EFFECTS OF SEASONAL REST IN ABOVEGROUND BIOMASS FOR A NATIVE GRASSLAND OF THE FLOOD PAMPA, ARGENTINA

Changes in total biomass and botanical composition in a native pasture of the Flooding Pampa in the Salado River Basin (Province of Buenos Aires), under 3 grazing systems: spring-summer rest (November, December, and January); fall rest (April, May, and June), and continuous grazing were evaluated from October 1979 to August 1981. A variable stocking rate based on available forage was used. Total aboveground biomass was periodically sampled to ground level and separated into dead and green components. The green biomass was subdivided into individual species. Total aboveground biomass averaged 4,600 +/- 445 kg.ha-1 and 3,750 +/- 120 kg.ha-1 for the spring-summer rest treatment during the first and second years, respectively. In the same period, warm-season species increased, principally due to an increase in dallisgrass (Paspalum dilatatum Poir.) and bluestem (Bothriochloa laguroides Herter) biomass. Total aboveground biomass yield was 2,000 +/- 170 kg.ha-1 during the fall rest treatment, and cool-season species such as Poa spp. and Stipa spp. increased. In general, continuous grazing at a moderate intensity resulted in total aboveground biomass of about 2,000 kg DM.ha-1 throughout the experimental period. Contributions of warm-season and cool-season species did not change. Only West Indies smutgrass (Sporobolus indicus (L.) R. Br.) increased under continuous grazing.