• Understory Herbage Production of Major Soils within the Black Hills of South Dakota

      Bennett, D. L.; Lemme, G. D.; Evenson, P. D. (Society for Range Management, 1987-03-01)
      Two-year understory production was determined on 6 major forest soils across 2 geomorphic regions in the Black Hills of South Dakota. Stepwise multiple regression was used to determine those variables best explaining yield variability. Canopy cover, basal area, soils, May-June precipitation, and soil × cover interactions further improved the models, which accounted for 65 to 76% of the variability in herbage production. Footslope, nonskeletal soils had the highest herbage production (yielding 1,800 kg/ha at 0% canopy cover). The least developed, backslope, skeletal soil had the lowest herbage production (producing only 550 kg/ha at 0% canopy cover) from comparable areas of the Black Hills. Developed models can be used in conjunction with soil survey reports to estimate the forage potential of a given soil mapping unit. Results from this study emphasize the importance of considering the understory vegetation production potential of individual soil series when developing grazable woodland management plans. Soil-related production differences were most strongly expressed under conditions of limited overstory canopy cover.
    • Using Leaf Fluorescence for Evaluating Atrazine Tolerance of Three Perennial Warm-Season Grasses

      Bahler, C. C.; Moser, L. E.; Vogel, K. P. (Society for Range Management, 1987-03-01)
      Atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] blocks photosynthetic electron transport in susceptible plants. The energy from the interrupted electron transport is fluoresced from the leaves of atrazine-treated plants. The purpose of this study was to evaluate leaf fluorescence as a nondestructive bioassay of the relative atrazine tolerance of 3 perennial, warm-season grasses. Leaf section of switchgrass [Panicum virgatum L.] (high tolerance), indiangrass [Sorghastrum nutans (L.) Nash] (intermediate tolerance), and sideoats grama [Bouteloua curtipendula (Michx.) Torr.] (lower tolerance) were placed in distilled water for 20 min and then in atrazine solutions. Fluorescence readings were taken prior to and after the atrazine treatment with a portable fluorometer. The difference between the 2 readings provided a reliable measure with low variability of the relative atrazine tolerance of the grasses studied and was effective on greenhouse-and field-grown plants. Optimum atrazine concentrations and incubation periods were 10^-3 M (atrazine in distilled H2O and 30 min, respectively.
    • Variation in Utilization of Big Sagebrush Accessions by Wintering Sheep

      Welch, B. L.; McArthur, E. D.; Rodriguez, R. L. (Society for Range Management, 1987-03-01)
      We observed the effects of accessions of big sagebrush (Artemisia tridentata) on big sagebrush utilization by wintering domestic sheep. The sheep had continuous access to high quality alfalfa hay and were fed 0.28 kg of rolled barley per head per day. Utilization was expressed as a percent of the current year's vegetative growth consumed by the sheep and also as grams of dry matter eaten per stem. Utilization of accessions varied from 0 to 98% over 3 sites and from 0 to 7.112 g of dry matter per stem. The sheep tended to remove significant (60 to 70%) amounts of current growth from the more preferred accessions before removing even small (15%) amounts of less preferred accessions. If this is typical grazing behavior, preferred big sagebrush plants may be lost in areas subject to repeated grazing.
    • Variations in Physiological Metabolites and Chlorophyll in Sexual Phenotypes of 'Rincon' Fourwing Saltbush

      Tiedemann, A. R.; McArthur, E. D.; Freeman, D. C. (Society for Range Management, 1987-03-01)
      An experiment was conducted to determine if concentrations of chlorophyll and basic metabolites (total organic nitrogen (TN), total phosphorus (TP), and total nonstructural carbohydrates (TNC)) were an indication of the physiological vigor of the 3 sexual phenotypes of fourwing saltbush (Atriplex canescens (Pursh) Nutt.). Our basic hypothesis was that males, females, and plants capable of male and female sex expression (sexually labile) were equally vigorous as was manifested in chlorophyll and metabolite levels. In June, concentrations of chlorophyll a, b, and total chlorophyll in the male phenotype were greater than in either the female or the labile phenotypes. There were no differences among phenotypes for the other dates. Male plants had the highest levels of metabolites (TN, TP, and TNC) when any differences among sexual phenotypes were significant. There were basically no differences in metabolite concentration between the female and labile sexual phenotypes. Results indicate that part of the hypothesis should be rejected-that male, female, and sexually labile plants are equally vigorous based on concentrations of chlorophyll and metabolites. Part of the hypothesis, however, can be accepted-that females and labile plants are comparable in physiological vigor. Levels of all 3 metabolites showed striking trends among sample dates, which indicated that fourwing saltbush has the capability of rebuilding its levels of metabolites in the spring at the physiologically costly time of flowering. This may be related to the photosynthetic efficiency associated with its C-4 photosynthetic pathway.