This demonstration trial was carried out in a dark red latosol with 0.24 cmol (+)/dm³ in the 00-10 cm layer of the soil. Potash as KCl was applied at soybean V1 stage in the doses of 40, 80, 120, 160 and 200 kg/ha of K₂O. Had also a check without K. Fungicides were applied at: R2 (flowering) stage (Impact, 0.6 l/ha of commercial product) and at R5.3 (pod filling) stage (Folicur, 0.4 l/ha of commercial product + Derosal, 0.207 l/ha of commercial product).
Conclusions: no response to K was observed in the treatments without the use of fungicides; small yield increases were observed in the treatments with fungicide up to the dosis of 120 kg/ha of K₂O; the average difference between treatments with and without fungicides was of 305 kg/ha; there was no effect of potash doses on rust resistance.