Do crops uptake potassium from the sub-soil?

University of Minnesota researcher Daniel Kaiser is testing whether crops draw potassium from deep subsoil layers or rely almost entirely on the top six inches. Because tracking potassium directly in the soil profile is difficult, the project uses a tracer called rubidium, which plants absorb in the same way as potassium.

Project Approach & Method

• Soil Injection: Researchers inject small amounts of a liquid tracer into the soil at specific depths—ranging from the surface down to 30 inches deep—right next to growing corn and soybean plants.
• Plant Testing: Tissue samples are harvested later in the growing season and analyzed in a lab to measure how much tracer made it into the crops from each depth.
• Testing Methods: Follow-up trials will place protective covers over injection spots so rain and irrigation water don’t wash the tracer deeper than intended.

Long-Term Goals

• Verify Subsoil Feeding: Determine if roots actively draw nutrients from subsoil depths, particularly in soils with higher subsoil fertility or lower clay content.
• Expand to More Soil Types: Expand field trials across multiple locations—starting with Becker and Rosemount—to compare crop root activity across different soil profiles.
• Improve Soil Testing: Provide clearer guidance on whether subsoil potassium contributes enough to crop growth to adjust standard 0-to-6-inch soil sampling methods and fertilizer recommendations.