Tillage and Residue Management Impact on Microbial and Nematode Abundance Under Diverse Rice-Based Cropping Systems in Calcareous and Non-calcareous Floodplain Soils

Switching from conventional to conservation agriculture (CA) practices may affect the soil microbial community; however, such information in rice-based systems is yet to be explored. Two field experiments were conducted from 2015 to 2020 on contrasting soils (calcareous vs non-calcareous) to evaluate the CA effects on soil microbial populations and their diversity. Experiment No. 1, non-calcareous soils, was comprised of two tillage systems (minimum tillage [MT] vs. conventional tillage, [CT]) in main plots, three cropping patterns (wheat-Aus-Aman rice, [WRR]; lentil-Aus-Aman rice, [LRR]; mustard-Boro-Aman rice, [MRR]) in the sub plots, and two residue levels (with and without 20% residue retention) in the sub-sub plots. Another experiment, calcareous soils, was comprised of three tillage treatments (strip-till [ST]; no-till [NT]; and conventional tillage [CT]) and two previous crop residues (high residue [HR], 50% by height) vs. low residue [LR], 15%). Non-calcareous soils had higher fungal populations with higher microbial biomass carbon but lower nematode and bacterial populations compared to the calcareous soils. In non-calcareous soils, the MT resulted in higher microbial populations than the CT at 0–7.5-cm depth, but not at 7.5–15-cm depth. Likewise, the LRR system maintained higher microbial populations compared to the WRR and MRR systems. In calcareous soils, all the microbial populations were higher in the NT and ST than in the CT, where the former two were alike. Reduced tillage with crop residue retention improved soil microbial populations and their diversity with higher fungal-to-bacteria ratios in both soils.