• 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.