EFFECTS OF DECREASING THE LIGHT INTENSITY ON THE GROWTH OF AGROPYRON REPENS (L.) BEAUV. IN THE FIELD

Abstract

Summary. Small plots of Agropyron repens (L.) Beauv, were shaded with ‘Tygan’ screening fabric which transmitted approximately 46% of daylight. In 1968, plots were either shaded or unshaded throughout the experiment (from mid‐May until September) and in 1969, some plots were also shaded early (mid‐May to mid‐July) or late (mid‐July to September). In both experiments continuous shading halved rhizome dry weight but had a much smaller effect on shoot dry weight. It also decreased rhizome dry matter by 5%. With early shading there were fewer shoots and ears until mid‐July but this difference disappeared by September, because plants shaded early produced more shoots and ears after mid‐July than unshaded plants. Early shading slightly decreased the final percentage of shoots that developed ears. Early shading increased shoot height by mid‐July and late shading increased it by the end of the experiment. Effets de la diminution de l'intensié lumineuse sur la croissance de l'Agropyron repens (L.) Beauv, au champ Résumé. De petites parcelles d'Agropyron repens (L.) Beauv. ont été ombragiés avec du ‘Tygan’écran en treillis qui ne laisse passer que 46% environ de la lumère du jour. En 1968, les parcelles furent ombragées ou non pendant toute la durée de l'expérience (de mi‐mai à septembre); en 1969 certaines parcelles furent aussi ombragées précocement (de mi‐mai à mi‐julliet) ou tardivement (de mi‐jmllet à septembre). Dans les deux expériences, l'ombrage continu réduisit de moitié le poids sec des rhizomes mais eut un effet beaucoup plus faible sur le poids sec de la partie aérienne. II réduisit également de 5% la matière sèche des rhizomes. Avec un ombrage précoce, il y eut moins de tiges et d'épis jusquà mi‐juillet, mais cette différence n'existait plus en septembre paree que les plantes ombragées précocement produisirent après la mi‐juillet, plus de tiges et d'épis que les plantes non ombragées. L'ombrage précoce diminua le pourcentage final des tiges qui produisirent des épis. L'ombrage précoce augmenta la hauteur des tiges à la mi‐juillet et l'ombrage tardif eut le même effet à la fin de I'expérience. Auswirkungen verringerter Lichtintensität auf das Wachstum von Agropyron repens (L.) Beauv. Im Feld Zusammenfassung. Kleine Parzellen mit Agropyron repens (L.) Beauv. wurden mit ‘Tygan’ Abschirmmaterial, das etwa 46% des Tageslichts durchliess, beschattet. Im Jahre 1968 wurden die Parzellen während der gesamten Versuchadauer (von Mitte Mai bis September) entweder beschattet oder nicht beschattet; 1969 wurden auch einige Parzellen früh (von Mitte Mai bis Mitte Juli) oder spät (von Mittc Juli bis September) beschattet. In beiden Experimenten reduzierte durchgehende Beschattung das Rhizom‐trockengewicht um die Hälfte, hatte jedoch eine weit geringere Auswirkung auf das Trockengewicht der oberirdischen Teile. Die Rhizomtrockensubstanz war um 5% vermindert, Bei früher Beschattung würden bis Mitte Juli weniger Schosse und Ahren gebildet; dieser Unterschied war jedoch bis September wieder verschwunden, da beschattete Pfla...

Elymus repensbiomass allocation and acquisition as affected by light and nutrient supply and companion crop competition

“…Our results, similarly to Williams (1971), indicate that light has a relatively strong and early effect on E. repens biomass acquisition, allocation and morphological traits such as tillering, while the effect of reduced nutrient supply on E. repens biomass acquisition appears later and is most pronounced when light is not limited. Although single resource studies cannot be used for direct comparisons between limitations of different resources, this pattern is seemingly confirmed by studies on the effect of either nutrient supply (McIntyre, 1965;Turner, 1966) or light supply (Williams, 1970;Skuterud, 1984) on E. repens biomass allocation and acquisition. Moreover, Cussans (1968) found that crops that close their canopy early were particularly competitive against E. repens and therefore suggested that E. repens is particularly sensitive to light competition.…”

“…The primary mode of resource competition may also be important in determining how efficiently E. repens is suppressed in systems with under-sown companion crops. A number of studies have investigated the effects of resource limitation on E. repens and, at least in regards to limited nutrient and light, the rhizome biomass allocation appears to follow the same pattern as the root biomass (McIntyre, 1965;Williams, 1970Williams, , 1971Skuterud, 1984). Thus, crops that compete heavily for light should have an especially high suppression rate as they would not only lower biomass acquisition, but also change the E. repens allocation away from rhizome production.…”

Some factors affecting the performance of fluazifop‐butyl against Elymus repens (L.) Gould (=Agropyron repens (L.) Beauv.)

“…The results are in agreement with the known shade effects on rhizome and aerial growth of E, repens. (Williams. 1970;Caseley.…”

EFFECTS OF LIGHT INTENSITY, PHOTOPERIOD AND NITROGEN ON THE GROWTH OF SEEDLINGS OF AGROPYRON REPENS (L.) BEAUV. AND AGROSTIS GIGANTEA ROTH

“…Rhizome production by Agropyron repens plants established from rhizome fragments is decreased most by crops that shade the weed most (Cussans, 1968); halving the light intensity halved rhizome production (Williams, 1970b). Nitrogen fertihzer decreased rhizome production in Bromus inermis (Watkins, 1940} andin Poa pratensis (Harrison, 1934) but it increased rhizome number in Agropyron repens^ although it slightly decreased the number of primary rhizomes (i.e.…”