• Biomass productivity and range condition on range sites in southern Arizona

      Frost, W. E.; Smith, E. L. (Society for Range Management, 1991-01-01)
      Range condition is usually defined by similarity of current to climax or potential vegetation. It is often assumed that rangelands in low condition are biologically less productive than those in higher condition. The objective of this study was to determine if range condition (ecological status) is related to total productivity or to forage production for livestock. Adjacent areas along fencelines representing differences in range condition were sampled in 58 locations. These comparisons represented 31 different range sites across southern Arizona. Weight by species of above-ground peak standing crop current year’s growth of vegetation was estimated using the dry-weight-rank/comparative yield methods. Range condition was rated with Soil Conservation Service range site descriptions. Species were classified as forage or non-forage to estimate forage available for cattle. In 75-85% of comparisons of good condition sites to fair condition, good to poor, and fair to poor, total current year’s standing crop did not differ significantly. Where differences were significant, productivity was not consistently more on the high condition class. Forage production, however, was more from the stand in the higher condition class in about 213 of the comparisons. We concluded that in southern Arizona rangelands in higher condition (higher seral) classes usually produce more forage for cattle than lower condition classes on the same range site. Nevertheless, it is not usually true that total biomass productivity on low condition range is less than the same range site in higher condition.
    • Blue grama response to Zn source and rates

      White, E. M. (Society for Range Management, 1991-01-01)
      Surface-applied zinc (Zn) in range with claypan soils could increase herbage production, but the Zn concentration could become toxic to the crown and roots of blue grama (Bouteloua grucilis). Metallic Zn, ZnCl2, and Zn chelate were applied in the greenhouse to the soil surface of pots with blue grama to determine the rate that would be toxic and the effect of Zn source on toxicity and herbage Zn content. Metallic Zn (dust, 30- and 40-mesh) was not toxic at rates below 0.40 g Zn kg soil-1, but Zn chelate was toxic and ZnCl2 at the 0.40 g Zn rate was toxic initially. After 2 years growth, salt was leached and herbage yields were not significantly different for different sources. Herbage Zn increased with increasing application up to about 0.9 g Zn kg-1. ZnCI2, applied to plants that were not Zn deficient, decreased growth; and half the plants died at rates of 2 g Zn kg soil-1. Herbage from the 2-gm rate had 7.4 g Zn kg-1. DTPA-extracted soil Zn increased with increasing applications but not at the same rate for different sources. Metallic Zn or ZnCl2, if applied at reasonable rates, is a satisfactory Zn source, but high rates of Zn chelate cause soil dispersion initially and should not be used on soil that disperses readily.
    • Cutting frequency and cutting height effects on rough fescue and parry oat grass yields

      Willms, W. D. (Society for Range Management, 1991-01-01)
      A study was made in the Rough Fescue Grasslands of southwestern Alberta to determine the yield response of rough fescue (Festuca scabrella var campestris Rydb.) and Parry oat grass (Danthonia parryi Scribn.) to 5 cutting frequencies and 3 heights over a 1-year period. The same plants were cut either 1, 2, 4, 8, or 16 times over a 16-week period beginning in mid-May, at 16-, 8-, 4-, 2-, or 1-week intervals, respectively, and at heights of either 5, 10, or 15 cm above ground level. Yield response to cutting treatments differed significantly from the flrst to the third treatment year. In the first year, rough fescue and Parry oat grass produced most forage when cut at a height of 5 cm with 1, 2, or 4 cuts. By the third year, rough fescue produced the greatest yields with a single cut after 16 weeks and Parry oat grass produced the greatest yields when cut at 10 or 15 cm at 1-week intervals. The data confirm the high sensitivity of rough fescue to grazing while the plant is growing and suggest that the greatest benefit from the Rough Fescue Grasslands may be derived by grazing in fall or winter. Summer grazing favors Parry oatgrass, which is more tolerant than rough fescue, but forage production on the grassland is reduced.
    • Economic evaluation of spotted knapweed [Centaurea maculosa] control using picloram

      Griffith, D.; Lacey, J. R. (Society for Range Management, 1991-01-01)
      Spotted knapweed is the most serious range weed problem in western Montana. Although picloram is often used to control knapweed, the economic feasibility of the practice has not been evaluated. We developed a model to economically evaluate spotted knapweed control on rangeland. Model functions describing the dynamics of the plant community preceding and following treatment were derived from field observations in western Montana. Economic returns per management unit were calculated for 3 scenarios: (1) no treatment, (2) containment, and (3) eradication of spotted knapweed. After tax costs and benefits of treatments were analyzed for a 20-year period and discounted to the present. An economic loss in current dollars of 2.38/ha was incurred under the no treatment strategy when 25% of the management unit was initiaily infested with spotted knapweed and the weed was spreading to new acres and replacing desirable forage. After-tax present value of added AUMs in the eradication strategy was greater than the after-tax present value of added costs, 3.41/ha and l.99/ha, respectively. As site productivity, value of an AUM, and rate of knapweed spread to new acres increased, economic returns increased relative to treatment costs. In contrast, herbicide treatment became least cost-effective as knapweed utilization by livestock increased. Thus, economic feasibility of spotted knapweed control varied with economic and biologic conditions.
    • Response of tap- and creeping-rooted alfalfas to defoliation patterns

      Gdara, A. O.; Hart, R. H.; Dean, J. G. (Society for Range Management, 1991-01-01)
      Under grazing, creeping-rooted alfalfa (Medicago sativa L.) cultivars have been reported to be more productive and have higher survival than tap-rooted cultivars. To determine if differences in persistence could be related to response to defoliation patterns, we clipped 3 tap- and 3 creeping-rooted alfalfa cultivars. Different fractions of the total number of stems were clipped to different stubble heights every 21 days. Both tap- and creeping- rooted cultivars responded similarly to defoliation. Maximum forage production was obtained when one-third of the stems on a plant were cut back to 5 cm above the ground at each harvest. The lowest forage production was obtained when all stems on a plant were cut back to 5 cm. The most lenient defoliation (one-third of the height of one-third of the stems removed at each harvest) maximized total herbage production (forage plus stubble) but only 32% of the herbage was harvested as forage, leaving 68% as unharvested stubble. Severe defoliation every 21 days decreased the concentration of total nonstructural carbohydrate in the roots and reduced total root biomass. Thirteen alfalfa cultivars responded similarly to grazing when seeded in dense stands. The greater persistence of creeping-rooted alfalfa cultivars under grazing does not appear to be a result of greater intrinsic productivity or more rapid recovery from defoliation. The lateral spread of individual creeping-rooted plants in open stands may increase the probability that some stems will escape defoliation at each grazing; these stems then contribute to rapid recovery from grazing and to plant survival.