Natural Herbicide Potential of Alfalfa Residue on Selected Weed Species

Alfalfa (Medicago saliva L.) contains water-soluble substances that are 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 germination, seedling growth, and development. Various weed species were germinated in aqueous extracts from dried alfalfa using cold (5°C), warm (24°C), and hot (80°C) treatments. Results indicated that inhibition of weed seed germination was dependent on the aqueous 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 various rates. Root length was more inhibited than increase in shoot length. 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 increased from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophrasti Medic.) seed germination (25%). When alfalfa residue was incorporated with silica sand, the growth and development of lambsquarters, pigweed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and total, shoot, leaf, and root dry weight, were significantly inhibited as the rate increased from 0.0 to 2.0 g kg⁻. Dried alfalfa residue significantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromus secalinus L.). Results suggest that alfalfa residue has a contrasting effect on weed growth and development due to water-soluble allelochemicals present in the residue