Crop rotation restructures soil microbial communities in Subtropical Oxisol, South Brazil

Crop rotation significantly influences agricultural sustainability through long-term effects on soil attributes, including the soil microbial communities. This study compared soil microbial communities within soil aggregates (SA) in a 26-year-old experiment with four randomized blocks involving two cropping systems: (1) succession, which consists of soybean-wheat-soybean, and (2) rotation, which consists of vetch-maize-oat-soybean-wheat-soybean. The objective was to validate the role of crop rotation in enhancing soil conditions for plant growth and mitigating the adverse effects of intensive agricultural practices. The soil samples were fractionated into macroaggregates (MACRO, > 0.25 mm mesh) and microaggregates (micro, < 0.25 mm mesh) using field-moist soil (5 - 10 cm trenches). The fractioned samples were subjected to a series of analyses, including biological assessments such as phospholipid fatty acid (PLFA) profiles of bacteria and arbuscular mycorrhizal fungi (AMF), as well as protozoa counting. Additionally, they underwent physical analysis, including texture assessment, and chemical analyses, including pH, total organic carbon, potential acidity, and sum of bases. In crop succession, MACRO (likely aerophilic) exhibited a larger number of amoebae, a smaller number of flagellate protozoa, as well as higher levels of gram-positive bacteria and actinobacteria and lower levels of gram-negative bacterial PLFA profiles in comparison to micro (likely anaerobic). In crop rotation, MACRO showed lower values of AMF and gran-positive bacteria, higher values of gran-negative bacteria PLFA profiles, and a reduction in the number of amoebae compared to their microaggregate counterparts. This suggests that the conditions of micro were enhanced to facilitate more aerobic growth. Crop rotation modifies the soil microaggregate environment, favoring aerobic heterotrophic microorganisms and inducing shifts in the microbial community structure, which may enhance biogeochemical cycling and agricultural sustainability.