Impact of soil moisture regimes on greenhouse gas emissions, soil microbial biomass and enzymatic activity in long-term fertilized paddy soil

Two potent greenhouse gases that are mostly found in agricultural soils are methane and nitrous oxide. This study monitored how different moisture regimes influence microbial stoichiometry, enzymatic activity and greenhouse gas emissions in paddy soils. The results revealed that 60% water-filled pore spaces (WFPS) produced higher amounts of N ₂ O than flooded soil, while compared with 60% WFPS, flooded soil significantly stimulated CH ₄ production. High N ₂ O flux values were recorded at 2.3, 3.1 and 3.5 µgkg ^− 1 in 60% WFPS in the control and treated with NPK and NPKM, respectively. In flooded soil, the highest CH ₄ flux values were recorded at 1.7, 3.2 and 3.8 µgkg ^− 1 in control, mineral fertilizer, and chemical fertilizer combine with manure treatments, respectively. Dissolved organic carbon (DOC) increased 15–27% under high moisture content. The highest microbial biomass carbon (MBC) was recorded in flooded conditions and was 8–12% higher than in the 60% WFPS soil. The microbial biomass nitrogen (MBN) was 14–21% higher in flooded soil than in the 60% WFPS soil. In the flooded condition, the microbial biomass phosphorus (MBP) was 4–22% greater than in the 60% WFPS soil. The urease enzyme was significantly increased by 42–54% in flooded soil compared with 60% WFPS soil. Under long-term fertilization, the NPKM treatment significantly increased β-glucosidase (BG) and acid phosphatase (AP) enzyme activities, whereas the moisture content contributed 1.2–6.1% and 2-6.6% of the effects on BG and AP, respectively. DOC, MBC and pH showed a significant positive relationship with cumulative CH ₄ , while DOC showed a significant relationship with cumulative N ₂ O. In the random forest model, soil moisture, MBC, DOC, pH and enzymatic activities were the most significant factors for GHG emissions. The PLS-PM analysis showed that soil properties and enzymes possessed a significantly significant direct impact on CH ₄ and N ₂ O emissions, while SMB had a highly positive indirect effect on CH ₄ and N ₂ O emissions.