• Brownseed Paspalum Response to Season of Burning

      Scifres, C. J.; Duncan, K. W. (Society for Range Management, 1982-03-01)
      Season of burning as related to plant phenology, maximum temperatures achieved, and soil water content rather than duration of heat exposure (5, 15 or 30 seconds) apparently regulated fire-induced mortality of brownseed paspalum. Burning or top removal by clipping to ground line during the summer caused greatest mortality of brownseed paspalum and reduced herbage volume of surviving plants, whereas burning in early or mid-spring resulted in favorable growth responses. Fall burning was less damaging than summer burning but caused greater mortality of brownseed paspalum than did burning in the spring. Regrowth of brownseed paspalum after spring burning was equivalent to that following top removal by clipping during the same season. However, responses to summer or fall burning indicated that heat-induced damage (and/or perhaps subsequent winter kill following fall burns) occurred in addition to the effects of simple top removal.
    • Cow-Calf Response to Stocking Rates, Grazing Systems, and Winter Supplementation at the Texas Experimental Ranch

      Heitschmidt, R. K.; Kothmann, M. M.; Rawlins, W. J. (Society for Range Management, 1982-03-01)
      Cow-calf performance from 1960 through 1978 was contrasted between three grazing treatments at the Texas Experimental Ranch. Grazing treatments were yearlong continuous stocked at annual rates averaging 5.1 and 7.6 ha/cow and a 4-pasture, 3-herd deferred rotation system stocked at an annual rate averaging 7.2 ha/cow. Averaged across three weighing periods, cows in the deferred rotation treatment averaged 447 kg while weight of cows in the heavily and moderately stocked continuous treatments averaged 427 and 438 kg, respectively. Calf weaning weights averaged 204, 212, and 217 kg for the heavy continuous, moderate continuous, and Merrill rotation treatments, respectively. Production-/cow averaged 182, 189, and 202 kg while production/ha averaged 35.9, 25.2, and 27.8 kg, respectively, for the heavy continuous, moderate continuous, and deferred rotation treatments. Cows fed winter supplement were significantly heavier in early spring and summer than nonsupplemented cows with no significant differences in weights by late summer. Supplemented cows weaned calves averaging 214 kg as compared to 208 kg for calves weaned from nonsupplemented cows. Winter supplementation significantly increased production in the heavily stocked treatment but not in either of the moderately stocked treatments. Numerous statistically significant interactions accompanied the significant main effects, and the biological significance of each was examined.
    • Destructive and Potentially Destructive Insects of Snakeweed in Western Texas and Eastern New Mexico and a Dioristic Model of Their Biotic Interactions

      Wangberg, J. K. (Society for Range Management, 1982-03-01)
      The relationships of the principal destructive and potentially destructive insects associated with Xanthocephalum microcephalum (DC) Shinners (threadleaf snakeweed) and Xanthocephalum sarothrae (Pursh) Shinners (broom snakeweed) have been identified and depicted with a dioristic model. Every region of the host plant is utilized by insects in one or more of the following feeding categories: defoliators, fluid feeders, borers, and gall-formers. Roots, stems, leaves, flowers, and fruit each have their own complement of insect associates. A system analysis reveals a complex picture of insect-host plant interactions as well as potential insect-insect interactions. The roles that these insects play in the natural biological control of threadleaf and broom snakeweed are poorly understood but the general information portrayed in the model of their interactions will help future workers to determine the most productive avenues of research.
    • Factors Influencing Bitterweed Seed Germination

      Whisenant, S. G.; Ueckert, D. N. (Society for Range Management, 1982-03-01)
      Bitterweed seed germination exceeded 90% at constant temperatures between 20 degrees and 25 degrees C and more than 65% between 15 degrees and 30 degrees C in a controlled environment chamber. Seeds germinated equally well in light and dark conditions. Germination percentages of seeds in aqueous media with a pH range of 5 to 9 were significantly different, but the range of germination (91 to 97%) probably is not sufficient to affect distribution. However, a decrease in water availability significantly decreased bitterweed seed germination. Viability of bitterweed seed did not change significantly after 39 months dry storage at room temperature, but was significantly reduced at 47 months.
    • Infiltration and Sediment Production on a Deep Hardland Range Site in North Central Texas

      Brock, J. H.; Blackburn, W. H.; Haas, R. H. (Society for Range Management, 1982-03-01)
      Greatest infiltration rate and lowest sediment production occurred in the honey mesquite canopy zone. Infiltration on shortgrass interspace areas was about one-half of the canopy zone rate. Terminal infiltration rates within the canopy zone and shortgrass interspace areas were affected little by brush control treatments. Infiltration rate improvement due to treatment occurred primarily in the midgrass interspace areas. Water-stable aggregates and the interaction of soil aggregate stability with the amount of bare ground were the dominant factors controlling infiltration. Sediment production on the shortgrass interspace was double that of the canopy zone or midgrass interspace areas. Low rate of sediment production on the midgrass interspace areas occurred on areas aerially sprayed or root plowed 3 years earlier. Sediment production was controlled primarily by an interaction of soil organic matter and amount of above-ground biomass or grass cover.