Corn Seeding Rates in Kentucky

Chad Lee, Extension Professor, University of Kentucky

Corn yields have steadily increased over time in part to increasing the seeding rates. Identifying the proper seeding rate is a balance between having enough plants to maximize yields with having too many plants to hurt yield in stressful conditions.

The following is the University of Kentucky guidelines for corn populations on various soils in Kentucky.


Table 1. Corn Seeding Rates for Kentucky

Soil Productivity	Target Seeds per Acre	Comments
Low	24,000 to 26,000	Soils that are shallow, sloping, or non-tiled clays. Expected yields are less than 140 bu/acre on average.
Medium	26,000 to 30,000	Many soils in Kentucky with less than 12% slope and depth of about 3 feet.
High (non-irrigated)	32,000 to 34,000	Deeper soils (river bottoms) with about 6 feet of rooting depth and excellent water-holding capacity.
High (irrigated)	32,000 to 42,000	The lower range is for limited water supply. The upper range is for fields at very low risk for water stress. Stalk strength is extremely important at the upper range. Consult with seed representatives on stalk strength and hybrids suited to the very high populations.

These seeding rates were developed from research, from soil depth and water holding capacity, and from the risk of soils running short on water for the season. The logic behind these seeding rates is that soils at greater risk of running out of water will have a lower seeding rate. Deep soils that are more likely to carry sufficient water throughout the growing season will have higher seeding rates.

There are a range of rates for each soil type and that reflects the variability in the data we currently have. More data from more research may help us refine those numbers.

Water availability can drastically impact corn response to plant population as displayed in Figures 1 to 3. In Figure 1, the red line is corn yield response to plant population in 2009 (adequate and timely rainfall). In 2009, yields increased as plant population increased. Just the opposite occurred in 2008, where rainfall was scarce and water was limited. In 2008, yields dropped as plant population increased. The same four hybrids were planted each year into the same soil type with the same crop rotation and the same fertilizer program. Water - or the lack of - greatly influenced crop yield response to plant population.Corn yields in Figure 2 are during a very dry year (2012) and corn yields in Figure 3 are from a year with much better rainfall (2013). In a year with more water, corn yields increased as populations increased and in a year with very little water, corn yields decreased as population increased. The hybrids in Figures 2 and 3 are the same.

If we could predict how the frequency of rainfall and the quantity of rainfall during the growing season, we could very accurately predict a seeding rate. Until that happens, we are left with trying to find the correct balance between enough plants to produce high yields while not having too many plants to severely hurt yields in stressful years.