Increased plant densities are not appropriate for all situations because of the many factors that interact with plant population to place the crop under stress. Factors such as drought, weeds, insects, diseases, soil compaction, inadequate fertility and poor drainage all serve to exaggerate the stressful effects of increased plant populations. The more severe these other stresses are, the lower the optimum plant population will be. Many factors, including larger plant size and higher temperatures at silking, are responsible for this difference. In these warmer areas, optimum plant populations will be lower than those discussed below.
Hybrid selection is a critical factor in determining the optimum plant population.
Many hybrids yield well at 55,000 plants per hectare, but cannot tolerate higher densities, especially if growing conditions are less than ideal. Only a few hybrids can tolerate a population of 67,000 plants per hectare. The population selected must be suitable for the hybrid being grown and the growing conditions likely to be encountered. It may be necessary to change the plant population when changing hybrids or fields. Experience with previous corn crops can provide guidelines for choosing a plant population.