Productivity and Carbon Sequestration Potential of Re-Established Native Grassland in Canadian Prairie Following Grazing

Canadian native grasslands are recognized for providing high quality forage for grazing livestock and wildlife. The objective of the study was to determine changes in pasture productivity and soil organic carbon (SOC) level as affected by type of forage pasture mix and grazing management. In 2001, pasture was established on 32 ha of land (16 paddocks of 2.1 ha) that was cropped since the 1920`s. Treatments consisted of a completely randomized experimental design with two replicates: two pasture mixes (simple and diverse, with 7 and 12 species, respectively) and two grazing systems (continuous and deferred rotational grazing). Between 2005 and 2014, pasture was stocked with commercial yearling Angus steers (Bos taurus, 354 ± 13 kg) to an average stocking rate of 0.8 and 1.9 animal unit (AU) ha^-1 for continuous and deferred rotational grazing, respectively. All pastures were grazed to an average utilization rate of 50 to 60%. Body weight was measured at the beginning and end of the grazing season. Available pasture yield was estimated by taking ten representative 0.25 m² quadrat samples. Soil samples (at two depths: 0-15 and 15-30 cm) were collected in the fall of 2000, 2004, 2008, 2011 and 2014. Data were analyzed using the mixed procedure of SAS and differences are discussed at P ≤ 0.05. Above ground biomass and available pasture yield between simple and diverse pastures showed no difference but were varied among the experimental year (P < 0.001). Available pasture was greater (P < 0.01) for rotational (1328 kg/ha) relative to continuous grazing (855 kg/ha) which increased the number of grazing days per ha by 9% over the continuous grazing system (57 days/ha, P = 0.04). Conversely, average daily gain was 18% higher (P = 0.02) for continuous grazing than rotational grazing (0.88 kg/d), likely related to higher organic matter digestibility and digestible energy of pasture under continuous grazing. Total live weight production per ha was slightly higher for the diverse pasture mix. Over the ten years of production, average SOC level was 5% (0-30 cm) and 9% (0-15 cm) higher for complex pasture on continuous grazing than deferred rotational grazing (P < 0.01). Furthermore, SOC level was affected by year (P < 0.0001) which was expected with the different environmental conditions experienced among the different soil sampling years. Overall, our study indicated that pasture diversity with grazing management affected productivity and SOC level of grazing lands.