Effect of cropping frequency on C storage in Canadian prairie soils
Available water is the main constraint to crop production on the Canadian prairies. Summerfallow has been used to counter this problem, but frequent summerfallowing promotes soil organic matter (SOC) loss. Although summerfallow use has decreased substantially over the past 20 years, there is still considerable land devoted to this practice each year. This paper reviews research literature and assesses the influence of cropping frequency on SOC and discusses how this is influenced by ecoregion, tillage, fertility, and crop type. Results from 17 studies in the Canadian prairies were analyzed. In most soils, SOC increased with cropping frequency, but this relationship was not linear. In semiarid regions, SOC gains under no-till management were about 250 kg ha-1 yr-1 greater than for tilled systems at any specified cropping frequency; in subhumid environments, this advantage ranged from 50 kg ha-1 yr-1 for fallowcrop- crop rotations to 250 kg ha-1 yr-1 for continuously cropped rotations. In tilled systems, SOC gains were unaffected by soil zone. SOC gains in wheat-lentil rotations were similar to those in continuous wheat, but when low yielding flax replaced wheat in the rotation, SOC gains were substantially lower. Replacing wheat with fall rye increased SOC gains significantly, because of greater N efficiency and erosion control with the latter. Cropping frequency had no effect on SOC gains in unfertilized systems, but in systems fertilized according to soil tests, SOC gains were directly proportional to cropping frequency (except in the high SOC thick Black Chernozems such as at Melfort).
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