Glyphosate [N-(phosphonomethyl)glycine] was less phytotoxic when applied in 190 L/ha of well water with ionic strengths of 0.005 or greater than in distilled water. At a carrier volume of 24 L/ha, this inhibition of glyphosate was reduced or eliminated. Glyphosate was less phytotoxic when applied in 10-mM solutions of CaCl2, FeSO4, Fe2(SO4)3, MgSO4, NaHCO3, Na2CO3, and ZnSO4 than in distilled water. Adding H2SO4, HCl, HClO4, acetic, and lactic acids at 5, 10, and 50 mM to the spray solution resulted in variable increases in glyphosate phytotoxicity. H2SO4 was the most effective acid tested in increasing glyphosate phytotoxicity when added to well water. Lowering the pH of the spray solution by using potassium biphthalate and phosphoric acid buffers did not increase glyphosate phytotoxicity.

Several inorganic salts added to the spray solution reduced the herbicidal activity of glyphosate [N-(phosphonomethyl)glycine]. Of the salts tested, iron and aluminum reduced herbicidal activity most. Reductions by calcium and zinc were moderately severe; by magnesium, moderate; by potassium and sodium, none. The reduction in phytotoxicity seems to be caused by cations, but factors other than valence also may be involved.

Reduction in phytotoxicity was related to salt concentration and spray volume. Glyphosate at 0.84 kg/ha in 93 to 374 L/ha distilled water killed test plants. Tap water was an equally effective carrier at 93 and 187 L/ha volumes, but was significantly less effective at the 374 L/ha volume. Activity decreased as the molar concentration of CaCl2 increased to 0.01. Herbicidal activity was eliminated at 0.01 M and 374 L/ha; however, concentrations of CaCl2 exceeding 0.04 M reversed the trend and reacted similarly to a 0.005 M solution, which approximates the minimum hardness of most ground waters in Kansas.