the deposition of agricultural effluents hazardous to all living beings.
The agriculture sector became a major contributor of damages to biodiversity, with intensifying influences due to altering consumption patterns and growing inhabitants by transforming natural habitats to extremely sophisticated arrangements and discharging pollutants and greenhouse gases. A massive percentage of organic pollutants infiltrate the soil, as well as several manufactured toxic substances.
Besides, the enormous use of extremely destructive chemical pesticides has a drastic impact on human health and ecosystems. These chemicals are capable of deposition, sorption with leaching tendencies that impact massive accumulation inside the soil particles, biological molecules, and metabolic transmutation of microorganisms. Farmers are still using a huge amount of agrochemicals (pesticides, fertilizers, and organometallics) and increasing these major issues, like air pollution, soil toxicity, different agricultural degradation, residue buildup, pesticide tolerance in pests and microorganisms.
Organic farming is an up-to-date and viable agriculture system that delivers fresh and natural farm produces to consumers. In the perspective of return to nature using scientific and technical progress for improved living standards, people began to search for solutions to alleviate environmental pollution. Researchers intend to make clean, affordable products that are gentle yet effective. Recently, several different polymers are introduced. Some innovative methodologies are being searched to control the release of fertilizers and pesticides for excellent agriculture, reducing the various hazardous impacts of these substances.
Adopting several polysaccharides as delivery methodologies have presented considerable advantages like biocompatibility, non-toxicity, the propensity to biomolecules, excellent formulation, sustained release, and so on. However, most other concerns to encounter in agriculture research are diseases and pests, nutrient wastage, insufficient crop production because of water scarcity, fertilizers (nitrogenous, phosphoric, potassium, and organometal), and pesticide misapplication. To tackle the concerns discussed from the widespread overuse of synthetic agrochemicals, this also becomes crucial to building alternative practices enabling the safe and productive use of such chemicals .
Numerous researchers assumed that restricting nutrient distribution using naturally degradable materials and rapidly developing smart nanomaterials can contribute a vital role in developing agricultural activities, regarding the latest progress in nanotechnology, coating of such agrochemicals (fertilizers, pesticides, and herbicides) (Figure 1) which could deliver the most incredible platform to end it. Currently, the adoption of nano-carriers and nanosensors had attracted the interest of re- search groups from several areas of plant sciences; therefore, considerable scientific contributions are ongoing to focus on improving the formulation of biopolymer-based nano-carriers. Scientists seem to be eager to discover the capabilities of nanomaterials that enable it so convenient for promoting crop productivity.
Chitosan is a polycationic polymer synthesised deacetylation of chitin (a structural material present in multitudinous invertebrates) commonly collected by crustacean’s exoskeletons, particularly shrimps and crabs, as well as fungus and yeast cell walls and diatom spines . Because it has been relatively hydrophobic, it is primarily insoluble in water and various organic solvents. This context has a tremendous potential and demand for advantageous and eco- logically hospitable plant growth regulators within agriculture.
Use Of Chitosan As Controlled-Release Fertiliser
The indiscriminate practice of chemical fertilizers application is a grave problem worldwide. The reasonable application of fertilizer and increased nutrient utilization capability while limiting deleterious toxicity depends on nutrient delivery to plant requirements and sustaining nutrient absorption. Controlled-release fertilizers (CRF) are considered by the delayed release of nutrients that extends for a limited amount. However, the aspects, such as duration of release, can be potently affected by management situations such as storage, transportation, supply in the field, and soil state’s moisture content and biological activity.
Recently, the application of chitosan in controlled-release fertilizer is still in the primary stage. However, it can be an excellent fertilizer based on its biodegradable, environment-friendly, and other excellent characteristics . In addition, the porous structure on the surface is conducive to water and nutrient permeation. After the controlled-release microspheres made of chitosan, loaded with nitrogen elements in the microspheres could be slowly released into the soil to meet the nutrient requirements of plants at various stages and improve the utilization rate of fertilizer and reduce the loss of chemical fertilizer.
Preparation and formulation of CRF
Chitosan nanoparticles were initially synthesised in 1994, applying the emulsification and cross-linking technique used as drug carriers. After that, various technologies such as ionic gelation, reversed micellar approach, precipitation, sieving, emulsion droplet coalescence, and spray drying were developed. These technologies have already been developed for agricultural purposes. The mechanism and function mostly determine the methodologies of preparation; for example, the rate of releasing such active components is usually determined by the size and morphology of the nanocomposites, the thermal- mechanical performance, and the level of hazardous materials effects of the degradable remnants. Chitosan- based controlled release techniques are mostly used as a CRF application.
Some studies have determined that the water absorbency of chitosan-coated CRF influences its distribution characteristics . Whereas chitosan has been observed to possess tremendous biodegradability, according to the delayed-release rate of polymer linkages, it has a decreased swelling potential while forming a hydrogel. However, combining chitosan with all various hydrophilic polymeric materials enhances its gel-state water absorption capabilities.
The emulsification and cross-linking method is an excellent methodology for preparing CRF, stabilizing a particle structure, and modifying the controlled- release characteristics of that particle. Modification of the degree of cross-linking in a particulate alters the permeability of fertilizers throughout this . Cross-linking improves the mechanical stability of the resulting particulate or chitosan microspheres (fertilizers loaded) via utilizing a nano-emulsion. The procedure occurs with the chitosan solution’s emulsion in an oil droplet (water-in-oil emulsion). Sufficient surfactants initially stabilize the chitosan phase before combining using a relevant cross-linking agent (e.g., formaldehyde, glutaraldehyde, genipin, glyoxal, etc.). After that, the chitosan microsphere- based controlled-release fertilizers are required to be washed and dried Figure 2.
The controlled release mechanism of CRF
It is important to understand the controlled release process, which would be the direct assessment of a CRF’s performance. In a broad sense, the controlled release system is challenging to conceive because it depends on various factors such as the composition of the coatings materials, the type of CRF, farming contexts, and more. Chitosan hydrogel-based CRF can improve soil water retention. Hydrophilic polymers, which constitute hydrogels (e.g., polyvinyl alcohol), release active chemical compounds through diffusion, whereas chitosan releases active components by degradation and diffusion. It is unusual to notice an immediate “burst” releasing active components from particulates that normally distribute them during diffusion or degradation.
This occurs in response to active substances adsorbing over the exterior parts of the particulates . Whenever this bursting is exhausted, a sustainable release would be noticed, which increases while the particle-matrix proceeds to degrade. The synthesised chitosan-polyvinyl alcohol (PVA) particulates were utilized to evaluate the release of the active compo nent throughout a variety of situations. Researchers determined diffusion-controlled releasing by investigating the linear interaction among the level of active component released and the square root of the time.
The controlled-release fertilizers developed by chitosan hydrogels possess a quasi- Fickian diffusion process that controls potassium releasing kinetics and water absorption. A strong connection is seen between accumulated drug released and the square root of duration, indicating that drug-releasing through the microcapsules is diffusion-controlled and follows the Higuchi equations.
The connection between matrix degradation and indomethacin releasing kinetics via chitosan microparticles . The retention time of chitosan inside the microcapsules and the pH of the released media have been revealed to be interrelated to release kinetics. The in vitro discharge assessment of drug-loaded chitosan nanoparticles the dynamical swelling information of chitosan nanoparticles and indicated that the swelling of chitosan nanoparticles reduces as cross-linking accumulates . The expansion response of chitosan/poly (vinyl alcohol) hydrogels as a factor of pH, polymeric formulations, and cross-linking degrees.
Physically controlled fertilizers
Chitosan and its composites occur in several physical forms, including resins, microspheres, hydrogels, membranes, and fibres. The variety of one specific physical method depends on the system configuration for limited applications. Determining chitosan assortments into preferred physical form starts from mixing the blend components in the liquid form and applying the appropriate shaping method.
Coated fertilizers development has been progressively increased in the current decade, where 95% of them have controlled-release fertilizers. Matrix-based fertilizers, also known as the physical type of CRF, are unique, low-cost, and controlled release. Current advancements in fertilizers have been progressively increased, and 95% of them are controlled-release fertilizers. Matrix-based fertilizers are also classified as a physical type of CRF with unique, low cost, and controlled release properties.
Chemically controlled fertilizers
Chemically controlled-release fertilizers can delay-release by preventing fertilizer decomposition or nutrient transformation through chemical activity. The chemical type of CRF is divided into two categories: Chemically bonded fertilizers and chemically inhibited fertilizers . This category of slow-release fertilizer has a more significant impact, but its cost is comparatively high. Chemically bonded fertilizers allow fertilizers mixed with one or more chemical components via cross-linking or ionic linking to develop a partially soluble or unsolvable substance.
It delivers required nutrients through plant roots and biological activity. The amount of resources has often been assessed via the particle size-water content throughout the soil; chemically controlled fertilizers release where nitrogen could incorporate into controlled substances . Widely utilized are urease inhibitors and nitrifies, which reduce urea’s hydrolysis, although the latter inactivates the nitrified of ammonium and several various sources.
Chitosan water-retaining controlled-release fertilizer
The water-retaining controlled-release fertilizer is a high-tech product that combines water-retaining agents with modern plant nutrition fertilization theory and controlled release technology to determine the nutrient supply rate and fertilizer-effective period. At present, most of the water-retaining controlled-release fertilizers on the market are coated with water-retaining agents as the coating material. The microspheres on the coating material are used to realize the controlled release of nutrients.
Conclusion
In conclusion, chitosan stands out as a multifunctional, biodegradable, and non-toxic biopolymer that offers a promising pathway toward more sustainable and environmentally responsible agricultural practices. Its application as a controlled-release fertilizer carrier not only improves nutrient use efficiency and reduces the frequency of agrochemical applications but also mitigates the severe ecological and health risks associated with the overuse of synthetic fertilizers and pesticides.
Despite the encouraging progress made in chitosan-based formulations—ranging from hydrogels and microspheres to nanocomposites—significant challenges remain. These include scaling up production, standardizing preparation methods, reducing costs, and adapting formulations to diverse soil types and climatic conditions. Future research should prioritize field-scale trials, long-term ecological safety assessments, and the integration of chitosan with smart sensing technologies for precision agriculture.
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