Engineering and slow-release properties of lignin-based double-layer coated fertilizer

Abstract

Chemical fertilizer has become a necessary condition for increasing the production and income of agricultural products in modern agriculture. However, excessive fertilization and fertilizer leakage could cause environmental pollution. To improve the utilization rate of agricultural fertilizers and reduce environmental pollution, the degradability of slow-release fertilizers (SRFs) has become a research hotspot. In this work, a double-layer coating material of slow-release fertilizer was fabricated using low-cost polyvinyl alcohol (PVA) and methylcellulose (MC) as the inner coating materials, and attapulgite was doped into super absorbent polymer poly acrylic acid (PAA) and polyacrylamide (PAM) grafted natural biodegradable lignin as the outer coating materials. We investigated the chemical structures, mechanical properties, hydrophilic properties, and water retention properties of the double-layer coating material coated on the surface of urea particles, and optimized the synthesis parameters to obtain the best water absorption properties of the outer layer water absorbent. Simultaneously, urea release was evaluated in dissolution experiments. The results show that at the PVA concentration of 5 wt% and the MC addition amount of 2.0 g, the performance indicators of the inner coating liquid were better than other contents. At the same time, more urea molecules (>30 days) were released in the single-layer and double-coated fertilizers, and the cumulative release rates of urea molecules were 92.36% and 85.10%, respectively. Therefore, this work provides research ideas for the preparation of double-coated slow-release fertilizers, which can improve soil water retention and fertilizer utilization.