Thesis (M.Sc.)--Chulalongkorn University, 2004

The preparation of controlled-release fertilizer coated with drying oil i.e. linseed oil, tung oil, and soybean oil was investigated. The fluidized bed and pan coating were used for coating process. It was observed that pan coating was appropriate in the preparation of controlled-release fertilizer. It was found that factors that influence fertilizer coating process in pan coating method were 80 ํC temperature using 1% cobalt naphthenate as catalyst. Products from this coating process were smooth, sparkle and water resistant. In this experiment linseed oil and soybean oil were appropriate to be used as coating material but tung oil was not suitable. The optimum amount of drying oil for coating by pan coating method was 10 pph. Atomic absorption spectroscopy and UV-visible spectrophotometry were used to investigate the releasing rate of potassium from NPK fertilizer and urea from urea fertilizer, respectively. It was found that linseed oil coated fertilizers were slowest in nutrient release, while soybean oil and a mixture of linseed oil and soybean oil were inferior. When thickness of the coating film was increased, the releasing rate of nutrient decreased and increasing ambient temperature resulted in increasing of releasing rate. Furthermore, low pH was found to increase releasing rate of nutrient