Soil water regimes of annual and perennial forages during drought years in the Aspen Parkland ecoregion of Alberta

Periodic and prolonged drought can be devastating to pasture production, which increases the financial risk for grazing enterprises. A study was conducted during 2 drought years (2002 and 2003) in the aspen parkland at Lacombe, Alberta, Canada, to compare the soil water regime of meadow bromegrass (Bromus riparius Rhein.), alfalfa (Medicago sativa L.), and annual [oat (Avena sativa L.) and winter triticale (X Triticosecale Wittmack)] pastures with a naturalized, old grass pasture consisting of quackgrass (Elytrigia repens L.), smooth bromegrass (Bromus inermis Leyss.), and Kentucky bluegrass (Poa partensis L.). The pasture soil was an Orthic Black Chernozem of fine sandy loam to loam texture. Soil water measurements were conducted between May and October over 2 yr using a neutron scattering hydroprobe to a depth of 1.6 m. Annual and meadow bromegrass had similar and highest cumulative and volumetric water contents and old grass had the lowest. All pastures tended to use all water available by the end of the season, but annual pasture had higher soil water in spring and early summer due to delayed canopy development. Soil in the upper 40 cm of annual and meadow bromegrass pastures was at wilting point 5 to 10% of all measurement times compared with 65 to 71% of measurement times for alfalfa and old grass. Annual and meadow bromegrass pastures did not extract water below 1.2 m, while the other pastures did, and on the basis of soil water regimes, appear to be lower risk options than status quo old grass and alfalfa pastures during drought.