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The influence of time of emergence of wild oat {Avena fatua L.) on its competition with wheat {Triticum aestivum L.) was studied, using boxes that allowed separation of root and shoot competition. The relative yield total for mixtures of wild oat and wheat, grown under different forms of competition and with different wild oat sowing times, was very close to unity, indicating that the two species competed fully for limiting resources. Wild oat was more competitive than wheat when the two species were sown simultaneously, due largely to its greater root competitive ability; the two species had similar shoot competitive abilities. When wild oat was sown 3 or 6 weeks later than wheat, wheat was more competitive than wild oat and the production of wild oat panicles was prevented. This was mainly the result of greater root competitive ability of the wheat, although shoot competitive ability was also greater. The effects of root and shoot competition were additive. It is concluded that in order to prevent the return of wild oat seeds to the soil, and hence obtain long-term benefit, it is necessary to control the wild oat seedlings emerging within the first 3 weeks after drilling a wheat crop. Influence de la date de levee de lafotle avoine sur sa competition avec le bleL'infiuence de la date de levee de la folle avoine {Avena fatua L.) sur sa competition avec le ble * To whom correspondence should be addressed.{Triticum aestivum L.) a ete etudiee en utilisant des containers permettant de differencier la competition des tiges et des racines. Le poids relatif total du ble et de la folle avoine en melange, tant sous differents ratios de competition et avec des dates de semis de folle avoine differentes, n'a pas beaucoup varie: ceci montre que les deux especes sont en competition totale pour les ressources limitantes. La folle avoine est plus competitive que le ble quand les deux especes sont semees simultanement, ceci etant du en plus grande part a sa competitivite racinaire: les deux especes ont une competition au niveau des tiges comparable. Quand la folle avoine a ete semee 3 a 6 semaines apres le ble, le ble s'est montre plus competitif et la production de panicules par la folle avoine a ete empechee. Ceci etait du principalement au resultat d'une competitivite racinaire du ble plus elevee, bien que la competitivite de la tige soit egalement plus elevee. Les effets de la competition de la tige et de la racine ont ete additifs. On en arrive a la conclusion que pour empecher le retour au sol des graines de folle avoine, et done d'obtenir un avantage a long terme, il est necessaire de lutter contre les plantules de folle avoine levant dans les 3 premieres semaines suivant le semis du ble. Einfluss der Keimperiode des Flug-Hafers auf dieKonkurrenz mit Weizen Der Einfiuss der Keimperiode des Flug-Hafers {Avena fatua L.) auf seine Konkurrenz mit Weizen {Triticum aestivum L.) wurde untersucht. Dabei wurde zwischen der Wurzel-und der Sprosskonkurrenz unterschieden. Der relative Gesamtertrag fur Mischbestande der beiden Arten ...

Summary Competition between wild oat (Avena fatua L.) and wheat (Triticum aestivum L.) was studied in two experiments; a replacement series model and a technique for separation of root and shoot systems. Wild oat and wheat in association resulted in a relative yield total very close to unity showing that the two species were‘crowding for the same space’(or competing for the same resources) and were‘mutually exclusive'. Wild oat was more competitive than wheat, as shown by its aggressivity relative to wheat, relative yields, shoot dry weights and other plant attributes. The greater competitive ability of wild oat was predominantly due to its greater root competitive ability, while the two species had similar shoot competitive ability. Root competition had a much greater effect on the relative performance of the two species than did shoot competition. The effects of root and shoot competition were additive.

Barley (Hordeum sativum) and field beans (Vicia faba) were grown in pure stands, alternaterow mixtures and within-row mixtures in two field experiments. In both experiments the Land Equivalent Ratio (LER), based on seed yield, was consistently greater than 1.0 only when the crops were grown in alternate rows. The LER was greatest (1.8) when the mixture included more barley than beans. Reasons for the yield advantage of alternate row planting are discussed. Barley was more competitive than beans in mixtures, but this was not significantly affected by planting pattern.