By Alexandra Knight, Ph.D., Pioneer field agronomist
As the sun is shining and the air becomes warmer across Ohio, growers continue to question if it’s time to get the planter in the field. The next question becomes, “Does it make more sense to plant corn or soybeans early?” While historically corn has been planted before soybeans, many growers have experienced that their earliest planted soybean acres also tend to be their highest yielding fields. Modern-day soybean varieties have a greater yield response to planting date than varieties grown several decades ago. Looking at corn, there is long-term data suggesting that mid-April to mid-May is ideal for planting. However, the recent past has shown that later planted corn can continue to yield well as our season seems to be shifting later. Regardless, planting either crop early comes with both risk and reward.
When soybeans are planted early, they spend more time in vegetative growth giving the plants more time to add nodes. Nodes are the location where the soybean leaf petiole is attached. Each additional node provides more opportunity for yield as pods form at these attachment points. Every 3 to 4 days another main stem node is added on a soybean plant. This early growth will mean a quicker canopy closure. In an age of herbicide resistant weeds, quicker canopy closure can be advantageous for crops competing with weeds. A third advantage to highlight is that an early planting date will lead to an earlier flowering soybean. Earlier flowering will provide a longer window from flowering to full seed which gives additional calendar days to capture sunlight, moisture, nutrients and ultimately achieve yield.
While there are large rewards for early planted soybeans, there are also some risks. Cool, wet soils are prone to early season seed rots and seedling blights. For this reason, fungicide seed treatments will be crucial on early planted beans. An early planting can also result in cool wet rains or freezing temperatures following emergence which can cause a reduction in soybean stands. Temperatures below 32 degrees F can cause frost damage while temperatures below 28 degrees F for four or more hours can be lethal to emerged soybeans. Waiting five days following freezing weather is critical in assessing soybean stands.
Early planted corn has some of the same risks as early planted soybeans. Approximately 120 GDUs are required for corn emergence. In a cool, wet spring, this could easily take greater than two weeks. For an ideal corn planting scenario, soil temperatures maintaining above 50 degrees F, a rain-free 24-hour forecast and a 3- to 5-day prediction of warming temperatures is needed. Planting just ahead of a cold front can be detrimental to establishing a stand and can lead to corkscrewing and seed rots among other issues. Seed treatment is as critical in protecting against early diseases with corn just as it is in soybeans but, it will not prevent all issues encountered by planting ahead of a cool rain.
With risk also comes reward. Planting corn in early spring with a favorable forecast ahead can lead to accelerated corn yields. Eight-years of Pioneer data (2011-2018) suggests that, on average, corn yields drop 0.8 bushels per day in the central Corn Belt. A corn plant’s growing point will remain beneath the surface through approximately V5 allowing the soil to provide some protection to the plant from cooler air temperatures. A consistent seeding depth of 2 inches will help in achieving an even stand which prevents competition between corn plants. Ultimately the stand achieved represents the potential for ears and yield at the end of the season.
Timely planting is generally favorable for achieving maximum corn and soybean yields, but is only one of many yield influencing factors. It is important to recognize the potential upside of yield by planting early but also weighing the risks that accompany this decision. “Mudding in” a crop early to avoid planting late will almost always end up being an unwise decision.