One-time strategic tillage does not cause major impacts on soil microbial properties in a no-till Calcisol

Strategic tillage (or occasional tillage) has been touted as a potential solution for the severe weed infestations of long-term no-till (NT). Nevertheless, there is little information on the influence of strategic tillage on microbial properties of Australian NT soils. In the present study, we assessed the influence of strategic tillage on the microbial properties of a seven years' NT Calcisol in Moonie, Queensland, Australia. We tested the hypothesis that the application of one-time strategic tillage with chisel or offset disc does not cause major impacts on soil biological health in a NT system. Strategic tillage was applied once and soil samples were collected 13 months after tillage from the depths 0-10 and 10-20 cm. The measured biological indicators included soil microbial biomass carbon, catabolic activity (MicroResp™ assay) and total microbial activity (fluorescein diacetate method). The structure of bacterial communities was profiled by quantitative polymerase chain reaction (qPCR) and terminal reaction fragment length polymorphism (T-RFLP). Principal components analyses based on qPCR and T-RFLP data did not show tillage effects on soil bacterial communities. However, relative to the NT, chisel tillage led to significant increases in microbial biomass carbon (+34.4%), abundances of Alphaproteobacteria (+74.6%), Bacteroidetes (+113.7%) and Firmicutes (+36.5%), and the utilisation of D+ cellubiose (+178.4%) as well as mannitol (+167.2%) at 0-10 cm depth. In contrast, the influence of offset disc tillage was restricted to an increased abundance of Alphaproteobacteria (+64.6%) at 0-10 cm depth. Our study suggests that, overall, one-time strategic tillage using either chisel or offset disc had a minor positive influence on soil biological attributes of the NT Calcisol 13 months after tillage.