ESTIMATED LONG-TERM SOIL MOISTURE VARIABILITY ON THE CANADIAN PRAIRIES

Abstract

Soil water contents under wheat production systems on the Canadian prairies were estimated using the Versatile Soil Moisture Budget, which was modified to include an estimated seeding date and a biometeorological time scale. Large year-to-year variability required the use of long term (60 yr) data to describe seasonal and probable occurrences of soil water contents for 27 stations. Regression and correlation analyses were used to simplify presentation of the data and to display their spatial distribution. On average, summerfallowing was most effective in conserving water in areas with intermediate spring soil water contents and on soils with a higher available water-holding capacity (AWC). In abnormally dry years (i.e., 10% probability) summerfallowing conserved more water in the wetter areas while increasing the AWCs had the greatest effect on conserved water in the intermediate areas. Soil water contents at heading were greater under wheat-fallow rotation compared to continuous wheat and increased with increasing AWCs. Water contents of less than 50% of AWC at heading occurred with a probability of 80% or higher in most areas, indicating some stress is experienced in most years. Summerfallowing lowered the probability only slightly on soils with a low AWC, but by 10–20% on the higher AWC soils. The probability of extreme water stress at heading (i.e. water contents ≤ 10% of AWC) ranged from 0% in the wettest areas to 40–60% in the driest climatic area. Key words: Soil water content, versatile soil moisture budget, summer fallowing, zonation, wheat (spring), seeding date