Phosphorus Can Be Used as a Fertilizer and Stimulant for Avocados

  • Mar 26, 2019

Phosphorus (P) is an element that plays an important role in California avocado groves. The role it plays, however, depends on its oxidation state.

As a phosphate or phosphoric acid (H3PO4), phosphorus acts as a fertilizer.

When it is in the H3PO3 form, or as a phosphonate, phosphonite, phosphite or phosphorous acid, it acts like a stimulant that can help protect avocado trees from Phytophthora, Pythium or root rot. Phosphite products are commonly used as fungicides and bactericides. Phosphite is easily absorbed by plants through their leaves — sometimes within 15 minutes according to an article by Arnold W Schumann.

It’s important to remember the difference because “phosphite cannot substitute for phosphate as a plant nutrient.” In other words, if you are applying phosphorous acid to your groves, the phosphorus is not acting as a fertilizer — and therefore your trees could be deficient in phosphorus. 

Studies have shown that phosphorus-deficient trees are more susceptible to stunted growth if phosphite is applied. Therefore, before applying a phosphite product it’s important to determine whether the avocado trees are phosphorus deficient. Also, it’s important to note that leaf tissue analyses can mask phosphate deficiencies if phosphites are applied to the leaves of the tree because labs cannot distinguish between nutrient (from phosphates) and non-nutrient (from phosphites) phosphorus. The best method is to apply phosphate and phosphite together in a foliar spray to prevent a negative effect on the tree caused by undetected sub-optimal phosphorus levels. Today, many products include a blend of phosphites and phosphates — in this manner, you can address phosphorus deficiencies and boost the tree’s immune system at the same time.

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