APBI402-2

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Background

Before the 1970s the traditional grazing system on rangelands in the southern interior of British Columbia (BC) consisted of extended periods of fall and spring grazing without any rest, which resulted in deterioration of the rangeland ecosystems. Seasonal-suitability grazing systems were consequently established in late 1970s to improve rangeland conditions. These systems employ grazing only in late spring or fall on bunchgrass rangelands at middle and higher elevations. To date, the effects of various grazing systems on vegetation changes and animal

production have been well documented, while less attention has been given to impacts of grazing on the soil.

The study site was located on the Lac du Bois Grassland Provincial Park (50°45’N and 120°25’W) northwest of Kamloops, BC. Soil of the study site is a Dark Brown Chernozem (soil series – McQueen) loam developed on glacial till. The elevation within the study site is 600-850 m above sea level. The climate is semiarid with an average annual precipitation of 270 mm (Environment Canada, 2004). Canadian climate normals 1971-2000. Kamloops airport meteorological records, http://www.climate.weatheroffice.ec.gc.ca/climate_normals/. The study sites are located within the Bunchgrass biogeoclimatic zone where dominant vegetation consists of bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) Scribn. & Smith) and big sagebrush (Artemisia tridentata Nutt.).

The long-term grazing experiment, established in 1978, consists of two pastures (replicates). Each pasture is covering an area of 65 ha. The following grazing systems are present on these two pastures:

  • fall only each year,
  • spring only each year, and
  • fall and spring (FS) the same year.

Within each grazing treatment there were two exclosures (25 x 50 m) established to prohibit livestock grazing. All grazing treatments were grazed at 0.6 animal unit months (AUM) per ha-1 (corresponding to 45-50% use of available forage)[1]. The fall and spring (FS) grazing treatment had half as many animals (cows and calves) in fall and again in spring as the other two treatments grazed only once per year. The spring grazing period was from mid-April to mid-May, while fall grazing occurred from mid-September to mid-October. Soil sampling was done 20 years after the experiment was established, i.e. in June 1998.

Learning objective for week 1

Identify and discuss the soil formation factors focusing on the soil type present on the study sites north of Kamloops, BC.

Student tasks for week 1

  1. Review background information on soil formation, and classification, focusing on the Chernozemic soil order.
  2. Share individual learning with group members (ongoing for weeks 1-4).

NOTE: Before next week’s session, your team should research any gaps in knowledge regarding the guiding questions for today’s session.

Guiding questions for week 1

  1. What are key properties of Chernozems?
  2. What soil properties are of an importance for management considerations on McQueen soil?

Key references for week 1

  1. Soils of the Ashcroft Map Area by Young, G., Fenger, M.A., and Luttmerding, H.A. 1992. (MOE technical report no. 23 / BC soil survey report no. 26). [this book is available at http://www.llbc.leg.bc.ca/public/pubdocs/bcdocs/104459/bc26_report.pdf
  2. Canadian System of Soil Classification by Agriculture Canada Expert Committee. 1998. (3rd edition) available at http://sis.agr.gc.ca/cansis/publications/manuals/1998-cssc-ed3/cssc3_manual.pdf
  3. van Ryswyk, A.L., McLean, A., and Marchand, L.S. 1966. The climate, native vegetation, and soils of some grasslands at different elevations in British Columbia. Can. J. Plant Sci. 46:35-50.
  4. Rangeland Handbook for BC by Campbell, C.W. and Bawtree A.H. 1998. BC Cattlemen’s Association, Kamloops, BC.203 p. [this book is available on 2-hour reserve in the Woodward Library]
  5. Dyanatkar, S., M. Krzic, J. Wilson, C. Crowley, N. Sidles, K. Watson, A. Bedard-Haughn, N. Basiliko, and P. Sanborn. 2013. SOILx. Virtual Soil Science Learning Resources. [www.soilx.ca]

NOTE: It might be useful that you view section on Chernozemic soils presented on the following web site http://soilweb.landfood.ubc.ca/classification/

Footnotes

  1. Knowing how much forage an animal needs is the first step in determining how many animals can be supported on the land available. The amount of forage required by one animal unit (AU) for one month is called an Animal Unit Month (AUM). One animal unit is defined as a 1,000 lb (450 kg) beef cow with or without a nursing calf with a daily requirement of 26 lb (11.8 kg) of dry matter forage. Therefore, 1 AUM is equal to 780 lb (355 kg) of dry matter forage (30 days x daily forage requirement).