A.J.N. CABRERA1, D. STOSIEK1, A. GLATZLE1, H.M. SHELTON2 and R. SCHULTZE-KRAFT3
1Estación Experimental Chaco Central (MAG/GTZ), Cruce de los Pioneros, Paraguay
2University of Queensland, Brisbane, Australia
3Universität Hohenheim, Stuttgart, Germany
A grazing trial to study the effect of stocking rate on animal production and botanical composition of Gatton panic (Panicum maximum) and Estrella grass (Cynodon nlemfuensis) was conducted in the central region of the Paraguayan Chaco between 1992 and 1998.
The experiment included 6 stocking rates (0.5, 0.8, 1.1, 1.4, 1.7 and 2.0 AU/ha) on individual 4-ha paddocks. The pasture treatments were continuously grazed by yearling steers, replaced annually, over a 4-year grazing period. No fertiliser was used. Botanical composition was recorded annually in autumn from 1992 to 1998 while animal production data were recorded monthly from 1992 to 1996. Relationships between animal productivity and stocking rates were determined by regression analysis.
Gatton panic produced greater liveweight gains per head than Estrella grass at low and intermediate stocking rates. However, the slope of the linear relationship between liveweight gain per head and stocking rate increased each year in Gatton panic indicating that the productivity of this grass progressively declined at higher stocking rates over the period of observation. Estrella grass showed less sensitivity to stocking rate but was affected severely by periods of low rainfall.