This study aimed to evaluate the morpho-physiology and oil yield of castor bean (cultivar 'BRS Energia') as a function of irrigation water salinity and cationic nature. The experiment was carried out using an Ultisol of sandy loam texture, in Campina Grande, Paraíba, Brazil. Six combinations of cations and water electrical conductivity (ECw) were studied (S 1 a randomized block design, with four replicates and five plants in each plot. Plants in the control treatment (S 1 ) were irrigated using

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... water of 0.6 dS m -1 , while the other treatments were irrigated using water of 4.5 dS m -1 , prepared using chloride salts of different cations. Gas exchanges, growth and oil yield of castor bean were more affected by ECw variation than by the cationic nature of the water. Among the tested cations, potassium promoted the highest values of gas exchange and growth except in the flowering and fruiting stages. Oil yield is the most sensitive variable to the cationic nature of irrigation water.