Integrated-preparation and application methods of urea-formaldehyde (uf)-based multi-nutrient biodegradable polymeric slow-release (sr) liquid and granular fertilizers

A method for integrated preparation of a urea-formaldehyde (UF)-based multi-nutrient biodegradable polymeric slow-release (SR) liquid fertilizer and a UF-based multi-nutrient biodegradable polymeric SR granular fertilizer, comprising:

• (1) adding urea, formaldehyde, a catalyst, and water to a first reactor followed by a reaction at 50-90° C. for 0.5-3 h to obtain a hydroxymethylurea solution;
• wherein a molar ratio of the urea to the formaldehyde is 1.2-5:1;
• the catalyst is 0-5%, excluding 0%, of a total weight of the urea and the formaldehyde;
• and the water in the first reactor is 15-35% of the total weight of the urea and the formaldehyde;
• and
• (2) adding a first portion of the hydroxymethylurea solution obtained in step (1) to a second reactor containing an acidic suspension followed by a reaction at a first temperature T1 for a first time t1 to obtain a viscous UF liquid, wherein the acidic suspension is prepared from an acidic substance, water, and a suspending agent;
• and adding the viscous UF liquid to a mixed liquid prepared from an alkaline substance, a first fertilizer system containing at least one nutrient element except nitrogen, and a nutrient synergist, followed by mixing to obtain the UF-based multi-nutrient biodegradable polymeric SR liquid fertilizer;
• and
• feeding a second portion of the hydroxymethylurea solution obtained in step (1) and a second fertilizer system containing at least one nutrient element except nitrogen into a twin-screw reaction extruder of a reaction unit of a reaction-extrusion integrated machine, followed by a reactive extrusion process at a second temperature T2 and a first screw speed R1 for a second time t2 to form a reaction mixture, wherein during the reactive extrusion process, hydroxymethylurea is transformed into a UF polymer through a polycondensation reaction;
• conveying, by the twin-screw reaction extruder, the reaction mixture to a twin-screw extruder of an extrusion unit of the reaction-extrusion integrated machine followed by extrusion at a third temperature T3 and a second screw speed R2 to obtain a strip-shaped extrudate;
• drying the strip-shaped extrudate at a fourth temperature T4, followed by granulation to obtain the UF-based multi-nutrient biodegradable polymeric SR granular fertilizer.