Effect of Nitrogen Application Management on Nitrogen Use Efficiency in Rainfed Wheat Using 15N Isotope

In order to study the effects of nitrogen application management on nitrogen use efficiency (NUE) in rainfed wheat, a field experiment was conducted as split plot experiment, based on randomized complete block design, included five rates of nitrogen (0, 30, 60, 90 and 120 kgN ha-1) using urea (labeled with 8% and 6% atom excess 15N) as the main plot in Kurdistan province during 2012-13. The sub-plots were consisted of three application times such as T1: Total nitrogen in the fall, T2: 2/3 nitrogen in the fall 1/3 nitrogen in the spring, and T3:1/2 nitrogen in the fall 1/2 nitrogen in the spring (at tillering stage). The isotopic (15N) technique was applied to estimate fertilizer N recovery efficiency based on recovery of labeled urea-15N in the aboveground portion of wheat (grain and straw). Results showed that the effects of nitrogen timing on grain yield and total N uptake were significant at 5% level. The effect of nitrogen rates were significant on grain yield, total N uptake,fertilizer N uptake, fraction of N in the plant derived from the 15N-labeled fertilizer (Ndff%), and NUE of 15N (p