Explore the relationship between soil pH and nutrients from a UF/IFAS citrus Extension agent for Florida citrus growers.

There are important relationships between soil pH and nutrients that can impact the health and production of Florida citrus trees. The big three nutrients, nitrogen, phosphorus and potassium, can be affected by elevated pH values, according to a Citrus Industry article outlining the information provided by multi-county citrus Extension agent Chris Oswalt in a Central Florida citrus Extension newsletter on nutrients and soil pH. Explore the details below.

Soil pH and Nutrients

Oswalt outlined how elevated soil pH and nutrients interact, specifically nitrogen, phosphorus and potassium.

Nitrogen. “Nitrification, the conversion of ammonium to nitrate, is done by soil bacteria and is most rapid in soils with a pH between 7 and 8. Nitrification in the soil is nearly zero at a soil pH of 5. So simply put, if a grower is using ammonium nitrate as a nitrogen source, then at a pH between 7 and 8, the ammonium would be rapidly converted to nitrate. This would result in the nitrogen applied being significantly susceptible to leaching due to the quick conversion of the ammonium nitrogen to the more soluble nitrate. At a lower soil pH, the ammonium in this ammonium nitrate would be more slowly converted to nitrate due to the reduced activity of soil bacteria.”

“Soils with elevated pH values can cause the loss of nitrogen due to the volatilization of ammonia (NH3) in the atmosphere. This volatilization of nitrogen occurs when ammonium sources of nitrogen are applied to a soil surface with pH values greater than 7. In the management of nitrogen applied to soils, when pH values are above 7, there is a greater loss of nitrogen when ammonium forms of nitrogen are used.”

Phosphorus. “In higher pH soils, phosphorus reacts with soil calcium resulting in a decreased solubility of phosphorus (a process called phosphorus fixation). In this situation, the availability of phosphorus is determined by the amount of soluble phosphorus applied and any phosphorus that is released from that fixed phosphorus. Application of soluble phosphorus in these soils will only be available to plants for a short time due to the rapid phosphorus fixation at high soil pH.”

Potassium. “Potassium availability in high pH soils is difficult to achieve due to the occupation of the nutrient holding sites of the soil particle surface by excessive calcium. The occupation of these exchangeable soil particle sites will suppress the uptake of potassium by citrus trees due to competition between calcium and potassium for the exchangeable soil particle sites.”

In all instances, Oswalt maintained that lowering the soil pH would improve the availability of nutrients and limit leaching.

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