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

- A sandy loam soil was amended with composts from urban sewage sludge and rice husk.
- Biosolid impact on soil functionality was investigated at three different doses.
- The aerobic biosolid mainly affected enzyme activities and soil quality indicators.
- The highest dose had significant effects on soil functionality than the other ones.
- Biosolid application rate does not increase the bioavailability of trace metals.

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 anaerobic municipal 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 ×) mg N kg− 1ds, on a sandy loam soil. 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 diminished with application rate. On the whole, soil functionality was not negatively affected by biosolid application.