Crop rotations and weed community dynamics on the Canadian prairies

Lengthening crop rotations and reducing the proportion of tallow are important goals for soil conservation on the Canadian prairies. Fallow is used, in part, to reduce weed populations. Producers reducing or eliminating fallow may be concerned about increased weed problems. A number of long-term crop rotation experiments have been conducted throughout the Canadian prairies to determine sustainable rotations for different ecoregions. Many of these included fallow. In the experiments reported here, weed communities under continuous cropping differed slightly in composition from rotations that included fallow. Longer rotations that included hay had slightly different weed communities than shorter rotations without hay. The differences among rotations were small, and were not detectable in many years. Changes in weed communities should not discourage farmers from reducing fallow or lengthening rotations throughout the Canadian prairies.