Galia Panayotova Trakia University, Faculty of Agriculture, Stara Zagora, Bulgaria

Svetla Kostadinova Agricultural University, Faculty of Agronomy, Plovdiv, Bulgaria

The aim of the study was to analyze the agronomic response of durum wheat during 1990-2014 to nitrogen rates 0, 40, 80, 120 and 160 kg.ha-1. It was found that without N durum wheat realized grain yield of 2.34 t.ha-1. The highest yield was obtained at 120 kg N.ha-1. The partial factor of productivity decreased with the increase of N from 74.7 kg.kg-1 (N40) to 24.1 kg.kg-1 (N160). No proven differences were found in the agronomic efficiency for rates of N40 to N120, as the values were 17.0 - 14.9 kg grain.kg-1. The use of 160 kg N.ha-1 reduced the N agronomic efficiency by 40% compared to N40. A strong positive correlation was obtained between N rates and yield (r = 0.930*). The strong negative relationship was proven by N and by partial factor productivity and agronomic efficiency.