In order to evaluate the effect of irrigation intervals and cattle manure levels on morphological traits, essential oil content and yield of oregano, an experiment was conducted at the experimental Farm of the Faculty of Agriculture, Urmia University, Iran. The experimental design was split-plots, arranged in randomized complete blocks with three replications. Main plots including irrigation intervals (1, 2 and 3 weeks) and four levels of cattle manure at 0, 10, 20 and 30 t ha-1 were allocated to sub plots. Our results showed that increasing irrigation intervals reduced values of all morphological traits except for proportion of stems. Also, values for stems number, plant spread, stem diameter, leaf area, fresh and dry herb yield increased by increasing cattle manure levels. On the other hand, morphological traits not influenced by interaction of treatments except for plant spread and leaf area. The highest essential oil content (2.07%) and yield (66.62 kg ha-1) obtained in highest irrigation intervals and cattle manure levels. Whereas, 1 week irrigation interval without use of cattle manure produce lowest essential oil content (1.55%). For essential oil yield, the lowest value (46.37 kg ha-1) was found in 2 weeks irrigation interval with application of 20 t ha-1 cattle manure.

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