• Effect of Phosphate Fertilization on Flooding Pampa Grasslands (Argentina)

      Rodrígues, Adriana M.; Jacobo, Elizabeth J.; Scardaoni, Pablo; Deregibus, Víctor A. (Society for Range Management, 2007-09-01)
      We postulate that phosphorus (P) fertilization may increase above-ground net primary productivity (ANPP) of rotationally grazed rangelands without reducing the legume component, as does N fertilization. In doing so, we evaluated the effect of phosphate fertilization on the production and relative contribution of legumes and grasses of native and old tall fescue (Festuca arundinacea Schreb) grasslands; we recorded annual production, seasonal productivity, and biomass contribution of each component. The experiment was conducted in a commercial farm located in the Flooding Pampa and managed under rotational grazing. Treatments consisted of two fertilization programs (66 (P66) and 29 (P29) kg P ha-1 supplied as rock phosphate and/ or monoammonium phosphate from 1997 to 1999) and a nonfertilized control. A paddock dominated by native grassland and another dominated by old tall fescue grassland were selected. Nine 5-ha plots were established in each paddock, and treatments were randomly assigned. During the experimental period, from October 1998 to October 1999, total above-ground biomass was harvested from each plot before and after each grazing period and separated into components: tall fescue, other C3 perennial grasses, legumes, C3 annual grasses, C4 grasses, forbs, and standing dead material. ANPP of each component was estimated during the warm (October 1998-February 1999) and the cool (March 1999-September 1999) season. In native grassland, phosphate fertilization increased ANPP of C3 annual grasses and legumes during both the warm and the cool seasons; therefore annual ANPP of the grassland under P66 was 40% higher than under P29 and doubled ANPP of nonfertilized plots. Phosphate fertilization didn’t increase total annual ANPP of old tall fescue grassland, but it did increase ANPP of legumes during both seasons. 
    • Rotational Grazing Effects on Rangeland Vegetation at a Farm Scale

      Jacobo, Elizabeth J.; Rodríguez, Adriana M.; Bartoloni, Norberto; Deregibus, Víctor A. (Society for Range Management, 2006-05-01)
      We evaluated the adequacy of rotational grazing to improve rangeland condition in the Flooding Pampa region, eastern Argentina, comparing the floristic composition dynamic of the 2 main plant communities under rotational and continuous grazing over a study period of 4 years (1993-1996). The experiment was conducted in commercial farms located in 4 sites of the Flooding Pampa region. In each site, a couple of farms, one managed under rotational grazing (implemented in 1989) and an adjacent one managed under continuous grazing at a similar stocking rate (1 AU ha-1), constituted the replications of the experiment. Basal cover of species, litter, and bare soil were monitored in midslope and lowland grassland communities on each farm. Total plant basal cover in midslope and in lowland communities remained unchanged over the whole experimental period under both grazing methods. Under rotational grazing, litter cover was higher in both communities while the amount of bare soil showed a significant reduction in lowlands and a tendency to be lower in midslope. Basal cover of legumes, C3 annual and C3 perennial grasses was higher, while cover of C4 prostrate grasses was lower under rotational grazing in the midslope community. In the lowland community, rotational grazing effects were evident only in the drier years, when higher cover of hydrophytic grasses and legumes and lower cover of forbs occurred. Plant species diversity did not change in response to grazing. In conclusion, rotational grazing promoted functional groups composed of high forage value species and reduced bare soil through the accumulation of litter. These changes indicate an improvement in rangeland condition and in carrying capacity. As the stocking rate was approximately 60% higher than the average stocking rate of the Flooding Pampa region, we believe that productivity and sustainability may be compatible by replacing continuous with rotational grazing.