• Some effects of precipitation patterns on mesa dropseed phenology

      Gibbens, R. P. (Society for Range Management, 1991-01-01)
      Phenology of mesa dropseed [Sporobolus flexuosus (Thurb.) Rydb.] was studied from 1979 to 1987 on the Jornada Experimental Range in southern New Mexico. Growing season (March through November) precipitation ranged from 99 to 308 mm during the 8-year period. Foliage height and number of leaves were recorded weekly for individually marked culms on 20 plants. New culms usually appeared during the first week in March and green leaf tissue often persisted until the end of November. Correlation analyses of accumulated weekly height increments and accumulated weekly precipitation showed that growth was highly dependent upon rainfall (r = 0.81 to 0.97). Leaf formation was also correlated with rainfall (r = 0.79 to 0.98). Even in relatively wet years tbere were 1 or 2 periods of no growth. In drier years, no growth periods totaled as much as 87 days. Periods of rapid growth occurred only after rainfall events > 13 mm. The first exsertion of seed heads occurred as early as the last week of July and as iate as the second week of October. The temporal plasticity of mesa dropseed phenology indicates that it is well adapted to the arid environment.
    • Substrate relations for rillscale [Atriplex suckleyi] on bentonite mine spoil

      Voorhees, M. E.; Uresk, D. W.; Trlica, M. J. (Society for Range Management, 1991-01-01)
      Rillscale (Atriplex suckleyi), the dominant native invader of bentonite mine spoil in northern Wyoming, is apparently uniquely adapted to this extremely harsh plant growth substrate. The objective of this study was to determine which chemical properties of spoil influence growth of rillscale. Plant production, foliar and spoil chemistry on spoils were treated as a factorial arrangement of treatments, each of 3 spoil amendments (gypsum, fertilizer, sawdust). Regression analyses with analysis of covariance and factorial analysis of variance model were used to control for effects of amendments on plant production. Calcium and nitrogen were growth-limiting nutrients for this plant. The species was very sensitive to an increase in the level of spoil molybdenum and in the ratio of copper to molybdenum, but was very tolerant of high levels of soluble sodium. Rillscale acted as a molybdenum accumulator.