Fungal species inhabiting calcareous soil in western Maharashtra, India, and their role in the release of soil-bonded Fe and Zn micronutrients for crop plant availability in such soils

Abstract

Calcareous soils which are around 30 per cent of the world over are unproductive for agricultural crop cultivation and productivity. In calcareous soils, most of the plant nutrients and micronutrients are not freely available to the crop plants as these often lie in fixed or bonded form. Therefore, these nutrients have to be released from their bonded form to freely available form in such soils to make them available for crop plant growth. The application of microbial species native to such calcareous soils and having the ability and capacity to release such bonded nutrients is a need of the day to convert these unproductive soils into productive ones. The microbial species that work as nutrient/micronutrient-salt solubilizing agents generally form a salt solubilization zone around the microbial colony while salt-mobilizing /salt-releasing microbes do not form such a solubilization zone around the microbial colonies. In the present investigation, we studied the presence of microbial flora particularly the fungal species in the calcareous soil in western Maharashtra, India, and their role in the release of the bonded Fe and Zn micronutrients from the calcareous soil to make them available for the kidney-bean plant growth grown in such soil. Six fungal cultures of distinct colony morphology were isolated from the calcareous soil as the calcareous soil- inhabiting fungal species, on a specialized enriched media. They did not form the solubilization zone on the Fe and Zn enriched media and therefore were considered and tested for their efficacy as Fe and Zn salt-releasing/demineralizing microbes. The release for Fe and Zn from their fixed form was 1.68 and 1.91µg/g of calcareous soil respectively by these demineralizing fungal bio-inoculants. The release of Fe and Zn in calcareous soil was found to play a role in the growth and yield-attributing parameters of kidney-bean plants in calcareous soil. These fungal cultures were identified as species of Glomus, Mucor, and Aspergillus. Therefore, these calcareous soils inhabiting fungal species having demineralization activity can be applied as demineralizing bio-inoculants to the calcareous soil regularly to make them crop productive, and for their reclamation.