Adding up to be the nation’s third most valued crop as an $8.7 billion industry per year, alfalfa is a common sight on many dairies because of its nutrient profile. This perennial forage crop is known for its high crude protein level, energy content, and ability to adjust nitrogen levels. Unfortunately, alfalfa is also prone to autotoxicity and autosupression. In a Michigan State Extension article, Kim Cassida explained the challenges of autotoxicity.

The first sign of autotoxicity is direct failure of germination and seeding establishment when planting new alfalfa into soil that previously grew alfalfa, the extension specialist said. This explains why producers who overseed new alfalfa into aging stands see little to no growth.

Another common consequence of autotoxicity is also known as autosuppression. When this occurs, newly planted seedlings emerge and grow as normal. “Unbeknownst to aboveground observers, their taproots are permanently damaged, even when the new seedlings look superficially normal,” Cassida noted. Although the plant may make up for itself by side branching, it will not compensate for the damaged taproot, resulting in reduced persistence and limited lifetime yield. The extension specialist warned, “It will never be the plant it could have been.”

The question is, why does autotoxicity and autosuppression happen and what measures can we take to prevent them from taking place? Unfortunately, the root cause of alfalfa autotoxicity has not been identified. “Growth inhibiting chemical compounds released from alfalfa tissues into soil have been the leading suspects, including a large range of phenolics and saponins, but no single compounds or combination of compounds have been proven,” Cassida said. To prove this suspicion, which is known as chemical allelopathy, Cassida listed three requirements:

1. A plant must produce compounds capable of suppressing germination and growth.
2. Those compounds must be present at high concentrations in soil.
3. There must be no other plausible environmental or biological factors that could explain the problem.

While it is difficult to set up field trials to identify the causes of autoxicity because of the challenge of controlling all environmental, genetic, and management factors, researchers from Michigan State University are working to identify the issues. As they begin to unravel the answers, researchers are also aiming to find the compounds responsible and are studying how to determine the correlation of root function and soil microbiology in influencing chemical development and release.