• SMART: a Simple Model to Assess Range Technology

      Hart, R. H. (Society for Range Management, 1989-09-01)
      A model, more detailed than a set of stocking rate response curves but less detailed than large process models such as SPUR, was needed to evaluate the short-term effect of grazing management practices on range herbage growth and livestock production. SMART (Simple Model to Assess Range Technology) simulates the effects of stocking rate and rotation on herbage production and steer performance. Herbage growth rate is a quadratic function of herbage biomass and is adjusted for seasonal differences. Herbage intake increases with herbage biomass and digestibility and animal weight. Animal gain increases logarithmically with digestible dry matter intake and decreases with animal weight. Output of these simulations confirms that early removal of steers from pasture in autumn will increase net returns, and that short-duration rotation grazing will produce little increase in gains or returns over those achieved under season-long grazing. Development of the SMART model revealed deficiencies in our understanding of the factors controlling herbage intake.
    • Technical Notes: A pocket computer program for collecting forage selection frequency data in the field

      Cincotta, R. P. (Society for Range Management, 1989-09-01)
      An algorithm was developed to conduct bite-count sampling employing a programmable pocket computer. The BASIC program was successfully employed to collect forage selection data on rangeland livestock at a remote field site in Tibet. The program features techniques that are applicable to developing programs for sustained frequency data collection using similar battery-powered computers. Pocket computers have been demonstrated to be powerful field tools, and their potential promise to increase as new units become available with larger memories and added features.
    • The effect of cattle grazing on the growth and miserotoxin content of Columbia milkvetch

      Quinton, D. A.; Majak, W.; Hall, J. W. (Society for Range Management, 1989-09-01)
      The growth and miserotoxin content of Columbia milkvetch (Astragalus miser Dougl. var. serotinus (Gray) Barneby) were examined following grazing of early growth by cows at a grassland site in southern British Columbia. Grazing behavior and forage consumption of cows were observed. Growth of Columbia milkvetch was determined by measuring the freeze-dried weight of each plant and miserotoxin levels were determined by a rapid screening method. Cows had a tendency to either avoid Columbia milkvetch or to consume it incidentally with other forage so long as there was adequate grass available. As grass became scarce the use of Columbia milkvetch increased. After being grazed, the rate of growth and the toxicity of Columbia milkvetch were substantially reduced. In comparison to ungrazed plants, the aboveground biomass of grazed plants was reduced by more than 50% and the average miserotoxin content per plant was reduced by more than 75% during a 6-week period of regrowth. While early grazing may reduce the potential hazard of Columbia milkvetch to livestock, the plant is not a preferred species and may not be consumed by cattle until other forage becomes scarce. Heavy grazing intensity may, in turn, result in low vigor of bunchgrasses and a deterioration of range condition which may result in more weeds in the plant community. Clearly these aspects of management require further study.
    • Toxicological investigations on Toano, Wasatch, and stinking milkvetches

      Williams, M. C. (Society for Range Management, 1989-09-01)
      Toano milkvetch (Astragalus toanus Jones) synthesizes the beta-D-glucoside of 3-nitro-1-propanol (miserotoxin), a highly toxic aliphatic nitro compound, and also accumulates toxic levels of selenium. The toxicity of Toano milkvetch to 1-week-old chicks was compared with Wasatch milkvetch [Astragalus miser var. oblongifolius (Rydb.) Cronq.], which contains only miserotoxin but does not accumulate selenium; stinking milkvetch (Astragalus praelongus Sheld.), which accumulates selenium but does not contain miserotoxin; and a combination of Wasatch milkvetch and stinking milkvetch. The LD50 for chicks fed Toano milkvetch was 67.8 mg NO2/kg plus 2.7 mg Se/kg of body weight. The LD50 for Wasatch milkvetch was 105 mg NO2/kg and for stinking milkvetch 5.9 mg Se/kg. The LD50s of a combination of Wasatch milkvetch and stinking milkvetch were 66.1 mg NO2/kg and 2.7 mg Se/kg. When miserotoxin and selenium were fed together, either in Toano milkvetch or the Wasatch-stinking milkvetch combination, the LD50 for each compound was significantly lower than when they were fed separately. If seleniferous and nitro-bearing species grow sympatrically, livestock might be poisoned at lower concentrations of the individual toxic compounds if they grazed both species.
    • Viewpoint: Do your digits betray you or does rounding raises your reputation?

      Wheeler, J. L.; Prasetyo, L. H.; Davies, H. I. (Society for Range Management, 1989-09-01)
    • Winter forb control for increased grass yield on sandy rangeland

      Dahl, B. E.; Mosley, J. C.; Cotter, P. F.; Dickerson, R. L. (Society for Range Management, 1989-09-01)
      Four separate studies evaluated several herbicides for reducing competition from overwintering weeds on sandy rangeland in west Texas. Air temperature was 10 degrees C with soil moisture adequate for plant growth at herbicide application (0.28 kg ae/ha) on 14 March 1985. Trichlopyr ([3,5,6-trichloro-2-pyridinyl)oxy]acetic acid); 2,4-D [(2,4-dichlorophenoxy)acetic acid]; and dicamba (3,6-dichloro-2-methoxybenzoic acid) plus 2,4-D were ineffective, while picloram 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid); picloram plus 2,4-D; and dicamba alone adequately controlled western ragweed (Ambrosia psilostachya DC.), the major targeted weed. These treatments were repeated on 4 April 1986 when air temperature was 24 degrees C but with dry surface soils. Results were similar to those of 1985, except trichlopyr also controlled western ragweed under the warmer temperature. In another study, various rates of picloram and trichlopyr aerially applied 5 April 1986 showed that 0.07 kg ae/ha of picloram or 0.28 kg ae/ha of trichlopyr reduced (P < 0.05) western ragweed with a corresponding increase in grass production. Picloram more effectively controlled targeted forbs while trichlopyr suppressed sand shinnery oak (Quercus havardii Rydb.) more effectively. Two companion studies also evaluated picloram and picloram plus 2,4-D. In one study 0.28 kg ae/ha of picloram was applied to sand shinnery oak range on 11 March 1985. Grass yield increased from 359 kg/ha in untreated plots to 1,222 kg/ha in treated plots. Grass yield in treated areas remained greater (P < 0.05) for 3 growing seasons post-treatment. Sand shinnery oak plants at the bud burst stage were top-killed by picloram. On 14 March 1985 picloram (0.056 kg ae/ha) plus 2,4-D (0.224 kg ae/ha) was applied to sand shinnery oak rangeland. This treatment reduced forb production with a corresponding increase in grass production the year of application (P < 0.05), but effects did not persist into the second growing season. Picloram plus 2,4-D did not suppress sand shinnery oak.