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Influence of Soil Texture on Alfalfa Autotoxicity

Coop. Extension Service, Univ. of Arkansas, Arkansas, P.O. Box 391, Little Rock, AR 72203
Nelson, Dep. of Agronomy, Univ. of Missouri, Agronomy, 210 Waters Hall, Missouri, Columbia, MO 65211

^* Corresponding author (jjennings{at}uaex.edu).

A rotation interval is recommended between alfalfa (Medicago sativa L.) stands to avoid negative effects of autotoxicity. Differences in soil properties such as texture can strongly influence allelopathic expression in plants and may explain the large variation in research results and recommended rotation intervals among states. A laboratory experiment was conducted to determine the influence of soil texture on alfalfa autotoxicity. Alfalfa extracts were passed though leaching columns filled with topsoil of either Sarpy fine sandy loam (mixed, mesic Typic Udipsamments) or Carlow silty clay loam (fine, smectitic, mesic Vertic Endoaquulls) and fractions were collected. Control columns for each soil were leached with distilled water only. Sequential fractions were added to 50 alfalfa seed in petri dishes. Radicle length and percentage germination were measured after 3 d. Active fractions reduced radicle growth more than percentage germination in both soils. The autotoxic chemical or chemicals moved through the Sarpy soil faster than through the Carlow soil. Fifty percent more water was required to move the active fraction of the extract through 10-cm colomns of the Carlow soil than the Sarpy soil. Maximum autotoxicity within a fraction was greater for the Sarpy soil, but the effects appeared in more fractions for the Carlow soil. The results indicate that similar amounts of the autotoxic factor in sandy soil will have a greater influence on alfalfa seedling growth than in the clay soil. Conversely, the same amount of rainfall will leach the autotoxic factor from a sandy soil while only diluting it in a clay soil. Soil texture and rain water throughput may interact to affect length of rotation intervals needed for successful reseeding of alfalfa. Field research is needed to determine if rotation intervals can be modified based on soil texture and irrigation or expected rainfall.

Received for publication April 14, 1997.

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