Alfalfa fields wanted to test method for detecting autotoxicity before planting

Paige Baisley and Kim Cassida

Alfalfa is an important crop in American agriculture. It is especially valuable as a perennial forage crop for its high crude protein and energy content and ability to fix nitrogen. One ongoing challenge to alfalfa production is the unexplained phenomenon of alfalfa autotoxicity. Alfalfa autotoxicity occurs when alfalfa releases chemicals into the soil that inhibit establishment and productivity of new alfalfa seedlings. Autotoxicity sometimes prevents germination outright, or if seedlings do succeed in emerging, taproots may be permanently damaged. Plants may compensate by increasing branching roots, but these cannot fully replace the taproot function. In this case, stands may appear successful and healthy during the planting year but have low lifetime yield and decreased persistence.Many environmental and management factors influence the severity and persistence of autotoxicity. The variety, age, fertility and general stress of the original stand can influence the severity of autotoxicity. Soil type, decomposition conditions, rotation interval and irrigation can influence how long autotoxicity remains in a field. The compounds causing autotoxicity remain unidentified but are likely phenols and water soluble. Because of these complexities, best management practices for avoiding autotoxicity in a production field remain unclear.A major drawback of alfalfa autotoxicity is that it prevents growers from being able to thicken declining alfalfa stands by over seeding more alfalfa. Autotoxicity also inhibits alfalfa from successfully reseeding itself. This means that perennial stand density will inevitably decline until yields are no longer economical. To reduce the risk of autotoxicity in new alfalfa seedings, Michigan State University Extension recommends rotating out of alfalfa for six months up to two years. We are unable to be more specific because we simply have no way to know exactly when the autotoxicity is gone. More precise predictions regarding autotoxic potential of the soil would assist alfalfa producers to make appropriate planting decisions.To address this issue, researchers at Michigan State University are developing a soil bioassay that can be conducted as a mail in soil test for alfalfa growers through plant diagnostic service laboratories. The bioassay primarily measures root development in response to autotoxicity. It involves planting alfalfa in a thin layer of field soil on top of clear agar. The clear agar base allows us to observe root growth and root appearance, reduce the amount of soil required, and easily remove roots for fine-tuned measuring. The test takes only four days. This will allow producers to make quick planting decisions with confidence based on autotoxicity conditions, reduce yield losses from autotoxicity and allow collection of data that can be used to further understand alfalfa autotoxicity.Initial trials of the soil bioassay are promising and we are refining the test for consistency and accuracy. The next step is to validate that the soil bioassay accurately predicts autotoxicity under many different field conditions. We are now looking for production farms to assist with this task.We are looking for alfalfa producers in Michigan who will allow us to test their soils for alfalfa autotoxicity prior to planting alfalfa and then monitor seedling growth. We are looking for fields where alfalfa has been grown within the past year and will be replanted into alfalfa in 2023.We will visit farms to test the soils right before or at planting and then monitor alfalfa growth throughout the growing season to determine how the observed autotoxicity levels impact the new stand.If you can help us by providing a field, please contact Paige Baisley at