Effects of supplemental irrigation on the accumulation, partitioning, and remobilization of nitrogen, yield and water use efficiency of wheat cultivars

In the Mediterranean, unbalanced precipitation distribution causes drought stress in rainfed wheat cultivation. Under such conditions, supplemental irrigation (SI) is a highly efficient practice to reduce the adverse effects of drought stress and improve yield. The present study aimed to assess the effects of SI on traits related to N accumulation and remobilization, chlorophyll concentration, yield and yield components, and water use efficiency (WUE) in different cultivars. Two field experiments with four irrigation levels (I0= rainfed, I1= SI at booting stage, I2= SI at booting and anthesis stages, I3= SI at booting, anthesis, and grain filling stages) and five cultivars (Rejaw, Sardari, Homa, Azar2, and Sirwan) was conducted during the 2015-2016 and 2016-2017 wheat growing seasons. Overall, results showed that SI notably had a positive effect on chlorophyll concentration, N content of plant parts, N remobilization (NR), grain number per spike, 1000-grain weight, biological yield, and grain yield in cultivars. Although the grain yield in the three SI treatments was 237.1 kg ha(-1) and 630.4 kg ha(-1) more than the other two (I2) and one (I1) SI, respectively, but the WUE was slightly lower in this treatment. The cultivars exhibited apparent differences in their responses to SI. The Sirwan cultivar showed a higher reaction to SI amongst cultivars. The highest N remobilization efficiency (NRE) was observed in I1 (73.69%) and I0 (73.34%) irrigation treatments. Sardari (74.03%) and Azar2 (73.60%) cultivars had higher NRE than other cultivars. The minimum contribution of NR to grain appeared in the I3 treatment (74.54%).