The first one is obvious—direct failure of germination and seedling establishment when planting new alfalfa into soil that previously grew alfalfa. This is the reason that producers cannot effectively thicken aging alfalfa stands by overseeding with more alfalfa seed. The second consequence of autotoxicity, autosuppression, is both more common and harder to recognize. The specific cause of alfalfa autotoxicity has never been identified. This could explain why some failing alfalfa stands are more autotoxic than others.