A mechanism of nutrient release from resin-coated fertilizers and its estimation by kinetic methods. 1. Effects of water vapor pressure on nutrient release.

摘要

Release of nutrients from resin-coated fertilizers was studied under different water vapour 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 vapour 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. and with the model proposed by Kochba et al. The results showed: (1) nutrient release from the resin-coated fertilizers was proportional to the differences in water vapour pressures between the inside and outside of the coated fertilizers, regardless of the different coating materials; and (2) the release of nutrients fitted well to either model or to the curves simulated with the method by Sugihara and Konno. No conceptual differences were found between these two methods, and it was concluded that the temperatures firstly affected the vapour pressures, and the latter then directly controlled the release of nutrients from the coated fertilizers.