1. Converting Between Mehlich-3P and Olsen-P Soil Tests: What Can Go Wrong?

Varying methodologies for extracting plant-available phosphorus (P) have been proposed since the initiation of soil test development in the early 1900s. Two tests that were developed and are still used widely in both the United States and Europe are the Olsen and Mehlich-3 test. Olsen P is predominately used in high-pH soils and Mehlich-3 is  more common in neutral to acidic soils due to the nature of the extracting solutions. Many Western US soils are high pH and, thus, have used Olsen P... C. Rogers, Z. Simpson, J. Mott, P. Kleinman