Influence of organic and inorganic sources of nutrients on the functional diversity of microbial communities in the vegetable cropping system of the Indo-Gangetic plains

The aim of the present study was to assess the effects of different organic and inorganic fertilizers on the functional diversity of soil microbial community under a vegetable production system. The Biolog^® Eco-plate technique and indices, such as average well-colour development (AWCD), McIntosh and Shannon diversity were employed to study the diversity of soil microorganisms. The AWCD, i.e. overall utilization of carbon sources, suggested that different organic treatments had a significant impact on the metabolic activity of soil microorganisms. After 120h, the highest AWCD values were observed in poultry manure (2.5 t·ha^-1)+vermicompost (3.5 t·ha^-1) (0.63) and farm yard manure (FYM) (10 t·ha^-1)+vermicompost (3.5 t·ha^-1) (0.61). After 72h, the highest value of the McIntosh diversity index was recorded in poultry manure (2.5 t·ha^-1)+vermicompost (3.5 t·ha^-1) (3.87), followed by poultry manure (2.5 t·ha^-1)+vermicompost (3.5 t·ha^-1)+biofertilizers (Azotobacter 500 g·ha^-1 applied as seed treatment) (3.12). In the case of the Shannon diversity index, the highest values were noticed in organic treatments; however, there was no significant differences between organic and inorganic treatments. Biplot analysis showed a clear differentiation of organic treatments from the inorganic control. The amino acids, phenolics and polymer utilizing microorganisms were dominant in organic treatments. Inorganic control recorded the lowest values of the microbial diversity indices. Through this study, we have identified the best combination of organic nutrients, i.e. poultry manure (2.5 t·ha^-1)+vermicompost (3.5 t·ha^-1) for the stimulation of metabolically active soil microbial communities.