Warm Soils Key for Uniform Corn and Soybean Growth

By Blake Jackson

As planting season begins, many producers aim for a uniform “picket fence” stand, where crops emerge evenly and are spaced consistently. However, earlier planting often into cooler soils can challenge that goal.

Research led by Dr. Dennis Egli, Professor Emeritus at the University of Kentucky, examined how soil temperature and planting conditions affect emergence timing and uniformity in corn and soybean.

In controlled greenhouse and growth chamber studies, multiple seed lots of both crops were planted under ideal moisture and depth conditions. When corn was planted in warm soil (around 75°F), seedlings emerged within about four days, with most plants appearing within a narrow 24-hour window.

In cooler soil (near 60°F), emergence was delayed up to 12 days, and the spread between early and late seedlings widened significantly.

Soybeans showed a similar trend. Warm soils (about 72°F) produced uniform emergence within roughly a day and a half, while cooler temperatures (around 64°F) extended emergence time and reduced uniformity. Deeper planting also delayed soybean emergence, though it had little effect on corn.

The findings highlight a clear pattern: slower emergence caused by low temperatures leads to less uniform stands. Even under near-perfect conditions, variability increased as temperatures dropped suggesting even greater challenges in real field environments.

This reduced uniformity can impact yield differently depending on the crop. Corn is less adaptable, meaning late-emerging plants often produce fewer kernels due to shading and limited ear size.

Early plants cannot fully compensate, potentially lowering overall yield. Soybeans, however, are more flexible and can adjust by producing more pods and seeds, helping maintain yield even with uneven emergence.

While early planting can offer yield advantages, growers should be cautious. Planting soybeans earlier than corn may be beneficial, but both crops should ideally be planted when soil temperatures are favorable to ensure strong, uniform emergence.

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