Field experiment was carried out at FayoumAgric. Res. Station, Tameia, Fayoum Governorate, Egypt. during 2013/14 and 2014/2015 winter seasons to study the effect of 80 and 100 kg N fed-1 (as liquid ammonia, 82.4 % N) and irrigating at 40, 60 and 80% of total available soil moisture were depleted (ASMD) on yield, yield components and some crop - water relations of wheat (Giza 168). A split plot design with four replications was applied, where N rates were assigned to main plots, whereas irrigation regimes were arranged in the split plots. The obtained results exhibited that:
*Wheat grain and straw yields as well as yield components i.e. plant height, spike number m-2 and 1000-grain weigh were significantly affected by N fertilizer rates, irrigation regimes and their interaction in 1st and 2nd seasons. Applying 100 kg N fed-1 and/or irrigating at 40% ASMD regime exhibited the highest values of the abovementioned parameters.
* Applying 100 kg N fed-1 and/or irrigating at 40% ASMD regime exhibited higher water use (Cu) values, whereas, 80 kg N fed-1 and/or irrigating at 80% ASMD regime resulted in the lowest values at 1st and 2nd seasons.The values of daily ETC was increased with increasing N rate, and the same trend was observed with irrigating at 40% ASMD regime and such findings were recorded in the two seasons of study. Reducing N rate from 100 to 80 kg Nfed-1 decreased the KC values during the entire growing seasons, and increasing the SMD from 40 to be 60 or 80% exhibited similar trends 1st and 2nd seasons.
* Values of WUE, as a function of N fertilization rates and irrigation regimes, were 1.25 and 1.22 kg grain m-3 water consumed at 1st and 2nd seasons, respectively. Applying 100 kg N fed-1 resulted in higher WUE values which comprised 1.26 and 1.23 kg grains m-3 water consumed at 1st and 2nd seasons, respectively. Irrigating wheat crop at 40% ASMD regime resulted in the highest WUE values, which reached to 1.28 and 1.25 kg grains m-3 water consumed at 1st and 2nd seasons, respectively. The interaction data reveal that the highest WUE values (1.29 and 1.26 kg grains m-3 water consumed) were occurred with 100 kg Nfed-1 rate as interacted with 40 % ASMD regime in 1st and 2nd seasons, respectively,