Soil Microbial Community Change and Recovery after One-Time Tillage of Continuous No-Till

Continuous no-till (NT) results in soil improvements, primarily in the surface 5 cm of soil. One-time tillage may improve NT systems by inverting surface soil with less improved deeper soil. Research was conducted to determine the change in abundance of soil microbial groups after a one-time tillage of NT and their recovery dynamics. Experiments were conducted under rainfed corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench] rotated with soybean [Glycine max (L.) Merr.] in eastern Nebraska with one-time moldboard plow (MP) and mini-moldboard plow (mini-MP) tillage compared with continuous NT. Fatty acid methyl ester (FAME) profiles were used as biomarkers of soil microbial groups. The biomass of microbial groups within the soil profile was affected by tillage treatment, soil depth, and time after one-time tillage. Soil microbial biomass under NT was greatest at the 0- to 5-cm depth with 50% less in the 5- to 20-cm depth, and least in the 20- to 30-cm depth. Microbial group biomass was decreased by one-time MP tillage, and generally by mini-MP tillage, compared with NT. On an equivalent soil mass basis, the quantity of the arbuscular mycorrhizal (AM) biomarker C16:1(c11) in the second year after tillage was 22% less for tilled treatmerits compared with NT. In contrast, the fungal biomarker C18:2(c9,12) was 6% more in the second year after tillage for tilled compared with NT. Tillage affected biomass and recovery of microbial groups differently, with all except AM returning to the NT microbial biomass levels within 1 to 3 yr.