Soil pH plays a huge role in nutrient availability, especially where micro-sprinkler irrigation has raised soil pH.

“Soil pH influences nutrient availability;”is the sentiment of a Citrus Industry article written by UF/IFAS citrus Extension agent, Chris Oswalt. The article also explains how soil pH affects the availability of the big three—nitrogen, phosphorus, and potassium. See the details below.

Nutrient Availability Affected by Nutrient Availability

The article shared that the effects of soil pH on nutrient availability are “similar to conditions in the wetted zone where micro-sprinkler irrigation has raised soil pH..” The effects for the “big three” are:

Nitrogen. “Soil pH can affect several reactions involving nitrogen in the soil solution and the efficient use of this nitrogen by plants. Nitrification, the conversion of ammonium to nitrite and nitrate, is done by soil bacteria and is most rapid in soils with a pH between 7 and 8. The process of nitrification in the soil slows down at a soil pH of 5 or less. If a grower is using ammonium nitrate as a nitrogen source, then at a pH between 7 and 8, this ammonium nitrate would be rapidly converted to nitrate.

This would make the nitrogen applied significantly susceptible to leaching due to the quick conversion of the ammoniacal nitrogen to the more soluble nitrate form.”

Phosphorus. “The availability of phosphorus in calcareous soils is also limited. The amount of phosphorus in soil is closely related to the availability of this phosphorus to plants. In high-pH soils, phosphorus reacts with soil calcium, resulting in a decreased solubility and availability of phosphorus (a process called phosphorus fixation). In this situation, phosphorus availability is determined by the amount of soluble phosphorus applied and any phosphorus 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. Lowering the soil pH to a range of about 6.5 to 7.2 will decrease the amount of fixed phosphorus, resulting in the availability of previously insoluble phosphorus.

Potassium. “Availability of potassium 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 potassium uptake by citrus trees due to competition between calcium and potassium for the exchangeable soil particle sites. Although potassium would typically be available for plant uptake at a higher soil pH, the competition with soil calcium can negate this availability. Lowering the soil pH in this situation will reduce the exchangeable sites of the soil particle that could be occupied by potassium or other basic cations (calcium and magnesium). This would result in the release of potassium and other basic cations, making it more likely that leaching could affect the soil levels of these nutrients.”

The article added that “Huanglongbing (HLB)-affected trees tend to have smaller and weaker root systems when compared with healthy trees. Even though this increases nutrient deficiency and stress on the plant, the roots are still functional. Nutrient uptake and soil pH are of utmost importance to ensure tree health.

The optimal soil pH for effective Florida citrus production ranges from 5.8 to 6.5. Research suggests that pH ranging between 6 and 6.5 can help increase the availability of potassium, phosphorus, calcium, manganese, zinc and iron in the soil. Even though a lower pH seems to benefit HLB-affected trees more than healthy trees, the pH of your soil should not be lower than 5.”

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