NATURAL HERBICIDE POTENTIAL OF ALFALFA RESIDUE ON SELECTED WEED SPECIES

Alfalfa (Medicago sativa L.) contains water-soluble substances that ar e toxic: to itself (autotoxicity) and to other species (allelopathy). Experiments were conducted to determine the potential of using alfalfa residue as a natural herbicide for inhibition of weed seed germinatio n, seedling growth, and development. Various weed species were germina ted in aqueous extracts from dried alfalfa using cold (5 degrees C), w arm (24 degrees C), and hot (80 degrees C) treatments. Results indicat ed that inhibition of weed seed germination was dependent on the aqueo us extraction method, residue application rate (w/v or w/w), and weed species. The greatest inhibition of germination was 44%, when 60% (w/v ) warm aqueous extract was applied to lambsquarters (Chenopodium album L.). Seedling growth was also inhibited by residue application at var ious rates. Root length was more inhibited than increase in shoot leng th. In terms of total seedling length, giant foxtail (Setaria faberii Herrm.) was the most resistant species and lambsquarters was the most susceptible among the weed species studied to alfalfa aqueous extracts . Weed seed germination percentage decreased as incubation time increa sed from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophras ti Medic.) seed germination (25%). When alfalfa residue was incorporat ed with silica sand, the growth and development of lambsquarters, pigw eed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and t otal, shoot, leaf, and root dry weight, were significantly inhibited a s the rate increased from 0.0 to 2.0 g kg(-1). Dried alfalfa residue s ignificantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromu s secalinus L.). Results suggest that alfalfa residue has a contrastin g effect on weed growth and development due to water-soluble alleloche micals present in the residue.