This work was conduzed at the Experimental Estation in Goiânia, from 1977 until 1982, with the objetive to determinate the effect of nitrogen rates and time of aplication upon the productivity and quality of colonião grass seeds. The experimental design was a factorial randomized complete block. The treatments were: five nitrogen rates (0, 30, 60, 120 and 240kg/ha of ammonium sulfate and three times of aplícations (second fornnght of october, second fortnight of november and initial floral primordium). The parameters analyzed were: seed yield, pure Iive seeds, germination, yield of pure germinating seeds, dry mater yield, head length and head density. The analysis of data led to the following conclusions: a) for seed yield, emergence and head density, the best time for nitrogen aplication was at the initial floral primordium, with rates between 150 and 180kg/ha; b) for the others parameters, the best time for nitrogen fertilization was at the second fortnight of november, with rates between 120 and 180kg/ha.