Yields and leaf elemental composition of cotton grown on sludge-amended soil

A 3-yr field study was conducted to determine the effects of land application of anaerobically digested, air-dried sewage sludge on growth of upland cotton (Gossypium hirsutum L.). Cotton lint yields obtained with sludge rates from 20 to 80 Mg/ha were comparable with those obtained by area farmers employing conventional fertilizer practices. Rates of 80 Mg/ha had no significant effect on lint yields, although lint/seed ratios tended to decrease with increased sludge rate for all years. After 3 yr of sludge application, the leaf and seed concentrations of Cd, Zn, Ni, and Cu were not significantly different from those on the fertilized check plots. Leaf concentrations of Cd were higher than seed concentrations, but the reverse trend was true for Zn, indicating that Zn may not be directly useable as a model for Cd behavior in cotton.