• Comparison of Season-Long Grazing Applied Annually and a 2-Year Rotation of Intensive Early Stocking Plus Late-Season Grazing and Season-Long Grazing

      Owensby, Clenton E.; Auen, Lisa M. (Society for Range Management, 2013-11-01)
      This research measured steer gains, aboveground biomass remaining at the end of the growing season, and economic returns of tallgrass prairie grazed under season long stocking (SLS-C) and a grazing system that included a 2-yr rotation of SLS rotated (SLS-R) and intensive early stocking (IES; 2X normal stocking rate) + late season grazing at the normal stocking rate (IES + LSG-R). We hypothesized that even though the stocking rate on the IES + LSG-R pasture was above the recommended rate, the greater regrowth availability in the late season would result in steers gaining as well as or better than those stocked SLS at the normal rate. By rotating the IES + LSG treatment with SLS over 2 yr, we anticipated that the aboveground biomass productive capacity of the IES + LSG pasture would be restored in one growing season. Further, we hypothesized that the increased stocking rate with IES + LSG would increase net profit. Comparing traditional season-long stocking to the system, which was a combination of SLS and IES + LSG rotated sequentially over a 2 yr period, the system increased steer gains by 7 kg . hd-1 and by 30 kg ha-1, had a consistent reduction of 429 kg ha-1 biomass productivity, and increased net profit by 55.19 per steer and 34.28 per hectare.
    • Fluxes of CO2 From Grazed and Ungrazed Tallgrass Prairie

      Owensby, Clenton E.; Ham, Jay M.; Auen, Lisa M. (Society for Range Management, 2006-03-01)
      To determine the impact of seasonal steer grazing on annual CO2 fluxes of annually burned native tallgrass prairie, we used relaxed eddy accumulation on adjacent pastures of grazed and ungrazed tallgrass prairie from 1998 to 2001. Fluxes of CO2 were measured almost continuously from immediately following burning through the burn date the following year. Aboveground biomass and leaf area were determined by clipping biweekly during the growing season. Carbon lost because of burning was estimated by clipping immediately prior to burning. Soil CO2 flux was measured biweekly each year using portable chambers. Steers were stocked at twice the normal season-long stocking rate (0.81 ha steer-1) for the first half of the grazing season (– May 1 to July 15) and the area was left ungrazed the remainder of the year. That system of grazing is termed ‘‘intensive-early stocking.’’ During the early growing season, grazing reduced net carbon exchange relative to the reduction in green leaf area, but as the growing season progressed on the grazed area, regrowth produced younger leaves that had an apparent higher photosynthetic efficiency. Despite a substantially greater green leaf area on the ungrazed area, greater positive net carbon flux occurred on the grazed area during the late season. Net CO2 exchange efficiency was greatest when grazing utilization was highest. We conclude that with grazing the reduced ecosystem respiration, the open canopy architecture, and the presence of young, highly photosynthetic leaves are responsible for the increased net carbon exchange efficiency. Both GR and UG tallgrass prairie appeared to be carbon-storage neutral for the 3 years of data collection (1998 ungrazed: – 31 g C m-2, 1998 grazed: –5 g C m-2; 1999 ungrazed: –40 g C m-2, 1999 grazed: –11 g C m-2; 2000 ungrazed: +66 g C m-2, 2000 grazed: 0 g C m-2). 
    • Grazing Systems for Yearling Cattle on Tallgrass Prairie

      Owensby, Clenton E.; Auen, Lisa M.; Berns, Hannah F.; Dhuyvetter, Kevin C. (Society for Range Management, 2008-03-01)
      This 9-yr study tested steer gains, residual aboveground biomass (AGB) in mid-July and early October, and economic returns and risk for tallgrass prairie grazed annually under season-long stocking (SLS) at 1.62 ha steer-1 until early October or intensive early stocking (IES) at 0.81 ha steer-1 until mid-July compared to a composite grazing system. The three-pasture, three-herd ‘‘IES+ System’’ is a 3-yr fixed sequence of SLS, IES, and IES (0.81 ha steer-1) plus late-season grazing (LSG; 1.62 ha steer-1) until early October (IES/LSG). All grazing treatments began in late April. Average gains per steer for SLS and SLS in the IES+ System did not differ, but were significantly less than gains for steers that grazed the entire season under IES/LSG. Gains per steer in mid-July under IES alone or in combination with LSG were similar to the same repeated grazing treatments, but were significantly less than those for steers grazed season-long. Gains per hectare under SLS did not differ, but were significantly less than those for IES treatments and the IES+ System. Gain per hectare in July was similar for IES repeated annually and IES/LSG, but there was greater gain per hectare for IES-treated pastures rotated within the system. Residual grass and total aboveground biomass (AGB) in mid-July did not vary among years and was generally greater on SLS than IES. In early October, grass AGB was similar for all treatments except IES/LSG, which had less residual AGB. When pasture rent was charged per head, the IES+ System increased the 20-yr mean return per hectare by 5.98 compared to repeated use of IES, and 8.52 compared to using only SLS. Measures of economic risk were generally intermediate for the IES+ system compared to IES, which consistently had the highest risk, and SLS.