Appropriate bandwidth achieves a high yield by reducing maize intraspecific competition in additive maize–soybean strip intercropping

Maize–soybean strip intercropping can effectively alleviate arable land competition, improve land output, and be conducive to the sustainable development. The key to achieve these advantages is to stabilize the maize yield. Suitable narrow row spacing could maximize the benefit of maize–soybean strip intercropping, and an increasing bandwidth with suitable narrow row spacing is beneficial to the mechanized production of soybean. In practice, to ensure the maize yield in additive maize strip intercropping, maize plant spacing decreases and intraspecific competition intensifies as the bandwidth increases. However, interspecific interactions have been the primary focus of studies because of the better rhizosphere nitrogen fixation ability of soybean and the activation of maize rhizosphere nutrients. Therefore, it is particularly urgent to identify the trade-offs between intraspecific competition and interspecific interactions in maize and the regulatory effects on maize yield. Field experiments were conducted from 2017 to 2020 to analyze the results of interindividual competition in maize and interactions with soybeans under different bandwidths. It was found that maize biomass and yield at the maturity stage decreased by 8.0% and 6.4%; 20.5% and 19.4%; and 28.7% and 44.1% from 2 m to 2.8 m, respectively, but the biomass proportion in ears showed no significant difference. Intraspecific competition of maize was weakened by special promotion in intercropping, but stable yield was achieved only at 2 m. In response to suitable competition, maize roots can flourish only on the basis of ensuring aboveground biomass. The results revealed that the primary negative determinant of maize yield was intraspecific aboveground competition and strengthening intraspecific competition reduced biomass accumulation without altering the allocation ratio to the ear. We concluded that maize yield was guaranteed at 2 m due to the special strip planting design compensated for the enhanced intraspecific competition of maize aboveground parts in the additive maize–soybean strip intercropping system.