Effect of nitrogen forms and placement methods on grain yield, total biomass production of wheat and nitrogen use efficiency using 15N tracer technique

A field experiment was conducted at Agricultural Research Station of ACSAD (Deir-Ezzor district in eastern of Syria) to assess the effect of nitrogen forms, rates and placement methods on the grain yield, the biomass yield, total N-uptake, nitrogen derived from fertilizer and nitrogen use efficiency using N-15 technique. The experimental design was split-split plot design with three replicates. Main plots were N fertilizer levels, placement methods were the sub-plots and source of N was the sub-sub-plot. The treatments consisted of two N sources (NH4 and NO3), four different N rates 0, 50, 100, 200 kg N/ha, and two placement methods (top-dressed TD and side-dressed SD). While only one rate of phosphorus fertilizer (80 kg P2O5/ha) was broadcasted to all plots. Wheat variety ACSAD-65 was tested in the experiment. Results indicated that, the grain yield, biomass yield and N-uptake increased significantly with increasing N rates in all treatments. The optimal grain yield was 6.5 and 6.1 t/ha for NO3 and NH4 at 100 kg N/ha rate under SD placement, respectively. The maximum N yield in whole crop yield of wheat was 250.3 and 237.2 kg N/ha at SID and 174.1 to 166.8 kg N/ha at TD placement for nitrate and ammonium respectively at 200 kg N/ha applied as NO3 or NH4. Also, the effect of placement methods on above parameters was significant in most cases. The nitrogen use efficiency in grain and biomass yield was decrease significantly with increasing N rate.