Research HighlightsAgronomy: Rethinking Planting Depth
By Agronomist Dr. Daniel Davidson
What depth are you planting at and should you be planting deeper?
For a long time now the recommended soybean planting depth was 1 to 1.5 inches, while corn planting depth was 1.5 to 2 inches. But does that soybean depth still hold true today?
A recent article from Michigan State University stated that soybean planting depth still matters. Their field surveys showed that only 20 percent of the fields planted with drills were planted at the intended depth and 68% were planted too deep.
The long-held belief is that soybeans should be planted between 1 and 1.5 inches deep, shallower when planting early, into cool and moist soils, or in no-till. And planted at the deeper end with later planting and when soils are warm and dry or sandy.
But recent data shows there is a benefit when soybeans are planted deeper. Jim Specht, retired professor at the University of Nebraska, released results from his 3-year study which show that 1.75 inches is now the optimal depth regardless of soil conditions, planting date, population or tillage system. And when I looked at his raw data, I felt that the depth ranged anywhere from 1.75 and 2 inches—almost the same range as corn seed depth.
Specht’s theory is that a deeper planting depth has more stable moisture and temperature conditions, which lead to more consistent germination and emergence timing. He was surprised by the results and said that he had recommended planting at 1 to 1.25 inches when planting early and 1.25 to 1.5 inches when planting late but realizes that is now out of date.
Seed that is placed deeper, into more consistent moisture and temperature conditions and further away from any residue, results in a better stand that emerges more evenly. Soybean seed requires 50% more moisture to germinate than corn seed and having a better source of available moisture means more consistent, faster germination.
Today’s soybean seed has better tolerance of cold conditions and can withstand cooler and wetter no-till soils and emerge just fine. And don’t forget the value of seed treatments in protecting the seed during a longer germination and emergence window.
So, the data and logic support planting deeper. Are you ready to take the plunge to 1.75 inches or even 2 inches? Are the benefits of a better stand and, perhaps, fewer gaps and voids enough to consider going deeper than one and a half inches?
Davidson blogs on agronomy-related topics at ILSoyAdvisor