Corn and Soybean Response to Allelopathic Effects of Weed and Crop Residues1

Abstract Many crop plants and perennial weed species have been known for their allelopathic effects. The question of whether annual weed species can be allelopathic remains unanswered. Consequently, studies were conducted in laboratory, greenhouse, and in the field to determine the allelopathic potential of weed and crop residues (above ground biomass) on corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. Water extracts of dried residues of common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), fall panicum (Panicum dichotomiflorum Michx.), giant foxtail (Setaria faberi Herrm.), green foxtail [Setaria viridis (L.) Beauv.], and yellow foxtail [Setaria glauca (L.) Beauv.] inhibited radicle elongation in corn; whereas, only common lambsquarters extract reduced coleoptile growth. Redroot pigweed, fall panicum, and green foxtail extracts inhibited hypocotyl elongation in soybeans. Residues of common ragweed (Ambrosia artemisifolia L.), velvetleaf (Abutilon theophrasti Medic.), and barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] as well as the above species inhibited corn and soybean growth in the greenhouse. Inhibition of the receiver species (corn and soybeans) was greater with the double‐pot watering method than subsurface and surface watering methods. Corn was inhibited most in silica sand, less in a silica sand and silt loam mixture (Typic Agriudoll fine, silty, mixed mesic), and least in silt loam soil under each method of watering. In the field, residues of barnyardgrass and giant foxtail reduced corn yield. Soybean yield reductions occurred ranging from 14 to 19% with common lambsquarters, redroot pigweed, velvetleaf, soybeans, and sunflower (Helianthus annuus L.) residues. Corn and giant foxtail residues enhanced soybean yield in the field. These results demonstrate the allelopathic potential of the residues and suggest that these residues may affect crop yields due to the inhibitory or stimulatory effects of allelochemicals present in the residues.