Supplementing Inorganic with Organic Nitrogen Sources Augments Microbial Dynamics favoring Yield in Rice Ecosystem

Abstract

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 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. 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) @25g/ha + 2, 4-D (post-emergent @0.5 kg/ha), but with 5 different sources of nutrients, viz, T₀- absolute control, T₁- 100% N-P₂O₅-K₂O through inorganic fertilizers (recommended dose of 40-20-20 kg/ha)), T₂- 75% N through inorganic + 25% N through FYM (P₂O₅ & K₂O recommended doses), T₃- 75% N through inorganic + 25% N through vermicompost (P₂O₅ & K₂O recommended doses) and T₄- 75% N through inorganic + 25% N through crop residues and bio-fertilizer (P₂O₅ & K₂O recommended doses). Based on the amplicon DNA sequencing approach, it was observed that though there was 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, where, soil treated with vermicompost (TH₃) showed a dramatic increase in the population of Firmicutes. Amongst fungal populations, Actinomycetes increased in all the soils from 0 DAS to physiological maturity, the increase was lowest in soil treated with vermicompost while it was highest in soil having crop residues (T₄). The results were concomitant to the biological yield of rice that was observed highest in the soil treated with vermicompost along with inorganic fertilizers. The results could be attributed to the favourable niche provided by vermicompost that resulted in synthesis and release of plant hormones, metabolites and antibiotics by the bacterial population leading to dominance of the bacteria as compared to the other treatments.