Phytotoxicity of vulpia residues .1. Investigation of aqueous extracts

Phytotoxic properties of vulpia (V. myuros) residue extracts on wheat (Triticum aestivum L. cv. Vulcan) were examined in the laboratory. Vulpia residues contained water-soluble materials that were toxic to germination and to coleoptile and root growth of wheat. There were strong correlations between extract concentration and toxicity, between extraction times and toxicity, and between extract pH and phytotoxicity. The phytotoxicity was residue rate dependent. There was no significant correlation between the phytotoxicity of residue extracts and the electrical conductivity of aqueous extracts. Milled residues were more toxic than chopped residues. The toxicity of vulpia residues increased as their decomposition proceeded, reaching a peak phytotoxicity after decomposition for 40 days and remaining potent for up to 60 days, gradually declining thereafter. Radicle elongation of wheat was the most sensitive indicator, germination was the least sensitive, and coleoptile growth was intermediate. The phytoxic effects of residue extracts on seed germination had two aspects: germination delay and inhibition. The relative magnitude of each aspect depended upon the potency of the extracts. With a strong phytotoxic potential, inhibition of germination was dominant over seed germination, whereas with a weak toxic level, delay was dominant over seed germination.