A Review on Chitosan Nanoparticles as a Biostimulant and Their Applications in Agriculture

Abstract

The increasing worldwide demand for food production exerts a significant strain on agriculture, which faces ongoing challenges from biotic and abiotic stressors that restrict crop growth. Chitosan nanoparticles (ChNPs) have emerged as a sustainable biostimulant alternative to chemical agro-inputs owing to their biodegradability, biocompatibility, and multifunctional biological properties. Chitosan, obtained from the deacetylation of chitin, which is largely derived from crustacean waste, can be converted into nanoparticles via ionic gelation. This process results in increased surface area, better penetration, and superior biological efficacy. ChNPs act as an effective biostimulant by activating plant defence systems, enhancing photosynthesis, improving nutrient absorption, promoting root growth, and increasing resilience to abiotic stresses such as drought, salinity, and heat. They also improve yield characteristics and postharvest quality in various crops. Moreover, ChNPs exhibit antibacterial, antiviral, antifungal, and insecticidal properties, providing robust protection against a wide range of diseases and pests. In addition to regulating plant growth, ChNPs serve as non-viral gene delivery vehicles and contribute to soil health by enhancing microbial activity and enabling controlled-release fertiliser formulations. Hybrid ChNPs-based nanocomposites that incorporate metals, polymers, microalgae, and bacteria further enhance their agricultural efficacy by improving nutrient delivery, stress tolerance, and biocontrol effectiveness. Despite considerable progress, future research should prioritise field-scale validation and optimisation of hybrid nanostructures for broader agricultural applications. ChNPs represent a versatile, environmentally sustainable nanotechnology platform with broad potential for sustainable agriculture and soil management.