Three different levels of biochar addition in soil (0, 1, 2 kg m-2) and simultaneous irrigation treatments (50, 85, and 120% of crop Evapotranspiration (ETc)) were applied to basil (Ocimum basilicum L.) for two consecutive years (2018 and 2019). Central Composite Design (CCD) was used as an experimental optimization method, and 13 given experiments were carried out. The study was performed at the research farm of the Ferdowsi University of Mashhad, Iran. The effects of these treatments were evaluated on biochemical attributes (total chlorophyll, total phenol, and total soluble carbohydrates) and morphological criteria (biological yield, height, seed yield, and harvest index). Then, all the results were statistically analyzed. The results revealed that biochar amendment in the soil decreased all examined biochemical characteristics. Meanwhile, biochar in the soil strengthened the morphological properties of the basil plant. Also, the basil plant significantly responded to the amount of irrigation levels. High levels of water treatments reduced total phenol and total soluble carbohydrates and raised all other measured factors. Statistical analysis shows no significant relationship between 2-way-interaction (biochar×irrigation) and measured factors, except total soluble carbohydrates.

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