The varieties IAC 13-1, IAC 16 and IAC 17, from the State of São Paulo, Brazil, were studied in a permanent trial on a Dusk Red Latosol soil, of low fertility, during the growing seasons of 1974/75,1975/76 and 1976/77. They received different levels of P2O5 through 0, 225, 450 and 675kg/ha of ordinary superphosphate. The experimental design was a split plot, with four replications, containing superphosphate fertilization on the main plots and varieties on sub plots. Lime was applied before the first year of cropping and annual applications of 50kg/ha of N and 75kg/ha of K2O, were made on all plots. The IAC 13-1, IAC 16 and IAC 17 cotton varieties had similar responses to the application of ordinary superphosphate for all studied characteristics. However, IAC 13-1 and IAC 16 showed a more efficient fertilization use throughout tine years, concerning the fiber length, while IAC 17 did not show any improvement in this characteristic. The use of ordinary superphosphate tended to increase the fiber strength, seed weight and boll weight, independently of the variety used. Length uniformity, Micronaire and fiber percentage were not improved by fertilization.
cotton; varieties; fiber quality; fertilization