Effect of corn plant residue and mixture of atrazine plus metolachlor on the weeds control in no-till corn system

The objective of this work was to study the effect of corn plant residue an d mixture of atrazine plus metolachlor on weed control in no-till corn syst em. This experiment was performed in an Oxisol, and the weed desiccation wa s done using glyphosate, 15 days before planting. The experimental design w as a randomized block, with three replications. Before corn planting, five levels of corn plant residues (0, 3, 6, 9 e 12 t ha(-1)) were equally distr ibuted in the plots. Two treatments were applied in subplots after corn pla nting: one without herbicide and the other one using the commercial mixture of atrazine plus metolachlor (1,200 + 1,800 g ha(-1)). Different weed spec ies were evaluated, at 26 and 41 days after planting. The total grass weeds number was significantly affected by the plant residue levels, independent ly of herbicide treatments and of evaluation period. The herbicide did not show a significant effect in the first evaluation period. However, in the s econd evaluation period, the herbicide reduced about 53% the total number o f weeds compared to the plots without herbicide. It was verified that in th e herbicide absence the total population of weeds were significantly higher in the second evaluation period. However, in the herbicide presence there was no significant difference in the total population of weeds between the two evaluated periods.