Field experiments, conducted during 1997/98 in Londrina, Parana, Brazil, bioassays and chromatographic analyses were conducted to investigate the effect of mulch (oat residues) on crop-weed competition and retention of imazaquin in no-till soyabean crop. Imazaquin was applied at 0, 75, 150 and 300 g/ha on 7000 and 14 000 kg/ha of oat residues and on soil without mulch. Twenty-four hours after imazaquin application, the field was irrigated and more samples were collected for bioassays and chromatographic analyses. The weed population consisted of Brachiaria plantaginea, Euphorbia heterophylla and Bidens pilosa. Oat residues intercepted 90% of the imazaquin before irrigation, indicating the potential of this herbicide in no-till system.
