Influence of tree shading on the desiccation of grasses with glyphosate and straw decomposition in a silvopastoral system
摘要
The use of herbicides in agroforestry systems does not consider the light intensity in the understory of trees. Interactions between plants, herbicides, and the environment can influence the response of Urochloa spp. to glyphosate. The objective was to evaluate the effect of glyphosate on Urochloa decumbens and U. brizantha and straw decomposition in a Silvopastoral System with different levels of shading. Two experiments were conducted with U. decumbens and U. brizantha in a completely randomized design with split plots and four replications. In the plots, four crop strips were allocated at 1–4, 4–7, and 7–10 m from the eucalyptus row, and a monoculture of grasses in full sun. In the subplots, rates of 1,440, 1,080, 720, 360, and 0.0 g a.e. ha−1 were applied to U. decumbens, and 2,160, 1,680, 1,200, 720, and 0.0 g a.e. ha−1 to U. brizantha. All rates controlled U. decumbens in shaded areas, and control was achieved from 1080 g a.e. ha−1 in full sun. For U. brizantha, all rates above 1200 g a.e. ha−1 resulted in 100% control. At 720 g a.e. ha−1, control of U. brizantha was greater than 80% in full sun and less than 100% in the center of the tree rows. In a no-till system with 20 m row spacing, U. decumbens and U. brizantha were controlled with 360 and 720 g a.e. ha−1, respectively, regardless of tree spacing. In the Silvopastoral System, the savings with the use of glyphosate at lower rates were 67% for U. decumbens and 40% for U. brizantha, compared to grass monoculture.