Pot experiments are being used to study the potassium supplying capacity of soils. A greenhouse experiment with this objective evaluated samples of two Planosols, a Chernosol and a Gleisol, where flooded rice did not respond to potassium fertilization. The soils were cropped during 50 days with rice (Oriza sativa - BR-IRGA 409). Potassium uptake by the plant shoot, the exchangeable and non-exchangeable soil K, extracted by NH4OAc 1 mol L-1 and boiling HNO3 1 mol L-1, respectively, were evaluated, before and after cropping. Potassium accumulated by the rice plants differed between the soils and decreased in the order: Gleisol > Chernosol > Planosol 1 > Planosol 2. Exchangeable K was not the only element form in the soil that supplied the nutrient to the rice plants, since non-exchangeable K forms contributed as well.
exchangeable K; non-exchangeable K; nutrient availability; soil analysis; chemical extractores; Oryza sativa