Crop Nutrition

Managing Phosphorus Inputs into Soybeans – When Should Application Occur?

Robert Mullen, Ph.D.

Robert Mullen

Robert Mullen, Ph.D.


Director of Agronomy

To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.

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When it comes to fertilizing crops with phosphorus in the Midwest, the typical perspective is that the timing is not overly critical. Phosphorus applications can occur in the fall or the spring, and application can occur every year or every other year. Historically, phosphorus applications occur in the fall (or the spring) ahead of corn planting at a rate that usually covers both crops in the corn-soybean rotation. The goal is to ensure an adequate supply of phosphorus to maintain soil test values at a level that is considered adequate.

Some recent research out of the University of Minnesota is challenging that notion on soybeans grown on high pH soils (>8.0). Researchers have found that high pH soils (specifically soils below the medium range of soil test phosphorus) can be responsive to fertilizer applied specifically for soybeans in the soybean year rather than an application for the rotation (where phosphorus is supplied for both crops prior to corn, but not the soybeans). Soybean yields were increased by 20 percent when phosphorus was applied prior to soybean planting.

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