Water hardness antagonism and the effect of ammonium sulphate (AMS) on efficacy of glyphosate have been well documented. However conflicting results between weed species were noted by the authors. Greenhouse experiment were conducted twice at the Ferdowsi University of Mashhad in a randomized complete block design with a factorial arrangement and three replications during 2014-2015. Four experiments were arranged separately on cypress (Kochia scoparia), redroot pigweed (Amaranthus retroflexus), little seed canary grass( Phalaris minor ) and winter wild oat (Avena ludoviciana) using ammonium sulphate and deionizad water and in the presence of different salts, (i.e. NaHCO3, CaCO3, MgCl2 and CaCl2 at 500 ppm) against three doses of glyphosate (256.25, 512.5 and 1025 g a.e. ha-1), with and without ammonium sulphate (AMS) as adjuvant (2% w/v). The results showed the application of AMS overcomes the inhibitory effects of salts in the spray solution in tested species. The degree of effectiveness in A. retroflexus was more than A. ludoviciana and P. minor . Glyphosate with AMS caused reduction in dry matter in grasses from 0.34 g to 0.28, while glyphosate toxicity in A. retroflexus with AMS was 100 percent and all of the plants were destroyed (0.82 to 0). The application of AMS in overcoming the inhibitory effects of water hardness had no effect on K. scoparia control. However, Increasing AMS, could overcome the inhibitory effects of hard water in the spray solution on glyphosate efficacy in A. retroflexus and K. scoparia, but it had no effect on tested grassy weeds. We may conclude that glyphosate work differently on weed species using AMS and hard water.

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