The increasing needs of global agriculture require novel, eco-friendly approaches to increase crop yields under climate uncertainty, dwindling arable land, and biotic stresses. Nanochitosan, a nanoscale compound of chitosan, a readily biodegradable polymer derived from crustacean shells and fungal biomass, appears as a revolutionary agent in sustainable agriculture. This chapter delves into the synthesis, physicochemical characteristics, and diverse applications of nanochitosan for resolving agricultural issues. Synthesized through ionic gelation, ultrasonication, and emulsion-based methods, nanochitosan has high solubility, a cationic surface charge (+20 to +40 mV), and a high surface-area-to-volume ratio, making it efficient for interaction with microbial membranes and plant tissues. Mechanisms involve reinforcing plant stress resistance by improving stomatal regulation, root morphology, and antioxidant defense activation, along with preventing drought, salinity, and pathogen attack. As a biopesticide, nanochitosan interferes with pest physiology through chitin binding, the induction of oxidative stress, and synergistic activation of systemic acquired resistance (SAR), with narrow-spectrum targeted efficacy against insects, nematodes, and pathogens with low environmental persistence. In addition, nanochitosan upregulates secondary metabolite production (e.g., alkaloids, phenolics) through the induction of defense-related genes and enzymatic activity, enhancing crop quality and resistance. Despite its potential, difficulties remain in synthesizing protocol standardization, scaling up, and implementing regulatory regimes, calling for long-term ecotoxicological effects to be studied. By combining molecular, physiological, and ecological impact assessments, this chapter highlights nanochitosan’s value as a biodegradable, economically viable alternative to traditional agrochemicals and aligning with precision agriculture and sustainable food security principles.
