EFFECT OF 44 YEARS OF GRAZING ON FESCUE GRASSLAND SOILS

A grazing study was initiated in the foothills of southwestern Alberta on the rough fescue grasslands (Festuca campestris (Rydb.) in 1949 co mparing various grazing intensities. In 1992, soil samples were obtain ed from the Ah horizon of paddocks grazed at 1.2 (light), 2.4 (heavy), and 4.8 (very heavy) animal unit month ha(-1) and from an ungrazed ex closure (control). The thickness of the Ah horizon of the control aver aged 22 cm while that of the lightly, heavily and very heavily grazed paddocks averaged 18, 12, and 8 cm, respectively. Soil color changed f rom 10YR 2/1 (black) to 10YR 4/3 (dark brown to brown) in response to very heavy grazing. Grazing pressures decreased the mean-weight diamet er of water-stable aggregates, total C and P, monosaccharide content a nd the galactose + mannose/xylose + arabinose ratio, while it increase d bulk density, pH-CaCl2, and total N. The loss of P must be viewed wi th concern. Treatment effects on most soil parameters were most pronou nced at the two heavier grazing pressures. Particularly, the heavy gra zing pressure jeopardized the sustainability of the ecosystem by reduc ing fertility and water-holding capacity.