Effect of irrigation and drainage practices on soil microbial community composition and physicochemical properties in typical saline–alkaline soil

Abstract Irrigation and subsurface drainage (ISD) is used to improve physicochemical properties of soil; however, its effects on soil microorganism characteristics are not well understood, particularly in saline–alkaline soils. In this study, a 1‐year (2023–2024) field experiment was conducted in the Inner Mongolia to assess the effects of three ISD practices on soil salinity–alkalinity (electrical conductivity [EC] and pH), exchangeable cation (Exchangeable‐Na + , K + , Ca 2+ , and Mg 2+ ), organic carbon and nitrogen (soil organic carbon and total nitrogen), microbial biomass carbon and nitrogen (MBC and MBN), dissolved organic carbon and nitrogen (DOC and DON), and soil microbial community structures. Three treatments were conducted: CK, no ISD; 1.5D, irrigation and 1.5‐m depth of subsurface drainage; and 1.8D, irrigation and 1.8‐m depth of subsurface drainage. Results showed that ISD decreased the soil EC (59%–75%), pH (10.8%–11.5%), and Na + (85.4%–82.7%) in comparison with CK, particularly in 1.5D treatment. ISD increased the soil MBC (82.3%–170.3%) and MBN contents (65.9%–134.1%), and it also increased the Chao1 and Shannon indices (23.5% and 12% in 1.5D, 18.5% and 7.7% in 1.8D) of soil bacteria. Note that 1.5D and 1.8D increased the diversity and richness of bacteria and fungi, such as Choloflexi, Acidobacteriota, Anaerolineae, Mucoromycetes, Chytridiomycota, Pezizomyceyes, Agaricomycetes, and Glomeromycetes. However, subsurface drainage could decrease DOC (26.7%‐34.6%) and DON contents (30.8%–59.8%) after irrigation. In conclusion, ISD is a powerful practice for improving soil physicochemical properties and microbial community structures. Future studies should also consider the soil textures and combine ISD with the application of organic fertilizers to improve soil fertility.