Author(s): Sims JT
Land application of cocomposted sewage sludge (CCSS), produced by the aerobic digestion of municipal refuse and anaerobically digested sewage sludge, represents an alternative use for organic wastes that are currently landfilled, incinerated, or disposed of by ocean dumping. Laboratory and greenhouse studies were conducted with four types of CCSS to determine their suitability for agricultural use, based on mineralizable N and the availability of plant nutrients and certain nonessential heavy metals (Cd, Cr, Ni, Pb). Nitrogen mineralization studies, conducted for 20 wk with three soils amended with 22 Mg/ha of each CCSS type (total N added = 250 to 398 kg N/ha), indicated that immobilization of N could be a serious problem with these composts. Negative values, ranging from −7 to −39 mg/kg, were obtained for net N mineralization (N mineralized adjusted for inorganic N added in the CCSS and mineralized soil N). Additionally, wheat (Triticum aestivum L.) plants grown in the greenhouse for 8 wk with the same CCSS applied at rates of 0, 11, 22, and 44 Mg/ha, and supplemented with 100 mg/kg of N as NH4NO3, exhibited N deficiency symptoms, reduced dry matter production, and lower plant N concentrations. Only slight differences in plant and soil (Mehlich I-extractable) concentrations of P, K, Ca, Mg, Cu, Cd, Cr, Ni, and Pb were noted among CCSS types in the greenhouse study. The CCSS rate also had little influence on plant and soil concentrations of these elements. Soil pH, however, was increased by a lime-amended CCSS, resulting in significant decreases in plant concentrations of Mn nd Zn. In summary, results from laboratory and greenhouse studies suggest that, when applied at agronomic rates, these composts can produce satisfactory plant growth, if adequate amounts of supplemental N fertilizers are applied, and that increases in soil and plant concentrations of nonessential heavy metals should not be a limiting factor in compost use.