comparison of complete and sulfur coated urea fertilizers with pre-plant urea in increasing grain yield and nitrogen use efficiency in wheat

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 5 or 6 treatments and 3 or 4 replications in 14 locations at 22 different sites in iran during the 2004-05 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 t1= the control; t2= 150 kg ha-1 of n as urea in 3-split applica-tions; t3= 150 kg ha-1 of n as urea in 2-split applications; t4= 150 kg ha-1 n as scu as the base fertilizer; t5= 1/3 n as scu as the base fertilizer +2-split urea applications and t6=1/3 n as complete fertilizer as the base fertilizer +2-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 2,840 kg ha-1 and 10.03%; the yield and protein for t2, t3 and t4 were 4,160 kg ha-1 and 11.66%; 4,278 kg ha-1 and 11.78%; and 3,921 kg ha-1 and 11.60%, respectively. grain yield and protein content for t5 were 4,330 kg kg-1 and 11.89%. yield of 4,674 kg ha-1 and protein content of 12.01% were ob-tained by substituting complete fertilizer with 1/3 urea (t6). the grain yield for t6 was significantly different from t2 for various reasons, including higher levels of available p, k, s, zn, lower n-leaching and appropriate n-timing. nue for t2, t3, t4, t5, and t6 was measured to be 8.8, 9.6, 7.3, 9.9, and 12.2 kg kg-1, respectively, and narf were calculated to be 23.2, 25.3, 19.4, 26.3 and 31.6%, 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 12%, nue up to 39 kg kg-1 and narf up to 36% in comparison with the best wheat growers’ n-fertilization practice.