A correct potassium fertilization management, using adequate fertilizer amounts, can minimize K losses and avoid soil K depletion. The objective of this study was to evaluate potassium dynamics in the soil profile as affected by different textures and exchangeable K levels resulting from previous soybean fertilizations. Soils with sandy loam and clayey texture previously planted with soybean and fertilized with 0, 60, 120 and 180 kg ha-1 K2O were sampled during 6 years. The experiment was carried out in a greenhouse, using 40 cm high and 5 cm diameter PVC tubes, where it was stratified the 0-5, 5-10, 10-20 and 20-40 cm soil layers. On the column surface, 80 kg ha-1 of K2O was applied as KCl and 100 mm water was applied weekly, for 16 weeks. At each application, the drainage solution volume and the K concentration in the leacheate were determined. After the disassembly of the soil columns, exchangeable and non-exchangeable K contents were determined for each layer. Potassium leaching was higher in the clay soil, where available K was higher due to the residual effect of previous K fertilization. Leaching intensity was proportional to available K contents. In the sandy soil initial leaching intensity was higher but decreased along time, whereas in the clayey soil K losses were more constant. The soil K level and leaching in soil profile were proportional to the exchangeable and non-exchangeable K for both soils. The residual effect of K fertilizer during the years under soybean, increasing its availability, can result in intensive exchangeable K losses, irrespective of soil texture. Potassium transformation from non exchangeable to exchangeable K is very fast, and affects the amount of leached K.
exchangeable K; non-exchangeable K; CEC; residual effect
