A long term split-plot field trial with cotton was initiated in 1976, with four limestone rates (0, 2, 4 and 6 t/ha) in the main plots and four yearly applied rates of potassium in the subplots (0, 50, 100, 150 kg/ha of K2O as KCl), in a Distrofic Dusk Red Latosol, at Guaíra, State of São Paulo, Brazil. After five years liming was reapplied. The soil pH and base saturation in the plow layer increased fastly after re-liming, and decreased down to previous rates two years later, due to an intensive Ca and Mg leaching to the subsoil layers. Potassium effect on cotton yield was more evident with liming. Potassium deficiency symptoms were noted in plants from the limed plots with no K-fertilization. In the abscence of liming, the highest K rate promoted plant injury. A 90% index of the maximum expected yield was reached in presence of K-fertilization and when the soil base saturation increased up to 60% in the plow layer and 40% in the subsoil layers (20-40 and 40-60 cm depths).
cotton; liming and potassium; interactions and soil analyses