Spatiotemporal Shift of Soil Microbes in Conservation Agriculture under a Rice-Based Cropping System at the New Alluvial Zone of Lower Gangetic Plain

Optimizing microbial potential (population and biomass) in low input-based conservation agriculture (CA) can be utilized to address the various problems like low soil productivity. Population of broad (bacteria, fungi, actinomycetes) and specific microbial groups (viz. free-living nitrogen-fixer (FLNF), phosphate solubilizing bacteria (PSB), cellulolytic bacteria (CDB) and arbuscular mycorrhizal fungi (AMF)) was captured under rice-maize-cowpea(RMCp ), rice-wheat–green gram: (RWGg ), and rice-cauliflower-bororice (RCfBr ) with 3 tillage practices: conventional tillage (CT), reduced tillage ( RT ), and zero tillage (ZT ) and 5- levels of residue and fertilizer (RDF) application: 0% Residue and100% RDF(R1), 100% Residue and 50% RDF (R2), 100% Residue and 75% RDF (R3), 50% Residue and100% RDF(R4), 50%Residue and 75%RDF (R5), through split plot designing from 2018 to 2020. Following methods were involved: microbial population by pour plate and serial dilution AMF spore by sieving and spore counting and microbial biomass by fumigation and extraction technique. The early stage of CA adoption showed a sharp decline in microbial population (29, 15 and 16%, by bacteria, actinomycetes and FLNB, respectively) compared to initial population, however population of fungi, CDB, PSB and AMF increased by 31, 28, 9 and 19%, respectively. Observed microbial population and biomass indicated ZT excelled over RT and CT. Comparative study showed that 100% residue and 50% RDF combination increased population of CDB (8–15%) and PSB (8–10%) than 100% residue and 75%RDF under three distinct cropping system. Desirable microbial biomass C: N ratio was achieved by the application of R4 tailored with RT practices under different cropping systems whereas contrasting values of microbial biomass C: P ratio was found. RMCp and RWGg cropping systems performed similar and excelled over RCfBr by 56 and 52%, respectively. Although transition stage of CA adoption (zero tillage, residue application and crop diversification) show drastic decline in microbial population but long term adoption of conservation agriculture practices gradually restored the higher microbial population and biomass in soil.