Afield experiment were conducted in winter season 2011-2012 at three different environmental locations, namely, the koya city /Erbil (570m above sea level and 44°38'E, 36°40' N), Mosul city (223m above sea level and 43°09'E, 36°19' N), and the Alton- koprey/kirkuk (276m above sea level and 44°15'E, 35°73' N) to determine the effect of seeding rates (200 , 300 , 400 , 500 and 600 seed/m2) on yield and its components of Five oat varieties (kangaroo , Mitika , Possum , ICARDA Short and ICARDA Tall). the experiment were conducted by randomized complete Block Design (RCBD) with split-split plot design with three replicates. The interactions between the three studied factors significantly affected the panicles number /m2, grains yield/h, grains filling rate, biological yield and harvest index. All studied characters of oat varieties increased with increasing seeding rates at the three locations expect harvest index of varieties (kangaroo , Mitika , Possum and ICARDA Short) at Alton-koprey location which affected negatively. The highest seed and biological yield for varieties Kangaroo and Mitika were achieved at koya location and seeding rate 600 seed/m2 while the highest seed and biological yield for varieties Possum and ICARDA Short were achieved at the same location with seeding rate 500 seed/m2, at the same location
The highest seed and biological yield for variety ICARDA Tall was achieved with seeding rate 400 seed/m2, All varieties in koya location significantly surpassed on mosul location varieties and the variety of last location surpassed on Alton-koprey location varieties. And the negative effect was on characters panicle length , grain number/panicle, seed index ,seed weight /panicle which gives low rates in Alton-koprey location at seeding rate 600 seed/m2. No significant effect for length of grain filling period was shown by increasing the seeding rate for varieties expect Possum variety in koya location.