Effects of salt source and irrigation water salinity on growth, yield and quality parameters of Stevia rebaudiana Bertoni

摘要

Soils and irrigation waters contain multiple types of salt, each of which may exert different effects on plant cultivation. In this study, it was aimed to investigate the effects of different salt sources (CaCl2, Ca(NO3)(2), MgCl2, MgSO4, NaCl and Na2SO4) in irrigation water with different salinity levels (0.7, 1.5, 2.5 and 4.0 dS/m) on growth, yield and quality parameters of stevia in addition to soil, and drainage water. It was found that seasonal evapotranspiration, plant growth, yield and quality parameters of stevia plant generally showed less variation among irrigation water salinity levels for salt sources containing SO4 than those containing Cl and NO3. Water-yield response factors of stevia plant were determined as 1.58, 1.37, 1.45, 2.04, 1.68 and 2.15 for CaCl2, Ca(NO3)(2), MgCl2, MgSO4, NaCl and Na2SO4 salts, respectively. These values indicate that stevia plant is very sensitive to water stress originating from osmotic effect of each salt source. The order of salt sources for threshold salinity values of dry herbaceous yields of stevia plant were determined as Ca(NO3)(2) > Na2SO4 > MgSO4 > NaCl > CaCl2 > MgCl2. Similarly, the order salt sources for slope values indicating the relative yield decrease for per unit increase in salinity after the threshold values were obtained as Na2SO4 < MgSO4 < MgCl2 < Ca(NO3)(2) < NaCl < CaCl2. These results show that salt type in irrigation water is as important as the level of irrigation water salinity. In general, it can be concluded that water resources containing Cl should not be used for irrigation purposes in stevia cultivation.