With the objective to evaluate the effects of different tillage systems and different methods of control on mulch of black oat (Avena strigosa) on evolution and control of weeds in soybean crop (cultivar 'IAC 14'), a field experiment was carried out in Fazenda Experimental Lageado - UNESP Botucatu - SP, in 1993/94. The different cultivation systems were no tillage and conventional tillage, and the last cultivation system was made with disk harrow and three tandem disk harrow. The weed control methods were: control (weedy check), pre-emergence herbicides (0,28 kg/ha of metribuzim + 1,29 kg/ha of oryzalin), post-emergence herbicides (0,25 kg/ha of Fluacifop-p-butil +0,25 kg/ha of fomesafen) and pre and post-emergence treatments (with the four herbicides in the same rates). Glyphosate was applied for weed and black oat elimination before the crop establishment. The experimental design used was a randomized block arranged in split-plots scheme with four replications. The different cultivation systems were applied on plots and the different weed control on sub-plots. In the early stages of crop development, the rain was scarce, limiting crop growth and performance of the preemergence herbicides. The number the weeds/m2 was evaluated at 14, 28 and 35 days after soybean emergency, showing differences between cultivation systems and among different control systems. Brachiaria plantaginea and Amaranthus viridis were predominant on conventional tillage, and less important on no-tillage system; the most important species in this system was Euphorbia heterophylla. On the conventional system, preemergence herbicides were the best control for A. viridis than to B. plantaginea; the control with post-emergence herbicides was unsatisfactory in both tillage systems. On the no-tillage systems the control of E. heterophylla was unsatisfactory in all studied situations. No-tillage systems showed a smaller number of weeds than conventional systems. The germination of weeds was restricted until 15 days after crop emergency in both tillage systems.
Avena strigosa; mulching; herbicide; tillage