Comparative performance of different urea coating materials for slow release

Approximately 70% of the applied urea fertilizer may be lost into the environment. This loss is due to leaching, decomposition and ammonium volatilization in soil, water and air. Through coating, the slow release technology can be used to reduce losses and to increase the fertilizer efficiency. Sulfur has been used as a coating material, but the coating cracks easily because of its friability, sometimes being peeled off from the urea surface. In this study, four types of materials, namely, gypsum, cement, sulfur and zeolite, were mixed and used as coating materials to search for the most effective and cheap coating materials. The primary reasons for selecting these materials were improving fruit quality and preventing plant diseases, providing a plant nutrient, increasing soil fertility and water retention. The materials were also selected based on their availability, processiblity and price. The effects of the coating materials, thickness, drying time, sieving and sealant on the crushing strength and dissolution rate of urea were investigated. Coated urea with the same proportion of gypsum sulfur exhibited high crushing strength and lower dissolution rate. However, the performance was further enhanced by applying molten paraffin wax on the hot urea surface. SEM images demonstrated that the micro-structure of gypsum sulfur coated urea after sieving resulted in a smoother coated layer. The efficiency of the coated urea was improved by 26% using gypsum sulfur (20% total coating), 3% paraffin wax and sieving the coating materials before application. (C) 2014 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.