Effects of Metam-Sodium on Weeds, Broomrape (Phelipanche aegyptiaca Pers.) and Soil Microbial Respiration in Tomato (Lycopersicon esculentum Mill.) Field

Broomrape is one of the most troublesome parasite weeds in the tomato fields of Iran that use of fumigant material is one of the way for its control. Five application doses 0, 500, 750, 1000, 1250, 1500 l ha-1 of Metam-Sodium were applied by shank injection in a tomato filed of Astan Qods in Mashhad during 2011. The experiment was arranged in a completely randomized block design with four replications. Plots were divided in two parts so that in one half only weeds were removed and in the other one both weeds and broomrapes were maintained throughout the growing season. Densities and dry weights of broomrape as well as weed size were measured in each half part separately. The results showed that Metam-Sodium was able to reduce weed density as three-parameter logistic dose response curve. The most tolerant weeds were pigweed and common lambs-quarters with ED50 of 474 and 775 l ha-1 respectively while common purslane, black night-shade and barnyardgrass were more sensitive. Despite weed reduction, there was no harvest for tomato because of high remained weed density that is probably more than weed threshold. Broomrape was not affected by metam-sodium but corresponding tomato yield increased in linear form. A decrease of soil respiration by Metam–sodium was expressed by the four-parameter Gompertze equation.