A field experiment was conducted at the Universidade Federal do Rio Grande do Sul, in Eldorado do Sul, RS, Brazil, during 1996/97, to assess alexandergrass (Brachiaria plantaginea) seed mortality placed under five levels (0 to 10,5 t/ha) of black oat residues, two seed depths (0 and 2 cm), and five burial periods (40 to 300 days after straw management). Straw levels below 5,2 t/ha increase seed mortality. Seeds placed at 2 cm had higher mortality than at 10 cm, except at bare soil, when the seed mortality was similar at both seed depths. The time necessary to get 50% seed mortality was 5 and 72 days after straw placement, for straw levels of 0 and 10,5 t/ha, respectively. The results suggest crop management techniques that keep weed seeds unburried have more potential to reduce the weed infestation than techniques that accumulate high levels of residues at the soil surface, because of increased weed seed mortality.
No-till; soil conservation; crop residues; weed; Brachiaria plantaginea