Adubação da cana-de-acúcar: XIV. Adubação NPK em latossolo roxo

Nineteen 33 NPK factorial experiments with sugar cane were carried out in 1958/59 on dusky red latosol soils of various sugar plant owned lands, in the State of Sao Paulo, Brazil. The amounts of nutrients applied corresponded to: 0, 90 and 180 kg/ha of N; 0, 80 and 160kg/ha of P205; and 0, 100 and 200kg/ha of K2O. The experiments were separated in two types of areas, based on former soil use: one group in areas where sugar cane was cultivated over ten years, and the other group in areas where which sugar cane had never been cultivated. The results were in accordance with former management, indicating residual effect of phosphorus applications and potassium depletion on the areas former cultivated with sugar cane. However, responses to nitrogen could not be related to former soil usage. Responses of sugar cane to nitrogen were related to soil organic matter (r = 0.695**) and to phosphorus with resin extractable P (r = 0.709**), but the response to potassium fertilizer was not related to soil K (r = 0.284 n.s). With adjusted response functions, the optimal economical amount of nutrients were shown to be in general, higher than the current recommendations. Yield increases promoted by NPK were directly related to the maximum economic yield (r = 0.773**).