Experiments were conducted to determine the effects of phosphate fertilizer on yield and quality of grass Stylosanthes guianensis CIA T 184 (Stylo CIA T 184) planted in Thai Nguyen. Four treatments with four levels of phosphate fertilizers: 0
250
500 and 750kglha have been applied. The same basic fertilizers formulated for 4 treatments are: 20 tons of manure, 50 kg urea nitrogen, 200 kg potassium chloride/ha/year. The monitoring indicators including plant height and yield were recorded. Chemical composition of grass was analyzed. The results showed the lowest plant height was 73.85 cm after 105 days old in control, while the highest plant height in treatment 2 (80040 cm). Total fresh yield was vary from 49.]6 to 63.70 tons/ha in the first year harvesting
and 30.21 - 34.33 tons/ha in the second year. Formula phosphorus (500 kglha/year) is the best for the development of Stylo CIA T 184. The chemical composition of Stylosanthes guianensis CIA T 184 grass was influenced by different levels of phosphorus fertilizer. Increased levels of phosphate fertilizers are not only increases the productivity of fresh yield, but also reduce the fiber percentage in fresh grass.