What phosphorus test is commonly used in the Tri-State Fertilizer Recommendations?

• A. Mehlich 3.
• B. Bray 1.
• C. Olsen.
• D. Morgan.

Answer: (A)

Measuring plant-available phosphorus across a wide range of soil types is best done with a universal extractant, and in the Tri-State Fertilizer Recommendations that role is filled by Mehlich-3. This extractant is designed to pull phosphorus from soils with different pH levels and mineral compositions, so a single test can be used for acidic, neutral, and alkaline soils and still correlate well with crop-uptake and yield responses. That broad applicability makes Mehlich-3 the preferred phosphorus test in the Tri-State guidance, providing consistent, comparable results across Ohio and neighboring states.

Bray-1 is mainly effective in strongly acidic soils but doesn’t perform as well across the full pH range. Olsen targets alkaline soils and can underestimate phosphorus in acidic or mixed soils. Morgan is an older method that has largely been supplanted by Mehlich-3 due to its narrower applicability.