Conservation tillage has become a major soil management strategy to reduce soil erosion and improve soil quality, yet the impacts of crop rotation on soil responses to conservation tillage remain poorly described. We investigated the effects of (i) perennial grass cover versus annual cropping and (ii) type of break crop in a wheat (Triticum aestivum L.)-based crop rotation system on surface-soil (0-10 cm) structural and organic matter properties towards the end of a decade of continuous management on an Albic Luvisol in the cold, semiarid region of northwestern Canada. Soil aggregation was at state to resist water erosion more under perennial grass (i.e. bromegrass (Bromus inermis Leyss.) and red fescue (Festuca rubra L.)) than under annual cropping systems (mean-weight diameter of 2.1 and 1.6 mm under perennial and annual systems, respectively). Soil organic C was higher (44 g C kg-1 soil versus 38 g C kg-1 soil), but total soil N was lower (3.5 g N kg-1 soil versus 3.9 g N kg-1 soil) under perennial compared with annual cropping systems. There were few significant differences in soil-structural properties among the various annual cropping systems. The largest effect was greater light-fraction C and N under continuous wheat (4.0 g C kg-1 soil and 0.27 g N kg-1 soil) compared with other rotations, especially wheat-wheat-fallow (2.4 g C kg-1 soil and 0.16 g N kg-1 soil), as a result of higher residue inputs. Relationships between mean-weight diameter of water-stable aggregates and biochemical properties were strongest for soil microbial biomass C and soil organic C. Perennial grass cover exhibited greater potential to preserve soil-structural properties than no-tillage annual cropping.
