M. Gerdzhikova*

Department of Plant Growing, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria (Manuscript received 12 December 2016; accepted for publication 20 February 2017)

Abstract. During the period 2008-2011 the influence of the predecessors wintering peas, spring peas, sunflower and common wheat and different levels of nitrogen fertilization: 0 (N0), 40 (N40), 80 (N80), 120 (N120) kg/ha after legumes and 0 (N0), 60 (N60), 120 (N120), 180 (N180) kg/ha after the other predecessors on the productivity of common wheat was studied on the experimental field of the Department of Plant Growing, Trakia University. It was found that with cultivation of common wheat without fertilization after legume predecessors higher yields by 9.4 % were obtained compared to the other predecessors. The highest yields were obtained at fertilization with the highest nitrogen rates: after legume predecessors 4069.8 kg/ha grain; after sunflower and wheat 3853.2 kg/ha of grain. The strongest influence on the productivity of common wheat had nitrogen fertilization as a factor with 79.80 %. The yield of wheat grain correlates very well with the level of nitrogen fertilization and can be determined approximately by regression equations based on the quantity of nitrogen as an independent variable.