On-farm Assessment of Critical Soil Test P Values in Minnesota


Start Date: 2010

Principal Investigator: Daniel Kaiser

Organization: University of Minnesota, Southern, Southwest and Northwest Research and Outreach Centers

Status: Project merged with Evaluation of Critical Potassium Levels in Minnesota Soils in 2011

Background Information:

Fluctuating fertilizer prices can make the management of nutrients, especially phosphorus, challenging. Phosphorus (P) soil tests are used to estimate the potential availability and response to P. However, these tests only measure a small fraction of the total P in the soil, and can be affected by soil chemical properties (i.e., pH, organic matter, etc.).


Across Minnesota, soils can differ in their relative potential to retain or fix phosphorus. In general, soils in the western part of the state tend to be high in calcium carbonate. This can be problematic since calcium can react with P, making it unavailable for crop uptake.


Critical values should be established so producers know how much additional P is required to support crop production in their region. The critical level is the level where there is only a very small chance (less than 5%) the crop will respond to additional fertilizer.

Key Findings:

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