Bacillus Strains as an Effective Treatment of Mobile Forms of Phosphorus in Bulgarian Soils

Abstract

Strains of genus Bacillus have the potential to increase the availability of phosphorus to plants by the dissolution of inorganic phosphate, which favours the growth of plant species and that has an important economic and agricultural impact. Soils with low phosphate intensity (Lеаched chernozem) were enriched with poorly soluble phosphorus compounds and inoculated with the tested newly isolated strains from genus Bacillus (Bacillus subtilis T 2, Bacillus amyloliquefaciens T 3, Bacillus subtilis T 4, Bacillus subtilis T 10, Bacillus thuringiensis T 17 and Bacillus cereus Т 18). Six newly isolated strains from different regions in Bulgaria were identified by classical phenotypic techniques and 16S rDNA sequence analysis. Tested strains were inoculated (2 ml and 15 ml) in the soil and incubated for 25 days at 28oC. After the incubation period, the degradation of phosphorite flour to available phosphorus was examined by the classical method of Egner-Riehm and by extraction with CaCl2. A vegetation experiment was conducted with a test plant Pelargonium zonale, characterized by its ability to absorb large amounts of phosphorus. A peat substrate enriched with all macro-and microelements was used, and phosphorus was added to the medium in the form of phosphorite flour. The amounts of phosphorus absorbed by one plant Pelargonium zonale treated with newly isolated strains Bacillus subtilis T 10 and Bacillus cereus T 18 absorbed 23% more phosphorus than the control variant. As a result of the experiments, it was found that the studied strains have a positive impact on the increase of phosphorus mobility in soils with low phosphate intensity treated with hardly degradable phosphors.