عنوان مقاله [English]
Among all the fertilizers applied in the field, nitrogen (N) is the most important element for plant growth, plant productivity and grain quality. It is important to define the complex trait of nitrogen-use efficiency (NUE) before considering its improvement through breeding and N management strategies. NUE defined as grain dry matter yield per unit of available N (from the soil and/or fertilizer) divided it into two components, including (i) N-uptake efficiency (crop N uptake/N available; UPE) and (ii) N-utilization efficiency (grain dry matter yield/crop N uptake; UTE). N utilization efficiency (UTE) divided into two components, including harvest index (HI) and biomass production efficiency (BPE). Nitrogen utilization efficiency comprises harvest index (HI) and biomass production efficiency (BPE). The objective of this study was to determine the significance and magnitude of variation in N content, NUE, NUpE, NUtE, and grain protein concentration among diverse barely genotypes in years of release. Specifically, we wanted to determine if there was a positive correlation between these factors and grain yield.
Materials and Methods
This field experiment was conducted under optimal condition, at the Gonbad University of Agricultural Sciences Research Farm, during the growing seasons of 2014-2015. The eight cultivars were sown in a randomized complete block design with four replications. Plots consisted of 5 rows with 5 m long and 0.20 m apart. Seeding rate was calculated for each cultivar using percentage germination and 1000-seed weight to achieve a density of 270 plant m-2. Plant samples were separated in two components at anthesis (leaf + culm and chaff-flowered spikes) and three components at maturity [leaf + culm, chaff (rachis, glumes, awns), and grain]. Samples were dried at 70˚C for 3 d and dry matter (DM) were weighed. N content of the plant parts was measured using a modified version of the Kjeldahl procedure. At harvest, a 1.5 m2 portions at the center of each wheat plot was sampled to determine their biomass and harvest index. Statistical analysis was carried out using the SAS software package. Differences among the treatments were evaluated with the least significant difference (LSD).
Results and Discussion
Analysis of variance for grain yield, NUE, NUtE and NHI traits showed that cultivars had significant differences in %1 level while protein percent and NUpE was significant in %5 levels. Nitrogen use efficiency ranged from 4.30 to 14.13 g m-2, depending on cultivar. Low yielding cultivars had the lowest NUE values. Average value for NUE was 6.99 g m-2. Relationships between NUE measurements with NUtE and NUpE were evaluated by linear regression. There was a strong and statistically significant relationship between NUE with NUtE and NUpE for all barely cultivars. Grain yield ranged from 184.87 to 603.11 gr m-2. Grain yield positively correlated with NUE and a negatively correlated with grain protein concentration.
The results revealed that during breeding activities for barely yield improvement, NUE and nitrogen utilization efficiency (NUtE) were increased; while there was no changes for nitrogen uptake efficiency (NUpE). Because NUE divided into two components of NUtE and NUpE, most of the breeding effects on NUE were associated with change in nitrogen utilization efficiency (NUtE). It seems that during year of release of barely cultivars no changes was observed for improvement of protein concentration. It appears that in studied cultivars, grain harvest index increased more rapidly than nitrogen harvest index which means no changes or decline of grain protein percent.