An expressive area is cultivated during winter with black oat (Avena strigosa Schreb.) in Rio Grande do Sul State, Brazil, which provides a dense cover, affecting weed growth in soybean fields. Management systems for oat straw are variable, depending on the farmer's available equipment and desired management effects. The objective of this study was to evaluate black oat straw management effects on weed suppression and soybean yield. The experiment was carried out during 1997/98 growing season, at the Federal University of Santa Maria, Santa Maria, RS, on a typic Hapludalf soil. A completely randomized block design was used in a split-plot distribution with five replications. The straw managements were assigned as main plots: (i) combine harvested; (ii) not managed, stand-up straw; (iii) rolled with a knife-roll; (iv) disked; (v) mowed; (vi) without straw and no weed control; (vii) without straw and with weed control. The split plots consisted of with and without post-emergency herbicide control of weeds . Above ground weed dry biomass, density of weeds and soybean grain yield were measured. The black oat straw management tested had no effect on total weed density and Brachiaria plantaginea (Link) Hitchc. density until 15 days after soybean seeding. Management disked and without straw and no weed control reduced total weed biomass and B. plantaginea biomass, with the option of post-emergency herbicide control. Management combine harvested, stand-up straw, mowed and without straw and weed control were efficient in weed suppression, presenting no differences for the treatments with the option of weed control in post-emergency. Management combine harvested, stand-up straw, rolled with a knife roll, disked and mowed neither affect grain moisture at harvest nor the first legume height insertion. However, grain moisture at harvest was higher in treatment without straw and no weed control and lower in treatment without straw and weed control.
straw; weed biomass; herbicides
