Ecology of phosphate solubilizers in semi-arid agricultural soils

Ecology and diversity of phosphate solubilizing microorganisms in 20 soil samples comprising organic and non-organic farming, virgin and barren soils of Gujarat, India were studied. No considerable seasonal variation in population densities of various phosphate solubilizers was observed. Out of 40 phosphate solubilizing microorganisms, Pseudomonas spp., Bacillus spp., Saccharomyces spp. and Aspergillus niger were found to be most prevalent as they were present in more than 50% of the soil samples. The phosphate solubilization index for different cultures varied between 1.04 to 2.40. When the isolates, which gave good phosphate solubilization on solid medium, were further explored for phosphate solubilization in liquid medium, the phosphate solubilization ability decreased to as low as 8% and increased to as high as 99% by these cultures. Moreover, phosphate solubilization in the range of 18.1 to 66.3% was recorded when microbial consortia in the form of soil suspension were inoculated. Inspite of semi-arid nature of the ecosystem, considerable phosphate solubilizing microbial activity observed indicate the fertility status of the soil in terms of phosphate mobilisation.