• Grazing impacts on soil nitrogen and phosphorus under Parkland pastures

      Baron, V. S.; Dick, A. C.; Mapfumo, E.; Malhi, S. S.; Naeth, M. A.; Chanasyk, D. S. (Society for Range Management, 2001-11-01)
      Because intensive grazing is new to the humid western Canadian parkland (prairies), there is little information available about its effects on soil N and P status. This study addressed the question of grazing intensity and pasture species effects on soil macronutrient status in a Typic Haplustoll at Lacombe, Alberta. Paddocks of smooth bromegrass (Bromus inermis Leyss.), meadow bromegrass (Bromus riparius Rhem.), and winter triticale (X Triticosecale Wittmack.), replicated 4 times, were subjected to 3 grazing intensities (heavy, medium, and light as defined by frequency and severity of defoliation) using yearling beef heifers. Nitrogen (N), P and K fertilisers were broadcast annually at 100, 22 and 42 kg ha(-1) during production years. The experiment was maintained on the same paddocks for 4 years. In the establishment year and in the third and fourth production years, soil samples were taken randomly from each paddock to a depth of 60 cm. Concentrations of nitrate-N (NO3-N), ammonium-N (NH4-N), mineral-N (the sum of NO3-N and NH4-N), total Kjeldahl-N, and extractable-P were determined in the 0-15, 15-30, 30-60, and 0-60-cm depths. Nitrate-N concentration was (1.7 to 2.4 times) greater for heavy than light grazed treatments for each soil depth increment and the amount of NO3-N in the 0-60 cm depth was 2.2 times greater than light paddocks. More NO3-N was measured under perennials than triticale (22.2 vs 13.6 mg kg(-1), respectively) at the 30-60-cm depth. Ammonium-N amount (0-60 cm) was greater in meadow bromegrass (30 kg ha(-1)) than in triticale (25 kg ha(-1)), but not smooth bromegrass paddocks for the 0-15-cm depth. Extractable-P concentration was greater in the 0-15-cm depth of heavy (154 mg kg(-1)) than in medium (138 mg kg(-1)) or light-grazed (127 mg kg(-1)) paddocks and was higher under meadow bromegrass than under triticale. Given the large amounts of NO3-N in the heavy paddocks, there is potential for loss through both leaching and denitrification. Differences among treatments for NH4-N, and P concentrations are not of particular concern environmentally, but are important from a fertility management point of view.
    • Long-term plant community development as influenced by revegetation techniques

      Newman, G. J.; Redente, E. F. (Society for Range Management, 2001-11-01)
      A revegetation techniques study was initiated during the fall of 1976 in northwestern Colorado in a disturbed sagebrush (Artemisia tridentata Nutt.) community. The study included 2 irrigation treatments, three seed mixtures, 2 seeding techniques, and 2 fertilization treatments. Short-term results were published and conclusions were made regarding the initial success of each treatment. The objective of the current study was to determine the effects of each treatment on plant community production, species composition, and species diversity after 20 years of plant community development. Among irrigated plots, the native seed mixture produced greater aboveground biomass compared to an introduced mixture and a mixture of both native and introduced species (combination seed mixture). The native seed mixture also resulted in greater total species richness than the introduced mixture when averaging over all other treatments. Altered seeding rate ratios among life forms as well as altered seeding methods (drill versus broadcast seeding) did not significantly alter plant community development after 20 years. However, a single application of nitrogen and phosphorus significantly increased grass production on plots seeded to the combination seed mixture. All revegetation plots have remained grass-dominated. However, shrub biomass was greater in the native and combination mixtures than in the introduced mixture under initial irrigated conditions in part due to successful establishment and growth of four-wing saltbush (Atriplex canescens Pursh Nutt.). Thus, the seed mixtures evaluated in this study have resulted in distinctly different plant communities and demonstrate that such initial treatments can influence long-term plant community development on severely disturbed rangelands. Broadcast seeding a native seed mixture that has been irrigated for 2 growing seasons without fertilization appears to be an effective long-term combination of cultural revegetation practices.