• Seasonal dynamics of minerals in forages at the Texas Experimental Ranch

      Greene, L. W.; Pinchak, W. E.; Heitschmidt, R. K. (Society for Range Management, 1987-11-01)
      Range livestock derive the bulk of their dietary mineral intake from forages that are often deficient in one or more essential minerals. The objective of this study was to quantify the seasonal dynamics of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations in the dominant native forages at the Texas Experimental Ranch. Concentrations were estimated by class of tissue (live and dead) for 5 species/species groups: sideoats grama (Bouteloua curtipendula Michx.), Texas wintergrass (Stipa leucotricha Trin. and Rupr.), annual grasses, other warm-season grasses, and forbs. The study spanned a period of 2 years and included 16 sample dates. Although P, Mg, and K concentrations varied significantly among species and date, they varied primarily as a function of class of tissue. Averaged across dates and species, concentrations of P, Mg, and K in live tissue averaged 0.12, 0.13, and 2.02%, respectively, while concentrations in dead tissue averaged 0.04, 0.09, 0.57%, respectively. As a result, seasonal differences in whole plant concentrations of P, Mg, and K were closely linked to seasonal growth dynamics as they affect live/dead ratios. Ca concentrations were affected more by species than class of tissue. Averaged across dates, Ca concentrations in live tissue averaged 0.55, 0.40, 0.42, 0.35, and 1.80% in annual grasses, Texas wintergrass, sideoats grama, other warm-season grasses and forbs, respectively, while concentrations in dead tissue averaged 0.41, 0.40, 0.41, 0.36, and 0.96%, respectively. It is concluded that considerations must be given to the potential effect that a given treatment may have on plant growth dynamics to properly interpret its effect on whole plant concentrations of minerals.
    • Selective control of annual bromes in perennial grass stands

      Currie, P. O.; Volesky, J. D.; Hilken, T. O.; White, R. S. (Society for Range Management, 1987-11-01)
      Three soil-active herbicides: atrazine [6-chloro-N-ethyl]-N1-(1-methyethyl)-1,3,5-triazine-2,4-diamine]; propham (1-methylethyl phenyl carbamate); and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] were applied in the fall, postemergence to annual bromegrasses at 2 rates. These herbicides were evaluated for their efficacy in selective control of cheatgrass (Bromus tectorum L.) and Japanese brome (Bromus japonicus Thunb.) in perennial stands of crested wheatgrass (Agropyron cristatum [L.] Gaertn.), pubescent wheatgrass (Thinopyrum intermedium Host), Russian wildrye (Psathrostachys juncea [Fisch.] Nevski), and western wheatgrass (Pascopyrum smithii (Rydb.) Löve) and blue grama (Bouteloua gracilis) [H.B.K.] Lag. Ex Griffiths. Yields of annual bromegrasses and perennial grasses and crude protein (CP), phosphorus and total nonstructural carbohydrate (TNC) content of perennial grasses were measured 2 consecutive years after the single herbicide application. Yields of annual bromegrasses from the 3 herbicide treatments averaged 91 and 47% less than those of the control the first and second year posttreatment, respectively. Pronamide provided substantially better control the second year posttreatment than the other 2 herbicides. Yields of perennial grasses in the majority of the herbicide treatment-study site combinations were significantly increased the first year posttreatment (P<0.10). Crude protein of perennial grasses was increased in the atrazine treatment. Atrazine at 0.6 kg/ha was the most cost-effective herbicide for decreasing competition of annual bromegrasses and increasing yield of perennial grasses.