Plant Availability of Potassium in Soil Minerals: What’s Happening Near the Roots? (PART 2)

(continued): Plant roots can also exude their own acids and carbon compounds into the rhizosphere. These substances are released as the plant regulates the types and amounts of nutrients and other molecules in its roots. Finally, as roots take up K from the soil, they deplete K in the rhizosphere to concentrations much lower than the bulk soil. Very low concentrations of K near the root can trigger the release of K from mineral structures. All of these mechanisms arise from chemical and physical forces considered part of weathering. Rather than taking years, however, these processes working in the rhizosphere release K in a matter of days or weeks. Even with all these mechanisms, a plant may still not be able to access enough K from the soil to meet its nutritional requirements. Scientists have come up with a variety of measurements that differentiate conditions when plants are accessing enough K and when they are not. Soil tests and plant tissue tests that are calibrated to crop growth and development have been extremely helpful in this regard. Future improvements in the accuracy and precision of these tests will need to consider how plant varieties differ in their abilities to acquire K. How different varieties alter their rhizosphere environment will be an important consideration. [International Plant Nutrition Institute. Issue #1 2018]