Abstract
Results of approximately 3000 trials carried out throughout Uganda to determine the effects of N and P fertilizers on yield of cotton on different soils are reported. Little of the variation in cotton performance in individual trials could be accounted for by differences in soil properties, but the average cotton yields and responses to fertilizer at centres where a number of trials were carried out over several years were found to be largely dependent on four basic factors: soil organic matter and soil pH average hours of sunshine per day and intensity of previous cropping. It is suggested that the last two factors influence the availability of major nutrients to cotton by altering the soil organic matter.
