Study on the Allelopathy of Alfalfa(Medicago sativa L.). I. Observation of allelopathy and survey for substances inducing growth inhibition.

Allelopathic effects of alfalfa (Medicago sativa L.) plants were investigated using soil previously grown with alfalfa (alfalfa soil). Alfalfa soil inhibited the emergence of alfalfa seeds and also the growth of alfalfa and radish. Methanol extracts from the alfalfa soil markedly inhibited the elongation of radish hypocotyl and alfalfa radicle, suggesting the presence of allelopathic substances. The incorporation of cut pieces of alfalfa shoots in the soil reduced seed emergence, hypocotyl elongation and dry weight in radish seedlings to 65, 73 and 81%, respectively, compared to the control. Aqueous extracts of alfalfa plants inhibited the elongation of radish hypocotyl and alfalfa radicle. Inhibition increased with increasing concentrations. Inhibition of radish hypocotyl and alfalfa radicle elongation was greater in root extracts than in shoot extracts. The presence of phenolic compounds as allelopathic substances in alfalfa soil, as well as in the alfalfa plant, was suggested using color reaction with diazotized sulfanilic acid.