Class "A" Pan method was used for scheduling faba, cv. Gz 402, irrigation, under some potassium levels, through 1997/1998 and 1998/1999 seasons, In both seasons, a split plot design with four replications was used, where three irrigation levels (0.7 , 1.0 and 1.3 accumulative pan evaporation using Class "A" Pan, A.P.E.) were allotted at the main plots, meanwhile three levels of K (48,60 and 72 Kg / fed) occupied the sub-plots . A combined analysis was performed
The obtained data showed that most of important studied traits were significantly affected by both irrigation and potassium as well as their interaction . The sounded seed yield / fed, i.e. 1507 Kg was produced by the combination (1.3 A.P.E. X K72), without significant difference with the combination (1.0 A.P.E. X K72). The replacement between each irrigation and potassium levels was reported .
For achieving highest seed yield , faba could be irrigated by 1861.8 m3 / fed, allotted on five irrigations, of 21, 46, 39, 34 and 19 day intervals, at 250.0, 283.5, 371.7, 451.5 and 505.1 m3 / fed, respectively The lowest values of both ETp and Kc were estimated by the use of modified Penman method , while the use of Blaney and Criddle method gave the highest values. The general mean of Kc was 0.67. The highest W.U.E., among treatments of both irrigation and K was the same, i.e. 0.93 Kg / m3. Such valuewas shown on the highest level of both irrigation and potassium. The highest W. U.E. allover the study, i.e. 1.02 Kg / m3 was resulted by applying the combination (1.3 A.P.E. X K72) .