Effect of Saline Irrigation Water on Alfalfa Growth and Development in Saline–Alkali Soils

Saline irrigation water can enhance agricultural production in water-scarce regions. Alfalfa (Medicago sativa L.) is a moderately saline-tolerant legume forage grass, and growing alfalfa in saline–alkali areas under irrigated conditions has high economic and ecological benefits. However, the effects of saline water irrigation on sodium chloride (NaCl)-dominated saline–alkali soils for alfalfa growth and development remain unclear. We evaluated the change in salinity of saline–alkali soils and monitored leaf photosynthetic and respiratory indicators, biomass allocation, and ion content of different organs of alfalfa plants under five treatments: irrigation with freshwater (S0); irrigation with saline water of ECiw = 4 mS cm−1 (S1), ECiw = 8 mS cm−1 (S2), and ECiw = 12 mS cm−1 (S3); and drought treatment (H). The results showed that there were no significant differences in leaf relative conductivity, belowground biomass, and yield in the S1 treatment compared with those of the S0 treatment; the biomass was significantly decreased by 21.42% and 31.83% under S2 and S3 treatments, but both were higher than the H treatment. Soil salinity increased with the increase in water salinity, and the difference in total soil salinity was not significant between the S0 and S1 treatments, while the total soil salinity of the S2 and S3 treatments was significantly higher than that of the S0 treatment. In conclusion, irrigation with NaCl saline water of ECiw = 4 mS cm−1 does not significantly affect alfalfa growth and physiology. This study provides theoretical support for the safe use of saline water for irrigation in sodium chloride-dominated saline–alkali soils.