GAP COLONIZATION BY WEEDS IN A WHEAT CROP GROWN UNDER DIFFERENT CULTIVATION REGIMES

The effects of tillage systems (mouldboard plough, chisel, disk and no n-tillage, over 3 years) and gap openings during August and October of 0, 0.30 m x 0.30 m and 0.45 m x 0.45 m on the weed community were inv estigated in a wheat (Triticum aestivum L.) crop. Weed flora compositi on and species abundance were recorded in August, September and Novemb er and the data analysed with MULVA programs and non-parametric tests. The tillage system was more important than the timing or gap size on the weed floristic composition, and the changes in weed communities we re evident within a 3-year period in spite of herbicide use. Less dist urbing tillage systems (non-tillage and chisel plough) allowed the bui ld-up of a more diverse community, whereas the most disturbing one (mo uldboard plough) prevented high diversity in the weed community.