THE LONG-TERM EFFECTS OF FERTILIZER APPLICATION AND THREE ROTATIONS ON WEED COMMUNITIES IN WHEAT (AFTER 21–22 YEARS AT INDIAN HEAD, SASKATCHEWAN)

Abstract

The effect of fertilizer application and three rotations (continuous cropping, fallow-wheat, and fallow-wheat-wheat rotations) on the species composition of the weed community was examined using rotations that had been running for 21–22 yr at Indian Head, Saskatchewan. Before spring seeding, stinkweed and lamb’s-quarters were more abundant on wheat after fallow than they were on either wheat following wheat after fallow or on continuous cropping. After seeding, continuous cropping produced the largest weed densities of green foxtail, thyme-leaved spurge, and vetch. In most instances, Canada thistle was most abundant on continuously cropped and nonfertilized plots. After spring seeding, green foxtail was the only species with a larger density on fertilized plots. Interactions between fertilizer application and rotation, and among species, influenced species composition in the weed community. Fertilizer application tended to reduce community differences between continuous cropping and short-term wheat-fallow rotations. Allelopathic effects of Canada thistle may have reduced green foxtail and redroot pigweed densities. With the use of 2-or 3-yr wheat-fallow rotations and herbicide application, weed problems can be minimized in southeastern Saskatchewan.