ALFALFA Alfalfa Autotoxicity: Effects of Reseeding Delay, Original Stand Age, and Cultivar

autotoxicity has been most frequently identified as aAutotoxicity may reduce plant population and productivity of al-cause of reseeding failure (Webster et al., 1967; Tesar,falfa (Medicago sativa L.) reseeded into winterkilled alfalfa stands; however, the interaction of important variables such as reseeding 1993; Miller, 1996). delay, stand age, and cultivar with autotoxicity has not been evaluated. Autotoxicity is an intraspecific type of allelopathy We determined the effects of stand age (1-, 2-, or 3-yr-old alfalfa that occurs when a plant releases chemicals harmful to stands), reseeding delay (none or 2-wk delay) after plowing the origi- plant growth and development (Miller, 1996). Alfalfa nal stands in May, and cultivar reseeded (‘5262 ’ or ‘Wrangler’) on autotoxicity reduces establishment of alfalfa by reducing populations and productivity of reseeded alfalfa. Oat (Avena sativa seed germination and seedling growth on soils whereL.), corn (Zea mays L.), or tall fescue (Festuca arundinaceae Schreb.) alfalfa was recently grown. Root growth and forage yieldserved as controls. There was no consistent evidence for autotoxicity may also be decreased (Nelson et al., 1997). Alfalfain the reseeding year, as populations and forage yields were similar plants contain water-soluble compounds that are re-when seeding followed alfalfa or the control crops, regardless of the age of the previous alfalfa stand or the alfalfa cultivar reseeded. leased from fresh leaf, stem, and crown tissue as well Delaying seeding had inconsistent effects on alfalfa plant population as from seeds, hay, and dried roots (Nielsen et al., 1960; but consistently reduced yields in the seeding year, with yields averag- Hall and Henderlong, 1989; Hegde and Miller, 1992, ing 4.9 and 6.3 Mg ha1 with and without a 2-wk reseeding delay, Chung and Miller, 1995b; Miller, 1996); however, base