The Stabilization Method of Sewage Sludge Affects Soil Microbial Attributes and Boosts Soil P Content and Maize Yield in a Sludge-Amended Soil in the Field

This study aims to compare two stabilization methods of sewage sludge to determine soil total organic carbon (TOC), soil microbial biomass and activity (C-CO2 emission), microbial, metabolic, and mineralization quotients, as well as nitrogen (N) and phosphorus (P) availability throughout the maize harvest and its final yield. The experiment was conducted using chemical stabilization sludge by adding calcium oxide (CSS) and thermal stabilization sludge (TSS), which consisted of composting sludge and material from tree pruning. The experiment was developed in a randomized block design, with control and four treatments with doses (10, 20, 30, and 40 t ha−1) of CSS or TSS applied to the soil. Soil samples were collected at 0–20-cm layer at 3, 15, 30, 60, and 90 days after sludge application. After maize cultivation, the contents of N and P and dry matter were evaluated, as well as grain yield. The results showed that the addition of sludge increased the TOC content by roughly 27% and 32% for TSS and CSS, respectively, which stimulated the microbial activity on the 3rd day after sludge application at the highest dose (~ 80 mg kg−1 day−1 of C-CO2 emission). The soil C-mineralization quotient was higher in CSS and this method promoted a higher and faster P mineralization in the soil (~ 350 mg kg−1 at the 30th day of cultivation). The CSS method made the microbial activity more efficient, resulting in higher degradation of soil carbon and phosphorus; hence, this method is more appropriate for the rapid release of nutrients into the soil, promoting higher maize crop yield.