The physiological contribution of the main stem and the three primary tillers to some components of wheat yield
A factorial experiment was conducted at the Experimental Station (A) of the Field Crops Department / College of Agricultural Engineering Sciences, University of Baghdad (Jadiria) during the winter season of 2014-2015.The study aimed to investigate the role of seeding rates and nitrogen levels in regulating tillering in wheat and its relationship to grain yield and its components. Treatments were distributed in the factorial experiment within Randomized Complete Black Design with three Replicates and four seeding rates 60, 80, 100 and 120 kg ha-1 and fertilized with four nitrogen levels 50,100,150 and 200 kg N. ha-1. The results showed that the interaction was differed significant into the effect on biological yield ton.ha-1 and harvest index% during the growing season, as the main stem MS was superior in giving average highest of biological yield value 0.257 ton.ha-1 and harvest index of 0.879% compared to the three primary tillers (the first tiller T1, the second tiller T2 and the third tiller T3), Concerning seeding rates 100 kg. ha-1 resulted in the highest average of total biological yield of 13.84 kg. ha-1. compared to other seed rates. The nitrogen levels have exceeded 150 kg N. ha-1. gave the highest average biological yield of 16.365 kg. ha-1. compared to the other levels. The proportions of the contribution of the main stem differed from the three primary tillers in the biological yield and harvest index by the influence of the within two study factors. The percentage of the main stem contribution amounted to 57.59 and 37.21%, respectively, compared to the three primary tillers (T3, T2, T1), which amounted to 23.59, 12.21 and 3.81, respectively, for the biological yield of 33.66, 18.23 and 7.94%, respectively, for the harvest index within the two study factors. We concluded that the ratio of the contribution of the lower (older) tillers in the formation (location) is the highest compared to the higher (late) tillers in the formation within the two study factors.