• Germination of green and gray rubber rabbitbrush and their establishment on coal mined land

      Romo, J. T.; Eddleman, L. E. (Society for Range Management, 1988-11-01)
      The objectives of this study were to: (1) determine the effects of temperature and water stress on germination, and; (2) evaluate effects of seeding date on emergence and survival of green and gray rubber rabbitbrush (Chrysothamnus nauseosus (Pallas) Britt. subsp. graveolens (Nutt.) Piper. and Chrysothamnus nauseosus (Pallas) Britt. subsp. nauseosus (Nutt.) Piper.). Seeds of both shrubs were incubated at 10, 20, and 30 degrees C in a gradient of osmotic potentials ranging from 0.0 to -1.5 MPa. Seedings were also made in the field on seeding dates over a period of 3 years. Total germination and germination rate declined as temperatures and osmotic potentials decreased; they were highest for both shrubs at 20 and 30 degrees C and lowest at 10 degrees C. Under field conditions seedling populations were limited by low emergence and survival relative to viable seed planted. Emergence and survival of seedlings were highest in an exceptionally wet year, declining in subsequent years that were drier. Emergence ranged from 0 to 6.9% and 0 to 7.1% and survival of emerged seedlings ranged from 6.6 to 55% and 0 to 60% for green and gray rubber rabbitbrush, respectively. Survival of green rubber rabbitbrush was highest from mid-spring plantings, but no distinctively favorable seeding date was found for gray rubber rabbitbrush. Results suggest that seeds of these shrubs should be planted prior to or during periods when seedbed temperatures are in the 20 to 30 degrees C range and soil moisture is expected near its seasonal high.
    • Grazing effects of the bulk density in a Natraquoll of the flooding pampa of Argentina

      Taboada, M. A.; Lavado, R. S. (Society for Range Management, 1988-11-01)
      The influence of grazing by cattle on soil bulk density was studied in a typic Natraquoll of the Flooding Pampa of Argentina for a period of 33 months, by comparing a grazed situation to an enclosure deferred from grazing for 7 years. Floods took place in this period as usual. Bulk density (BD) at -33.3 kPa of water retention varied from 1.00 to 1.11 Mg m-3 in the ungrazed soil and in the grazed soil from 1.04 to 1.16 Mg m-3. Environmental factors were the primary agent controlling BD; only in some periods were there significant differences between treatments. Slight increases in BD occurred under grazing after the recession of the flood water, and significant decreases occurred in the ungrazed soil during the large and sudden falls in water content. In this case the effect of trampling, therefore, would consist mainly of impeding the decrease in BD. No compaction was observed in periods when no flood occurred or while soil remained submerged in water. The results indicated that the variations of bulk density caused by cattle trampling were superimposed on those produced by floods and showed an interaction between the effects of land-use and the particular environmental conditions of the region.