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Weed species diversity in spring barley varies with crop rotation and tillage, but not with nutrient source
- F. Craig Stevenson, Anne Légère, Régis R. Simard, Denis A. Angers, Denis Pageau, Jean Lafond
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- Journal:
- Weed Science / Volume 45 / Issue 6 / December 1997
- Published online by Cambridge University Press:
- 12 June 2017, pp. 798-806
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The development of sustainable farming systems depends on our ability to predict and manage the response of weed communities to changes in cropping practices. A study was established at Normandin, Québec, Canada, to investigate the influence of liquid dairy manure and mineral fertilizer, as well as chisel and moldboard plow tillage systems, in a spring barley monoculture and a 3-yr spring barley-forage rotation that included red clover and timothy. Weed species richness (Margalef's DMG), evenness (Shannon's E), and diversity (Shannon's H') were examined in these treatments from 1992 to 1995. Nutrient source had no effect on any of the three diversity indices. Evenness values were extremely low in all years, suggesting dominance of a few weed species in most treatments. Weed species richness and diversity generally were greater in the barley-forage rotation compared with the monoculture. Tillage effects on richness and diversity varied with crop rotation. Margalef's DMG and Shannon's H' were greater in 1993 and 1995, but they were lower in 1994 when chisel was compared with moldboard plowing in the monoculture. In 1994, chickweed density was about five times greater in the chisel-plowed monoculture compared with other treatment combinations of rotation and tillage. In 1995, only one species with a density of six plants m−2 occurred in the moldboard-plowed monoculture compared with three to six species and densities of 51 to 832 plants m−2 in the other rotation by tillage treatments. Climatic conditions and herbicide use patterns in the different crop rotation treatments may have contributed to the more dynamic nature of weed species diversity in the barley monoculture. Reduced frequency of tillage and herbicide application; management of the forage stands, especially with regard to their termination; and improved soil resource availability likely explained the increased but more stable diversity of the weed communities in the barley-forage rotation.
Determination of allelochemicals in spring cereal cultivars of different competitiveness
- Ali Baghestani, Claudel Lemieux, Gilles D. Leroux, Regis Baziramakenga, Regis R. Simard
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- Journal:
- Weed Science / Volume 47 / Issue 5 / October 1999
- Published online by Cambridge University Press:
- 12 June 2017, pp. 498-504
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Competitive cereal cultivars are less susceptible than others to weed interference. Their characterization may provide selection criteria that can be used as guidelines to develop new, even more competitive cultivars. Root exudates are a potential means by which competitive cultivars reduce weed growth. The objectives of this study were to evaluate the effect of cereal root exudates on Brassica kaber (DC.) L. C. Wheeler growth, to isolate and characterize the allelochemical compounds released by spring cereal cultivars, and to determine if a relation exists between these allelochemicals and cultivar competitiveness. Highly competitive (HC) and lesser competitive (LC) cultivars of four crop kinds (Triticum aestivum L. [wheat], Avena sativa L. [wild oat], two- and six-rowed Hordeum vulgare L. [barley]) were selected based on previous work. Exudates from undisturbed root systems of B. kaber and cereals were collected and used in a bioassay test with B. kaber. Root exudates were analyzed for 16 common phenolic compounds using high-performance liquid chromatography (HPLC). Bioassays indicated that cereal exudates had no negative effect on B. kaber germination, but all concentrations of cereal root exudates inhibited B. kaber root and hypocotyl growth. As cereal root exudate concentration increased, B. kaber growth decreased. For each crop kind, B. kaber growth inhibition was greater with HC cultivars than with LC cultivars. The root exudates of all crop kinds and cultivars contained benzoic, caffeic, ferulic, o-coumaric, and vanillic acids as well as scopoletin. Para-hydroxybenzoic acid was found in exudates from T. aestivum, A. sativa, and two-rowed H. vulgare cultivars. Para-coumaric acid was not identified in root exudates from LC H. vulgare cultivars. Gentisic acid was produced by A. sativa and H. vulgare. Vanillic and o-coumaric acids along with scopoletin may be responsible for the allelopathic effects of H. vulgare, T. aestivum, and A. sativa cultivars. These three compounds may be useful as possible indicators of allelopathic potential of genotypes under development and thus considered for use in breeding programs.