Zinc Solubilizing Potential of Enterobacter cloacae Strain ZSB14 in Three Different Semi-arid Tropical Soils

Microbial transformation of soil unavailable zinc (Zn) into available form is an important agronomical approach not only to alleviate the Zn deficiency of stable food crops but also to improve the nutritional quality of human diet. Zinc solubilizing bacteria (ZSB) as an inoculant to the crop plants could be a sustainable input for Zn-fertilization as well as for Zn-biofortification. In order to explore these bacteria, we have conducted a microcosm study to assess its potential in terms of Zn availability in three different soils of semi-arid tropics and its interaction effects with different insoluble Zn amendments. The ZSB strain, Enterobacter cloacae ZSB14 was inoculated to semi-arid tropical red lateritic, wetland and calcareous soils with or without zinc amendments viz, zinc oxide (ZnO), zinc carbonate (ZnCO3) and zinc phosphate (Zn3(PO4)2) under controlled condition and assessed for its Zn-releasing potential. The incubation study conducted up to 40 days revealed that the ZSB inoculation alone could not increase the Zn availability significantly in any of the three tested soils and the inoculation should be supplemented with insoluble Zn amendments. The preferred order of Zn amendments for ZSB-bound Zn release in all the three tested soils was ZnO>ZnCO3>Zn3(PO4)2. The results also revealed that the ZSB inoculation with Zn amendment was more effective for increasing the Zn availability of red lateritic (8.57 mg/kg) and wetland (6.35 mg/kg) soils than calcareous soil (4.47 mg/kg). ZSB inoculation alone and with zinc phosphate amendment increased the soil available potassium and phosphorus contents, respectively in all the soils. From the results, it is evident that pH and calcium carbonate contents of the soil are the major drivers of ZSB-bound Zn release in these soils. This study made progress to understand the efficacy of zinc solubilizing bacteria and its interaction with Zn amendments in different semi-arid tropical soils, which could be used as inoculant for Zn-fertilization.