Soil microbial communities are crucial for ecosystem services, soil fertility, and
the resilience of agroecosystems. This study investigated how long-term (31 years)
agronomic practices—tillage, NPK fertilization, and cropping system—along with measured
environmental variables influence the microbial biomass and its community composition
in Chernozem soil under corn cultivation. The polyfactorial field experiment included
three tillage treatments ((moldboard (MT), ripped (RT), strip (ST)), two fertilization
regimes (NPK (N: 160; P: 26; K: 74 kg/ha), and unfertilized control) and two cropping
systems (corn monoculture and corn–wheat biculture). The soil samples (0–30 cm) were
collected in June and September 2023. Microbial biomass and community structure were
quantified using phospholipid fatty acid (PLFA) analysis, which allowed the estimation
of total microbial biomass and community composition (arbuscular mycorrhizal (AM)
fungi, fungi, Gram-negative (GN) and Gram-positive (GP) bacteria, actinomycetes).
Our results showed that microbial biomass increased from June to September, rising
by 270% in unfertilized plots and by 135% in NPK-fertilized plots, due to higher soil
moisture. Reduced tillage, especially ST, promoted significantly higher microbial
biomass, with biomass reaching 290% and 182% of that in MT plots in June and September,
respectively. MT had a higher ratio of bacteria-to-fungi compared to RT and ST, indicating
a greater sensitivity of fungi to disturbance. NPK fertilization lowered soil pH by
about one unit (to 4.1–4.8) and reduced microbial biomass—by 2% in June and 48% in
September—compared to the control, with the particular suppression of AM fungi. The
cropping system had a smaller overall effect on microbial biomass.
