Within the Ocimum genus there occur about 200 species in different varieties and forms. They differ in the essential oil content and quality, as well as in many morphological features. The studies conducted in the years 2008–2009 were aimed at defining the effect of basil cultivar (‘Kasia’ and ‘Wala’), as well as of the differentiated doses of CaCO₃ (6 or 12 g·dm^-3 of substratum) upon the biological value and chemical composition of the oil in the examined plants, grown in pots filled with transitory peat. A significant interaction was reported between the examined cultivar and CaCO₃ dose upon the yield of fresh basil plant weight. The highest yield (172.3 g·plant^-1) was obtained from plants of ‛Kasia’ cultivar, when a higher dose of CaCO₃ was applied (12 g·dm^-3 substratum). Lack of significant effect of calcium carbonate dose was reported upon the yield of fresh basil plant weight. In the examined objects similar fresh weight yield values were obtained. At a higher dose of calcium carbonate the unit plant weight equaled 165.9 g·plant^-1, and at a lower dose of CaCO₃ it was 160.2 g·plant^-1. The percentage of dry matter significantly depended on the cultivar. Basil of ‘Wala’ cultivar had higher dry matter content, (32.0%) compared to ‘Kasia’ (25.6%). Both the cultivar and calcium carbonate dose significantly affected the vitamin C contents in fresh basil herb. Increasing the CaCO₃ dose from 6 g·dm^-3 to 12 g·dm^-3 caused the increase of vitamin C concentration by 12.6%. Higher essential oil contents was characteristic of the herb of ‘Kasia’ plants – 1.33% compared to ‘Wala’ cultivar, in whose herb 1.03% of oil was determined. The qualitative composition of isolated oil depended on the examined factors. The predominating compounds were: linalool, 1.8-cineole, geranyl, D germacrene, γ-cadinene, Epi-α -cadinole. A certain differentiation was found in the contents of particular compounds in the essential oils of ‘Kasia’ and ‘Wala’ plants, as the effect of calcium nutrition.

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