Corn yields have improved with advancements in seed genetics. New hybrids handle environmental stresses while utilizing water, nitrogen and other crop nutrients more efficiently. Achieving higher corn yields requires an increase in the number of corn kernels per acre and/or an increase in weight of each kernel of corn. Improved corn genetics and better understanding of plant nutrition will contribute to more kernels and higher test weights, but maximum corn yields also require optimizing plant populations.
Currently, many farmers use a standard planting rate for corn, with no deviation from field to field, or hybrid to hybrid change. Equipment capabilities may determine desired planting rate, but many farmers have invested in electronic rate-controlled planters, making tweaks to population from field to field or hybrid to hybrid a less painful experience. Regional bias or risk management is how many planting rates are determined. Risk management is reducing plant populations to minimize drought stress and better utilize plant available water. A reduction in plant population on stress acres is often necessary, but with significant differences between hybrids in drought tolerance, physical characteristics, and ear type, planting a static rate across every acre can limit yield potential. Better management would include adjusting planting population according to hybrid, soil fertility, and yield environment on a field by field basis.
Hybrids classified as fixed ear will develop similar sized ears of equal length and number of kernels around the ear when planted in a range of populations. Hybrids with ear flex have the ability to increase the numbers of kernels long or the numbers of kernels around the ear when plants are spaced farther apart. This means the optimum population of a flex ear hybrid will typically be less than a fixed ear hybrid, but this does not mean that these types of hybrids do not respond to increases in population. More space between plants increases ear size, but the additional kernels may not exceed yield potential of another plant when spaced too far apart. Just as a flex ear hybrid can add kernels when spaced farther apart, the number of kernels can decrease when the population exceeds the optimum rate. Individual hybrids may exhibit flex ear properties in one environment, while more fixed ear in others. Agronomic characteristics are also influential in determining the optimum population of a hybrid. These characteristics would include leaf structure, late season standability, tolerance to disease, and resilience to green snap.
Thirty-inch row spacing is standard for most population studies. Farmers with planting equipment wider than 30 inches need to adjust populations accordingly, and will need to be more subjective on their hybrid selection. On wide row setups, higher populations will decrease spacing and farmers should avoid flex hybrids that respond negatively to tighter plant spacing. Row spacing of 20 inches or less and twin row spacing is the next advancement in maximizing plant populations, but population data is still limited with narrow row equipment.
It is always best to work with your local seed agronomist for individual hybrid recommendations for your environment and yield potential. Along with optimizing plant populations, farmers must also limit soil compaction, plant in ideal soil conditions when possible, and utilize seed treatments to ensure a well-established stand. Specific hybrids may also require more nitrogen and application of disease preventing fungicides.