Fig. 5. Effect of the exchangeable Ca/Mg ratio (0.25:1–31:1) on the relative shoot dry weight of alfalfa at two P fertilization levels. Soils were prepared by mixing homoionic clays at various ratios, with K-saturated clays accounting for 10% of the total. Data taken from Hunter (1949). The dotted line indicates the "ideal" Ca/Mg ratio of 6.5:1 as stated by Bear et al. (1945).