Agronomy: Planting Priorities

Planting corn or soybeans first, how to prioritize and does it really make a difference?

Waiting after corn planting is done until May 1 to start with soybeans is a tactic from the past. Today many growers start planting in April and some even plant both crops at the same time. Personally, I think that is a good tactic as long as corn can get planted in the April window and growers have the equipment and manpower to get this done.

Soybean yield probably benefits more from early planting than corn because of greater node and pod set. Corn benefits from being planted during the April window, but whether it is the 2^nd or 4^th week really makes no difference to final yield. However, corn seed will emerge better under cooler and wetter conditions than soybean seed, supporting the argument that corn should be the first priority.

Late spring frosts (28⁰ F or lower) for a couple hours can damage an emerged crop and soybeans are more vulnerable than corn because their growing point is above ground. But late spring frosts are increasingly rare and probably should not factor much into the decision once soil temperatures reach 50⁰ F and trend upwards.

Emerson Nafziger at the University of Illinois wrote about how to prioritize in his posting on The Bulletin. “Does the similarity in yield response to planting date mean that we should move soybeans ahead of, or at least equal to, corn in terms of planting priority once planting can begin? Probably not, at least when planting can begin by mid-April. That’s in part because corn seed emerges better under tough conditions than soybean seed, so there’s less (but not zero) chance of poor corn stands with early planting.”

Nafziger explained that spring rains after planting are the primary cause of stand loss for both corn and beans.

• “The chances of getting such rain don’t depend much on planting date, but the crop takes longer to come up if it’s planted early, and this increases the chances of getting rain before emergence.
• Corn is not immune to this problem, but damage to corn stands usually requires low temperature at the same time the soil is wet, so is somewhat less likely.
• In 2015 there were corn stand problems related to rain followed by cool temperatures in late April, which resulted in what was ‘imbibitional chilling injury’ or physiological damage to the seed and seedlings caused by the intake of cold water.”

Nafziger concludes that both crops benefit if planted after mid-April if soil and weather conditions permit. He pointed out that once you are past that mid-April point, plant the fields in best condition first whether it be soybeans or corn.

Lastly, there is no need to fret if everything is planted by May 1, neither crop has given up any yield potential. Any yields losses from late planting begin to accumulate slowly after May 1. Late plant dates in May are usually due to rain that prevents early planting.

To read Dr. Nafziger’s full posting “Planting Date: Corn or Soybean First?” click here.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.