Planting Considerations and Stand Assessments

By Delbert G. Voight and Joseph Akins

Key points for planting corn and soybeans

Depending on the hybrid, optimal final corn plant populations may range from 28,000 to 35,000 plants/acre. It is common to add 20% to the seed drop in order to achieve the desired final population. For example, if a final stand of 30,000 plants/acre is desired, one would drop 36,000 corn seeds/acre. Assuming 80% emergence, the soybean planter or drill should be set to drop 150,000 seeds/acre to achieve a final population of 120,000 plants/acre at harvest. Whether planting corn or beans, the goal of a high-yielding uniform stand relies upon same-day germination and emergence. Emergence differences related to pests and weather may be out of the growers' control, but controlling other variables helps ensure a good start to the growing season. Good planter maintenance and proper planting depth both help reduce germination variability. A planting depth of 1.5 inches is ideal for corn, while 1.25 inches is ideal for soybeans. Once germination begins, the actual plant population will need to be determined. Taking some time to evaluate the field after crop emergence provides valuable information for replant decisions and yield estimations.

To assess the stand, follow these steps:

1. Determine row spacing in inches.

   Crop	Row spacing
   Small grains	6, 7, or 8 inches
   Corn	7, 15, or 30 inches
   Soybeans	15 or 30 inches

2. Convert the row width from inches to feet by dividing by 12.
3. To get the amount of row feet per acre, divide 43,560 ft² by the feet of row calculated in step 2.
4. Using a ruler across multiple rows in the field, count the number of plants you find per foot to find an average. Multiply that average by row feet per acre (from step 3) to get the amount of plants per acre.

Let's look at a corn example:

If corn is planted in 30" rows, 30 divided by 12 is 2.5 feet. 43,560 ft² divided by 2.5 results in 17,424 row feet/acre. If you use your ruler in multiple spots around the field and find an average of 1.7 corn plants per foot, multiply that by the 17,424 feet. Now you know that your final plant population is approximately 30,000 plants per acre.

Importance of planting date

Knowing the key planting times and how they relate to yield is important, especially if stands are deemed inadequate and a replant is in question. Yield potential for corn when planting on April 25th is 100%, the 19th of May is 90% and the 29th of May is 80%. Yes, a full 20% yield loss may be observed just by delaying the planting date by three weeks. Knowing the expected yield loss from delayed planting can help guide replant decisions. For example, if a tape measure is used to evaluate plant stand evenness within a row and the stand is found to be very uneven, that can rob up to 12% of the corn yield. However, if that uneven corn stand was planted on April 25^th, then it would not pay to replant on May 29^th if the expected yield loss is 20% versus 12%. Assessing the plant stand for skips is also important, as weeds can invade anywhere that light is allowed through to the soil.

Check with the seed dealer to determine policy for replant support. More information on replanting can also be found in the  Agronomy Guide  .