M. J. Malakouti - College of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
A. Baybordi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
M. Lotfolahi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
A. A. Shahabi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
K. Siavoshi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
R. Vakil - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
J. Ghaderi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
J. Shahabifar - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
A. Majidi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
A. Jafarnejadi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
F. Dehghani - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
M. H. Keshavarz - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
M. Ghasemzadeh - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
R. Ghanbarpouri - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
M. Dashadi - Soil and Water Research Institute, Tehran, Islamic Republic of Iran.
M. Babaakbari - College of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
N. Zaynalifard - College of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.

In order to increase grain yield, nitrogen use efficiency (NUE) and nitrogen apparent recovery fraction (NARF) in wheat (Triticum aestivum L.), this experiment was carried out with ۵ or ۶ treatments and ۳ or ۴ replications in ۱۴ locations at ۲۲ different sites in Iran during the ۲۰۰۴-۰۵ growing season. The experiment was designed as a completely randomized block. The effect of N sources and timing on the grain yield, protein content, NUE and NARF of the current best adapted cultivars of different regions were evaluated. The treatments included T۱= the control; T۲= ۱۵۰ kg ha-۱ of N as urea in ۳-split applica-tions; T۳= ۱۵۰ kg ha-۱ of N as urea in ۲-split applications; T۴= ۱۵۰ kg ha-۱ N as SCU as the base fertilizer; T۵= ۱/۳ N as SCU as the base fertilizer +۲-split urea applications and T۶=۱/۳ N as complete fertilizer as the base fertilizer +۲-split urea applications. Protein content, NUE and NARF were calculated by measuring grain yield, N% and N-uptake. While the average grain yield and protein% for the control plots were ۲,۸۴۰ kg ha-۱ and ۱۰.۰۳%; the yield and protein for T۲, T۳ and T۴ were ۴,۱۶۰ kg ha-۱ and ۱۱.۶۶%; ۴,۲۷۸ kg ha-۱ and ۱۱.۷۸%; and ۳,۹۲۱ kg ha-۱ and ۱۱.۶۰%, respectively. Grain yield and protein content for T۵ were ۴,۳۳۰ kg kg-۱ and ۱۱.۸۹%. Yield of ۴,۶۷۴ kg ha-۱ and protein content of ۱۲.۰۱% were ob-tained by substituting complete fertilizer with ۱/۳ urea (T۶). The grain yield for T۶ was significantly different from T۲ for various reasons, including higher levels of available P, K, S, Zn, lower N-leaching and appropriate N-timing. NUE for T۲, T۳, T۴, T۵, and T۶ was measured to be ۸.۸, ۹.۶, ۷.۳, ۹.۹, and ۱۲.۲ kg kg-۱, respectively, and NARF were calculated to be ۲۳.۲, ۲۵.۳, ۱۹.۴, ۲۶.۳ and ۳۱.۶%, respectively. While the superiority of complete and SCU fertilizers over pre-plant urea has been proven, especially in the light-textured soils, it is highly recommended that the experiment be further tested and evaluated, since this practice has been increased the grain yield up to ۱۲%, NUE up to ۳۹ kg kg-۱ and NARF up to ۳۶% in comparison with the best wheat growers’ N-fertilization practice.

Wheat, Yield, Complete fertilizer, NUE and NARF, Sulfur Coated Urea (SCU), Urea