evaluating the effect of wheat residue and different rates of trifluralin (%48 ec) herbicide on the yield and oil content of sunflower (helianthus annuus l.)

leaving crop residues on the soil surface may significantly affect the behavior and activity of herbicides. in order to study the effect of wheat residue and different rates of trifluralin (%48 ec) herbicide on the yield and oil content of sunflower (helianthus annuus) a field experiment was done in agricultural research station, the university of birjand in summer 2008. experimental design was randomized complete block design with three replications that arranged as factorial. factors were included wheat residue rates with 4 levels (0, 1250, 2500 and 3750 kg ha-1) and trifluralin (%48 ec) rates with 4 levels (720, 1200, 1680 g ai.ha-1 and control (herbicide free)). result showed that using 2500 kg.ha-1 wheat residue increased head diameter, oil content, yield and yield components expect harvest index significantly; whereas, decreasing of measured indices were observed at residue rate of 3750 kg ha-1. the highest seed yield obtained from 1200 g ai ha-1 and residue rate of 2500 kg ha-1 residue treatment.