Madhusmitha Baruah

The study addresses the critical issues of nutrient deficiency hindering plant growth and the environmental hazards associated with excessive fertilizer use. A novel synthetic protocol is proposed, involving the preparation of nickel–zinc oxide cross-linked carboxymethyl cellulose (CMC) nanocomposite hydrogel beads loaded with phosphorus (P) for slow-release of phosphatic fertilizer. A 1:0.15 ratio of 4% CMC solution and zinc chloride (ZnCl2) was found to be optimum for the formation of stable spherical hydrogel beads when added drop-wise in nickel chloride (NiCl2) solution (3g in 10mL). For the phosphate loading and release study, CMC was introduced onto disodium hydrogen phosphate solution (4%) during the synthesis process keeping the rest of the procedure same. The prepared composite beads having P, Ni and Zn were thoroughly characterized using Fourier-transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), and SEM-energy dispersive X-Ray (SEM-EDX) mapping analysis. At optimized conditions hydrogel beads showed the maximum swelling ratio of 185%, 3770% and 5552% in distilled water, buffer pH 7 and buffer pH 9.2 respectively. These composite beads, designed as slow-release phosphatic fertilizers, demonstrated effectiveness over a 21-day period. Degradability evaluation at a low soil pH of 4.5 indicated potential release of cross-linker Zn and Ni as plant-available micronutrients post- degradation. This innovative approach aligns with sustainable nutrient release strategies for agricultural applications, emphasizing the eco-friendly and plant-friendly attributes of the developed hydrogel composite beads.

Keywords: Hydrogel, Chemical Fertilizer, Slow release fertilizer

Key Takeaways:

• Chemical fertilizers inherently limited by their low nutrient use efficiency. This incurs in huge wastage of fertilizer and imped the development of sustainable agriculture. One significant limitation of soluble phosphate fertilizers is their tendency to leach, rendering them inaccessible to plant roots and contributing to eutrophication and environmental pollution. In our study, we successfully mitigated the release of phosphate fertilizer in distilled water over a 21-day period, addressing this drawback.
• Prepared hydrogel beads are sensitive to pH, temperature and ionic strength of external environment. A stimuli- responsive controlled release system is an effective approach to enhance the fertilizer use efficiency and reduce the environmental impact. After degradation, the prepared composite effectively supplied the plant micronutrients Zn and Ni.
• The prepared hydrogel composite demonstrates effective applicability in dry land areas due to its elevated water absorption and retention capacities. This quality renders it valuable for farmers to use in agricultural settings.
• The hydrogel beads that have been prepared will be utilized in agricultural research to investigate plant growth and study the physiochemical properties of soil. This study not only showcases the development of novel slow- release fertilizer systems for the delivery of phosphorus (P), nickel (Ni), and zinc (Zn), but it also lays the foundation for the exploration of enhanced techniques for other essential macro and micro nutrients. This work contributes to a more sustainable and environmentally friendly future, providing a valuable solution for a wider audience.