Effects of tillage on microbial populations associated to soil aggregation in dryland spring wheat system

Tillage may influence the microbial populations involved in soil aggregation. We evaluated the effects of no till (NT) and conventional tillage (CT, tillage depth about 7 cm) continuous spring wheat system on culturable heterotrophic bacterial communities predominant in microaggregates (0.25–0.05 mm) and on soil-aggregating basidiomycete fungi in aggregate-size classes (4.75–2.00, 2.00–0.25, and 0.25–0.05 mm) at 0–20 cm depth of a Williams loam (fine-loamy, mixed, Typic Argiustolls) in dryland Montana, USA. Enzyme-linked immunosorbent assay used to quantify antigenic response to basidiomycete cell walls, was higher in NT than in CT in 4.75–2.00 mm size class in 2007 and higher in all classes and years at 0–5 cm depth, but was not different between tillage, years, and classes at 5–20 cm. The culturable bacteria from microaggregates were subjected to a soil sedimentation assay to determine their soil binding capability. The proportion of isolates which can function as soil aggregators was higher in NT than in CT at 0–5 cm but was not different at 5–20 cm. Our results provide a first insight into the beneficial effects of dryland NT compared to CT in reducing soil disturbance and residue incorporation and enriching the proportion of microorganisms responsible for aggregation, especially at the soil surface.