AGRONOMIC EVALUATION OF MINIMUM TILLAGE SYSTEMS FOR SUMMER FALLOW IN SOUTHERN ALBERTA

Eight summer-fallow methods for spring wheat production were compared in terms of weed control, crop residue conservation, soil erodibility, moisture conservation, NO 3 -N of the soil, and wheat yield on a clay loam soil from 1968 to 1976. Repeated applications of herbicides were as effective as tillage for controlling weeds during the summer-fallow season. Crop residue and soil moisture conservation were greatest when weeds were controlled with herbicides instead of tillage. Chemical fallows conserved 67% of the original crop residue compared with 43% of bladed fallows. Wheat yields from treatments involving little or no tillage during the fallow season were consistently greater than those from conventionally tilled treatments. The chemical fallow treatment with one tillage operation in the fall of the fallow season generally produced the highest yields. Although differences were small, there was some evidence, in terms of soil NO 3 -N levels and protein content of wheat, that wheat grown on chemical fallow may require additional nitrogen to improve moisture utilization and give maximum yields.