This pot experiment was conducted to find out the forage productivity and quality in a grasslclover sward as affected by the application of three different fertilizers; double superphosphate(DS), fused Mg-phosphate (FP), and complex fertilizer(CF) on newly reclaimed hilly soil. This part was concerned with the mutual balances of mineral nutrients in the soils and mixed grass/clover sward in relation to grass tetany hazard. The results obtained are summarized as follows : 1. Concentration of exchangeable Mg and relative proportion of Mg to CEC in the soils before experiment were considerably below the critical level for good forage growth and prevention of grass tetany. It seems that these properties would be able to handicap by liming and NPK applications. 2. Comparing with the critical level for likelihood of tetany(Mg <0.2%, K >2.5%, and W(Ca+Mg) >2.2 in forages), mean concentration of Mg ranged from 0.14 in DS plot and 0.18 in FP plot to 0.24% in CF plot. Meanwhile, hazards of grass tetany in relation to the %K and ratio of K/(Ca+Mg) were not recognized. 3. Comparing with the optimum level of Carp(% ratio)=2.0 in forages for animal health, these ranged from 6.1 to 7.1. (Key words : Grass tetany, Fertilizer. Soil. Mineral nutrients)