RESIDUAL EFFECT OF POTASSIUM AND PHOSPHORUS FERTILIZATION ON NATIVE PASTURES

The objectives of this study were to study the residual effect of phos phorus and potassium fertilization on a native pasture soil, a pasture that is livestock grazed continuously. Soil analyses showed that ther e were significant differences in the phosphorus and potassium values between fertilized and non-fertilized plots. The residual effect of po tassium in the soil was shown in the potassium values found in the pas tures but a similar effect was not observed for phosphorus. This resid ual potassium level could be related to the possibility that potassium applied with fertilizer became fixed. To verify this fixing capacity of the soil, an incubation experiment with different levels of potassi um was conducted. Then the adsortion isotherms, Q/I, were determined a nd the existence of fixation confirmed.