PurposeSaline stress limits agricultural production, which is more severe in semiarid regions. The umbu-cajazeira (Spondias sp.) is native to the semiarid region of Brazil. Studies on sources and forms of silicon application in Spondias sp. are unpublished. To evaluate the effect of Si applied through different methods on ecophysiology, biochemistry, osmotic and ionic homeostasis of Umbu-Cajazeira seedlings under salt stress.MethodsThe experiment was conducted in a plant nursery using a completely randomized design with five treatments: [T1 = ECw 0.5 dS m(-)1 (control); T2 = ECw 3.5 dS m(-)1 (salt stress); T3 = salt stress + 3.5 g of CaSiO3 (soil application); T4 = salt stress + 2.2 mL L(-)1 of K2SiO3 (foliar application); and T5 = T3 + T4], with eight replications.ResultsSalt stress negatively affected the growth, gas exchange, and photosynthetic activity of Umbu-Cajazeira seedlings. Si fertilization did not positively affect these traits compared to the salt stress treatment, differing only in the content of chlorophyll a, carotenoids, proline, amino acids, and sodium in leaves. Silicate fertilization was insufficient to mitigate the effects of irrigation water salinity (3.5 dS m1) on the photosynthetic activity and growth of Umbu-Cajazeira seedlings.ConclusionsCalcium silicate improves osmotic adjustment, amino acid accumulation, and calcium accumulation and reduces sodium content in the leaves of the Umbu-Cajazeira seedlings under salt stress.