Strategy for Multinutrient Application in Integrated Granules Using Zein as a Coating Layer

The efficiency of phosphate fertilizers is strongly limited by the acidity and high iron content and aluminum-based compounds in soils due to high P fixation. Coatings have been proposed as an alternative solution to reduce P losses by controlling the fertilizer release, but the literature is not conclusive about the most adequate material for that purpose. Herein we report a novel Zn-based coating for monoammonium phosphate (MAP) granules comprising ZnO nanoparticles and zein as a bicoating structure. Samples were prepared by dispersing ZnO and zein on the MAP surface and characterized, comparing the release in neutral and acidic solutions over time. Coating thickness/quality determined the nutrient release by a physical barrier effect. The results show that the zein coating overprotection avoids a fast nutrient release, keeping the local acid medium necessary to suppress ZnPO₄ precipitation. A range of 2.5 to 10.0 wt % of zein was studied, indicating that 2.5 wt % coatings just present significant release control, which is similar until 10.0 wt % coating.