Use of Plant Growth-Promoting Bacteria and Humic Acids for Phytostabilization of Acid-Generating Mining Wastes

Abstract

Svetlana Bratkova, Katerina Nikolova, Petya Genova, Anatoliy Angelov

An interdisciplinary study was conducted on the effect of application of plant growth-promoting bacteria and humic acids in the reclamation of acid-generating mining wastes through a vegetation cover. The drainage water from the mining waste was characterized by a pH of 3.58 and high concentrations of sulfate, copper, manganese, and zinc. Strains of the Bacillus and Pseudomonas genera and humic substances produced by biotransformation from lignite were applied. The usage of plant growthpromoting bacteria and humic acid in the reclamation of acid-generating mining wastes produced several beneficial effects. The combined application resulted in a significant decrease in Cu, Fe, Zn and sulfate concentrations in a variety of drainage water samples, due to the suppression of pyrite oxidation. Both plant growth-promoting bacteria and humic acid improve plant growth, when used separately. The highest yield of fresh (between 22% and 43 %) and dry biomass of plants (between 31% and 41 %) was observed after combining both treatments, but the effect depended strongly on the dose of application. Yields of fresh and dry biomass in the combined application increased by treating plants with 0.42 g/kg humic acids, but decreased significantly when applying humic acids in a concentration of 0.84 g/kg soil. The treatment with a microbial consortium and humic substances enhanced significantly the uptake of nitrogen, phosphorus, and potassium by the plants. Furthermore, the addition of Bacillus and Pseudomonas bacteria in combination with humic acids to poor soil for reclamation reduced the Cu and Zn uptake.

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