• Determination of root mass ratios in alfalfa-grass mixtures using near infrared reflectance spectroscopy

      Rumbaugh, M. D.; Clark, D. H.; Pendery, B. M. (Society for Range Management, 1988-11-01)
      Hand separation of roots of 2 or more plants species from soil cores is a tedious and labor-intensive task. Our objective was to determine whether near-infrared reflectance spectroscopy (NIRS) could be employed to estimate root biomass proportions in binary mixtures of alfalfa (Medicago sativa L.) with each of 4 grasses. Grasses chosen for experimentation were crested wheatgrass (Agropyron cristatum L.), intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], an intergeneric hybrid [Elytrigia repens (L.) Nevski × Pseudoroegneria spicata (Pursh) Love], and Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski]. In the first experiment, roots from single-species field plots were washed from soil cores, dried, ground, and mechanically mixed in preselected alfalfa-grass ratios in which the percentage of grass varied from 0 to 100. Equations to measure the proportion of alfalfa or grass were developed from near infrared reflectance data using 84 randomly selected samples. In the second experiment, the 5 plant species were grown in greenhouse pots in pure stands and in binary mixtures that included all combinations of the grasses. Root systems were separated while attached to the topgrowth, dried, and ground. Tissues from single species treatments were mixed and calibration equations developed from these mixtures were used to estimate the proportion of alfalfa and the proportion of grass in samples. Samples contained either one type of root or a mixture of roots in proportions similar to those that occurred naturally in the pots. Coefficients of determination (r2) between the estimated and the actual root mass ratios ranged from 0.92 to 0.99. Determination of the proportion of grass in the samples was more accurate and precise than determination of the proportion of alfalfa. After the appropriate calibration equations have been developed, NIRS is more efficient than hand separation for estimating alfalfa-grass root mass ratios. The utility of the techniques can be increased by developing equations that encompass more complex mixtures and a wider range of environmental circumstances.
    • Floristic changes induced by flooding on grazed and ungrazed lowland grasslands in Argentina

      Chaneton, E. J.; Facelli, J. M.; Leon, R. J. C. (Society for Range Management, 1988-11-01)
      Changes in community composition of 2 grassland sites exposed to a flood of unusual intensity and duration were investigated in the Flooding Pampa. These grasslands are subject almost annually to floodings of lesser magnitude. The study sites were adjacent to each other, and differed in vegetation structure and composition. One had been grazed continuously by cattle and was showing signs of intense deterioration. The other had remained ungrazed during 15 years. Basal cover by species was measured in summer, before and after the flooding event. Compositional difference between sites decreased with flooding from 68.9 to 39.1%. In the grazed site the cover of alien forbs was reduced by 48%. After the flooding native graminoids represented 99.7 and 86.7% of the cover, inside and outside the exclosure respectively. Total basal cover was not affected but was redistributed among species already present before the flood. Floristic changes would have led to an improvement of the forage source. We conclude that plant community response to the event was influenced by the previous grazing history of the site. The large flood acted as an overriding environmental factor which partially reverted the effects of grazing upon grassland composition.
    • Species diversity and diversity profiles: concept, measurement, and application to timber and range management

      Lewis, C. E.; Swindel, B. F.; Tanner, G. W. (Society for Range Management, 1988-11-01)
      The concepts and use of several diversity assessments are presented and applied to a practical situation. Burning, mechanical methods of site preparation, and cattle grazing are common disturbances in forests of the South. Their influence on plant diversity indices are examined in a longleaf-slash pine forest of north Florida. Species richness, Shannon's index, and Simpson's index showed increases in diversity shortly following burning and site preparation and a trend toward pre-treatment conditions after 6 years. Deferred-rotation grazing systems had no influence. Comparative diversity profiles showed similar trends but were more informative by providing both qualitative and quantitative information. These techniques are useful for assessing community responses to management practices, that is, they are effective methods for understanding the impacts of forest management and range management practices on plant community structure and succession.
    • Stability of grazed patches on rough fescue grasslands

      Willms, W. D.; Dormaar, J. F.; Schaalje, G. B. (Society for Range Management, 1988-11-01)
      Continuous stocking usually leads to the formation of grazed patches. However, the effect of patches on the grassland community is related to their stability. Therefore, we studied the spatial stability of grazed patches on Rough Fescue Grasslands by mapping forage removal classes on 10 sites over a 4-year period, testing stability using the Kappa index (K), and characterizing the soils and vegetation of overgrazed and undergrazed patches. Spatial stability of grazed patches between consecutive years was good (K is greater than or equal to 0.26) on sites experiencing low grazing pressure. However, on sites having high grazing pressure, spatial stability was less consistent between consecutive years (0>K is lesser than or equal to 0.45) and low over a 4-year period (K is lesser than or equal to 0.10). Overgrazed patches were dominated by grazing-resistant seral species, but undergrazed patches were dominated by climax species. Rough fescue (Festuca scabrella) and Parry oat grass (Danthonia parryi) plants were 50% shorter, and forage production was about 35% less, on overgrazed than on undergrazed patches. Soil organic matter, carbohydrates, and depth of Ah horizon were significantly greater on undergrazed patches but urease activity, NO3-N, NH4, and available phosphorus were greater on overgrazed patches. Overgrazed and undergrazed patches were stable in the long term, although patch boundaries fluctuated.