Effect of annual and perennial forage systems on soil microbial communities, activity, and carbon dynamics

Annual and perennial forage systems serve as valuable pasture resources for beef producers, due to their diverse growth forms, yield, and nutritional value. However, limited research has compared the effects of these forage systems on the soil and its associated microbial communities. We collected soil samples prior to grazing from two perennial and two annual forage systems in 2022 and 2023 which were analyzed and compared for microbial phospholipid fatty acid (PLFA) abundance and composition, microbial extracellular enzyme activity (EEA), microbial biomass carbon (MBC) and potentially mineralizable carbon (C). Soil N-acetyl-β-glucosaminidase activity was greater in perennial systems than annual systems in 2023 (p = 0.02). Potentially mineralizable C was consistently higher in soil from perennial systems as compared to annual systems, but no differences were seen in MBC. Perennial system soils had greater mineralizable C compared to those from annual system soils. The microbial metabolic quotient (qCO2) was higher in 2022 than 2023 and was greatest in 2023 perennial forage systems (p < 0.01). Fungal microbial PLFA indicators were more abundant in perennial system soil than in annual system soil, but overall microbial abundance was not strongly affected. The annual system soil microbial community had a greater proportion of bacteria than perennial system. Fungal abundance was greater under perennial forage system because of differences in plant composition, reduced soil disturbance, and the more continuous soil cover which buffered extreme climate conditions better than annual systems. These findings can guide livestock operations in adopting new regenerative strategies that enhance soil microbiota.