The effect of nitrogen rates on wheat morphological traits and grain yield in different irrigation conditions

In a 2-yrs field study, growth pattern and grain yield of wheat as affected by different nitrogen levels under varied irrigation conditions were evaluated in Shiraz University during 2013-15 growing seasons. The results showed that in both years at anthesis and ripening stages in all irrigation treatments, except rainfed, 300 kg N ha-1 had the highest plant height, while the highest plant height in rainfed for all sampling stages was achieved in 225 kg N ha-1 treatment. In all irrigation treatments, except rainfed, the plots receiving more N had the higher leaf area index for all sampling stages. As water deficit was applied and intensified, the less N fertilizer was needed for achieving the higher dry matter production; so that the highest final dry matter in normal irrigation, irrigation cutting at grain filling and spike emergence and rainfed conditions for both years were obtained from 225, 225, 150 and 75 kg N ha-1, by 1195.1, 1115.2, 931.1 kg ha-1 and 517.6 at the first and by 1015.8, 957.9, 791.5 kg ha-1 and 389.9 kg N ha-1 at the second year, respectively. In both years, the highest SPAD index was observed from rainfed conditions and 375 kg N ha-1, and the highest grain yield was observed in normal irrigation with 150 kg N ha-1 by 568.1 and 515.5 kg ha-1 at the first and second years, respectively.