اثر ميزان و زمان مصرف نيتروژن بر آستانه خسارت اقتصادي خردل وحشي در گندم پاييزه

Effect of amount and timing of nitrogen application on economic threshold of wild mustard (Sinapis arvensis) in winter wheat

To study the effect of amount and timing of nitrogen application on economic threshold of wild mustard (Sinapis arvensis) in winter wheat, an experiment was conducted in 2001 at Farm Research of Mashhad College of Agriculture. Split plot design with three replications was used with factorial of weed density (0, 8, 16, and 32 plant.m^-2) and nitrogen (low=100,optimum= 150, and high= 225 Kg.ha^-1) as main plot. The sub plot included nitrogen split pattern (P1=113 at planting time+213 at tillering, P2= 113 at planting time + 113 at tillering + 113 at Shooting). Three-parameter rectangular hyperbolic model (Cousens, 1985) was fitted to yield loss data, and then economic threshold densities estimated from another model (OʹDonovan, 1991). Our results showed that nitrogen split pattern had no significant effect on wild mustard economic threshold in wheat. Economic thresholds of wild mustard in wheat were 0.94, 0.79, and 0.14 plant .m^-2 at low, optimum, and high nitrogen rates, respectively. Results showed that economic threshold of wild mustard in winter wheat at high nitrogen rate was the lowest; consequently high nitrogen rate application increased the competitive ability of wild mustard.