Lignin–Clay Nanohybrid Biocomposite-Based Double-Layer Coating Materials for Controllable-Release Fertilizer

Abstract

Bio-based slow-release fertilizers (SRFs) have drawn significant attention because their applications for crop production can improve nutrient utilization efficiency as well as prevent environmental pollution. However, current commercial SRFs still exhibit uncontrollable release patterns, use a large quantity of synthetic coating materials, and are unable to adapt to complex soil conditions (e.g., arid soil). In this study, a double-layer SRF was formulated from a low-cost lignin–clay nanohybrid composite to not only achieve controllable and slow nitrogen fertilizer release but also improve the water-holding property. The low-cost and hydrophobic lignin–clay nanohybrid was cross-linked with bio-based alginate to prepare the core-layer material, followed by a coating process using a highly water-absorbent polymer poly(acrylic acid) (PAA) to achieve a double-layer SRF. We examined the chemical structures, urea release rates, and water-holding capacities of the double-layer PAA–lignin–clay nanohybrid composite coated SRF (PLC-SRF). The results showed that PLC-SRF released 13–40% less urea and absorbed 23% more water than SRFs coated with only alginate. Its urea release rate is slower than that of previously reported SRFs using other materials. This nanocomposite coating material has great potential for producing a new type of bio-based SRFs that are beneficial to sustainable crop production.