• 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.
    • Herbage characteristics and performance of steers grazing old world bluestem

      Coleman, S. W.; Forbes, T. D. A. (Society for Range Management, 1998-07-01)
      Old World bluestem (OWB; Bothriocloa spp.) are popular in the southern Great Plains but little is known about the relationships between forage characteristics and animal productivity. The influence of differences in herbage mass and sward height of OWB on rate of gain during the summer grazing season was examined during 2 years at El Reno, Okla. Soils were fine, silty Pachic Haplustolls of the Dale series. Swards of caucasian [B. caucasica (Trin.) C. E. Hubb.] and 'Plains' [B. ischaemum var ischaemum (L.) Keng.] OWB were maintained at different levels of forage mass (low, medium, and high) by continuous variable stocking and were grazed from mid- May to late September by steers with an initial weight of about 225 kg. Weight gains were depressed in late August, but in 1985 gains recovered due to late season rains. Season-long gains averaged 0.61 kg day-1 in 1984 and 0.69 kg day-1 in 1985. Daily gains of steers increased linearly with increased herbage mass (P < 0.05), but slopes were different due to a year X species interaction. Daily gains peaked at a herbage height of 41 cm in 1984, but increased linearly throughout the range of the data (75 cm) in 1985. Individual animal gains decreased linearly with increasing stocking rate such that maximum gain per hectare was achieved at about 5 animals ha-1 (standard 500 kg). The data suggest that maintaining higher herbage mass and height of OWB forage improves animal performance and support the practice of intensive early grazing and removing cattle by late July when rate of gain declines.
    • 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.