Synergistic effect of Bacillus isolates and biomass ash on soil and plant quality: A preliminary potexperiment with the analysis of potentially toxic elements

The use of biomass ash in agriculture can have advantages such as improved soil quality and environmentally friendly ash disposal. Moreover, in combination with microbial inoculants, biomass ash can have a beneficial effect on plant growth. The study investigated the effect of biomass ash and inoculums of three Bacillus isolates on the quality of soil and barley plants. The greenhouse pot experiment included five treatments and two control soils: control - without any amendment and control with mineral fertilizer (CAN). Treatments included soil (3 kg/pot) and biomass ash (30 g/pot) with and without calcium ammonium nitrate or with bacterial inoculum. Biomass ash was collected after combustion of soybean straw. Bacillus sp. were isolated from the rhizosphere soil of alfalfa. The presence of PGP traits (Indole-3-Acetic Acid and siderophores) was confirmed by the quantitative tests for the three Bacillus isolates used (B1, BS1, BMG1). The ash, soil and plant (collected in crop maturity stage) samples were tested for: total N, C, S, and plant available P2O5 and K2O as well as for the content of potentially toxic and hazardous microelements (As, Cd, So, Cr, Cu, Mn, Ni, Pb, Zn). Inoculation of seeds with Bacillus inoculums (in vitro) showed a significant effect on seedling growth compared to the non-inoculated control. Addition of ash significantly reduced soil acidity and increased content of plant available P and K compared to the controls, while combination of ash and microorganism, increased amount of available P compared to the treatment with ash only. Barley biomass yield was increased more than double when treated with ash and by 87.62% when treated with ash+BMG1 compared to control. The lowest yield was obtained in the treatment where only CAN was added. The content of potentially toxic microelements in the soil and barley shoots was below the maximum allowed concentrations. The use of biomass ash alone was effective in terms of soil nutritional and physical properties resulting in yield increase. However, the use of ash in combination with Bacillus isolates in addition to positive effect on soil and plant quality resulted in a higher barley biomass than the combination of ash with CAN. This study showed that biomass ash can be used as fertilizer on acidic soils with low nutrient content alone or in combination with bacterial inoculants. The synergistic effect of ash with microorganisms can provide an environmentally friendly approach in agriculture to reduce the need for chemical fertilizers and solve the problem of biomass ash disposal.