Effect of nitrogen fertilizer levels on some agronomic and physiological traits of wheat cultivars (Triticum aestivum)

In order to evaluate radiation absorption and use efficiency for wheat cultivars under effect of nitrogen fertilizer levels, a split-plot experiment based on the randomized complete block design with three replications was conducted during 2015-2016. The treatments were four nitrogen fertilizer levels (90, 180, 300, 360 kg.ha-1 of urea) as main-plot and four wheat cultivars (Parsi, Zare, Pishgam and Orum) as sub-plot. The evaluated traits were included leaf area index, radiation absorption, crop growth rate, relative growth ratio, leaf dry weight, stem dry weight, total dry weight, radiation use efficiency and grain yield. The results showed that Pishgam cultivar compared to other cultivars had the most satisfying in terms of evaluated characteristics under nitrogen fertilizer rate treatments. By increasing the rate of urea fertilizer from 90 to 360 kg.ha-1, maximum leaf area index, radiation absorption, crop growth rate, relative growth ratio, leaf dry weight, stem dry weight, total dry weight and grain yield were improved. The most (8950 kg.ha-1) and the lowest (1264 kg.ha-1) grain yield weight were observed for Pishgam cultivar in 360 kgurea. ha-1 treatment and for cultivar variety in 90 kgurea. ha-1 treatment, respectively. The results also showed that the highest and the lowest radiation use efficiency were related to Pishgam cultivar (1.59 g.MJ-1) in 360 kgurea.ha-1 treatment and Orum cultivar (0.67 g.MJ-1) in 90 kgurea.ha-1 treatment, respectively. It seems that rising of nitrogen fertilizer by improvement of photosynthesis and crop growth rate caused to pick up dry matter accumulation and finally increased wheat radiation use efficiency.