Effect of soil type on the allelotoxic activity of Medicago sativa L. residues in Vicia faba L. agroecosystems

The inhibitory effects of alfalfa (Medicago sativa L.) residues on seed germination, nutrient uptake and growth of broad beans (Vicia faba L.) grown in two soil types (clay and sandy soil) were investigated. An 8% aqueous extract of M. sativa strongly inhibited (41.2%) the seed germination index and the plumule and radicle lengths (by 8.6 and 4.1 cm, respectively) as compared with controls. The phytotoxicity of the aqueous extract increased from 9.9% to 59% when the concentration was increased from 1% to 8%.Addition of M. sativa crude powder significantly reduced the accumulation of total stem, leaf and root dry matter when applied at the maximum concentration (8%) in both clay and sandy soil, with greater inhibition in plants grown in clay than in sandy soil. The maximum concentration of the crude powder had a greater negative effect on N, P and K uptake when applied to clay soil than when applied to sandy soil. The study indicates that soil type is an important factor in the allelopathic effects of alfalfa on broad beans.