Abstract
Release of nutrients from resin-coated fertilizers was studied in atmospheres of different water vapor pressures. The coated fertilizers tested were : urea coated with thermoplastic resin or thermosetting resin ; and a NK mixed fertilizer coated with thermosetting resin. The water vapor pressures were adjusted by placing the coated fertilizers in bottles containing saturated solutions of different salts. The rates of nutrient release were simulated with the kinetic method proposed by SUGIHARA et al. (1986) and with the model proposed by KOCHBA et al. (1990). 1) The nutrient release from the resin-coated fertilizers was proportional to the differences in water vapor pressures between the inside and outside of the coated fertilizers, regardless of the different coating materials. 2) The release of nutrients fitted well either to the model by KOCHBA et al. or to the curves simulated with the method by SUGIHARA and KONNO. We did not find and conceptual differences between these two methods, and concluded that the temperatures firstly affected the vapor pressures, and the latter then directly controlled the release of nutrients from the coated fertilizers.
