What is the common solution used to determine potassium in soil?

• A. Distilled water
• B. Mehlich 3
• C. Sodium chloride solution
• D. Ammonium acetate extraction

Answer: (B)

When testing soil potassium, you want an extractant that pulls out the forms of potassium plants can actually use, not just what’s dissolved in a drop of water. Mehlich 3 is a buffered, mildly acidic extractant used widely in soil testing to release potassium from both exchangeable sites and some non-exchangeable pools. This gives a practical estimate of plant-available potassium that remains consistent across many soil types, which is why laboratories commonly use it and crop recommendations are tied to its results. Distilled water only dissolves the easily soluble potassium and misses much of what’s accessible in the soil. Ammonium acetate is another method that targets exchangeable potassium specifically, but Mehlich 3 is more versatile and broadly applicable, making it the common choice. Sodium chloride can extract some cations, but it’s not the standard for determining available potassium in typical soil tests.