Evaluation the Effect of Water Quality and Soil Nitrogen Content on Glyphosate Efficacy on Common Lambsquart(Chenopodium album L.) control

In order to study the effect of soil nitrogen content and water hardness on glyphosate efficacy on common lambsquart control, an experiment was carried out as a completely randomized design in a factorial arrangement with three replications in 2011 at the College of Agriculture, Ferdowsi University of Mashhad. Experimental treatments were included soil nitrogen content at 5 levels (0, 50, 90, 200 and 300 mg/kg soil), glyphosate doses at 7 levels (0, 75, 100, 125, 150, 175 and 200 % dose guideline glyphosate for common lambsquart), calcium carbonate concentration in water as index of water hardness at 5 levels (0, 100, 300, 600 and 1200 ppm). Spray was done at 8-10 common lambsquart leaf stage. 30 days after glyphosate spray, plants survival and shoot dry matter was measured. Results showed, herbicide rate, soil nitrogen content and water hardness had significantly affect (P<0.01) on growth and survival of common lambsquart. Increasing herbicide doses decreased common lambsquart survival and growth in pure water spraying. Increasing water hardness decreased glyphosate efficacy in control common lambsquart and increased glyphosate ED50 parameter. The lowest (1453.17 gr. a.i ha-1) and the highest (3424.45 gr. a.i ha-1) glyphosate ED50 for common lambsquart was observed in 0 and 1200 ppm of water hardness. Increasing soil nitrogen content from 18 to 300 (mg/kg soil) increased glyphosate efficacy in common lambsquart and glyphosate ED50 decreased from 3217.03 to 1612.58 (gr. a.i ha-1).