ACCUMULATION AND MOVEMENT OF RESIDUAL PHOSPHORUS IN SLUDGE-TREATED DECATUR SILTY CLAY LOAM SOIL

Phosphorus (P) is generally known to be immobile in soils due to sever al factors that include fixation processes. Nevertheless, this study h as attempted to evaluate the accumulation and/or movement of residual P in previously sewage sludge-amended plots of a Decatur silty clay lo am, six years after the final of five consecutive annual applications of Huntsville and Chicago sludges at 20 Mg/ha to separate plots, and 1 0 years after a single application of 100 Mg/ha of the same sludges to other plots. Two test crops, com (Zea mays L.) and sudangrass (Sorghu m sudanenses), were gown on these plots for one season. Treatment plot s - control, fertilizer (inorganic), Chicago 20 Mg/ha/yr, Chicago 100 Mg/ha, Huntsville 20 Mg/ha/yr, and Huntsville 100 Mg/ha - were sampled at depths of 0-15, 15-30, 30-45, 45-60, 60-75, and 75-90 cm before pl anting, and at 0-15, 15-30, and 30-45 cm after harvesting. Concentrati ons of Mehlich 3-extractable soil P, found to be inversely correlated with depth of sampling, were maximum at the 0-15 cm and minimum in the 75-90 cm profile depth. Generally, there were significant differences between the P concentrations of the control treatment and those of al l other sludge treatments within the 0-15 and 15-30 cm depths, indicat ing P accumulation in the 0-15 cm. surface layer and possible movement from the 0-15 cm to the 15-30 cm depth. There was no P movement beyon d the 30 cm depth.