Evaluation of Grain Yield and Protein Content of Barley in Response to Nitrogen and Weed Interference

In order to study the changes in leaf chlorophyll index (SPAD index), protein and grain yield of barley (Hordeum vulgare L. Var. Makoei) in response to nitrogen and weed interference, a set of experiments were conducted in the Research Station of the University of Tabriz, Iran. The experiment was carried out as split-plot, based on randomized complete block design with three replications. Different amounts of nitrogen (0, 40, 60 and 120 kg.ha-1) were allocated to the main plots and 10 weed interference periods (two sets) were assigned to the subplots. In the first set, the plots were kept weed-free up to Em (Emergence - 1st leaf emerged), El5 (5th leaf unfolded), Ti (Tillering - Main shoot and 3 tillers), Se (Stem elongation - 5th node detectable) and Ea em (Ear emergence - Emergence of head complete) growth stages (GS), corresponding to 10, 15, 23, 35 and 59 Zadok’s scales, respectively. In the second set, plots were left weed infested up to the corresponding periods and subsequently kept weed free. Results showed that nitrogen and weed interference period has significant effect on protein percentage and grain yield. The effect of nitrogen was also significant on SPAD index. All traits decreased with increasing weed interference duration. Moreover, SPAD index, protein percentage and grain yield of barley under weedy control were 7.35, 27.3 and 42.5 % lower than that under full season weed-free control treatment, respectively. There was positive relationship between nitrogen level increasing and improvement of SPAD index, protein and grain yield. Increasing amount of nitrogen to the stable level, increased tolerance of barley to the weed infestation. Also, with increasing nitrogen application, growth and grain yield of barley were increased. The results from this study can be applied in the transition period of intensive agriculture to low input and sustainable agriculture, in relation to the issues related to the desirable weed management and reduction of nitrogen fertilizer application.