Converting from no-tillage to pre-seeding tillage: Influence on weeds, spring wheat grain yields and N, and soil quality

On the Canadian prairies there has been a steady increase in no-till seeding coupled with more frequent cropping, facilitated by the greater use of snow management to increase stored soil water. Although no-till seeding can gradually improve soil conservation and soil quality, it may also increase the incidence of grassy weed infestations and thus cause more frequent use of costly herbicides, such as glyphosate. Our objective was to determine if no-till producers experiencing grassy weed problems could introduce pre-seeding tillage for a few years to more economically control perennial weeds, without adversely affecting grain yield and quality, and soil quality. An experiment in which spring wheat (Triticum aestivum L.) was grown for 9 years with no-tillage management on an Orthic Brown Chernozem (Typic Haplobroll) with treatments involving snow management and N rate, placement and timing, was converted to a study of pre-seeding shallow (5–7.5 cm) tillage with a cultivator, versus no-tillage, by replacing the N timing treatment in the tenth year. The experiment was then continued for three more years, during which we assessed the effect of tillage on weed populations, grain yield and N content, and on soil quality. Soil quality was also assessed following one more year during which the entire study site was summerfallowed and subjected to four tillage operations. Weed populations generally were not affected by tillage or snow management treatments, but differed among N rate and placement treatments, though not in a way that could be easily interpreted. Tillage had no effect on yield or grain N content. It increased the erodible fraction of soil (dry sieving), but did not affect wet aggregate stability. Neither microbial biomass C, nor C and N mineralization were affected by the change in tillage method. We conclude that the judicious use of shallow pre-seeding tillage in an otherwise no-till cropping system can be tolerated to manage persistent grassy weed problems without deleteriously influencing soil quality, grain yield or protein.