Synergy between castor oil polyurethane/starch polymer coating and local acidification by A. niger for increasing the efficiency of nitrogen fertilization using urea granules

The volatilization of nitrogen (N) in the form of greenhouse gases is the most significant environmental impact associated with fertilizer use. Losses of N may exceed 50 % of the quantity applied, especially when the nitrogen source is urea. This work describes an overcoating system for urea granules, based on starch (from maize or cassava crops) and elemental sulfur (S°) composites applied over a castor oil-based poly(urethane) coating, biologically activated by Aspergillus niger (A. niger). The results indicated that the system provided good control of urea dissolution and reduced NH3 volatilization after 28 days by 45.9 and 64.9 % for the U4%StA.niger and U4%CaA.niger treatments, compared to the control (uncoated urea). This effect occurs from the synergy between the starch and oil-based polyurethane coatings, improving the microorganism activity, due to increased acidity production. The findings support the use of A. niger in fertilizer management and evidence the suitability of natural-based polymer coatings for controlling N delivery and reducing environmental impacts.