Polymer coatings are used to control the rate of release of plant available nutrients from fertilizers as well as to reduce nutrient losses such as ammonia (NH 3) volatilization. Although the literature presents several examples of materials used to coat urea, little is known about nitrogen (N) release properties such as the mechanism involved and phenomena (e.g., pore opening) in the polymer coating. Thus, this study investigated urea release from polyurethane (PU) derived from two renewable raw materials (castor oil and soybean oil), to explain how the oil structure and coating microstructure influence release and urea-N dynamics in soil. The results demonstrated that the profile of urea release and the urea-N mineralization in the soil could be controlled by altering the thickness of the coating on the urea granules. Coating by eco-friendly polymer was efficient in controlling urea release in soil to reduce volatilization of ammonia and increase the availability of N in the soil.
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 ZnPO 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.
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