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The effects of neutral salt and alkali on the ion distribution were investigated in two alfalfa ( Medicago sativa L.) cultivars, including Zhongmu 1, a high salt-tolerant cultivar, and Algonquin, a low salt-tolerant cultivar. The alkali stress expressed more serious growth inhibition than the neutral salt stress at the same Na+ concentration. Compared with Algonquin, Zhongmu 1 did not exhibit a higher alkali tolerance under the Na 2 CO 3 -NaHCO 3 treatment with the low Na+ concentration (50 mmol L −1 ). The alkali increased the accumulation of Na+, Ca 2+ , and Mg 2+ in the root and changed the Ca 2+ and Mg 2+ balance in the entire alfalfa plant. The salt and alkali stresses decreased the K + and Fe 3+ contents of the roots and leaves, the root Mn 2+ content, and the shoot Zn 2+ content, but they increased the Fe 3+ accumulation of the shoots, the shoot and leaf Cu 2+ contents, and the leaf Zn 2+ content in both alfalfa cultivars. Based on the results obtained under the conditions of this experiment, we found that the salt and alkali stresses reduced the plant growth in both alfalfa cultivars, while the alkali caused a stronger stress than the neutral salt in alfalfa. Thus, we conclude that under hydroponic conditions, the deleterious effects of the alkali on plants are due to the distribution change of some trophic ion balance in the roots, shoots, and leaves of the plants by causing of Na + , CO 3 2− , and/or HCO 3 − stresses.