Abstract: Competition is a common phenomenon in agriculture production.  Research on the relationship between competitive ability and crop yield is extensive, but the results have been inconsistent.  Few studies have focused on the relationship between population competitive intensity and yield of maize (Zea mays L.) cultivars.  The main objective of this study was to determine if a consistent relationship exists between maize yield and competitive ability.  A two-year field experiment was conducted, employing a de Wit replacement series design.  When two maize cultivars were grown in a mixture, yield was reduced for the modern cultivar and increased for the older cultivar.  In each replacement series, per plant level yield of each cultivar, and population level yield of the mixture, decreased with increasing proportion of the older cultivar.  Competitive ratio (CR) reflected differences in competitive ability of the three maize cultivars.  In each replacement series, population competition pressure (PCP) increased with increasing proportion of the older cultivar, indicating that the older cultivar was a strong competitor.  Biomass yield, grain yield, harvest index, thousand-kernel weight, and kernel number per plant, were negatively correlated with PCP.  Our results demonstrated that inter-cultivar competition affects maize productivity, and increasing PCP will decrease translocation of assimilates to grain and, ultimately, reduce yield.  Therefore, there is a negative correlation between population competitive intensity and yield performance in maize, breeders should develop a communal ideotype that would not perform well in competition in future. 

Key words: maize, competition, competitive ability, population competitive pressure, yield