Emergence, Forage Production, and Ion Relations of Alfalfa in Response to Saline Waters

Alfalfa (Medicago sativa L.) is an important crop utilized in irrigated regions that are commonly impacted by salinity. We evaluated the effect of salinity continually from emergence to mature plant growth in successive harvests. We studied emergence, biomass production, salt tolerance, and shoot ion composition as potential physiological mechanisms in four nondormant salt-tolerant cultivars: Salado, SW 8421S, SW 9720, and SW 9215. Irrigation water salinity dominated by sodium sulfate ranging from 3.1 to 30 dS m(-1) of electrical conductivity (ECiw) was imposed at planting date. Plants were grown in outdoor sand tanks in Riverside, CA for 300 d. Relative emergence (%) decreased above ECiw 12.7 dS m(-1) and was reduced to 53 and 13.4% at 18.4 and 24 dS m(-1), respectively. At ECiw 30 dS m(-1) there were no survivor plants. Absolute and relative accumulated biomass from 6 harvests significantly decreased for ECiw above 12.7 dS m(-1) (6.0 dS m(-1) in the saturation extract [ECe]). Plants grown at 18.4 and 24 dS m(-1) produced 68% and 30% respectively of the biomass produced at 3.1 dS m(-1). Salado showed the least reduction in biomass at elevated salinity and, as with all the cultivars, exhibited yield increases in successive harvests from first through seventh. Increasing salinity increased shoot Na+, total-S, Cl-, Mg2+, and P and decreased K+ and Ca2+. The ability of Salado to maintain low shoot Na was the mechanism most associated with salt tolerance. Saline waters with resultant ECe values of up to 6 dS m(-1) did not significantly reduce total forage production of the second through the seventh harvests. This suggests that irrigation with saline waters resulting in ECe values less than 6 dS m(-1) can be used throughout the production cycle (planting to multiple harvests) without significant yield loss for the cultivars examined.