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Updated: Mar 18, 2026

Assessment of Waste-Derived Biochars on the Health and Biological Activity of Soil
Published on: October 10, 2025
Repeated application of composted tannery sludge affects differently soil microbial biomass, enzymes activity, and
Ademir Sérgio Ferreira Araújo1, Luciano Moura Lima2, Vilma Maria Santos2
1Soil Quality Laboratory Agricultural Science Center, Federal University of Piauí, Teresina, PI, Brazil. asfaruaj@yahoo.com.br.
Abstract:
Repeated application of composted tannery sludge (CTS) changes the soil chemical properties and, consequently, can affect the soil microbial properties. The aim of this study was to evaluate the responses of soil microbial biomass and ammonia-oxidizing organisms to repeated application of CTS. CTS was applied repeatedly during 6 years, and, at the sixth year, the soil microbial biomass, enzymes activity, and ammonia-oxidizing organisms were determined in the soil. The treatments consisted of 0 (without CTS application), 2.5, 5, 10, and 20 t ha(-1) of CTS (dry basis). Soil pH, EC, SOC, total N, and Cr concentration increased with the increase in CTS rate. Soil microbial biomass did not change significantly with the amendment of 2.5 Mg ha(-1), while it decreased at the higher rates. Total and specific enzymes activity responded differently after CTS application. The abundance of bacteria did not change with the 2.5-Mg ha(-1) CTS treatment and decreased after this rate, while the abundance of archaea increased significantly with the 2.5-Mg ha(-1) CTS treatment. Repeated application of different CTS rates for 6 years had different effects on the soil microbial biomass and ammonia-oxidizing organisms as a response to changes in soil chemical properties.
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