The evaluation of microbial diversity in a vegetable based cropping system under organic farming practices

Organic farming is becoming a major tool for sustaining the soil quality degraded by intensive use of synthetic chemicals for increasing crop production and therefore, use of bio-agents as biofertilizers or biopesticides is an integral part of organic farming especially in vegetable cultivation. An effort was, therefore, made to see the effect of arbuscular mycorrhizal fungi (AMF) and pseudomonads as the microbial inoculants in vegetable based cropping systems under organic farming practices. Three crops taken in rotation were okra, pea and cowpea in a year. The inoculants used were Glomus intraradices, an arbuscular mycorrhizal fungus, and four isolates of Pseudomonas fluorescens singly and in combinations. No chemical/organic fertilizer was added during two rotations of chosen vegetables except the crop residues, which was chopped and distributed equally onto the each plot after the harvest of the fruits. A significant increase in yield was observed in the inoculated plots over the control. Culturable microbial diversity was increased compared with the start of the experiment. Total microbial diversity as assessed by Denaturing Gradient Gel Electrophoresis confirmed the results of culturable total and functional diversity analysed using Shannon Weaver's diversity indices (H′). Functional diversity assessed in terms of cellulase, xylanase, amylase, protease producers and P-solubilizers showed that the inoculants worked beneficially for maintaining soil health. The mycorrhizal inoculation followed by combination of AMF and pseudomonads proved to be better. Present findings indicated that microbial gene pool especially the key helpers for the maintenance of soil health residing in the vicinity of roots, was positively affected by using pseudomonads and AMF. Under organic farming management practices, inoculated bioagents and crop residues increased the yield of vegetables.