ChileanJAR

Pastures can be modifed by the effects of different types of management, which produce structural and functional changes and determine variations in the availability and composition of animal diel. The purpose of this work was to asses the effect of spring and summer grazing and nitrogen fertilization of autumn on the botanical composition of perennial ryegrass sward. Eight treatments were applied from the combination of two grazing intensities in spring [high (H) and low (L)); two grazing frequencies in summer [grazing (G) and clausure (C)] and two levels of nitrogen application in autumn [60 Kg N/ha (F) and O Kg N/ha (WF)]. A complete randomized design was used, with three replications. The grazing period was 24 hr, and the stocking-rate was fitted each time. Every eight weeks ten samples were randomly cut from each plot, using wire!oard (0.20 x 0.20 m). The samples were separated by hand in five components (ryegrass, white clover, other grasses, other legumes and dead material), to estimate the percentage contribution of each of them. The number of tillers per unit area for the ryegrass fraction was counted. The results showed that the percentage of ryegrass was greater (P < 0.05) with summer grazing treatment and autum fertilizer application, due to a greater number of ryegrass tillers per unit area in these treatments. The dead material was higher in low intensity grazing during the spring, clausure in summer and not fertilized in autumn. There were no significant differences (P > 0.05) in the other components. These results reinforce the idea that some managements (grazing in summer and fertilization in autumn) would stimulate ryegrass, growth, and their absence would allow an increment of dead material, thus affecting pasture production and tillering of the main species.