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Understanding phosphorus in Minnesota soils

Quick facts about phosphorus in Minnesota

  • Soil pH is one of the most important factors influencing phosphorus management decisions.

  • To determine the available phosphorus (P) of Minnesota plants, use the Bray-1 test when soil pH is 7.4 or less and the Olsen test when soil pH exceeds 7.4.

  • Soil has both organic and inorganic P forms, but plants can only use inorganic P. Organic P can be converted into inorganic P, and used for growth.

Phosphorus (P) is essential for crop production. It stimulates early plant growth, giving it a healthy and vigorous start.

In Minnesota, most agricultural soils contain between 100 and about 4,000 pounds of total P per acre. Efficiently using this phosphorus is becoming more important due to economic and environmental concerns.

Phosphorus: The basics

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Forms of phosphorus in soils

Soils’ phosphorus (P) chemistry is very complex, and the P exists in many different forms.

However, in practical terms, think of P in soils as existing in three pools: The solution P, active P and fixed P pools.

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Phosphorus and soil

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Paulo H. Pagliari, Extension nutrient management specialist; Daniel E. Kaiser, Extension nutrient management specialist and Carl J. Rosen, Extension nutrient management specialist

Reviewed in 2018

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