Relationships between nitrogen utilization and grain technological quality in durum wheat: I. Nitrogen translocation and nitrogen use efficiency for protein.

Durum wheat (Triticum durum Desf.) is widely cultivated in the Mediterranean area where plants generally suffer from water stress during grain-filling period. This study was conducted to evaluate the influence of N levels and water regimes on N translocation and nitrogen use efficiency for protein (NUEP) in durum wheat grown under Mediterranean conditions. A 2-yr experiment was performed in southern Italy using four cultivars, two water regimes (irrigated and rainfed) and three N levels (0, 60, and 120 kg ha–1). Among the cultivars under study, Simeto showed the highest N translocation in both years and, together with Ofanto, also the highest NUEP values, especially in rainfed condition. This highlights their good adaptability to dry Southern Italy environment. Nitrogen fertilization caused a general decrease of NUEP and its components in both growing seasons; this was more evident in the first drier year, mainly due to a decrease in N uptake. Under water stress the higher N level caused a decrease in N translocation, N translocation efficiency, and grain N content. The contribution of translocated N to grain N content was 75% in the wetter year and 57% in the drier year, showing that in drought condition preanthesis N assimilation was lower. In conclusion under water stress condition the higher N level (120 kg ha–1), despite determining an increase in plant N content, did not imply an increase in grain N content, due to a decrease in N translocation and efficiency.