Department of Plant Production, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria (Manuscript received 30 June 2017; accepted for publication 10 October 2017)
Abstract. The effect of nitrogen-phosphorus fertilization at nitrogen rates 0, 80, 120 and 160 kg.ha-1 and 0, 80 and 120 kg.ha-1 for phosphorus has been studied in durum wheat Predel cultivar, grown on leached vertisol soil type during the period 2012-2014 in the field of the Field Crops Institute – Chirpan. The results show that at alone nitrogen fertilization grain yield reaches 3,75 t.ha-1 at moderate N120, while at alone phosphorus fertilization the increase compared to the non- fertilized control (2,50 t.ha-1) is insignificant. At combined N120P120 the highest grain yield was obtained during the period – 4.50 t.ha-1, with 57.41% above the control. The harvest index of durum wheat grain variety Predel is 0.353 on average. Good HI results are formed at fertilization with P120 and N80P80.