Effect of Leonardite and Zinc Solvent Bacteria on Release and Chemical Forms of Zinc in Calcareous Soil

The aim of researchers in order to revive sustainable agriculture is to increase the solubility and availability of nutrients in the soil. For this purpose, this study was carried out to assess the effect of leonardite and bacteria on the chemical forms of zinc (Zn) in calcareous soils. A factorial experiment was conducted with three levels of leonardite (0, 2 and 4%) and with two microbial factors (without bacteria and zinc-soluble bacteria) at three incubation time (30, 90, 150 days) in three replications. The chemical fractionation and available forms of Zn in the soil was assayed by using the Tessier and DTPA methods. The results showed that leonardite and bacterial significantly increased Zn available forms (54%) and decreased soil pH (4.1%) during incubation time. Soil biological properties such as microbial population, basal respiration and microbial carbon increased by 36.2%, 77% and 77%, respectively. The distribution of Zn chemical forms and mobility factor also had significant changes affected of leonardite and bacteria as, it increased the exchange forms, binds to organic carbon and the carbonate part, as well as decreased the Zinc binds to Fe and Mn oxides in the soil. The mobility index of Zn ranged from 3.8 to 11.59% and its maximum value was observed in the treatment of leonardite 4% + bacteria. As a result, leonardite as a fertilizer plays an important role in element motility and its application along with solvent bacteria has positive effects on dissolution and increasing the availability of the elements.