Journal of Crop Production and Processing

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Cultivation of winter cover crops such as wheat and barley is one of the practical approaches for weeds control in cereal-based rotations. In order to investigate the effect of cover crop species and nitrogen rates on weed control of rapeseed (Brassica napus L.), a field experiment was arranged in split-plot based on a RCBD with three replications during 2013-2014 growing season at Research Field of School of Agriculture, Shiraz University, Shiraz, Iran. Treatments included nitrogen levels (75 and 150 kg N ha^-1) as the main factor and cover crops (no cover crop as control, 25% wheat, 50% wheat, 75% wheat, 25% barley, 50% barley and 75% barley) as sub factor. The results showed that there was significant difference between the presence and absence of cover crop and its interaction with nitrogen level in terms of an array of measured traits. The lowest density, dry weight and height of weeds were obtained from the using barley as a cover crop at the presence of both nitrogen rates, suggesting that barley cover crop is more potent to suppress the weeds compared to wheat cover crop. The highest grain yield (5290 kg ha^-1) and oil yield (1760 kg ha^-1) of rapeseed were obtained from 50% barley cover crop and the highest rapeseed protein percentage (43%) was obtained from using 25% wheat cover crop at 150 kg N ha^-1. Overall, the highest grain and oil yields were achieved from application of 150 kg N ha^-1 along with using 50% barley cover crop treatment, though the latter combination did not significantly differ from 75 kg N ha^-1 at 50% wheat cover crop

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In order to evaluate the reaction of foreign genotypes and the indigenous cultivars of barley against drought and study their biochemical traits, eight genotypes with two barley cultivars were surveyed in a randomized complete block design with three replications in two states of sufficient irrigation and non-sufficient irrigation regimes (drought) at the Faculty of Agriculture, Shiraz University, Shiraz, Iran in the cropping year 2013-2014. The main factor included drought stress and complete irrigation treatments; the sub-factors included genotypes and barley cultivars. The results showed that drought reduced the content of chlorophyll a, chlorophyll b, and carotenoids in all genotypes, causing 18.9, 26.2 and 12.6% reduction in these traits, respectively. The chlorophyll a/b ratio in this study was increased under drought stress conditions. The least reduction in the concentration of pigments was related to Youssef genotype and genotypes 79 and 120, which were considered tolerant. The activity of superoxide dismutase, catalase and peroxidase enzymes was also increased significantly under drought stress. The results also showed that the catalase enzyme had a low activity among the enzymes examined in the study; therefore, it played a role in the plant protection against drought stress, while the peroxidase enzyme was recognized as the best biochemical criterion for drought tolerance. The highest activity of this enzyme in the drought stress conditions was obtained in Yousef (74.44%) and the genotype 120 (72.61%); on the other hand, the lowest activity in the stressed plants was found to be in Basil (50.78%). In general, the genotypes 95 and 120, with the mean grain yield of 8809.7 and 8925 kg ha^-1, were recognized as the best genotypes in both non-stress and drought stress conditions. Therefore, drought could have a different effect on the biochemical traits of barley genotypes, and this difference was probably related to their stress tolerance.