Abstract
Field experiment was conducted at Karaj, Iran to evaluate the growth and yield responses of winter wheat tovarious densities of wild barley and nitrogen (N) application rates. The experimental design was split-plot with 3replications. The main factor was four N levels of 0, 130, 260, and 390 kg Urea per ha and the sub factor was weeddensities. Results showed that in unfertilized plots, wild barley densities of 80 and 160 plants per sq. metersignificantly decreased wheat plant height, LAI and tillers. In comparison to excess N and N deficiency treatments,the optimal N rate decreased wheat LAI losses at weed densities of 80 and 160 plants per sq. m. Wild barley hadgreater plant height and the number of tillers per plant at densities of 20 and 40 plants per sq. meter. At 130 kg Nper ha, weed densities of 20, 40, and 80 plants per sq. meter did not reduce the number of crop ear compared tohand-weeded plots. On unfertilized plots with 40, 80, and 160 weed plants per sq. meter, the reduction in numberof grains per ear were 18 and 38%, respectively. Nitrogen rates of 130 and 260 kg per ha increased crop and weedGNCs, whereas their STNCs were increased by N rate up to of 390 kg per ha. Added N resulted in higher winterwheat ANUE compared to weed ANUE.
Highlights
Competition from weeds is the most important of all biological factors that reduce agricultural crop yield
Maximum losses for winter wheat plant height due to wild barley competition on unfertilized plots occurred at the density of 160 weeds per sq. meter
Maximum suppression was found in wheat tillers per plant and leaf area index (LAI) as compared to weed-free plots (Table 3)
Summary
Competition from weeds is the most important of all biological factors that reduce agricultural crop yield. This occurs primarily because weeds use resources that would otherwise be available to the crop (Zimdahl, 2004). The magnitude of yield loss is affected by many agronomic and environmental factors, but most importantly by the weed density, and time of emergence relative to the crop (Zimdahl, 2004). Weeds reduce crop yield and profits by competing with the crop for soil moisture and nutrients, light, CO2 and space (Klingman & Ashton, 1982). The effects of weed density, N fertilizer, crop planting date, and weed emergence on competition between wheat and blackgrass (Alopecurus agrestis L.) was studied by Exley and Snaydon (1992)
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