THE COMPETITIVE ABILITY OF WHEAT (TRITICUM-AESTIVUM) COMPARED TO RIGID RYEGRASS (LOLIUM-RIGIDUM) AND COWCOCKLE (VACCARIA-HISPANICA)

Greenhouse and field experiments were conducted to study competition b etween wheat and rigid ryegrass or between wheat and cowcockle using a dditive series and growth analysis. Wheat was the dominant competitor with either weed. One wheat plant was as competitive as 11 or 19 rigid ryegrass plants in greenhouse and field experiments, respectively. On e wheat plant was as competitive as three to 24 cowcockle plants, depe nding on environmental conditions. Dry weight of roots, leaves, stems, and spikes or capsules responded similarly to the effects of competit ion between wheat and rigid ryegrass or cowcockle. Shoot dry weight wa s the easiest, fastest, and least expensive component to measure compe tition. Growth analyses of individual plants showed that wheat had a g reater leaf area, shoot and root dry weight, and absolute growth rate than rigid ryegrass or cowcockle, particularly early in the season. A range of 120 to 240 wheat plants m(-2) can minimize rigid ryegrass or cowcockle competition and achieve an acceptable grain yield in semiari d areas in Morocco.