EFFECT OF ALFALFA PLANT AND SOIL EXTRACTS ON GERMINATION AND GROWTH OF ALFALFA

Alfalfa (Medicago sativa L.) plants contain water-soluble substances that inhibit the germination and seedling growth of alfalfa. Determining where allelochemicals may be found in alfalfa in the greatest concentration would aid in trying to isolate the compound or compounds responsible for autotoxicity. This study investigated the allelopathic effects of various alfalfa plant parts, and the soil in which alfalfa had been grown, on alfalfa germination and seedling growth. Aqueous extracts of alfalfa leaf, stem, flower, seed, and foot plant parts were made to determine their effects on germination and dry weights of hypocotyl, radicle and total length of 5-d-old alfalfa seedlings over a range of extract concentrations. Soil samples (Flanagan series: fine, montmorillonitic, mesic Aquic Argiudolls) from around alfalfa plants at the vegetative and reproductive stages were compared with sterilized and nonsterilized soil formerly seeded with alfalfa, hairy vetch (Vicia villosa Both), and winter rye (Secale cereale L.). Increasing the aqueous extracts concentrations of separated alfalfa plant parts significantly inhibited alfalfa germination, seedling length and weight. Radicle length was more sensitive to extract source than seed germination or hypocotyl length. Based on 5-d-old alfalfa radicle length growth, and averaged across all extract concentrations, the degree of toxicity of different alfalfa plant parts and soil from around alfalfa can be classified in order of decreasing inhibition as follows: leaf, seed, complete plant mixture, soil, root, flower, and stem. Leaf extracts (12 g kg(-1)) caused a 48% decrease in water uptake by alfalfa seed. Soil in which alfalfa had previously grown was the most inhibitory to alfalfa growth after 25 d of growth compared with soil where winter rye or hairy vetch had previously grown. Inhibitory effects were greater for soil collected around alfalfa grown at the reproductive than the vegetative growth stage. These data indicate that alfalfa autotoxicity may result from a release of one or more water-soluble compounds from alfalfa leaf tissue.