Changes in Soil Zinc Fractions Upon Inoculation of Zinc Solubilizing Bacteria (ZnSB) Under Rice Rhizospheric Soil

Zinc (Zn) is an essential micronutrient that is found in almost all classes of enzymes. Its deficiency is a well-documented problem among cereal crops that causes decreased crop yields and nutritional quality. Therefore, an experiment was implemented in a randomized block design which included the treatments of bacterial inoculation consisting of T1 (Control), T2 (100% RDF;100:40:20), T3(100% RDF + 25 kg ZnSO4.7 H2O), T4(100%RDF+ ZnSB1– Bacillus sp. strain BAU_A2 @750 ml ha−1), T5 (100%RDF+ ZnSB2– Priestia megaterium strain BAU_A3 @750 ml ha−1), T6 (100%RDF+ ZnSB3-Bacillus subtilis strain BAU_A5@750 ml ha−1). The mineral NPK was applied as per treatments. The results indicated the maximum values of water soluble exchangeable Zn and organically bounded Zn in treatments consisting ZnSB1, ZnSB2 and ZnSB3, respectively. The WS+EXCH-Zn was significantly increased by 68.57%, 28.26%, 18%, 98.14%, 41.30%, 30.00% and 128.12%, 55.55%, 37.25%, 43%, 62.22% and 43.13% in first year (2018–19) and second year (2019–2020) under the soil treated with ZnSB1-Peribacillus simplex strain BAU_A1, ZnSB2-Bacillus sp. strain BAU__A2 and ZnSB3-Bacillus subtilis strain BAU_A5 along with 100%RDF over control, application of recommended dose of fertilizer with and without application of 25 kg ZnSO4 ha−1, respectively. However, the maximum decrement in Mn-oxide-bounded zinc (1.12 mg kg−1 soil) was observed with T6 which was significantly higher by 158%, 194.4%, 185.71% over control, 100% RDF with and without application of 25 kg ZnSO4 ha−1, which showed the solubilization of zinc with the activity of ZnSB in soil. The study may be beneficial to mitigate the zinc deficiency in soil and malnutrition in children.