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 s eeding coupled with more frequent cropping, facilitated by the greater use of snow management to increase stored soil water. Although no-til l 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 we ed problems could introduce pre-seeding tillage for a few years to mor e economically control perennial weeds, without adversely affecting gr ain yield and quality, and soil quality. An experiment in which spring wheat (Triticum aestivum L.) was grown for 9 years with no-tillage ma nagement on an Orthic Brown Chernozem (Typic Haplobroll) with treatmen ts involving snow management and N rate, placement and timing, was con verted to a study of pre-seeding shallow (5-7.5 cm) tillage with a cul tivator, versus no-tillage, by replacing the N timing treatment in the tenth year. The experiment was then continued for three more years, d uring which we assessed the effect of tillage on weed populations, gra in yield and N content, and on soil quality. Soil quality was also ass essed following one more year during which the entire study site was s ummerfallowed and subjected to four tillage operations. Weed populatio ns generally were not affected by tillage or snow management treatment s, 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 si eving), but did not affect wet aggregate stability. Neither microbial biomass C, nor C and N mineralization were affected by the change in t illage method. We conclude that the judicious use of shallow pre-seedi ng tillage in an otherwise no-till cropping system can be tolerated to manage persistent grassy weed problems without deleteriously influenc ing soil quality, grain yield or protein. (C) 1998 Elsevier Science B. V. All rights reserved.