Porous geopolymer based eco-friendly multifunctional slow-release fertilizers for promoting plant growth

Nitrogen fertilizer is one of the most vital major nutrients that plants need. However, its utilization rate was only 30 similar to 35%, and most of nitrogen was lost due to volatilization and leaching, which not only led to environmental pollution but also wasting of resources. Therefore, developing cost-effective, eco-friendly and multifunctional slow-release fertilizer (SRF) is still great challenging in agricultural production, and its carriers are very important. In this paper, a novel SRF was successfully prepared by eco-friendly inorganic/organic composites containing porous geopolymer and biocompatible polymers including starch (Sta) and polyvinyl alcohol (PVA). Firstly, the loess particle (Lo), a kind of widely distributed and eco-friendly cheap natural silicate, was used to synthesize porous loess-based geopolymer (Lo-GP). Secondly, using Lo-GP as carrier, Sta and PVA as gel coatings, and boric acid as a crosslinking agent, a novel multifunctional SRF (NF@Lo-GP/Gel) including nutrition elements of N, P and K fer-tilizer was prepared. Its structure and micromorphology were characterized by FT-IR, XRD, TG-DTG, BET, SEM, and EDS. NF@Lo-GP/Gel in the soil environment exhibited well water retention capacity, water absorbency in salt solutions, remediation of soil pH value, partly degradation in soil and promoting the growth of maize plants because of the organic-inorganic composites in NF@Lo-GP/Gel. The N nutrient slow-release longevity of NF@Lo-GP/Gel was more than 90 days and the cumulative release rate could be kept in 51.4%. It indicated that three-dimensional network and eco-friendly geopolymer with high porosity represent capacity for N fertilizer, as well as persistent slow-release performance. These results showed that geopolymer could be used as a carrier to load nutrients and the obtained NF@Lo-GP/Gel was a slow-release fertilizer with multifunctional performances.