The plant residues are the main part of the no-tillage system. Although these soil covers reduce weed population density, they might intercept herbicides when applied on the mulch. Field experiment, bioassays and chromatographic analysis were made using trifluralin at the rates: zero, 1200, 2400, 3600 and 4800 g.a.i/ha applied on 6000 and 12000 kg/ha of oat residues and on soil without mulch. Soil and straw samples were collected immediately after trifluralin application. Twenty four hours after trifluralin application the field was irrigated and more samples were collected for bioassays and chromatographic analysis. The results showed that the weed-crop competition was reduced under mulch conditions. The weed population were formed by Brachiaria plantaginea only. Trifluralin was not leached to the soil surface. This product was not detected neither in the straw nor in the soil after irrigation.
no-till; chromatography; residue