Environmentally benign approach to formulate nanoclay/starch hydrogel for controlled release of zinc and its application in seed coating of Oryza Sativa plant

Improper use of conventional fertilizers has been linked to adverse effects on soil nutrient levels. To mitigate the negative impact of surface feeding fertilizers and reduce environmental pollution, a new type of seed coating material has been developed to provide nutrients in close proximity to the growing seed. In this study, a biodegradable seed coating film encapsulating micronutrients was fabricated by incorporating montmorillonite into a starch matrix using the melt processing technique. The dispersion of montmorillonite within the starch matrix was examined using X-ray diffraction (XRD), infrared spectroscopy (IR), and thermal gravimetric analysis (TGA). The results revealed polar interactions among starch, silicate layers, and the hydrogel. The XRD analysis demonstrated a shift in the diffraction peak (001) of the Zinc/montmorillonite/starch/glycerol nanocomposite film from 6.2° to 4.9°, indicating the successful intercalation of Zinc, starch, and glycerol. Furthermore, the inclusion of nanoclay improved the thermal stability of the resulting polymer composite and enhanced its ion exchange capacity, water retention, and micronutrient retention. The time-dependent release of zinc micronutrient from the montmorillonite/starch/glycerol composite film was investigated in Zn-deficient soil extract over a 20-day period. The composite film demonstrated extended release behavior of Zn2+. Subsequently, rice seeds were coated with the zinc-containing composite film using a dip-coating method, and their performance in Zn-deficient soil was evaluated. The results indicated that zinc-coated seeds exhibited improved germination percentage, vegetative growth, and yield compared to uncoated seeds.