Preparation and properties of multifunctional eco-friendly slow-release urea fertilizer encapsulated by diatomite filter aid waste-based superabsorbent

Due to the high cost, incomplete degradation, and limited raw material sources of traditional slow-release fertilizers, the development of environmentally friendly slow-release urea based on waste filter aids is of great significance in modern agriculture. In this study, beer diatomite filter aid waste-based superabsorbent resin (BDWSA)1 was synthesized by free radical grafting copolymerization through microwave radiation heating with beer diatomite filter aid waste (BDW), acrylic acid (AA), N, N-methylenebisacrylamide (MBA), and potassium persulfate (KPS). Then, BDWSA was used as the outer coating material, along with ethyl cellulose (EC) and Kaolin as the inner coating, urea and Phellinus igniarius biochar as the fertilizer core, to form a multifunctional eco-friendly double-coated slow-release urea (DSRU) for water-retaining and slow-release functionalities. The performance of slow release behavior of nitrogen was investigated, and showed that urea in soil released 86.02 % of nitrogen during 3 days, monolayer-coated slow-release urea (MSRU) released 94.02 % of nitrogen in 30 days, and DSRU released a total of 74.66 % of nitrogen in 30 days, indicating that DSRU can improve fertilizer utilization by delaying nutrient release. The biodegradation experiment showed that DSRU degraded 86.65 % wt% in 90 days, not only indicating a good biodegradation effect but also beneficial to the growth of soybeans under drought conditions in growth experiments. Therefore, the eco-friendly DSRU product with excellent slow-release capacity has broad application prospects in agriculture.