Salinity is an increasingly critical constraint on alfalfa production in arid and semi-arid regions. This study evaluated how alfalfa tissue Na accumulation and soil pH affect forage quality and biomass in saline-alkaline soils. During this work, paired field observational experiments were carried out in two ecologically contrasting alfalfa-producing regions of northern China: Huanghua (Hebei) with naturally saline-alkaline soils, and Hetao irrigation district (Inner Mongolia) characterized by controlled irrigation and lower salinity. Soil analyses followed a factorial design with location (2) & times; depth (0-20, 20-40 cm) & times; sampling cycle (3), resulting in 108 samples. Forage traits (biomass, CP, DMD, RFV, minerals) were evaluated in relation to location (2) & times; harvest cycle (3) & times; performance class (good, medium, poor; 3), adding up to 54 plots. In Huanghua, alfalfa accumulated up to 4.98 g Na kg(-)& sup1; DM, twice that of Hetao, while biomass declined by similar to 30 %, yet crude protein rose to 20 %, ADF fell below 22 %, and DMD reached 75 %. Soil pH showed weak correlations with forage traits (|r| <= 0.29), confirming Na as the dominant driver. Na content strongly reduced yield and height in Huanghua (r approximate to -1.0) but enhanced nutritional parameters (CP, DMD, RFV r >= +0.99), whereas in Hetao, reductions in yield (r = -0.68) and height (r = -0.67) were accompanied by moderate improvements in forage quality. Thus, Na concentration in alfalfa reliably indicates soil salinity and the inherent yield-quality trade-off, underscoring the potential of breeding salt-tolerant cultivars for sustainable forage systems.