Competition effects on yield, tissue nitrogen, and germination of winter wheat (Triticum aestivum) and Italian ryegrass (Lolium multiflorum)

Field experiments were conducted to study the competition effect of winter wheat planted in a square arrangement and Italian ryegrass planted randomly on biomass yields of both species, ryegrass seed yield, N use efficiency, and progeny seed germination. Increases in wheat density up to 800 plants/m (2) reduced ryegrass seed yield by 87% but increased its harvest index up t o 42% compared to its monoculture yield. Species densities and their intera ctions accounted for 66 to 73% of the total variation in per-unit area biom ass of species, and their association was more favorable to ryegrass biomas s than wheat. Seeds of each species had three times greater nitrogen percen tage than did shoots. Intra- and interspecific competition increased nitrog en percentage in wheat seeds. In Italian ryegrass, only interspecific compe tition increased N percentage in seeds. Although total nitrogen uptake by w inter wheat was three times greater than in Italian ryegrass, Italian ryegr ass was two times more efficient than wheat at producing biomass per unit o f N taken up and specific leaf area at heading stage in mixture. Germinatio n percentages of progeny seeds of both species in mixtures were greater in presence of high densities of the companion species than in their monocultu res. Nitrogen was not the main limiting factor for competition between wint er wheat and Italian ryegrass in this study.