Impact of organics on microbial activity and soil organic carbon build-up under rice in sodic soil

Abstract

Salt-affected soils cover 6.73 M ha in India, with ~56 % being sodic and 44 % saline. Sodic soils, particularly in the Indo-Gangetic plains, form due to alternate wetting and drying, leading to alkali hydrolysis, sodium saturation and high pH. Soil organic matter (SOM) turnover, primarily driven by microbial activity, is significantly impaired under these conditions. Reduced decomposition rates in salt-affected soils may enhance carbon (C) sequestration, lowering CO2 emissions, provided soil organic carbon (SOC) inputs are adequate. Navathania biomass consists of biomass from nine different crop seeds, improving soil organic matter and fertility. In contrast, Sunhemp biomass (Sesbania rostrata), a nitrogen-fixing green manure, enhances soil structure and microbial activity. A field experiment was conducted in sodic soil with seven treatments: T1- Navathania biomass @ 5.0 t ha-1, T2- Sunhemp biomass @ 6.25 t ha-1, T3- Crop residue @ 6.25 t ha-1, T4-Vermicompost @ 5.0 t ha-1, T5- Enriched Farmyard Manure @ 750 kg ha-1, T6-Gypsum @ 50 % GR and T7- Control. Navathania biomass incorporation significantly increased grain yield (4950 kg ha-1) and straw yield (7200 kg ha-1), with a 24.3 % yield increase over control. It also improved microbial biomass carbon (Cmb) (246 µg g-1 soil), Cmb/SOC ratio (1.92 %), SOC stock (23.7 Mg C ha-1), C buildup rate (4.73 Mg C ha-1 yr-1), basal respiration rate (43.7 mg CO2-C g-1 day-1) and enzyme activities. This treatment can enhance SOC conservation and soil productivity under sodic conditions.