Soybeans can be planted deeper than you think and do better than you hope.
Soybean planting will start soon, but will growers suffer from shallow thinking? New research shows soybeans need to be planted a bit deeper than most people think.
How deep do you plant soybeans — 1 inch, 1.25 inch or 1.5 inch? If so, you are out of step with the most recent data.
Jim Specht, University of Nebraska agronomist, just released results from a three-year study that show that 1.75 inches is now the optimal depth for planting soybeans, regardless of soil conditions, planting date, population or tillage system. When I look at his raw data, it suggests a planting depth between 1.75 and 2 inches is generally optimal.
The thinking is that deeper planting depth offers more stable moisture and temperature conditions for the seed than the shallower planting depths. It also reduces the risk of freeze damage. Treated seed becomes more important as you plant early or deeper.
Producers and agronomists have long used 1.5 inch as the average planting depth for soybeans. The rule of thumb has been to plant deeper when soil is drier or lighter (sandy) and shallower when soil is colder, wetter and heavier (clays).
Specht himself was surprised by the results. “I used to recommend planting at 1 to 1.25 inches when planting early and 1.25 to 1.5 inches when planting late. I was as surprised as anyone that 1.75 is the new optimal,” said Specht. He noted his counterparts at Clay Center, Neb., still recommend planting soybeans as deep as 2 inches in tilled and irrigated soil.
I called up one of my northeast Nebraska farming neighbors to tell him this latest news. Imagine my surprise when he told me they were already planting soybeans at 2 inches and corn at 3 inches and had good reasons for doing so. The following day, I was in St. Louis at Monsanto with fellow agronomists and they were still saying to plant no deeper than 1.5 inches. Hmmmm…
What is interesting about Specht’s data is that planting at 1.75 inches was optimal regardless of plant population (30,000 to 210,000 seeds per acre), tillage systems (no-till, conservation till or strip till) or planting date (early and late).
When planting 210,000 seeds per acre, his data shows that depth really isn’t that important since you have a surplus of seeds in the soil. On the flipside, if planting at 30,000 or 70,000 seeds per acre, planting deeper is even more responsive to depth (down to 1.75 inch) since you have so few seeds in the soil and getting each one to emerge counts.
So why does planting deep work so well? My no-till neighbor said they get the seed deeper into moisture and away from the trash, which results in a better stand that emerges more evenly. Specht confirms that when planting deeper, you plant into better moisture and more consistent temperatures, resulting in more even emergence. He also pointed out that soybean seeds require 50% more moisture to germinate compared to a corn seed, so having ample moisture supply available is critical.
Most soybean seed today has better cold tolerance and can withstand cooler and wet no-till soils and still emerge just fine. Seed companies have also been selecting for ability to emerge under no-till and high-residue conditions. There’s also the value of seed treatments in protecting the seed during germination and emergence.
Are you ready to take the plunge?
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.
Article reprinted with permission. Originally published by DTN/The Progressive Farmer.
About the Author: Dan Davidson
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