• Botanical composition of bison diets on tallgrass prairie in Oklahoma

      Coppedge, B. R.; Leslie, D. M.; Shaw, J. H. (Society for Range Management, 1998-07-01)
      Diets of bison (Bison bison L.) were examined using microhistological fecal analysis in a 2-yr study on a tallgrass prairie site in northcentral Oklahoma. Graminoids comprised at least 98% of the diet across all seasons. Bison showed strong feeding selectivity; grasses and sedges formed a significantly higher proportion of diets than was generally available in herbage on the landscape. Bison avoided forbs, which were less than or equal to 2% of the diet. Sedges were a large (17-44%) diet component in winter and spring but decreased substantially during summer and fall (11-16%). These changes in sedge use corresponded to seasonal variation in sedge availability. Our results confirm that bison are primarily grazers in prairie habitats, potentially having a significant role in shaping structure and function of tallgrass prairie.
    • Grazing intensities, vegetation, and heifer gains: 55 years on shortgrass

      Hart, R. H.; Ashby, M. M. (Society for Range Management, 1998-07-01)
      Shortgrass rangeland, dominated by blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud), was grazed at 3 intensities, equivalent to mean stocking rates of 16.7, 23.0, and 36.5 heifer-days ha-1, from 1939 through 1994. Few changes in plant communities had been documented by the early 1970's. In 1992-1994, frequency of occurrence, basal and foliar cover, and biomass at peak standing crop (PSC) were determined on the remaining pasture at each grazing intensity, and on 3 ungrazed exclosures. Blue grama and buffalograss (Buchloe dactyloides [Nutt.] Engelm.) increased, and western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) and needle-and-thread (Stipa comata Trin. &Rupr.) decreased, as grazing intensity increased. Redthree-awn (Aristida longiseta Steud.) was most plentiful under light grazing. Basal cover and biomass of forbs were lower under grazing than in exclosures, but differences in biomass were not significant. Shrubs and half-shrubs decreased as grazing intensity increased. Frequency and cover of plains pricklypear (Opuntia polyacantha Haw.) were higher in the exclosures and under light grazing than under moderate or heavy grazing; biomass was 4 to 6 times as high in the exclosures as under any grazing intensity. Heifer gains declined linearly with increasing grazing pressure index. Optimum (most profitable) stocking rate was about 20% higher than that under the moderate grazing intensity, under which biomass production was maintained and shrub and pricklypear remained at low levels. Returns to land, labor, and management were only slightly higher under the optimum stocking rate than under the moderate grazing intensity. The moderate grazing intensity appears to be both profitable and sustainable.
    • Nitrogen fertilization of a native grass planting in western Oklahoma

      Gillen, R. L.; Berg, W. A. (Society for Range Management, 1998-07-01)
      Native warm-season grass mixtures have been established on the Southern Plains under the USDA Conservation Reserve Program. We studied responses to N fertilizer on such pastures in western Oklahoma over a 4-year period. Experimental pastures were previously cultivated fields with loamy soils seeded to a mixture of native warm-season grasses. Fertilizer treatments were 0 and 35 kg N ha-1 year-1 as ammonium nitrate. Pastures were intensively grazed from early June to early August over 4 years. Stocking rates averaged 52 and 104 AUD ha-1 for the 0 and 35 kg N ha-1 treatments, respectively. These stocking rates are heavy for seasonal grazing in this region. Responses measured included forage mass and nutritive value before and after grazing, plant basal area, and livestock performance. Precipitation was variable but generally favorable over the study period. Peak forage mass was increased by N fertilization (2,480 versus 4,030 kg ha-1; P < 0.01), producing 45 kg forage per kg N applied. Nitrogen fertilization increased crude protein concentration in June (8.2 versus 10.3%; P < 0.05) and August (4.1 versus 4.6%; P < 0.05), but had inconsistent effects on in vitro dry matter digestibility. Total vegetative cover and basal cover of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths) increased in the fertilized pastures. Average daily steer gain was not different between treatments (0.96 versus 1.02 kg hd-1 day-1) even though stocking rates were substantially higher on fertilized pastures. Steer gain ha-1 was increased by fertilization (83 versus 176 kg ha-1, P < 0.01). This resulted in a fertilizer N use efficiency of 2.7 kg steer gain per kg N applied. Nitrogen fertilization combined with intensive summer grazing provided a net return of 0.65 to 0.94 per kg N applied.
    • Nitrogen fertilization, botanical composition and biomass production on mixed-grass rangeland

      Samuel, M. J.; Hart, R. H. (Society for Range Management, 1998-07-01)
      Many studies have reported nitrogen (N) fertilization of rangeland, but few have reported changes in botanical composition, which may be as important as changes in forage production, or were continued for as long as 14 years. We determined frequency of occurrence of over 90 plant species in 1976-1988 under rates of 0, 22, or 34 kg N ha-1 applied in spring or fall to mixed-grass rangeland in southeast Wyoming; frequency of 23 species will be reported. We also determined total biomass production and production of major species and species groups in 1982-1988. Blue grama Bouteloua gracilis (H.B.K.) Griffiths] frequency decreased during years 5 through 7 because of the interaction of N and drought. The effects of long-term application of N decreased blue grama in year 12 and beyond. Nitrogen fertilization increased frequency of western wheatgrass [Pascopyrum smithii (Rydb.) A. Love] in all years except the driest year of the study. Needleleaf sedge [Carex eleocharis Bailey] decreased because grazing had been removed from the study area; this occurred sooner and to a greater extent on fertilized than on unfertilized plots. Fourteen other perennial species were quite variable in response to the 3 rates and the 2 seasons of application. Frequency of 6 annual species fluctuated greatly among years and treatments. Nitrogen fertilization did not increase average forage production enough to be profitable for cattle production.
    • Soil depth assessment of sagebrush grazing treatments using electromagnetic induction

      Bork, E. W.; West, N. E.; Doolittle, J. A.; Boettinger, J. L. (Society for Range Management, 1998-07-01)
      Depth to a root restricting layer affects both soil moisture and nutrient availability, resources strongly correlated to plant cover and production. We evaluated the potential of 2 electromagnetic induction meters (EM38 and EM31) for non-destructively assessing soil depth to bedrock in 2 long-term seasonal sagebrush steppe sheep grazing treatments with different vegetational compositions. Apparent conductivity readings, measured with the EM38 and EM31 in both the horizontal (H) and vertical (V) dipole orientations, were positively related to soil depth. Apparent conductivity measured with the EM31H (r2 = 0.78) and EM38V (r2 = 0.75) were the best predictors of depth. Soil depth distributions were similar between grazing treatments based on Kolmogorov-Smirnov (K-S) tests of the EM38H apparent conductivity (P = 0.47) and EM38V apparent conductivity (P = 0.56). In constrast, K-S tests for the EM31H apparent conductivity (P = 0.09) and EM31V apparent conductivity (P < 0.01) indicated the fall-grazed treatment had a larger area in which soil depth exceeded 150 cm. Because less than 2% of each grazing treatment was predicted to have soils deeper than 150 cm, however, overall site differences between the 2 treatments appeared to be minor. Therefore, the vegetational differences between the treatments have probably resulted more from differences in the seasonality of grazing rather than ecological site characteristics as reflected in soil depth. Maps of soil depth indicated both treatments consisted of intermittent shallow and deep soils, created by several parallel basalt pressure ridges. Results suggest electromagnetic induction can effectively assess the spatial variability of soil depth and could aid in selecting sites for rangeland monitoring or manipulation.