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The effect of clipping date and height on forage yields, nutritive quality and stored food reserves of a Chilcotin wetland meadow Heyes, Glenn E.

Abstract

The objectives of the following research project were to 1) determine the optimum time and intensity of harvesting a wetland meadow in terms of forage yield, forage nutritive quality, and plant vigor; 2) to determine the carrying capacity of a wetland meadow under different seasons of use and; 3) to contribute to the development of a wetland classification scheme by characterizing a wetland meadow. The study site was located on the Fraser Plateau about 100 kms west of Williams Lake, British Columbia, at an elevation of 1250 m. Meadow water table, water pH, water conductivity, water calcium ion concentration, and soil temperatures were measured twice per month. The meadow and surrounding upland soils were classified. The species composition and foliar cover of 5 vegetation zones were described for the meadow and surrounding upland area. To asses meadow productivity and forage nutritive quality under different seasons of use 6 harvesting periods were employed, mid May to mid July, June and July, mid June to mid August, July and August and mid May through August. The standing crop seasonal trend was monitored by analysing forage samples collected twice monthly. Clipping samples were oven dried and weighed to determine harvest yields. The crude protein content of the samples was determined by a microkjeldhal technique. Phosphorus content was assessed by a vanadomolybdate method. Calcium, potassium, magnesium, zinc, copper, iron and manganese contents were determined by spectrophotometry. The relative plant stored food reserves were assessed by an etiolation experiment. Soil - vegetation plugs were collected from all harvest period treatment plots as well as undipped control plots and placed in a dark controlled environment chamber. The etiolated growth was collected, weighed and used to compare the relative plant stored food reserves among different harvest period treatments. A stepwise simple regression procedure was used to compare the seasonal trend data and a stepwise multiple regression procedure was used to compare the different harvest period treatments. A 2 step Student Newman Keuls multiple range test was performed on the etiolation experiment sod reserve indices and harvest treatment total yields data. Meadow water table, water pH, water calcium ion content, water conductivity, soil temperatures at 10 cm and soil temperatures at 50 cm ranged between +29 and -2 cm, 7.0 and 7.4, 14 and 89 ppm, 249 and 840 mmho/cm, 6.9 and 11.2°C and 6.8 and 10.6°C respectively. Meadow soils included a Typic Humisol - Mesic Humisol - Terric Mesic Humisol complex, a calcareous Gleyed Humic Regosol, a calcareous Gleyed Regosol, an Orthic Humic Gleysol and a Gleyed Gray Luvisol. The upland soil was an Orthic Gray Luvisol. The 5 vegetation zones were named according to the dominant plant species. Included were a Carex rostrata zone, a Carex - Betula glandulosa zone, a Carex praegracilis - Juncus balticus zone, a Salix - Betula glandulosa zone, arid a Pinus contorta - Calamagrostis rubescens zone. Productivity and nutritional data collection was restricted to the Carex rostrata zone. The standing crop varied from 1 to 6 mt/ha. The nutrient content of the standing crop varied between 0.35 and 0.51% of tissue, 2.1 - 5.7, 1.0 - 1.5% of tissue, 0.17 - 0.26% of tissue, 133 - 326 ppm, and 49 and 165 ppm for the calcium, calcium - phosphorus ratio, potassium, magnesium, manganese and iron contents respectively. The meadow forage crude protein, phosphorus, zinc and copper contents remained un- changed at 10.1% of tissue, 0.14% of tissue, 30 ppm and 11 ppm through the season. The 8 cm July and August harvest period produced the greatest treatment yield, 6807 kg/ha, followed by the 8 cm - mid June to mid August harvest treatment yield. The least productive treatments were the 8 and 23 cm harvests during the period mid May to mid August. The nutrient content of the meadow forage subjected to the 10 different harvest treatments varied as follows: crude protein - 8.3 to 12.0% of tissue, calcium - 0.368 to 0.646% of tissue, phosphorus - 0.21 to 0.27% of tissue, calcium: phosphorus ratio - 1.4 to 3.6, zinc - 35 to 46 ppm, copper - 13 ppm, potassium - 1.7 to 2.4% of tissue, magnesium-0.19 to 0.23% of tissue, manganese - 194 to 271 ppm and iron - 94 to 119 ppm. Repeated clipping increased the meadow forage crude protein, phosphorus, zinc, copper, potassium, manganese slightly, and iron contents. Repeated clipping reduced the meadow forage calcium: phosphorus ratio. The stored food reserves of the meadow vegetation was found not to vary with harvest treatment. Based on productivity, nutritive quality and plant vigot data, grazing during the period mid June to mid August and close utilization (an 8 cm as opposed to a 23 cm stubble height) appears most appropriate. Wet meadow hay should be cut as early as possible. The theoretical safe maximum carrying capacity is 23 AUM'S/ha (20 AUM'S/ ha when grazed to an 8 cm stubble height during the period mid June to mid August). The meadow characterization and productivity data will be useful to person(s) undertaking the task of formulating a classification scheme for British Columbia wetland meadows.

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