Determining the right corn plant population

article by Matt Hutcheson, CCA, Product Manager, Seed Consultants, Inc.
from Ohio Country Journal

Feed the World’s Growing Ohio includes lessons on growing corn and predicting yield. How can yield be maximized?

One factor that greatly influences corn yields is plant population. Determining the correct plant population may take some effort, however, it is a critical factor that every corn grower needs to get right in order to maximize yields. Recent research performed by universities and seed companies has determined that that yields increase significantly as populations are increased up to a point of 34,000 seeds per acre. In general, yields begin to level off at planting rates around 36,000 seeds per acre. Recent studies have also determined that even in low yield environments planting rates of 31,000 seeds per acre maximize yield and economic return. In very productive, 250 bushel per acre yield environments, research results show that higher populations (38,000+ seeds per acre) maximize yields. Breeding and advances in genetics have improved the modern corn plant’s ability to yield at higher populations when compared to corn hybrids from the past.

Although kernel weight and the number of kernels per ear are important factors in determining yield, yields are driven by the number of ears per acre. Higher numbers of smaller uniform ears will result in better yields than low numbers of large “flex” ears. Keep in mind, flex ears cannot make up for large gaps between plants that exist where populations are too low. In most situations, corn hybrid populations should be at least 32,000 plants/acre. According to Purdue corn agronomist Bob Nielsen: Results from 67 field-scale trials around Indiana suggest that optimum plant population for corn grown under typical yield levels and growing conditions is approximately 32,100 ppa or seeding rates of about 34,000 spa at 95% stand.” Determining the correct population for each field may be a challenge, but using university recommendations of 32,000 plants per acre is a good starting point. While rates of 38,000 seeds per acre are too high for much of our sales territory, rates of 28,000 seeds per acre are too low and may be keeping producers from maximizing yields.

The challenge in determining the right population is taking into consideration several factors, including: soil type and expected yield levels, flex vs. determinant ears, hybrid stress tolerance, etc. Below are some key points to keep in mind when determining plant populations.

• Plant populations should be adjusted based on field yield levels and soil types
• Modern hybrids perform best at higher populations when compared to hybrids from the past
• Ear flex cannot make up for large gaps in plant stands at a low population
• Yield is driven by ears per acre, more ears result in higher yields
• Hybrids with below average stress tolerance and flex ears should not be planted at excessively high populations, especially in lower yield environments where plant stress will occur
• Determinant-eared hybrids will perform better at higher populations and will maintain uniform ear size.