• Nutrient composition of whitetop

      McInnis, M. L.; Larson, L. L.; Miller, R. F. (Society for Range Management, 1993-05-01)
      Whitetop or heart-podded hoary cress (Cardaria draba (L.) Desv.) is an Eurasian native of the Cruciferae actively invading rangelands throughout western North America. The plant is reported to be unpalatable to livestock and contain potentially toxic glucosinolates. Practical experience indicates sheep consume whitetop during its early growth stages and cattle ingest large quantities of seedheads. Chemical analysis of whole plants from rosette to hard seed, respectively, indicated the following trends: crude protein (28.8 to 7.9%), neutral detergent fiber (13.1 to 52.8%), acid detergent fiber (12.0 to 41.8%), cellulose (9.9 to 32.1%), lignin (1.9 to 9.4%), ether extract (1.6 to 2.4%), in vitro organic matter digestibility (77.3 to 49.1%), digestible energy (2.9 to 1.8 Mcal/kg), and total glucosinolates (28.4 to 84.0 micromoles/g). Leaves were higher than stems in crude protein, ether extract, in vitro organic matter digestibility, and digestible energy. Analysis of 11 micro- and macroelements revealed sulfur (S) levels ranged from 0.73 to 2.69% and were therefore higher than the reported maximum tolerable level (0.4%). High S levels likely reflected the S moiety of glucosinolates and their hydrolysis products. Whitetop has some forage value, but until further research establishes the toxicity of this species to sheep and cattle, prudence suggests managers use caution when allowing animals to graze whitetop-infested rangelands by providing supplemental iodine, utilizing mature and nonlactating animals, and reducing opportunities for animals to consume the plant.
    • Plant structure and the acceptability of different grasses to sheep

      O'Reagain, P. J. (Society for Range Management, 1993-05-01)
      Plant structure should be an important determinant of species acceptability to grazing ungulates functioning under various time-energy constraints. The acceptability of 9 grasses to sheep grazing a secondary grassland community in spring, summer, and autumn in South Africa was related to the following species attributes: plant height, leaf table height, tussock diameter, stemminess, percent leaf, leaf density, percent dry matter (DM), leaf tensile strength, and leaf crude protein (CP). Species acceptability over the grazing season was positively related to tussock diameter (P less than or equal to 0.05) but negatively related (P less than or equal to 0.01) to leaf tensile strength and DM. Discriminant function analysis successfully discriminated between species in different acceptability classes in summer (P less than or equal to 0.05) and autumn (P less than or equal to 0.01) using a combination of plant structure and leaf quality attributes. Correspondence analysis indicated that preferred species were generally short and nonstemmy and had leaves of low DM, low tensile strength, and high crude protein content. Conversely, avoided species tended to be tall and stemmy with a high leaf table height, and had leaves of high DM and tensile strength but low CP levels. It is concluded that, for sheep, acceptability is determined by a combination of plant structure and leaf quality attributes.
    • Technical Notes: Botanical components of annual Mediterranean grassland as determined by point-intercept and clipping methods

      Glatzle, A.; Mechel, A.; Va, M. E. (Society for Range Management, 1993-05-01)
      Three methods for determining proportions of botanical components, i.e., grasses, legumes, and forbs (nonleguminous dicots), of continuously grazed Mediterranean pastures were compared. Percentage contribution to dry matter yield was determined by sample clipping and separating into botanical components. Both percentage of sward and specific contribution were determined by the point-intercept method. These were defined by the relative contribution of 1 botanical component to the total number of counted intercepts between 200 pins inserted vertically into the sward and all botanical components. For specific contribution only the number of pins contacted by the various botanical components were considered, whereas for percentage of sward even multiple contacts between a pin and plant parts of a particular botanical component were taken into account. Percentage contribution was highly significantly correlated with percentage of sward (R = 0.92) and specific contribution (R = 0.93) running the analyses across all botanical components, although there was a significant trend to underestimate forbs and overestimate legumes by the point-intercept methods. It is concluded, however, that for most practical purposes determination of specific contribution, the least laborious method, should give satisfactory estimates of percentage contribution.
    • Viewpoint: Selection for improved drought response in cool-season grasses

      Johnson, D. A.; Asay, K. H. (Society for Range Management, 1993-05-01)
      Water limits the establishment, growth, and production of cool-season grasses on semiarid rangelands, and plant improvement programs for these areas must be capable of screening breeding lines for response to drought. Although many techniques to evaluate various morphological and physiological characteristics have been proposed, few have been used successfully in plant breeding programs. Consequently, a need exists to identify and develop rapid, reliable screening techniques that can assess integrated plant response to drought in large plant populations. Improved seedling emergence has been achieved in Russian wildrye [Psathyrostachys juncea (Fischer) Nevski] by selecting for emergence from a deep seeding depth and long coleoptiles. Water uptake by roots is critical, and screening for enhanced seedling root growth in cool-season grasses offers considerable promise. In spite of the important role that stomatal control has in regulating plant water loss, limited success has been achieved in incorporating desirable stomatal characteristics into improved grass cultivars. Although osmotic adjustment appears beneficial in some crop species, more research is needed before cool-season grasses should be selected based on osmotic adjustment. Selection for improved water-use efficiency in cool-season grasses based on carbon isotope discrimination is a promising approach. Successful incorporation of these various traits into improved cool-season grass cultivars necessitates close cooperation between breeders and physiologists.
    • Water quality effects on stability and phytotoxicity of picloram and clopyralid

      Whisenant, S. G.; Bovey, R. W. (Society for Range Management, 1993-05-01)
      Water quality effects on stability of picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were evaluated by determining their concentrations in spray mixtures 0, 48, and 168 hours after mixing. Gas chromatography was used to evaluate picloram and clopyralid concentrations in spray solutions mixed with different water sources or buffered water solutions. At 168 hours picloram concentrations in water from La Copita and Midland, Texas, were 11 and 12% lower than at 0-hour and 5 and 6% lower than picloram concentrations in distilled water at 168 hours. Water quality effects on phytotoxicity to honey mesquite (Prosopis glandulosa) were evaluated at 0 and 168 hours after mixing the spray solution. Water quality had no effect on clopyralid phytotoxicity to honey mesquite at either 0 or 168 hours after mixing. Phytotoxicity to honey mesquite was reduced 42% when picloram mixtures were used 168 hours after mixing with water from La Copita. This indicates the potential for reduced phytotoxicity from picloram when prepared spray solutions are not used for 7 days.