| Summary: | Intraspecific competition is a common phenomenon in agricultural production, and maize is one of the most sensitive grass species to intraspecific competition due to its low tillering ability. This study evaluated and analyzed intraspecific competition in maize, and screened competitive indices that could be used to evaluate intraspecific competition in a maize population. A 2-year field experiment was conducted using the maize hybrid Zhongdan 2 at 12 plant densities ranging from 1.5 to 18.0 plants (pl) m−2. The results showed that the response of single-plant grain yield and dry matter at harvest to increased plant density decreased exponentially and that the harvest index decreased linearly. The response of population-level grain yield to plant density was curvilinear, producing a maximum value at the optimum population density. However, the yielddensity equation agreed well with the Steinhart-Hart equation curves, but not with the quadratic equation curves reported by most previous studies. Competitive indices are used to evaluate competition in a plant population or plant species. The present results show that competitive intensity (CI) and absolute severity of competition (ASC) increased with increasing plant density; however, relative yield (RY) and relative reproductive efficiency (RReff) decreased. The different responses of these indices reflect different aspects of competition. According to the analysis of CI, ASC, RY, and RReff, higher CI and ASC values indicate higher intraspecific competition, whereas higher RY and RReff values indirectly reflect lower intraspecific competition. These competitive indices evaluate not only the intraspecific competitive intensity under different plant densities of the same cultivar but also those of different cultivars under the same plant density. However, some overlap exists in the calculations of ASC, CI, and RY, so one could simply select any one of these indices to evaluate intraspecific competition in a maize population. In conclusion, the present study provides a method to evaluate intraspecific competition in maize populations, which may be beneficial for breeding high-yield maize varieties in the future.
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