Formononetin Levels in Subterranean Clover (Trifolium subterraneum L.) as Affected by Phosphorus and Sulfur Nutrition1

Effects of six rates of P and three of S on the level of the estrogenic isoflavone formononetin in ‘Dwalganup’ subterranean clover ( Trifolium subterraneum ; L.) were evaluated. With increasing rates of fertilizer P and S the concentration of formononetin in leaf blades decreased significantly (at the 1% level). The P ✕ S interaction was not statistically significant. The decrease in formononetin concentration may have resulted from a “dilution effect” and/or a decrease in isoflavone synthesis.