Purple nutsedge (Cyperus rotundus) foliage and tubers were tested for allelopathic potential against the following weeds; jute Chorchorus olitorius (broad leaved weed), and barnyard grass Echinochloa crus-galli (grassy weed) associated with soybean. In the greenhouse, during 2008 and 2009, foliage and tubers of C. rotundus were mixed with soil surface at 20, 40, 60 and 80 g/kg. C. rotundus negatively affected those of jute and barnyard grass particularly at 80 g. Jute was more susceptible to allelopathy by C. rotundus than barnyard grass. Inhibition in weed dry matter was higher with tuber than foliage residues. Tuber residues reduced the dry weight of jute and barnyard grass by 85.96% of the control and by 58.28% with 80 g, respectively. On the other hand, soybean growth and yield showed a high significant increase compared with unweeded pots. A high-performance liquid chromatography analysis showed that C. rotundus foliage contained the following phenolic acids: caffeic, ferulic, coumaric, benzoic, vanelic, chlorogenic and cinnamic.Tubers contained hydroxybenzoic, caffeic, ferulic, vanelic and chlorogenic.

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Two field experiments were conducted during two successive seasons of 2007 and 2008 in Meit Nagy Village, Meit Ghamr, Dakahlia Governorate, Egypt, to study the effect of some pre-or post-emergence herbicides either alone or accompanied with hoeing on soybean yield and its components and associated weeds. The results showed that the best treatments in controlling the annual bread leaves, annual grasses and total annual weeds throughout the vegetative period of soybean plants were : The pre-emergence application of Pendimethalin at 0.425 kg a.i./fed or Metribuzin at 0.140 kg a.i./fed followed by one hoeing (21 days after sowing) or post-emergence application of Bentazon at 0.180 kg a.i./fed preceded by one hoeing (21 days after sowing), or using hand hoeing twice (21 and 35 days after sowing) compared with single herbicidal treatments. Treatment of Pendimethalin at 0.425 kg a.i./fed followed by one hoeing improved the growth of soybean plants and resulting in the tallest plants, highest number of pods/plant, number of seeds/pod, seed index, seed yield/plant and per feddan and the highest oil % in the seeds as well as seed protein percentage compared to other weed control treatments.

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