Bicarbonates and carbonates are the main factors of alkalinity in irrigation water. In order to determine suitable growth medium for gerbera (Gerbera jamesonii L. cv. Dafne) under alkalinity stress condition, a factorial experiment with completely randomized design with 4 replications was carried out. The experiment consisted of 7 levels of substrate (100% perlite, 100% cocopeat, 75% perlite+ 25% zeolite, 75% peat+25% perlite, 75% cocochip+25% perlite, 75% cocopeat+25% perlite and 75% vermicompost+25% perlite) and NaHCO3 at three levels (0, 20 and 40 mM). The results showed that the highest and the lowest pH values amounts belong to 75% peat + 25% perlite and 100% cocopeat substrates. Sodium bicarbonate treatment, depending on the kind of growth substrate and NaHCO3 concentration, decreased number of flowers, flower fresh weight, flower stem length, flower diameter, flower neck diameter, flower vase life and chlorophyll index although, this treatment increased the phenolic compounds. The plants grown in 100% cocopeat substrate, when exposed to sodium bicarbonate, had better qualitative and quantitative traits, ability of higher accumulation of phenolic compounds and higher chlorophyll index, as compared to other substrates. Therefore, it is concluded that gerbera's tolerance to alkalinity is low and the use of pure cocopeat substrate could provide a useful tool to improve alkalinity tolerance of gerbera plants under NaHCO3 stress.

Keywords: Alkalinity of irrigation water, Cocopeat, Perlite, Hydroponics.

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