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Summary. The average air-dry yield of weeds on fallow plots was about four times as large (2660 kg/ha) as the yield of weeds which developed among spring cereal crops (740 kg/ha). Application of fertilizers increased the number of weeds and their average weight on both irrigated and non-irrigated plots. Treatment with MCPA reduced the weed yield to 36% on fallow plots and to 26% on weedy cereal plots. It was more effective on fertilized plots than on unfertilized plots, but irrigation made little difference to its effectiveness. The space left by the destroyed weeds was mainly occupied by Agropyron repens . Oats were better able to compete with weeds than were wheat and barley. On unfertilized and non-irrigated plots spraying with MCPA (1-26 kg/ha) at the beginning of shooting significantly reduced the yields of weed-free barley. The yields of sprayed oats and wheat were also below the yields from the unsprayed although the reductions were not significant at the 5% level. However, on a number of fertilized and irrigated plots, both weedy and hand-weeded , on which the plants had better growing conditions, MCPA resulted in a significant increase in the grain yield of barley and oats.
Influence de l'irrigation, de la fertilisation et du MCPA sur la compétition entre céréales de printemps et mauvaises herbes  相似文献   
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Summary. The preparation of ioxynil, bromoxynil, and their salts is described, and information on solubilities and stability to storage is summarized. Although the toxicology of the herbicides is to be reported in greater detail, a preliminary statement is made here. Evidence of herbicidat activity under glasshouse conditions is indicated briefly, and supports the conclusion that both compounds are effective when applied to the foliage of a wide range of dicotyledon weed species. Seedlings of some weed species resistant to the phenoxy alkanoic acids are controlled under glasshouse conditions at doses as low as 0.125 lb/ac, and ioxynil has a wider range of activity than bromoxynil at these low doses. Graminaceous species tolerate 4–8 lb/ac of both herbicides without injury, and certain leguminous crops tolerate one or other herbicide at doses of 0.5–0.75 lb/ac. The contact action of the herbicides is rapid, there are also slower systemic effects, and seed germination is inhibited. In susceptible species the level of post-emergence activity is shown to be influenced by the growth stage of the weed, the distribution of herbicide on the foliage, and environmental factors of which light intensity appears to be most important.
Propriétés chimiques et biologiques de deux nouveaux herbicides: ioxynil et bromoxynil  相似文献   
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