Natural grasslands have great seasonal fluctuation of forage production. The winter forage production may be increased using cool-season forage species established with no-till, reducing seasonal fluctuations. An experiment with winter grasses (black oat and rye grass) no-till sown on native grasses, was conducted during four years on a fine-loamy, mixed, active Mollic Hapludalf, sandy A horizon, in northern Uruguay. The experimental design was split-splitplot on randomized blocks, with types and dosis of herbicides (gliphosate 1L ha-1, gliphosate 4L ha-1, paraquat 3L ha-1, and a check without herbicides) as main treatments, applied in 1994. The application or not of the same treatments in 1995 constituted the splitplots, and their reapplication or not in 1996 constituted the split-splitplots.The results showed that the greatest disturbance on the botanical composition of the native grassland was caused with the application of the higher systemic herbicide dose every year. When herbicides were not applied, there were eleven species present, but with 4L ha-1 of glifosate every year there were only six species, as well as a substitution of perennial species by annual ones. The use of paraquat and the lower gliphosate dose showed intermediate effects between the native grassland without applied herbicides, and the treatment with the higher gliphosate dose. On the other hand, dry matter yield of the introduced winter forage species was 63% greater in the higher gliphosate dose than in the treatment without herbicide application, due to greater control of the competition by the native grasses.
forage production; no-tillage; native grasslands
