SPECIES, HERBICIDE AND TILLAGE EFFECTS ON SURFACE CROP RESIDUE COVER DURING FALLOW

Fallow continues to be a common agronomic practice on the Canadian pra iries but it has been associated with increased soil erosion. Risk of fallow erosion can be reduced by maintaining adequate levels of crop r esidue on the soil surface. Field experiments were conducted at Lethbr idge, Alberta from 1991 to 1993 to determine if commonly grown prairie crops differ in their rates of crop residue degradation during fallow and to assess the effect of herbicides and wide-blade tillage on loss of crop residues. The ranking of crop residue losses during fallow wa s lentil > canola > rye > barley > wheat > flax. High N content in res idues usually increased the rate of biomass loss. max straw, perhaps b ecause of its high lignin content, did not follow this pattern and was the most persistent of all crop residues. Up to three applications of the herbicides, glyphosate, paraquat, and 2,4-D, at recommended rates did not alter field degradation of any of these crops. These herbicid es maintained greater amounts of anchored and total surface crop resid ues than wide-blade tillage during both fallow seasons. Results are di scussed in terms of crops grown before fallow, weed control during fal low, and maintenance of sufficient surface plant residues to reduce th e risk of soil erosion.