Changes in the functional properties of a sandy loam soil amended with biosolids at different application rates

The goal of this research was to study the impact of the application rate of biosolids from municipal sewage sludge on soil functionality. The biosolids originated from the composting of aerobic or anaerobicmunicipal sewage sludge with rice husk in the ratio 1/1 v/v. The products were applied at increasing doses, 50 (1×), 150 (3×), and 300 (6×) mgN kg−1 ds, on a sandy loamsoil. In order to highlight their impact on soil properties and evaluate their possible deleterious effects, soil functional parameters (soil microbial biomass, soil enzyme activities, and soil bacterial population) were used. Outcomes showed that the increase of the application rate had significant impact on microbial biomass carbon, which increased by 5%, 9% and 21% in 1×, 3× and 6× with respect to the untreated soil. Biosolid application rate influenced soil enzyme activities, such as β-glucosidase, dehydrogenase, protease and alkaline phosphomonoesterase which sharply increased at 3× and 6×, especially in the soils amended with the aerobic biosolid. Soil total bacterial population proved to be stable and not affected, at any dose, by biosolid addition. Concerning total trace metals, no dose effect was registered, as their concentrations were the same for each dose and treatment; on the contrary, available copper diminishedwith application rate. On thewhole, soil functionality was not negatively affected by biosolid application.