Glyphosate residues in a sandy soil affect tomato transplants
1992
Cornish, P.S. (New South Wales Agriculture, Gosford (Australia). Horticultural Research and Advisory Station)
In a glasshouse experiment, visible symptoms of glyphosate toxicity occurred in tomato seedlings transplanted into soil that was sprayed 1, 5 or 15 days earlier with glyphosate (360 g a.i. per L) at 4 L product per ha. Glyphosate also reduced plant dry weight (16 days after transplanting), but only where soil nutrient deficiencies were corrected after transplanting. In the field, glyphosate residues reduced plant dry weight 16 days after transplanting, even when transplanting followed spraying by up to 9 days, and possibly as many as 30. The phytotoxicity of glyphosate residues in this loamy sand appears to result from a combination of inherently low P sorption capacity and application of superphosphate, leading to low adsorption of glyphosate by soil. This may be exacerbated when dry conditions occur between application and planting. On the present evidence, a plant-back period of 3 weeks could be considered safe when transplanting tomatoes into this sandy soil, provided some mixing of soil occurs at transplanting. It is recommended that farmers perform a simple bioassay to confirm safety.
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