Effects of Nitrogen on Hordeum spontaneum (Koch) Competition with Winter Wheat

Hordeum spontaneum is an important weed of winter wheat (Triticum aestivum) fields in many parts of Iran where its cultural control has recently been considered. Field experiments were conducted to evaluate the growth, yield, and yield components responses of winter wheat cv. Shiraz to various Hordeum spontaneum population densities of 20, 40, and 80 plants m-2 and nitrogen (N) application rates of 0, 130, 260, and 390 kg ha-1. The experimental design was split-plot with 3 replications. The results showed that with added N, wheat plant height and tillers plant-1 were significantly decreased by weed density of 80 plants m-2, whereas without N, weed densities of 20, 40, and 80 plants m-2 significantly decreased plant height. With N, weed density of 80 plants m-2 significantly decreased wheat leaf area index (LAI) compared to weed-free plots. At 390 kg N ha-1, weed could produce higher LAI than crop. In the presence of the weed density of 80 plants m-2, wheat grain yield was reduced by 35, 32, and 25% at 130, 260, and 390 kg N ha-1, respectively. The results suggest that H. spontaneum had higher competitive ability than wheat at all N levels. Weed management should emphasize prevention of high N application rates, which has conventionally used in winter wheat fields of Iran, because the weed uptakes more N than crop