This research aimed at evaluating the effect of increasing coexistence periods with weeds on the nutritional components of the forage grass Brachiaria brizantha cv. Marandú under pasture renewal conditions. The experiment was arranged in randomized blocks with four replications, and treatments were represented by eight coexistence periods, namely: 0, 15, 30, 45, 60, 75, 90 and 120 days after seedling emergence. A phytosociologic evaluation was performed on the weed community at the end of the coexistence periods; later, weeds were eliminated by an herbicide formulated with aminopyralid+2,4-D (40+320 g L-1) at 2.5 L ha-1, applied in post-emergence. The fodder plants were evaluated at the end of the experimental period as for leaf-stem ratio, volumetric density of green leaf, volumetric density of total dry matter and main nutritional components, including: crude protein, neutral detergent fiber, ether extract, organic matter and mineral matter, and from this, the total carbohydrate content was calculated. The presence of weeds altered the pasture structure, since it affected negatively the leaf/stem ratio and the volumetric leaf density of B. brizantha. The coexistence also reduced the nutritional components of B. brizantha and determined that control measures should be adopted before reaching 30 days of coexistence between fodder plants and weeds.

The occurrence of weeds has been the main obstacle to vegetation recovery in Cerrado areas unduly occupied by agricultural and livestock activities. This study evaluates the effect of different pre-emergent herbicides on the emergence, survival, and early development of seedlings of the native species jatobá (Hymenaea stigonocarpa), urucum (Bixa orellana), dry flour (Albizia hasslerii), and white jurema (Mimosa interrupta). The experiment was carried out under greenhouse conditions in a completely randomized experimental design with five replicates, where the treatments were constituted by herbicides: isoxaflutole, applied at the doses of 100, 200, and 300 g ai ha-1 ; pendimethalin, at 500, 1000, and 4000 g ai ha-1 ; and trifluralin, at 600, 1200, and 2400 g ai ha-1 ; in addition to a control treatment, without the application of herbicides. Herbicide phytotoxicity was evaluated at 35 days after emergence for the number of emerged seedlings, number of leaves per seedling, seedling height and diameter, and root and shoot dry weight. With the results obtained, it is possible to affirm that under the conditions of the experiment, all the herbicides and doses used did not affect the emergence and early development of seedlings of species H. stigonocarpa and B. orellana. For species A. hasslerii, the dose of 300 g ai ha-1 of herbicide isoxaflutole was not selective. All doses of the herbicide trifluralin showed selectivity for species M. interrupta.

Razor grass (Paspalum virgatum L) is one weed that has gain importance because of its high seed production capability, mainly when pasture fields need to be renewed. Understanding seedling emergence behavior is crucial to devise strategies to manage this weed. This trial was carried out to evaluate the emergence pattern of razor grass seedlings on the basis of seed depth in the soil profile. The experiment was conducted in a green-house in a completely randomized design, with six replications. The treatments performed in a 11 x 3 factorial arrangement: eleven seeding depths (surface, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 and 10.0 cm) by three ecotypes (Rondonópolis, Redenção and Cacoal, Brazil). The effect of origin and seed depth was measured by number of emerged seedlings, emergence speed index, relative emergence frequency, mean emergence time and emergence synchrony of seedlings at 35 days after planting. The seeds of ecotype Rondonópolis had higher vigor than those of ecotype Redenção, which had higher vigor that the ones of ecotype Cacoal. The highest seedling emergence percentage, uniformity and speed were found when the seeds were located at the soil surface, regardless of seed origin. There was no seedling emergence when the seeds of ecotypes Rondonópolis and Cacoal were located at a depth equal to or higher than 8.0 cm; and of ecotype Redenção when they were at a depth equal or higher than 7.0 cm.

The world population growth and the increasing purchasing power have raised the demand for animal proteins, especially meat and milk. This has made it essential to intensify livestock production by making it productive, efficient and at the same time sustainable, which today is a great challenge for cattle ranchers. The objective of this study is to evaluate the effects of coexistence with weeds on productivity, nutritional quality and potential of greenhouse gas (GHG) emission by Guinea grass (Panicum maximum cv. Mombasa) in pasture renewal conditions. The experiment was set up in randomized blocks, four replications, with treatments consisting of eight periods of coexistence: 0, 15, 30, 45, 60, 75, 90 and 120 days after seedlings emergence. Phyto-sociological evaluations were performed in the weed community at the end of each coexistence period. The Guinea grass was evaluated as for morphological, chemical and bromatological parameters and as for the potential of total gas, methane and carbon dioxide emission. The results show that productivity, nutritional quality and energy value of Guinea grass decreases proportionally to the increase in the period of coexistence with weeds. The non-coexistence with weeds provides a better in vitro digestibility of organic matter and, consequently, decreases the GHG emission potential by the dry matter of Guinea grass.

The increased world population has raised the demand for animal proteins, forcing livestock to become productive, efficient, and environmentally sustainable. This study aimed to assess the effect of weed coexistence on productivity, nutritional quality, and potential production of greenhouse gases (GHG) by Convert HD364 grass (Urochloa hibrida cv. Mulato II) under pasture renovation conditions. The experiment was carried out in a randomized block design with four replications and treatments consisting of eight coexistence periods: 0, 15, 30, 45, 60, 75, 90, and 120 days after seedling emergence. Phytosociological assessments were performed in the weed community at the end of each coexistence period. The Convert HD364 grass was assessed for the morphological and chemical-bromatological parameters and for the GHG emission potential. Productivity, nutritional quality, and energy value of the Convert HD364 grass decreased proportionally with the increased period of weed coexistence. The non-coexistence with weeds results in a better in vitro digestibility of organic matter and, consequently, decreases the potential of GHG emission by the dry matter of the Convert HD364 grass.