Degradation rate of anaerobically digested sewage sludge in soil

The objective of this study was to monitor the degradation and obtain the mineralization fraction of anaerobically digested sludge, also known as digestate, under field conditions, when applied to the surface or incorporated into the soil. Sludge was applied to a dystrophic Inceptisol at a dose of 500 kg ha^–1 yr^–1 of total nitrogen, where the monitoring period of the mineralization process lasted 131 days. Samples of the soil-residue mixture were collected for analysis of the total organic carbon (TOC) and easily oxidizable organic carbon (OOC), total, ammonia, nitrate and organic nitrogen (ON). The annual mineralization fractions of the digestate, estimated based on the difference between the initial and final contents of TOC, OOC and ON in samples of the material collected, were 99.5 and 100%, respectively, when incorporated with the soil or applied to the soil surface.