An experiment of alum sludge application was carried out on a mountainous site, to know its effect on the growth of forage sorghum hybrid, Pioneer 93 1 (Sorghum bicolor x S. bicolor). When alum sludge with 80% water content was applied at the level of 133 ton per ha, the effect of the application on the growth of Pioneer 931 was much smaller than that of chemical fertilizer. But Eresh yield of the forage, with the sludge application, was greater than that without fertilizer when the soil is not fertile. But when the soil was comparatively fertile, the sludge application gave an adverse affect on the growth of the forage plant. The content of exchangeable K in the soil has a very close positive relation with the Eresh yield and plant height of the plant, while that of exchangeable Ca has a close negative relation with those growing factors. There was a tendency of yield decrease of the forage plant, when alum or compost was applied with NPK to the comparatively infertile soil especially for alum sludge. As a result, when soil is not fertile more attention will be necessary for applying alum sludge with chemical fertilizers. But to soil with better fertility, it is recommended to use alum sludge with chemical fertilizer to obtain more yield of the forage plant.