| V.S. Baron*, A.C. Dick, E. Mapfumo, S.S. Malhi, M.A. Naeth, and D.S. Chanasyk |
| Research scientist and research associate with Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C&E Trail, Lacombe, Alberta, Canada T4L 1W1; Post-doctoral fellow with the Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2H1; research scientist with the Melfort Experimental Farm, Agriculture and Agri-Food Canada, Box 1240, Melfort, SK, S0E 1A0; and professors with the Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2H1. * Corresponding author (Email address: BARONV@EM.AGR.CA). |
Abstract |
| 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 NO3-1-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. |
| Key Words: Ammonium, faeces, grazing intensity, macronutrient status, urine |