Increasing the amount of surface crop residues (SCR) can reduce annual weed density in no-till systems. The objectives of this work were to compare the effect of SCR on the infestation of the grass weeds Brachiaria plantaginea (BRAPL) and Setaria faberi (SETFA), and to assess the impact of SCR and weed control on soybean yield. Two factorial experiments were conducted in no-till system under the rotation wheat-soybean infested with SETFA (USA) and oats-soybean infested with BRAPL (Brazil). One factor was SCR (0, 3, 6 and 9tha-1 of wheat or oat straw), whereas the other factor was weed control with and without herbicides. Increasing SCR on the soil surface reduced grass weed density in no-tilled soybean. When weed control depended on herbicides, SCR did not affect soybean yield. However, when weed control depended on SCR, soybean yield increased with increment of SCR, due to reduced weed infestation. Soybean yield cizanged linearly with SETFA density and changed logaritmicaly with BRAPL density.
Brachiaria plantaginea; Glycine max; Setaria faberi; giant foxtail; straw levels; weed
