What is the difference in uptake of immobile and mobile nutrients?

Robert Mullen Ph.D.

Robert Mullen Ph.D.

Ph.D., CCA, CPAg.

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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Immobile nutrients, like phosphorus, are available from a smaller fraction of soil that is near plant roots known as the root surface sorption zone (right). The size of the root surface sorption zone is influenced by soil texture. Coarser textured soils have a larger volume of soil that can provide immobile nutrients than fine textured soils. Immobile nutrients can be applied well before expected crop uptake as long as they are managed to avoid surface runoff.

Mobile nutrients are available from a larger fraction of soil known as the root system sorption zone (left). Mobile nutrients readily move with soil water, so applications of mobile forms (nitrate and sulfate specifically) should ideally be made near expected crop uptake, especially in high rainfall areas.

Visual difference between the root system sorption zone (left) and the root surface sorption zone (right).