Impact of Nitrogen Fertilization and Microbial Inoculants on Soil Microbial Biomass, Enzyme Activities and Carbon Respiration in DSR-rice Cultivation

Background: Rice is a staple crop grown globally, often requiring intensive nitrogen fertilization to achieve optimal yields. Excessive nitrogen use, however, can lead to environmental degradation and reduced soil health. Microbial inoculants, such as azospirillum, streptomyces and arbuscular mycorrhizal fungi (AMF), have shown potential in enhancing nutrient uptake and promoting sustainable agriculture. Methods: This study evaluated the impact of three nitrogen application levels (M1: 0 kg ha-1, M2: 40 kg ha-1, M3: 60 kg ha-1 as the main plot and four microbial inoculation treatments (S1: Control, S2: Azospirillum (618 g ha-1) + Streptomyces (618 g ha-1), S3: Consortium (1235 g ha-1) and S4: AMF (1235 g ha-1) as the sub plot. A split-plot design (SPD) with three replications was employed to analyze their effects on soil and plant parameters in rice. Result: The study revealed that the nitrogen levels and microbial inoculants significantly influenced soil and plant parameters in rice. The highest microbial biomass carbon (270.48 mg kg-1), dehydrogenase activity (20.32 mg TPF g-1 h-1) and soil respiration (199.63 mg CO‚ kg-1 day-1) were observed with the consortium inoculant at 40 kg N ha-1. AMF recorded maximum AMF colonization (56.20%) and enhanced microbial diversity (3.51 Shannon Index). Nitrogen application at 40 kg ha-1 improved root length density (2.46 cm cm-3), root biomass (18.23 g plant-1) and root-to-shoot ratio (0.35). Soil organic carbon peaked at 0.70% with the consortium, while available N, P and K reached 279, 29 and 232 kg ha-1, respectively, under 60 kg N ha-1 and consortium. Interactions showed synergistic effects, optimizing soil and crop performance.