A field experiment was carried out on the experimental field of Cotton and Durum Wheat Research Institute, Chirpan, during the period 2004-2006. The following varieties were studied: Progres; Neptun 2; Beloslava; Saturn 1 and Vozhod under four norms of nitrogen fertilization – N 0 , N 6 , N 12 , N 18 kg.da -1 – applied only once in the early spring, having had cotton predecessor. For the two years of research, as well as for the period on the average, the applying of increasing nitrogen norms changes considerably the grain yield of all durum wheat varieties. N 12 norm proved to be the optimum whereas the further increasing of the norm results in decreasing of the yield. Vozhod variety proved to be the most productive, while the least productive was Beloslava variety.

durum wheat; nitrogen fertilization; productivity

Presentation: oral