Plants uptake nutrients when they are in a water solution.
Soil-applied nutrients are moved into the root during water uptake and therefore distributed in the tree along with water.
Mobile and immobile nutrients have an equal and uniform distribution in all parts of the plant.
Granular fertilizer, controlled-release fertilizer, and fertigation are all soil-applied fertilization methods.
Huanglongbing (HLB) Consideration
HLB-affected trees have a small root system; therefore, the nutrient uptake capacity of roots is limited.
The constant availability of nutrients is critical.
Nutrient sprays should be timed at two-thirds-expanded to nearly fully expanded young leaves.
Mature leaves with thick leaf cuticles limit nutrient uptake.
Even when foliar sprays are applied at the right time, immobile nutrients can get locked in leaves and cannot move into growing leaves, roots, or fruit; as a result, their distribution within the plant is poor.
Soil pH and Nutrient Interactions
At high soil pH, most of the micronutrients bind to the soil and become unavailable for plant uptake.
At extremely low soil pH, most of the macro- and secondary nutrients become unavailable for plant uptake.
The goal is to have the right soil pH range for nutrient uptake.
The preferred range for soil pH in Florida citrus production with HLB-affected trees is 5.8–6.5.
Movement of Mobile Nutrients
Mobile nutrients move to areas of active growth within the plant.
Nutrients move in all directions.
These nutrients are transported via xylem and phloem.
Deficiency symptoms appear first in older leaves, and if the deficiency is not corrected, they show up in new growth.
Mobile nutrients include Nitrogen (N), Phosphorus (P), Potassium (K), Magnesium (Mg), and Sulfur (S).
Soil- and foliar-applied nutrients are both adequate.
Movement of Immobile Nutrients
Immobile nutrients do not redistribute within the plant.
These nutrients are transported only via xylem.
Immobile nutrients do not move to areas of active growth.
Deficiency symptoms show up in the new growth first, and if not corrected, they will show up in older leaves.
Immobile nutrients include Calcium (Ca), Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn), Boron (B), and Molybdenum (Mo).
Foliar applications have limited efficacy and distribution in the plant.