An Extension agent shared the “fate of phosphorus in Florida citrus soils” in the September Extension newsletter for citrus growers.

Phosphorus is a vital nutrient for all plants, including citrus, but it’s not always readily available, according to Multi-county citrus Extension agent Chris Oswalt. In the September Extension newsletter, Citrus from the Ridge to the Valley, he shared the different ways the nutrient can be tied up or bound in other compounds, making it unavailable to plants, and how growers can fix the issue. See the details below.

Phosphorus in Florida and Availability

According to Oswalt, the pH of the soil can have a great impact on the availability of phosphorus in Florida citrus soils.

High pH. “In higher-pH, alkaline soils, phosphate ions react with soil calcium ions resulting in a decreased solubility of phosphorus (a process called phosphorus fixation). Due to the rapid phosphorus fixation at high soil pH, applications of soluble phosphorus in these soils will only be available to plants for a short time. In this situation, lowering the soil pH will decrease the amount of fixed phosphorus, resulting in additional previously insoluble phosphorus becoming available.”

Low pH. “In acidic soils with lower soil pH, phosphorus faces a similar issue, but through a different mechanism. Under lower soil pH levels, soluble phosphorus will bind with iron, aluminum and manganese ions to form hydroxy phosphates, which are insoluble and unavailable to the plant. In this situation, raising the soil pH to 6.5 will disassociate these ions, resulting in phosphorus availability.”

Oswalt recommended that “The actual amount of soil phosphorus reported by a specific soil test should be considered, along with the soil pH and soil conditions from which the sample was collected. The review of this information should be in concert with leaf tissue analysis for phosphorus.”

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