• Seasonal Use of Soil Water by Mature Velvet Mesquite

      Cable, D. R. (Society for Range Management, 1977-01-01)
      Mesquites used water consistently to a depth of 3 m and outward to 10 m beyond the crowns, but use at 15 m was limited mainly to drier periods when water supplies closer to the trees were depleted. With the start of spring growth, water was extracted most rapidly from the surface layers. As the season advanced, the watersupply zone became increasingly thicker. Rates of extraction were highest immediately after recharge in early spring and early summer, and lowest in late fall. Differences in available water in the soil accounted for 72 to 88% of the variation in rates of extraction. The competitive effect of velvet mesquite on perennial grasses is most severe in the upper 37.5 cm of soil under and near the mesquite crowns, and gradually decreases with distance into adjacent openings. The competitive effect in the openings is much more severe in dry years than in wet years.
    • Species Susceptibility to Atrazine Herbicide on Shortgrass Range

      Houston, W. R. (Society for Range Management, 1977-01-01)
      Atrazine was applied at 2 kg/ha for three consecutive years on shortgrass range in northeastern Colorado. The atrazine controlled all annual plant species, greatly reduced frequency of occurrence of cool-season perennial grasses, and increased drought survival of warm-season perennial grasses and two warm-season perennial forbs. Other species varied in their susceptibility to atrazine. The species frequency method of vegetation sampling used in this study provided reliable data for 27 of the approximately 100 species encountered on this range.
    • Squirreltail Seed Germination

      Young, J. A.; Evans, R. A. (Society for Range Management, 1977-01-01)
      Germination tests on squirreltail seed showed that three temperature regimes always produced optimum germination of 76 to 100%. We defined optimum as not statistically (p = 0.01) different from maximum. The always optimum temperature regimes were: (1) a constant 15 degrees C, (2) alternating 10/15 degrees C (16 hours cold/8 hours warm each day), and (3) 10/20 degrees C. When seed was produced in a year with good growing conditions, optimum germination extended over a wide range of temperatures. At optimum temperatures, the rate of germination was very rapid with a high percentage of total germination occurring within a week. The lack of inherent germination requirements that restrict germination, high germinability, and a rapid rate of germination help to explain the colonizing ability of this species.