Estimation of Multi-species Weeds Competition in Corn Field (Zea mays L.) Using of Reciprocal Weight of Single Plant and Leaf Area Ratio of Weeds

In order to examine of the weed damage on corn and determination of the most suitable index for corn (Zea mays L.) yield reduction in field condition and multi-species weed competition, an experiment as an interval mapping was carried out in the researching field of Mashhad University during 2008-2009. Treatments were complete control (pre-planting Treflan and hand weeding), no control (no herbicide), broadleaf control (pre-emergence 2-4, D and hand weeding), and grasses control (pre-planting Tapik and hand weeding). 480 destructive and non-destructive quadrates with 20×70 cm2 in dimension were determined in the field. At 4-8 leaf stages, density of weed species was separately counted and leaf area index and dry mater of all species were separately measured. To compare and evaluate of the coefficient of inter-specific and intra-specific competitions, leaf area ratio as independent variable and reciprocal weight of both weeds and corn as dependent variable were measured. Results showed that reciprocal weight of single plant and leaf area ratio had high correlation (r2=99%) with yield loss and coefficients of competition. Based on reciprocal weight equation and equation coefficients, it was observed that the weed interference effects on the corn yield can be divided into two groups: inhibition (positive sign) and stimulation (negative sign), which Redroot pigweed (Amaranthus retroflexus L.) had a simulative effects on the corn yield, while inhibition effects of Prostate amaranth (Amaranthus blitoides S.Wats.), common purslane (Portulaca oleracea L.), Bindweed (Convolvulus arvensis L.), Purple nutsedge (Cyperus rotundus L.) and Barnyardgrass (Echinochloa crus-galli L.) resulted in reduction of corn yield, therefore, weeds have positive effects on corn by inhibition effect on other weeds that were inhibition effect on corn. Also the negative effect of broad-leaved and grasses weeds alone more than total impact on the yield.