A comparison of the effects of 20 and 30 years of grazing on grassland soil properties in southern British Columbia

Although numerous studies have been conducted on rangeland soil quality in Alberta, Manitoba, Saskatchewan, as well as in the Great Plains, there has been little documentation of the response of soil properties to time of grazing and stocking rate treatments for the grasslands of the southern interior of BC. In the Lac Du Bois range in Kamloops, BC, the current moderate stocking rate of 2 AUM ha⁻¹ was based on a desired available forage use of 50%. Livestock is moved up and down an elevation and productivity gradient over the grazing season so that pastures located midway up the gradient are grazed either in the spring or fall. The objectives of this study were to determine (1) the effects of spring and fall grazing treatments on selected soil properties after periods of 20 and 30 years and (2) the effects of 0 and 2 AUM ha⁻¹ grazing rates on selected soil properties after periods of 20 and 30 years. The spring grazing treatment led to greater soil bulk density, mechanical resistance, pH, as well as lower polysaccharides and CEC relative to the fall grazing treatment. The grazing rate of 2 AUM ha⁻¹ led to greater soil mechanical resistance and pH, as well as lower soil polysaccharides and LOMF relative to the ungrazed control. After 30 years of grazing, soil bulk density was greater in the 0-7.5-cm depth under the 2 AUM ha⁻¹ treatment relative to the ungrazed exclosure in spring-grazed but not in fall-grazed areas, indicating that this stocking rate, when used for spring grazing, has led to soil compaction. Rangeland managers in the southern interior of BC should consider adjustments of time of grazing and stocking rate recommendations when these have been solely on vegetation responses, and should consider including soil properties in rangeland health assessments.Land and Food Systems, Faculty ofGraduat