Zinc-Solubilizing Bacteria: A Boon for Sustainable Agriculture

Abstract

The continuous rise in world population requires more food to feed people. To fulfill this demand, farmers apply different agrochemicals, especially fertilizers, in indiscriminate quantity in fields to increase production per unit time per unit area. Blind and imbalanced doses of fertilizers cause various adverse effects on environmental conditions through the accumulation of various minerals and biomagnifications in different ecosystems. Generally, all macroelements are applied through high-analysis fertilizers. But micronutrients are neglected, not directly involved in yield expansion, and zinc (Zn) is one of them. Zinc (Zn) is a key micronutrient, required for all living forms including plants, humans, and microorganisms for their development. Humans and other living organisms require zinc in their lives in little amounts for proper physiological functions. Zinc is a crucial micronutrient for plants which plays various important functions in their life cycle. The deficiency of zinc in the soil is one of the very common micronutrient deficiencies and results in decreased crop production. Majority of the agricultural soil is either zinc deficient or contains zinc in a fixed form which is unavailable to plants, as a result reflecting zinc deficiency in plants and soils. Therefore, to solve the above problem, there is a requirement for alternative and eco-friendly technology such as plant growth-promoting rhizobacteria (PGPR) and organic farming practices to enhance zinc solubilization and its availability to plants. Zinc-solubilizing bacteria (Zn-SB) are promising bacteria to use for sustainable agriculture. Zn-SB have various plant growth-promoting (PGP) properties such as Zn solubilization, P solubilization, K solubilization, nitrogen fixation, and production of phytohormones like kinetin, indole-3-acetic acid (IAA), and gibberellic acid, besides production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and siderophores, hydrogen cyanide, and ammonia. Zn-SB secrete different organic acids that solubilize the fixed form of zinc to available form, which enhances plant growth promotion, yield, and fertility status of the soil. This chapter covers the efficient application of Zn-SB, the Zn solubilization mechanism, and their application to increase crop production. The indigenous Zn-SB have proved their effectiveness over exogenous ones in the various cropping systems or crop rotations for which they are intended.