high phosphorus level in garden soil test.

Asked May 26, 2017, 11:15 AM EDT

I recently received my garden soil test report from the UM soil testing laboratory which indicated very high phosphorus levels of 100+ppm on one soil plot and 84 ppm on another soil plot. These were reported as Bray 1. Five years ago my soil test report showed a Bray 1 phosphorus of 100+ ppm and Olsen phosphorus of 50+ ppm. Why are my phosphorus levels so high? How do I go about normalizing the phosphorus and how long will it take to normalize the phosphorus. Over the 5 year period between soil reports the phosphorus level has not changed much.

Stearns County Minnesota

1 Response

Many Minnesota soils contain naturally high amounts of phosphorus. These levels may increase in cultivation over time because organic matter and fertilizers that contain phosphorus are often used to improve soil structure and increase production.

The very high phosphorus levels measured in many soil tests do not affect production negatively. Nevertheless, the following bulletin lists things that can be done to stabilize or reduce soil phosphorus when that is a concern. Although the bulletin was prepared for Texas residents, most of the content also applies to Minnesota.

http://soiltesting.tamu.edu/publications/E-465.pdf

Phosphorus in soil and how it affects plants is a complex subject. The following bulletin may be of interest if you are comfortable with a rather technical discussion of the topic.
https://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/