Effect of Forty-Four Years of Grazing on Fescue Grassland Soils

Abstract

A grazing study was initiated in the foothills of southwestern Alberta on the rough fescue grasslands (Festuca campestris (Rydb.) in 1949 comparing various grazing intensities. In 1992, soil samples were obtained 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 exclosure (control). The thickness of the Ah horizon of the control averaged 22 cm while that of the lightly, heavily and very heavily grazed paddocks averaged 18, 12, and 8 cm, respectively. Soil color changed from 10YR 2/1 (black) to 10YR 4/3 (dark brown to brown) in response to very heavy grazing. Grazing pressures decreased the mean-weight diameter of water-stable aggregates, total C and P, monosaccharide content and the galactose + mannose/xylose + arabinose ratio, while it increased bulk density, pH-CaCl2, and total N. The loss of P must be viewed with concern. Treatment effects on most soil parameters were most pronounced at the two heavier grazing pressures. Particularly, the heavy grazing pressure jeopardized the sustainability of the ecosystem by reducing fertility and water-holding capacity.