Impact of grazing native prairie on soil and plant nutrients in southwestern Saskatchewan

A reduction in the sage grouse population could be a result of the export of nutrients from the long term grazing management that has been in place in grassland ecosystems such as southwestern Saskatchewan for the past century. The objective of this study was to measure the supply rates of nitrogen and phosphorus in the soils and their content in the sage plants and determine what impact grazing has had on nutrient availability. Plant and soil samples were taken from five side-by-side normally grazed and ungrazed for ~20 years, native grassland sites in southwestern Saskatchewan and analyzed for nitrogen, phosphorus and selected micronutrients. PRS™-probes were buried in situ for 21 days to measure soil supply rates of nitrogen and phosphorus. Sage plants and grasses were collected and analyzed for nutrient content. At four (Butte Creek Upland and Low Sage; Frenchman Mid and Low slope) of the five sites, grazing had relatively minor, non-statistically significant effects on soil and plant nutrients. At the Consul site, a site that may be considered a drier site of poorer inherent fertility, grazing significantly reduced soil and plant P. Introduction of beef cattle into the pasture in the spring significantly increased supply rates of available N, likely due to fresh addition of N as fecal material and urine. Plant analysis revealed that calcium levels were significantly higher in the ungrazed Butte Creek low-sage and potassium levels were significantly higher in the ungrazed sage at Frenchman low slope and Consul sites. Overall, well managed grazed pastures located on good quality soils do not appear to be at risk of nutrient depletion. Cessation of grazing for ~20 years did not cause major differences in nutrient amounts and supplies compared to normally grazed pastures.