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.
Rangeland Ecology & Management / Journal of Range Management Archives
Publication Year: 
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.DOI:10.2458/azu_jrm_v54i6_baron
Document Type: 
Journal Issue/Article
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Rangeland Ecology & Management (formerly the Journal of Range Management) serves as a forum for the presentation and discussion of facts, ideas, and philosophies pertaining to the study, management, ecology, and use of rangelands and their resources. The journal is peer-reviewed and provides international exchange of scholarly research and information among persons interested in rangelands. The Global Rangelands collection includes REM content up to 5 years from the current year. More recent content is available by subscription from BioOne and the Society for Range Management, and may be available at your local university library.
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