Application of lignin in preparation of slow-release fertilizer: Current status and future perspectives

Lignin is the most abundant renewable aromatic resource on the Earth, which can be used for producing bio-products to support human sustainable development. Due to the dual challenges of resources and environment, how to effectively utilize this kind of abundant, degradable, and renewable natural polymer has attracted great attention. In recent years, there are many studies on lignin-based slow-release fertilizer duo to its excellent slow release properties. As a carrier of nutrients, lignin-based physically impeded fertilizer can be realized by absorbing and wrapping nutrients, and lignin-based chemically modified fertilizer can be realized by chemical reaction between lignin and nutrients. In this paper, we reviewed the application of lignin in preparation of slow-release fertilizer. The possible pathways and release mechanisms of physically impeded and chemically modified slow-release fertilizer were discussed. Although there was no uniform evaluation standard for slow-release fertilizer, its three common evaluation criteria were analyzed. With the expansion of the function of slow-release fertilizer, the evaluation system should be broadened and diversified. Finally, the challenges and future prospects of lignin-based slow-release fertilizer were discussed. The application of lignin-based slow-release fertilizer has great potential for promoting resource utilization and environmental protection.