Effect of time and mode of applications, as well as of dose and kind (chloride and sulfate) of potassic fertilizer were observed in eight cotton field experiments, during the period 1962/1979, at three locations of the State of São Paulo, Brazil. In two experiments, potassium fertilizers, at 40, 80 and 120kg/ha of K2O, were applied in the furrows at planting time, or added to the soil in furrows 30 days before planting. In another experiments, potassium chloride at 80kg/ha de K2O, was applied in several manners; a) in the furrows at the planting time; b) just after thinning by spreading with N over the rows and covering or not with soil by subsequent cultivation; c) at flowering, by spreading over the rows or in furrows with incorporation; d) partial application, being part used at planting, and part spread over the rows, after thinning, or in furrows, at flowering, The statistical analysis of cotton yield were done individually, by experiment, or in groups according to the similarity in the treatments. One of the experiments was kept by four successive years in the same field, in order to check the cumulative effect of fertilization. In such case, it was also considered the contenta of K, Ca and Mg in the leaves. In general, cotton reacted positively to potassium fertilization. However, there was no appreciable difference between potassium chloride and sulfate. Fertilizer application in furrows bafore planting, showed to be inefficient, while the use of K with N in side-dressing, followed by cultivation, just after thinning, seems to be a good alternative. Due to potassium accumulation in successives annual fertilizations, the reaction of cotton to doses decreased regardless of the mode of nutrient application. About leaf analyses results, either petioles or leaf blades showed to be pieces of plant very sensitive to diagnosis of potassium nutrition. There was a negativa correlation between K and Mg content in leaf blades, and between K and Ca content with regard to leaf part analysed.
cotton; potassium fertilization; chloride and sulfate; time and way of application; residual effect and foliar analyse