Effect of Preceding Crops and Supplementary Irrigation on Yield and Yield Components of Two Varieties of Common Wheat (Triticum aestivum L.)

The experiment was carried out at the farm of the Faculty of Agriculture and Forestry, University of Duhok, Kurdistan Region, at Sumail county, for the growing season 2010-2011. A Randomized Complete Block Design (RCBD) in spilt-spilt plot arrangement, with three replications was designed including the preceding crops (Fallow, Barley, Sunflower and Cucumber) as the main plot, while the two supplement irrigations were allocated as a sub-plot, and the two wheat varieties (Abu Ghraib 3 and Sham 6) as sub-sub-plot. The results revealed that fallow land, sunflower and cucumber enhanced some traits and the highest values were recorded after cucumber for biological weight, grain weight per square meter and grain yield; which were (596.58 g, 270.64 g and 2.71 ton/ha), respectively. The increment in wheat grain yield after fallow, sunflower and cucumber in comparison with barley was 413.95%, 437.20% and 530.23%, respectively. The influence of supplementary irrigation was obvious, with the exception of harvest index and 1000-grain weight; all other traits were increased gradually by irrigation repetition. The increment in grain yield due to one and two irrigations was 37.5 and 84.55%, respectively, as compared to non-irrigation. Abu Ghraib 3 surpassed Sham 6 in the trait of number of grain/spike, it was 18.35 and 15.91, respectively. The weight of grain/spike was 0.55 and 0.50g, respectively. The least biological yield was noticed for barley with no irrigation (57.53), while application of two irrigations after fallow, sunflower and cucumber exceeded barley with an amount of 1104.59%, 1007.37%, and 1311.83%, respectively. The ultimate goal for growing wheat is grain yield; therefore it was raised after fallow, sunflower and cucumber in comparison to barley with no irrigation by 1195.45%, 1268.18%, 1536.36%, respectively. The results revealed significant interaction on some traits; they had no significant effect on grain yield and yield components between the three factors while the second order interaction was not significant.