The decline of summerfallow on the Canadian Prairies

The largest and most economically and environmentally significant change in agricultural land use in the Canadian Prairies during the past quarter-century has been the decline of summerfallow. To understand the geographical patterns of this decline, the reasons why fallow became so widespread and important in the Prairies are examined. Moisture accumulation, nitrogen release, weed control, the proportion of cropland sown to wheat, and marketing controls appear to be the main factors, although they vary in relative importance throughout the region. Geographical patterns of decline since 1971 are largely accounted for by increasing use of manufactured fertilizers and herbicides, expanding markets, and a growing awareness of the disadvantages of fallowing. Overall, the patterns of fallow have become more closely aligned with soil moisture zones.