Lignin-based controlled release fertilizers: A review

Lignin is the most abundant renewable aromatic resource on the planet, and it may be exploited to make the controlled release fertilizers (CRFs) that aid in human sustainable agriculture. Many researches on lignin-based CRFs have been conducted in recent years because of their exceptional controlled-release qualities. Lignin-based physically impeded CRFs can be produced by absorbing or wrapping nutrients and act as a longtime nutrient carrier, while chemically modified and chelated CRFs are produced by changing lignin structure to produce more active site and interaction between lignin and nutrients. In this review, lignin is evaluated on the basis of the manufacturing of various types of CRFs. The processes of lignin-based coated, chemically modified and chelated CRFs as well as lignin hydrogel-based CRFs are systematically summarized. Moreover, the general mechanism for controlled release of lignin-based CRFs is discussed. Finally, three common evaluation criteria of lignin-based CRFs efficiency are proposed. Overall, the use of lignin-based CRFs has the potential to greatly enhance resource efficiency and environmental protection.