Most of the competition studies between weeds and crops conducted lately quantify the interference that the weeds cause to crops; however, these researches do not show mechanistically neither the effects of density and proportion of plants in a mixture of species, nor the importance of intra and inter-specific competition and niche diferentiation. Therefore, this research was developed aiming to describe the competitive interaction and competitive indexes between corn (Zea mays L.) and pigweed (Amaranthus retroflexus L.) plants. The methodology was a replacement series experiment with a total density of 400 plants/m2 and 5 proportions, besides the monoculture that varied from 50 to 800 plants/m2, conducted in a randomized completely block desing, four replications. The results were analyzed through conventional replacement series analysis, using reciprocal total and per plant yield. Corn was the superior competitor and the intra-specific competition was more important than the inter-specific for this species. The reverse was true for pigweed. Both species were competing for the same natural resources since the niche diferentiation index was lower than 1,0. The influence of density and proportion of species in a competition study is very important in the understanding of competitive interactions.
Replacement series; competition index; intra-specific competition; inter-specific competition; ecological niche