Microbial dynamics in rice ecosystem under supplementation of organic sources of nitrogen with inorganics and their concomitant impact on yield.

Microorganisms play crucial role in the ecosystem building. Their presence or absence in a particular environment are indicative of the web of interactions they undergo to impact the life of other components of the system. The current experiment was undertaken in rice-rice cropping sequence, for two years, to understand the changes in composition of microorganism as a result of interaction of herbicide and different nutrient sources added to soil under lowland area and a resultant grain yield obtained in rice. The experiment was divided into two simultaneous studies, i.e., field experiment and metagenomic study, to obtain the rice yield and soil microbial dynamics, respectively. Pooled soil samples were collected from rice field with constant herbicide application, i.e. Pyraszosulfuron (pre-emergent) @25 g/ha + 2, 4-D (post-emergent @0.5 kg/ha), but with 5 different sources of nutrients, viz., T—absolute control, T—100% N-PO-KO through inorganic fertilizers (recommended dose of 40-20-20 kg/ha)), T—75% N through inorganic + 25% N through FYM (PO and KO recommended doses), T—75% N through inorganic + 25% N through vermicompost (PO and KO recommended doses) and T—75% N through inorganic + 25% N through crop residues and bio-fertilizer (PO and KO recommended doses). Based on the amplicon DNA sequencing approach, it was observed that though there was an overall increase in bacterial phyla, viz., Chloroflexi, Actinomycetes, Euryarchaeota, Firmicutes in all the treatments from 0 days after transplanting (DAT) to physiological maturity of plant, however, soil treated with vermicompost (TH) showed a dramatic increase in the population of one particular microbe viz., Firmicutes. Amongst fungal populations, Actinomycetes increased in soils of all the treatments from 0 DAS to physiological maturity, however, the increase was lowest in soil treated with vermicompost while it was highest in soil having crop residues (T). The result obtained in microbial dynamics in case of vermicompost supplementation are concomitant to the biological yield of rice that was observed to be the highest in the same. The findings highlighted that the soil with vermicompost supplementation outperformed in terms of beneficial microbial changes and highest grain yield which, again, could be attributed to the favourable niche provided by vermicompost. Hence, supplementing vermicompost along with inorganic N sources can surpass the other organic sources in preventing deleterious effects of the chemical build-up in soil, due to herbicides and inorganic fertilizers, while synthesizing and releasing plant hormones, metabolites and antibiotics to suitably allow the growth and dominance of beneficial bacterial population.