ALLELOPATHIC ACTIVITY OF QUACKGRASS (Agropyron repens) EXTRACTS AND RESIDUES ON ALFALFA (Medicago sativa)

Abstract

Experiments were conducted to characterize the allelopathic activity of quackgrass on alfalfa. Both percent germination and seedling length of alfalfa were recorded to evaluate the toxicity of aqueous extracts from rhizomes or shoots of field-grown quackgrass harvested at three stages of growth in 1984 and 1985. The length of alfalfa seedlings was more sensitive to extracts than was percentage of germination. Aqueous solutions simulating levels of salinity, cyanide content and osmotic pressure equivalent to those found in quackgrass extracts did not affect the growth of alfalfa seedlings. Only quackgrass extracts were phytotoxic to alfalfa. Similar results with hot and cold extraction procedures demonstrated that temperature did not influence the release of water-soluble toxins. Shoot extracts were generally more toxic than were rhizome extracts. Shoot extracts were more inhibitory to alfalfa seedlings when quackgrass was harvested at the vegetative stage than at later stages. Rhizome extracts did not influence the germination of alfalfa, whereas shoot extracts of vegetative quackgrass did in 1985 but not in 1984. The tolerance of alfalfa to rhizome and shoot extracts differed among eight alfalfa varieties. Incorporation of rhizome and shoot residues into the soil caused a similar level of yield reduction, whereas peat moss residues did not influence alfalfa yield. When quackgrass residues were incorporated into soil at various times before seeding, the yields of alfalfa were progressively reduced as the period of incubation was shortened. The incorporation of peat moss did not reduce the yield of alfalfa at any periods.Key words: Allelopathy, quackgrass, alfalfa, aqueous extracts, plant residues, Agropyron repens