Most phosphorus in the soil is found in inorganic form, such as phosphate ions H2PO4- and HPO42-, and these are the forms in which the plant preferentially absorbs them. In acid soils it is preferably absorbed as H2PO4- and in basic soils, such as HPO42-. However, with a pH below 6 and above 8, availability decreases rapidly. Unlike nitrogen, it does not need to be reduced inside the cell to become part of the molecules.

It is an essential element and is part of the trinomial: NITROGEN, PHOSPHORUS, POTASSIUM. Without phosphorus, photosynthesis and the formation of organic compounds would not be carried out correctly. It intervenes in energy storage processes as part of the ATP and ADP molecules. It is part of the phospholipids of cell membranes, allowing the active transport of nutrients to the cell interior. It is necessary to form carbohydrates, fats and proteins. It is found in enzymes, vitamins, and is part of the genetic material (DNA and RNA). It is part of the pyridine nucleotides (NAD, NADP) involved in the energetic reactions of metabolism.

Phosphorus favors the development of buds, apices and roots; It provides rigidity to the plant, anticipates ripening, unlike nitrogen, and improves the organoleptic characteristics of the fruits.

In the agricultural field, the P is an element used to:

• Ensure a good rooting. The P is found in the root tissues and is part of the functions related to absorption.
• Correct nitrogenous imbalances, to enhance the nutritional balance of P and K against N and stop excessive growth in favor of better flowering and fruit set.
• It is used to use the abundant “blocked” P in the soil, fruit of the excessive contributions that in traditional agricultural areas has been made of chemical fertilizers.
  phosphorus Deficiencies: It reduces the growth of plants. The leaves usually show a green/blue coloration due to formation of anthocyanins. Because it is a very mobile element, like nitrogen, the lack of phosphorus manifests first in the oldest leaves.

The most typical deficiencies observed in relation to P are:

• In citrus the old leaves pale and the fruit loses juice.
• In general, a worse root formation.
• Olive: discoloration and ocher tones.
• Tomato: bluish leaves, deformations.

Excess of phosphorus: it is mainly characterized by a great development of the roots in comparison with the aerial part and it is usually due to the excessive fertilization with phosphorus when compound NPK type fertilizers are used.