Amendment of Vermicompost by Phosphate Rock, Steel Dust, and Halothiobacillus neapolitanus

Abstract

The aim of the present study was to improve the nutrient content of vermicompost (VC) and make it a more suitable alternative to chemical fertilizers. VC samples were inoculated with Halothiobacillus neapolitanus and were subsequently amended with 5% mineral sulfur or left untreated as control. Both groups were supplemented with 5% or 10% of phosphate rock (PR) powder or steel dust at the final concentrations of 2.5% or 5%. Changes in pH, electrical conductivity (EC), phosphorous (P) and iron (Fe) contents of VC samples were monitored in a 60-day post-treatment period, in 20-day intervals. The sulfur containing samples, when compared with the untreated control, showed significant decrease in pH, which fell within the range of 4.6–5. The maximum EC values were observed in samples containing 5% sulfur with the highest amount of PR (S5P10) or steel dust but it did not exceed 3 dS m−1. A significant increase of 130% in P content was observed in the S5P10 sample and the highest concentration of Fe, 45%, was measured in the S5Fe5 sample after 40 days of incubation which was followed by a slight reduction. H. neapolitanus can provide a condition for solubilization of P and Fe from PR and steel dust, respectively, to improve the P and Fe content of VC.