effect of water hardness on sinosulfuron efficacy in redroot pigweed and common lambsquarter control

in order to study the effect of water hardness on sinosulforun efficacy an experiment was carried out under controlled conditions in 2010 at the college of agriculture, ferdowsi university of mashhad. treatments included herbicides doses at 6 levels (0, 200, 250, 300, 350 and 400 g.a.i ha-1), calcium carbonate concentration at 6 levels (0, 100, 300, 600, 1000 and 1500 ppm) and weeds at 2 levels (redroot pigweed and common lambsquart), were evaluated as a completely randomized design in a factorial arrangement with three replications. spray was done at 6-8 weeds leaf stag. 2 weeks after spray weeds survival and shoot dry matter measured. for results analysis, data analysis of variance was done and plants response to sinosulforun doses on deferent water hardness level was fitted with sigmoid 4 parametric equations to the shoot biomass data as a function of the herbicide doses and was used to calculate the herbicide dose for 50% inhibition of plants shoot growth (id50). results showed herbicide rate and water hardness had significant effect (p<0.01) on both weeds growth and survival. increasing of herbicide rate decreased survival and growth on both weeds in pure water spraying. increasing water hardness decreased sinosulforun efficacy in both weeds control. maximum and minimum weeds biomass production was obtained at 1500 and 0 ppm of calcium carbonate respectively in each rate of sinosulforun. common lambsquarter and redroot pigweed did not responed differently to increasing of herbicide doses, but by increasing of water hardness, common lambsquarter tolerance to sinosulforun was more than redroot pigweed. increasing water hardness, increased id50 parameter in both weeds. maximum (1485.5, 917.75 g ha-1) and minimum (1302, 768.8 g ha-1) of sinosulforun id50 indicated for common lambsquart and redroot pigweed at the highest level of water hardness and pure water respectively.