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

Abstract

. 2007. Soil water regimes of annual and perennial forages during drought years in the Aspen Parkland ecoregion of Alberta. Can. J. Soil Sci. 87: 523-533. 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 Rhem.), 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. ). Les pâturages s'étaient établis sur un tchernoziom noir orthique dont la texture allait du loam au loam sablonneux fin. Les auteurs ont déterminé la concentration d'eau de mai à octobre grâce à une sonde à dispersion des neutrons jusqu'à une profondeur de 1,6 m, les deux années. Les pâturages annuels et ceux de brome présentent la même concentration cumulative et volumétrique d'eau, la plus élevée aussi, comparativement aux anciennes graminées, qui présentaient la teneur la plus faible. Les pâturages ont tous tendance à utiliser la totalité de l'eau disponible avant la fin de la péri-ode végétative, mais les pâturages annuels avaient plus d'eau au printemps et au début de l'été en raison du développement plus tardif du feuillage. Les 40 premiers centimètres de sol des pâturages annuels et de brome des prés se situaient à 5 à 10 % du point de flétrissement à tous les relevés, contre 65 à 71 % pour la luzerne et les anciennes graminées. Les pâturages annuels et ceux de brome des prés ne tirent pas l'eau du sol au-delà de 1,2 m contrairement aux autres types de pâturages. Compte tenu du régime hydrique du sol, ils semblent donc constituer une solution moins risquée que les graminées rendues à l'état sauvage ou les prés de luzerne lors d'une sécheresse.

Effects of resting perennial pastures during the sensitive pre-dormancy period in western Manitoba: Pasture productivity and beef cattle performance

“…This period across western Canada could be as early as Aug. 01 in northern and central Alberta (McKenzie and McLean 1980) to Aug. 23 in south-central Manitoba (Friesen 2006). As perennial pastures begin using soil moisture as soon as green-up occurs in the spring (Twerdoff et al 1999), they frequently have utilized almost all-available soil moisture by late summer (Twerdoff et al 1999;Bradshaw 2007). In addition to the decreasing soil water, air temperatures in the southern prairies during the JulyÁ August period can exceed 308C, which exacerbates slow growth resulting in early dormancy of cool-season grasses (Frank et al 1996;Baron and Belanger 2007).…”