North Dakota State University * Dickinson Research Extension Center
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RANGE MANAGEMENT PRACTICES ADDRESSING PROBLEMS INHERENT IN THE NORTHERN GREAT PLAINS GRASSLANDS
Llewellyn L. Manske PhD Associate Range Scientist
If they are to be successful, range management practices must be developed to address the inherent problems and conditions of the geographic region in which the practices will be implemented. In the Northern Great Plains grassland ecosystem, the vegetation is characterized by three major features that have implications for animal production: 1) plant growth is limited by several environmental factors, 2) ungrazed grasses are low in nutritional quality during the later portion of the grazing season, and 3) plants grazed too early in the growing season or late in the growing season suffer negative effects. The twice-over rotation grazing system on native range with complementary domesticated grass spring and fall pastures was developed with consideration of these features and has demonstrated potential for successful implementation on the Northern Great Plains.
In this region, the most important of the environmental factors limiting plant growth (Manske 1998) are moderate annual precipitation, limited distribution of precipitation during part of the growing season, cool temperatures in the spring and fall, and hot temperatures in summer. The seasonal precipitation pattern is characterized by a period of maximum precipitation in late spring and early summer, tapering off to a moderately light amount during fall and winter. Periods with precipitation levels sufficiently low to place plants under water stress and limit growth occur frequently. Herbage production within grassland communities is also limited by temperature. The frost-free period is usually short, from 120 to 130 days. Perennial grassland plants are capable of sustaining growth for longer than the frost-free period, but they require temperatures above the level that freezes water in plant tissue and soil. Plant growth is greatly limited by low air temperatures during the early and late portions of the growing season and by high temperates, high evaporation, drying winds, and low precipitation during mid summer.
The growing season for perennial grasses covers about six months, from mid April to mid October. However, because favorable precipitation and temperature conditions occur during May, June, and July (Manske 1998), most plant growth in height is attained within this three-month period (Goetz 1963). Peak aboveground herbage biomass is usually reached during the last ten days of July. Herbage biomass of ungrazed plants increases in weight during May, June, and July; after the end of July the weight of the herbage biomass decreases because the rate of senescence (aging) of the grass leaves exceeds growth and the cell material in aboveground structures is being translocated to the belowground structures. This translocation causes a decrease in the nutritional quality of the aboveground structures. Ungrazed plants of the major upland sedges, cool-season grasses, and warm-season grasses drop below 9.6% crude protein level around mid July (Whitman et al. 1951), as they attain maximum growth in height and weight.
The nutritional quality of the native vegetation during the later portion of the grazing season is a limiting factor in animal performance. A thousand-pound lactating cow requires a crude protein level of at least 9.6% (NRC 1984). Most ruminant animals require a daily dry matter intake of about 2% (1.5-2.5%) of their body weight (Holechek et al. 1989). Cows may be able to compensate for lower quality forage for a short time by increasing intake and/or selecting plant parts higher in nutritional quality than average plant parts. However, cows on seasonlong and deferred grazing systems lose weight from early or mid August to the end of the grazing season (Manske et al. 1988). The loss of weight does not hurt the animals but does caus decreased milk production (Landblom 1989) and a subsequent reduction in the daily gain of calves (Manske 1996).
The negative effects suffered by plants on a seasonlong system with grazing begun too early include great reductions in herbage biomass production, which cause reductions in stocking rates and animal production per acre. Data from three studies indicate that if seasonlong grazing is started in mid May on native range, 45-60% of the potential peak herbage biomass will be lost and never be available for grazing livestock. If the starting date of seasonlong grazing is deferred until early or mid July, nearly all of the potential peak herbage biomass will grow and be available to the grazing livestock, but the nutritional quality of the available forage will be at or below the crude protein levels required by a lactating cow. If the starting date is deferred until after mid July, less than peak herbage biomass will be available to grazing livestock because of the senescence and translocation of cell material to belowground parts (Campbell 1952, Rogler et al. 1962, Manske 1994a), and the crude protein levels of the available forage will be insufficient to meet the nutritional requirements of a lactating cow.
The phenological growth stage of the grass plants is the best indicator of appropriate grazing starting dates. Grazing plants before the third-leaf stage causes negative effects in grass growth, while starting grazing after the third-leaf stage stimulates tiller production, a process that leads to increased aboveground herbage biomass and increased nutritional quality of available herbage. Most native cool-season grasses reach the third-leaf stage around early June, and most native warm-season grasses reach the third-leaf stage around mid June. This phenological development indicates that within each management system, starting grazing on each pasture sometime between early June and early July would produce the fewest negative effects on herbage biomass production and nutritional quality of the available forage. Seasonlong grazing management systems on native range should wait until mid June to begin grazing, but rotation grazing systems could start in early June.
Continuation of grazing late in the season can also produce detrimental effects on plants. Severe defoliation of grass plants during fall and winter reduces herbage production of the grasslands the following growing season. Late-stimulated tillers remain viable over winter and continue growth the following growing season. Cool-season species initiate tillers the previous fall and continue growth the following season. Defoliation of late-stimulated tillers and cool-season tillers during fall and winter reduces their contribution to the ecosystem the following season.
The twice-over rotation system on native range with complementary domesticated grass spring and fall pastures times grazing to maximize vegetation and animal performance. In the twice-over rotation system a spring pasture of crested wheatgrass is grazed during May. A three- or four-pasture native range rotation system is used from early June until mid October, with each pasture grazed for two periods. The first period is grazed for 15 or 11 days in each pasture of a three- or four-pasture system, respectively, during the 45-day period when grasses are between the third-leaf stage and flowering and can be stimulated to tiller (1 June to 15 July). The second period (after mid July and before mid October) is grazed for 30 or 22 days in each pasture of a three- or four-pasture system, respectively. A fall pasture of Altai wildrye is grazed with cows and calves from mid October until weaning in early or mid November and grazed by dry cows from mid November until mid or late December.
The twice-over rotation system with complementary domesticated grass pastures has a grazing season of over 7.5 months with the available forage above, at, or only slightly below the requirements for a lactating cow for nearly the entire grazing season. It requires fewer than 12 acres per cow-calf pair for the entire 7.5-month grazing season on grassland that when grazed for 6.0 months seasonlong requires 24 acres per cow-calf pair. The cow-calf weight performance on the twice-over rotation grazing system with complementary domesticated grass pastures is improved over the performance on other systems (Manske 1994b, Manske 1996).
It is possible that no range management practice can address all the problems inherent in an ecosystem, but successful practices will incorporate adjustment for the most serious problems. The twice-over rotation system with complementary domesticated grass pastures is one system that has been shown to be well adapted to the conditions of the Northern Great Plains grasslands and to produce positive results in vegetation and animal performance.
I am grateful to Amy M. Kraus for assistance in preparation of this manuscript.
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