A critical review on cross-linking based hydrogel synthesis methods for potential application in sustainable slow-release fertilizers

The rising global population has intensified the demand for agricultural productivity, leading to an extensive demand for synthetic fertilizers. However, synthetic fertilizers have detrimental effects on the environment including eutrophication and greenhouse gas (GHG) emission. Climate change has led to drought which in turn has led to water shortages. There is a need for sustainable methods to reduce environmental pollution and increase food production. This review examines the potential of hydrogels into reducing fertilizer loss, retaining water and promoting sustainability. Hydrogels exhibit excellent physicochemical properties which allow them to absorb and retain water and mineral nutrients. Hydrogels exhibit exceptional physicochemical properties such as high swelling, responsiveness to environmental stimuli, permeability and mechanical strength. In this review, various methods for the synthesis of hydrogels were analyzed. Hydrogel synthesis methods, including physical, chemical, and radiation methods, have been analyzed and their drawbacks and advantages have been discussed. Physical cross-linking methods are environmentally friendly, simple, and reversible, and they produce hydrogels that are highly sensitive to stimuli but have a shorter life span, making them less ideal for fertilizer application. However, chemically cross- linked hydrogels have longer span. Thus, for long term application chemically cross-linked or radiation induced cross-linked hydrogels are the best option