• Atrazine, Spring Burning, and Nitrogen for Improvement of Tallgrass Prairie

      Gillen, R. L.; Rollins, D.; Stritzke, J. F. (Society for Range Management, 1987-09-01)
      Spring application of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] (1.1 kg ha-1 a.i.), burning, and nitrogen (33 kg ha-1 as ammonium nitrate) were evaluated alone and in all combinations for improvement of mid-seral tallgrass prairie in northcentral Oklahoma. Studies were initiated in 1984 (Study I) and 1985 (Study II). Precipitation and successional status of the vegetation at treatment application were higher for Study II than for Study I. Atrazine effectively reduced forbs and annual grasses for 2 years after application. Atrazine stimulated warm-season perennial grasses but did not generally increase total herbage production. Burning was similar to atrazine for annual grass control in both studies. Burning was also similar to atrazine for forb control in Study I but had no impact on forb production in Study II. Burning increased perennial grass production only in the second year of Study I. Burning decreased total herbage production in the first year of Study I by reducing annual grasses and forbs but did not affect total herbage production on other dates. Nitrogen did not consistently increase perennial grass production but did increase forb production by 250-300% when applied alone. Both atrazine and burning rapidly shifted species composition in favor of desirable perennial grasses. Nitrogen was not as effective in changing species composition either alone or in combination with atrazine and burning. The number and complexity of treatment responses declined as successional status and/or precipitation improved.
    • Evaluation of the Forage-disk Method in Mixed-grass Rangelands of Kansas

      Karl, M. G.; Nicholson, R. A. (Society for Range Management, 1987-09-01)
      The forage disk meter, a double sampling device used to predict forage biomass, has been used extensively on improved pastures, but its use on rangelands has not been investigated thoroughly. Efficiency of the forage disk meter was investigated in predicting yields of forage biomass on different range sites in western Kansas. Using least squares regression methods, resting heights (forage bulk) and dry matter yields were used to calibrate the disk meter for each site and sampling date. Highly significant regressions (P<0.0001) were obtained on all the shortgrass sites, where several factors that had unfavorable effects on the regression relationship between forage bulk and forage biomass were not apparent. These factors, although not quantified, included accumulation of litter, microrelief, lodged vegetation, and presence of broadleaf species. Regression coefficients (b) and intercepts (a) varied between sites and dates, thus the forage disk meter should be calibrated for every range site. If a forage disk meter is calibrated for a specific range site, regression coefficients and intercepts might not differ from year to year if grazing pressure and species composition are temporally consistent, which implies that recalibration might be unnecessary. The forage disk meter was useful as a double sampling device on range sites dominated by shortgrasses, but its use was limited on areas dominated by annual forbs or midgrasses.
    • Frequency Sampling and Type II Errors

      Whysong, G. L.; Brady, W. W. (Society for Range Management, 1987-09-01)
      Probabilities of detecting frequency differences based on data obtained by random sampling were determined by computer simulation. Artificial, monotypic populations of known frequency were generated and sampled. Sample sizes of 100, 200, 500, and 1,000 plots were used to compare baseline populations of 20, 50, and 80% frequency to populations having progressively larger or smaller frequencies. Probabilities of detecting a difference in frequency from baseline populations were empirically estimated from 10,000 comparisons using a test of proportions (P<0.05). Results indicated that the power of the test was substantially reduced at lower sample sizes. Equating the probability of Type I and Type II errors at 0.05 resulted in sample sizes of approximately 500 plots being needed to statistically distinguish between differences of plus or minus 10% frequency.
    • Soil Seed Banks Associated with Individual Broom Snakeweed Plants

      Osman, A.; Pieper, R. D.; McDaniel, K. C. (Society for Range Management, 1987-09-01)
      The influence of individual broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rushby) plants on the distribution of buried viable seed and the distribution of plants in the field was studied in a desert grassland in southern New Mexico. Surface soil samples collected at 3 distances from a central broom snakeweed plant were watered in pots in a greenhouse and numbers of each species emerging were counted. Densities of each species were also determined in the field. Some species (Sporobolus flexuosus [Thurb.] Rybd., S. contractus Hitchc., Descurainia pinnata [Walt.] Britton, and Dithyrea wislizenii Engelm.) emerged in greatest numbers from soil collected in the zones closest and at the greatest distances from the broom snakeweed. Emergence of other species declined in relation to distance from the central snakeweed plant. In the field, grasses generally increased in relation to distance from the central broom snakeweed plant while the pattern for forbs was not consistent.
    • Steer and Vegetation Response to Short Duration and Continuous Grazing

      Pitts, J. S.; Bryant, F. C. (Society for Range Management, 1987-09-01)
      Comparisons were made over a 4-year period between 1-herd, 16-pasture short duration grazing (SDG) and continuous grazing (CG) on the Texas High Plains. Animal performance, vegetation response, and diet quality were evaluated. Stocking rate on SDG was equal to that on CG the first year (13.3 ha/AU), double that on CG in the second year, and 1.5 times that on CG the third and fourth years. Average daily gain (ADG) of steers was the same (0.33 kg/day) between SDG and CG the first year. When stocking was doubled on SDG the second year, steers on SDG gained 0.15 kg/day compared to 0.25 kg/day under CG. In the third and fourth years, with stocking under SDG at 1.5 times that on CG, gains were similar. Standing crop biomass on SDG fell below that on CG after 1 year of grazing. In the second year standing crop was greater (P<0.05) on SDG than on CG, but in years 3 and 4, standing crop on the SDG was less than on CG. Changes in species composition were the same on both CG and SDG. Steer diet composition and quality were evaluated during the growing season (May to October) of year 4. Steers on SDG consumed 15% more forbs (39% vs 24%) than steers on CG. No differences (P>0.05) between CG and SDG were observed for dietary crude protein or in vitro digestible organic matter. SDG did not improve animal performance, diet quality, or forage availability over CG when evaluated over 4 years.