Soil Tests and Phosphorous

The UF/IFAS Extension soil testing lab in Gainesville offers soil testing for $10 per sample. Soil tests determine limiting nutrients and recommendations for fertilizer needs. Phosphorous (P) is one of the important nutrients tested. Generally, phosphorus is readily available in Florida soils. Occasionally, the report will show the soil is P-deficient.

The report divides the phosphorous results into three categories:

Low: plant benefits or increased yield from addition of P

Medium: little to no response from addition of P

High: no response expected to added P

Fertilizer is applied to correct a nutrient deficiency, increase yields or obtain another plant response. Legally, and before applying fertilizer that contains phosphorous, you should have a soil test showing the soil is P-deficient.

If your soil test report shows medium to high phosphorous:

  • Buy and apply fertilizer with little to no P.
  • Phosphorous is the middle number on the bag. Look for products with 0 or 2 as the middle number.
  • Follow UF/IFAS recommendations for fertilizer. To look up fertilizer needs of the plant you’re growing, try searching the “Ask IFAS” website: https://edis.ifas.ufl.edu/. For example, you could go to the “Ask IFAS” website and search for mango, bahiagrass or St. Augustinegrass. There, you will get a list of free publications that explain how to maintain and fertilize these plants.

If your soil test report shows low phosphorous:

  • Apply a fertilizer that contains phosphorous based on UF/IFAS recommendations.
  • Some plants – such as palms – have specific fertilizer and nutrient needs. Other plants, like turfgrass, perform better when the fertilizer is in a balanced ratio of nitrogen to potassium (N:K) – the first and last numbers on the bag. And some plants respond best when the fertilizer is in slow-release, also known as controlled-release, form.
  • Contact your Extension office – or try “Ask IFAS” – for help determining the fertilizer needs of turfgrass, vegetables, and other plants or crops.

Be sure to follow local fertilizer ordinances if one exists in your area. These ordinances may prohibit the use of fertilizers during the rainy season of June – September.

Your soil test report – and the phosphorus level – is important to know because you don’t want to add more P if it isn’t necessary. Plants growing in P-sufficient soils won’t show a response when more phosphorous is added. Besides cost, excess fertilizer may impact groundwater and water bodies.

Contact your local Extension office for help interpreting your report.

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Posted: December 31, 2021


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