investigation of multiple competition of weeds at different corn (zea mays l.) densities

in order to study the weed damage and to determinate the influence of weed species and multiple weed species competition in corn (zea mays l.), a field experiment was conducted based on interval mapping at the agronomy research field of ferdowsi university of mashhad during 2009-2010. treatments consisted of four density level of crop (5, 6, 7 and 9 plant.m-2) and four type of weed management (completely removed weed, broadleaf control, non control, and grass weeds control). weed samples were taken at harvest time. dry matters of corn samples were measured. the density and dry matter of weed samples were recorded separately for each species. equations were fitted single plant weight ln of each weed species or crop as dependent variable to compare and evaluate the competition coefficient of inter and intra species. results indicated that single plant weight ln and plant density per m-2 had high correlation to evaluate competition coefficient. considering the coefficients of equation the function of single plant weight ln showed that crab grass and prostrate pigweed had the most stimulation effect on corn. while redroot pigweed prostate common purslane field bindweed black night shade common lambsquars barnyardgrass purple grown nutsedge and green foxtail had inhibition effect on corn. the positive of the former group on corn were resulted from the inhabitation effect on the latter group of weeds.