Evaluation of Nitrogen Rate and Weed Interference Duration on Wheat Grain Yield and Nitrogen Use Efficiency

Presence of weeds and crops together in agro-ecosystems requires the much attention intheselection of agricultural practices. This experiment conduced in 2009 to determine nitrogen requirement to take maximum winter wheat yield with weed interference at agricultural research site in agricultural college، university of Mohaghegh ardabili. The experiment was laid out as split-plot in randomized complete block design with three replications. The treatments consisted of three nitrogen levels: [0 (control)، 75 & 150 kgNha-1] and duration of weed interference [interference during all season growth (T75)، interference for 50 days after April (T50) and weed control (T0)]. The experimental design was Split-plot design in randomized complete block with three replications. Results showed that in weed control plots، increasing the amount of nitrogen، grain yield increased from 2900 to 5128 kg ha-1. In weed interference، doubling the amount of nitrogen fertilizer increased yield loss more than 2 times. In plots without weed interference، doubling the amount of nitrogen increased nitrogen use efficiency from 1. 86 to 7. 43. While the interaction of weeds and wheat declined nitrogen use efficiency.