Abstract
Precipitated hydroxy-apatite and rock-phosphate dissolvers consisting of bacteria (Gram+and Gram-rods and cocci), fungi (Aspergillus, Penicillium,
Rhizopus) and actinomycetes (Nocardia and Micromonospora) were isolated from 14 soils of Bihar in Eastern India on carrot-extract agar. Bacteria outnumbered fungi and actinomycetes. Fungi as a group had higher phosphate-dissolving capacity in a sucrose-peptone liquid medium than other organisms although some individual isolates of bacteria and actinomycetes could bring as much or more phosphate into solution. Many isolates which did not show clearance on carrot-extract agar could dissolve phosphate in the liquid medium suggesting that formation of solubilization zone is not sensitive to detect all phosphate-dissolving micro-organisms. Size of this zone was also not related with the phosphate-dissolving capacity of the organisms. Presence of calcium carbonate drastically reduced phosphate solubilization suggestive of a negligible role of micro-organisms in the availability of insoluble phosphates in calcareous soils. The solubilization of rock-phosphate was closely related to the growth of micro-organisms and aeration and pH conditions optimum for growth were also favourable to this process. Microbial solubilization of phosphate in these soils appeared to be a complex process involving diverse mechanisms such as formation of acids, alkalinity, hydrogen sulphide etc.
