Mineralization of composted municipal sludge under field conditions

Mineralization of nutrients from composted municipal sludge may vary due to sludge type and composting material. This study determined mineralization and release of selected elements from composted municipal sewage sludge to evaluate optimal land application rate under field conditions. Composted mu nicipal sludge was studied in two on-farm experiments, at rates of 0.0, 2.0 , 4.0, and 8.1 Mg ha(-1) (dry wt. basis) applied to peanuts and another fie ld incubation study consisting of 0.0 and 4.0 Mg ha-1 sludge rate (dry wt. basis). The on-farm studies were used to determine release of selected elem ents over a growing season, while third field experiment measured nutrient release periodically for an entire year. The on-farm studies used soil core s with resin bags placed on the bottom to trap any leached nutrient, while the soil in the PVC core was extracted to determine nutrient release. In th e latter study, decomposition bags with soil cores and resins were utilized to help determine the rate of nutrient release from the sludge. Nitrogen ( N) was immobilized. while phosphorus (P) was mineralized at Site A from mun icipal sludge, but the opposite occurred at Site B. Net release of calcium (Ca), magnesium (Mg), and zinc (Zn) into the soil from sludge occurred afte r I yr. Greatest increase was Ca, at 16 mg kg(-1) followed by Mg and Zn at 2 and 0.8 mg kg(-1), respectively. There was an initial release for all nut rients studied from sludge during the first 2 weeks after soil incorporatio n. Results show that under field conditions. nutrients from these organic a mendments can be readily immobilized, but not supply selected elements in c oncentrations that would support annual crop growth.