Effects of sodium sulphate, sodium chloride and manganese sulphate on kikuyu (Pennisetum clandestinum) growth and ion uptake

Irrigation with saline water is increasingly practised yet an understanding of plant response to different salt types remains largely elusive. Our study investigated the effects of irrigation with simulated effluent containing three salts on the growth and composition of a common South African pasture grass. We treated pots of kikuyu (Pennisetum clandestinum Hochst. ex Chiov.) in a controlled environment with solutions of sodium sulphate (Na2SO4) or chloride (NaCl) at saturated soil solution electrical conductivity (EC) of 0, 5, 10 and 20 dS m-1, combined with 0, 900 or 1800 mg kg-1 Mn as MnSO4. Kikuyu yields in the Na2SO4 treatments were significantly lower than in corresponding NaCl treatments. This could be explained by increased ion imbalance and osmotic stress as a result of higher ionic strength and a greater concentration of neutral ion pairs in the Na2SO4 system at similar EC. An apparent Na2SO4-induced Ca deficiency was attributed to suppressed Ca2+ activity through ion pairing at high ionic strengths. Under the conditions of this experiment ionic strength appeared to be more effective than EC as a measure of salinity stress when comparing the effects of SO4 and Cl on growth of kikuyu.