There’s plenty to love about early soybean planting. It spurs prolific node production and induces flowering before the summer solstice around June 21, says Tim Laatsch, director of agronomy for North America at Koch Agronomic Services. This enables soybeans to potentially pack more yield punch at harvest, he says.

This is in line with recommendations from Iowa State University. Soybeans in Iowa can be planted as early as April 10-15, as crop insurance protection kicks in the southern three crop reporting districts on April 10 and April 15 in the northern six districts.

Risk increases

However, early soybean planting also heightens risk. April snowfall and cold rains that spur cool and wet soils can deter germination, Laatsch says. Frost that clips soybeans once their growing points have emerged can trigger replanting — the ultimate in late planting.

Soils still need to be fit for planting, according to Mark Licht, Iowa State University Extension agronomist. If soils are excessively wet, wait.

“You want soybeans to have quick germination and emergence with little disease pressure,” Licht says. This won’t occur under cold soils, and chilly and wet weather, he says.

Laatsch recommends watching weather forecasts at planting. “If a cold snap is forecast with subfreezing temperatures, keep the soybeans in the shed until temperatures become warmer,” he says. “When soybeans emerge, the growing points are above the ground, and they are not going to tolerate freezing temperatures.”

And protect soybean seed with fungicide seed treatments. Planter box treatments packing nutrients aid early emergence while providing seed lubricity, which can help soybean seedlings withstand such stressors, he adds. 

The merits of early planting also apply to corn. Crop insurance protection kicks in April 10 for corn across Iowa.

Like soybeans, early planting of corn is a fine line to walk, Laatsch says. Waiting for warmer temperatures can cause farmers to miss optimal planting windows if cold and wet weather result. Conversely, waiting for warmer weather can enhance uniform emergence due to warmer soils, he says. 

“Corn is a tropical plant that actually emerges much better in warmer temperatures,” Laatsch says.

So which comes first?

Whether to plant corn or soybeans first hinges on acreage farmed and farmer planting capabilities, Licht says. Farmers who can complete corn and soybean planting by May 20 will sacrifice some yield potential, as opposed to finishing up in a few weeks earlier. However, differences are minimal, he says. In the case of soybeans, yield benefits may be gleaned by planting in mid-April, but that’s not a given. 

What is a given is that yields start crashing after May 20. ISU and other Midwest land-grant universities show soybean yields decline 0.62 bushel per day after May 20, with higher yield loss potential for corn.

“If you can’t get done planting by May 20, your yield loss for late planting is greater with corn,” Licht says. In these cases, farmers would want to opt to plant corn first and then soybeans, he says.