The invention relates to a process for preparing a complex fertilizer with controlled release. According to the invention, the process consists in pre-polymerizing a solution of pre-condensate of urea-formaldehyde and industrial urea granules at a formaldehyde : urea molar ratio of 0.75...1.5 : 1, while stirring and heating continuously for 2 h, at a temperature of 65...95°C, at a pH value of 8.5...9.5, by periodically dosing KOH or trisodic phosphate, after which the reaction mass is cooled down to the ambient temperature and an emulsion is admixed, the emulsion consisting of usual organic solvents and an aqueous solution containing 5...30% industrial glycerine and inorganic salts of N, P, K nutrients, the so formed emulsion being then admixed with urea up to a final urea : formaldehyde ratio of 1.65...2.4 : 1 and subjected to controlled heating at a temperature of 60...100°C, for 2 h, while correcting the pH to 2.5...4.5, after which the fertilizing precipitate is filtered at the ambient temperature and dried up to a constant mass.
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