Exudation of Glyphosate from Wheat (Triticum aestivum) Plants and Its Effects on Interplanted Corn (Zea mays) and Soybeans (Glycine max)

Abstract

Glyphosate [N-(phosphonomethyl)glycine] applied at 1.1 kg/ha to wheat [Triticum aestivum (L.) ‘Arthur 71′] plants increased height and fresh weight of soybean [Glycine max (L.) Merr. ‘Ransom′] seedlings planted in the pot at time of application of the glyphosate as the number of wheat plants treated increased from 5 to 30/pot. Height and fresh weight of the soybean seedlings also increased as the rate of glyphosate applied to wheat plants (5/pot) increased from 1.1 to 6.7 kg/ha. Increasing the rate of glyphosate from 1.1 to 6.7 kg/ha, however, reduced the height and fresh weight of soybeans when 30 wheat plants/pot were treated. In addition, when 6.7 kg/ha of glyphosate were applied to wheat plants, soybean-seedling plant height and fresh weight decreased as the density of wheat plants per pot increased from 5 to 30. The 14C-glyphosate exuded into the soil from treated wheat plants was characterized by thin-layer chromatography. Trace amounts of the radio-label were present on thin-layer plates of leaf and stem extracts of corn (Zea mays L.) plants, which were growing in the same pots with the treated wheat plants. The zone of activity had the same Rf value as the glyphosate standard.