Bulk blending (BB) fertilizer grade 25-32-0 resulted from mixing of granulated urea with diammonium phosphate, having granular sizes range between -6+8 to -10+14 mesh were let to move vertically in a hopper their components stability could be affected. It was found that BB fertilizers prepared by blending of the matched size materials did not segregate in the process. They also showed uniform physical and chemical properties. In contrast, BB fertilizers prepared from unmatched size materials tended to segregate variably and their degree of segregation increased with the increase in size difference of the materials used. The segregation of the blended fertilizers appeared to be caused by the greater amount of finer particles rapidly pass through the coned hopper in the initial phase which result in the accumulation of coarser particles on the upper part of the pile in the later stage. The best way to avoid the segregation was to use the matching size materiais in the blending. The use of egg.crate installed in the hopper also showed good tendency to prevent segregation of the fertilizer during packing period. The blended fertilizers having granule sized in a range of -6+8 to -10+14 mesh did not show segregation after being subjected to a truck transport over a distance of 100 kilometers. Bulk blending fertilizers of 16-20-0 grade prepared by using ammonium sulfate and diammonium phosphate could be kept for more than six months without showing sign of excessive moisture accumalation. However, prolonged storage under over burden pressure could lead to caking. Fertilizer of 25-32-0 grade prepared by bulk blending of granulated urea and diammonium phosphate showed sign of moisture increase after one month storage. Fertilizers could also show off-standard moisture content if the plastic bags used for their storage were not sufficiently moisture resisted. Eventhough they stay within the tolerant limits provided by the law, the analytical results of nutrients in bulk blending fertilizers show more variabilities than that in the compound fertilizers. The agronomic effectiveness trials with rice and maize grown on Rangsit and Lopburi soils respectively

The results shows that poorly mixed BB fertilizer, good BB fertilizer, and compound fertilizer showed no significant difference in rice and maize yields. Incorporated into the soil with the application of diammonium phosphate (18-46-0) as basal treatment and top dressing with urea to rice gave a tendency of higher yields than that of the compounds and the BB fertilizers. Consequently interm of economic aspect, BB fertilizers and using the straight fertilizers as basal and topdresing should have more advendtage over the compound fertilizers.