Organic Phosphorus and Colloidal Phosphate Fertilizer

The soil pH range at which maximum phosphorus (P) availability occurs is between 6.0 and 7.0.

Adequate soil phosphorus (P) is essential for optimal crop yields.  Phosphorus (P) enables a plant to store and transfer energy, promotes root, flower and fruit development, and allows early maturity. Soils with a pH of 7.5 and higher typically have a high calcium concentration that binds phosphorus (P) as calcium-phosphate, creating an insoluble compound that is not available to plants. Therefore, it is necessary to amend agricultural soils with available forms of P at the correct agronomic rate.

Take soil samples from 0 to 6 inches in no-till fields and 0 to 12 inches in tilled fields to determine the concentration of available phosphorus (P) in an agricultural field. Unlike nitrogen, phosphorus tends to move downhill across the field and is less likely to leach vertically into the ground water.

Cover crops offer another way to increase soil fertility. Cover crops can help recycle other nutrients, and legume cover crops fix atmospheric nitrogen.  Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S) and other nutrients are accumulated by cover crops during a growing season.

More information about cover crops is available through the Sustainable Agriculture Network (


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