Potassium is exported in large amounts through grain harvest and this, together with the low availability of potassium in Brazilian soils, leads to an evident need for restoration of this nutrient. When the application rates of potassium are greater than 50 kg.ha-1, the most effective manner of utilizing the potassium is through topdressed fertilization after sowing. As such, the aim of this study was to establish the best time for topdressed application of potassium after sowing, as well as to study the effect of this nutrient on grain yield, on agronomic traits, and on potassium content in the grain. The experiment was carried out in the municipality of Lavras in the 2012/13 crop season. A randomized block design in an 8 x 4 factorial arrangement was used, composed of eight cultivars and four different periods of topdressed potassium application (20, 30, 40, and 50 days after sowing) for a total of 32 treatments with three replications. Potassium chloride at the rate of 120 Kg.ha-1 of potassium was used as a source. The results show that there was no effect of the time of topdressed application of potassium on the soybean crop for grain yield, for agronomic traits, and for potassium content in the grain.