assessment of above- and below-ground competition between sesame (sesamume indicum l.) and pigweed (amaranthus retroflexus ) and its effects on sesame yield and yield components

this study carried out in a factorial layout on completely randomaized block design with three replications, to evaluate the above- and below- ground competition between sesame (sesamum indicum) and pigweed (amaranthus retroflexus), and their impacts on sesame yield and yield component. the experimental treatments were all combination of crop-weed competition (shoot competition, root competition and root-shoot competition) and sesame plant densitys (1, 2 and 4 plant per pot). plants were sown in plastic pots (24 cm diameter and 28 cm height) in year 2010, at feild of ferdowsi university of mashhad. for study the shoot competition of sesame-pigweed, the roots were separated by plastic when the pots were filled with soil before sowing the seeds. three weeks after emerging, shoots of plants were separated vertical barrier (30 x 70 cm) for studing root competition. results showed that competition treatments had a significant effect on seed weight per plant and yield components except 1000 seed weight. among competition produced higher yield and yield components compared to othere treatments. however, sesame and pigweed biological weight in root-shoot competition was 2.6 and 13.7 respectively, that was higher than other competition treatments and was significant. capsule number in main and sub branches, capsule number in plant, seed number in capsule and seed number in plant in complete competition treatment was 15, 2.58, 17.5, 43.7 and 693.89 respectively, that was higher than other treatments and differences among them was significant. sesame density also had a significant effect on seed weight per plant and yield components. when low density were used (one plant), yield and yield components was more, therefore in one plant per pot density biological weight of sesame was 3.82 gr, and in higher densities the mentioned traits decreased significantly.