Recent rains have slowed corn planting progress across the state. However, it’s important for producers to wait for optimal planting conditions to ensure they get good yields at harvest time, said Edwin Ritchey and Lloyd Murdock, extension soils specialists with the University of Kentucky College of Agriculture.

According to the Kentucky Weekly Crop and Weather Report, only 13 percent of the state’s corn was in the ground as of April 17. That is well below the 31 percent that was planted by this time in 2010 and lower than the five-year average of 22 percent.

Planting, tilling or trafficking in fields during wet conditions could cause compaction. In most soils, the greatest amount of compaction occurs when a field is at a moisture level that can be tilled but is a little too wet for tillage.

“If the soil stays moist during germination then the roots can penetrate the compacted soil and establish a root system,” Ritchey said. “However, if the soil dries and hardens after planting, the roots will not be able to penetrate it.”

When planting into wet soils, sidewall compaction can occur due to the opening discs smearing the sidewall of the planter furrow. When sidewall compaction occurs, plant roots will grow mainly in the planting furrow.

“Although plants may look normal at emergence, they will begin to show problems associated with nutrient deficiency and drought stress after the corn is several inches tall,” Murdock said. “This problem can be more common in no-till soils because they have better structure and are easier to traffic in wet conditions.”

The key to preventing sidewall compaction is waiting until the ground is dry enough to plant. Corn producers can test the moisture level in their fields by molding the soil into a ball with their hands. If the ball will not easily crumble, it’s too wet to plant.

Corn planted in the first part of May has an average yield decrease of 1 bushel per acre per day, and corn planted in the latter part of May has an average yield decrease of 2 bushels per acre per day. In a normal year, Kentucky’s corn crop is in the ground by May 15 to maintain average yield potential. 

Planting dates are important and do influence yields, but it is only one factor used in determining yields. Other factors, such as weather and soil conditions, influence yields too and, in some cases, have a greater impact on yields than planting dates. For example, flooding in 2008 slowed planting progress across the state, but due to rain in July and August, some of the state’s highest yielding corn was corn planted after May 1.