Culture-Dependent Comparison of Aerobic Bacterial Morphospecies Profiles in Paddy Soils Under Different Eco-Friendly Fertilizer Technologies

Purpose: To compare the key structural community parameters and functional group profiles of culturable aerobic bacteria in paddy rhizosphere maintained under different fertilizer regimes at two locations with different soil types in Sri Lanka across three stages (i.e. before transplanting, at maximum tillering and grain filling stages) of the crop cycle.
Research Method: Three locally developed eco-friendly fertilizer technologies were tested against the recommended dosages of synthetic nitrogen and phosphorous fertilizers and no application of fertilizers using rice variety Bg 352. The field experiments were conducted at Batalagoda and Maha-Illuppallama research stations, which located at two different agro ecological zones of Sri Lanka. Based on the culturable aerobic bacterial morphospecies in rhizosheric soil, microbial community parameters and functional groups were determined and compared among the fertilizer treatments at two locations and the three soil sampling stages of crop growth.
Findings and Values: Abundance, richness, diversity and percentages of phosphate-solubilizing, nitrogen-fixing and Gram-positive bacteria did not differ significantly among the fertilizer regimes but the abundance varied between locations and sampling stages (p<0.05). The interaction effect (location x fertilizer regime x sampling stage) was significant (p<0.05) on species richness, diversity, percentage of phosphate-solubilizing bacteria and N-fixing bacteria. Community structure of culturable aerobic bacteria in paddy-soils is largely determined by the soil type and crop growth stage than the short-term responses to the fertilizer regimes. This study highlights the effects of short-term exposure of reduced dosages of synthetic fertilizers on culturable rice rhizospheric bacteria.