Phosphorus nutritional elements: Generalities
Phosphorus is a basic element for ornamental and flowering plants because it is linked to flower formation, root development and bud structure.
In the soil it is present in significant quantities in the form of mineral (various types of phosphate), or it can be found contained in the organic component, namely the Humus.
The plant absorbs the phosphorus contained in the circulating solution in the form of a directly usable phosphoric ion. The mineral phosphorus contained in the soil is therefore subject to many interactions with the other elements present in the soil (formation of insoluble salts), which limit its diffusion and availability for plants. A classic example of retrogradation is given by the interaction between phosphates and calcium which leads to the formation of insoluble tricalcium phosphate.
The phosphorus in the plant performs plastic and energy functions since it enters the composition of fundamental molecules in plant biology such as nucleic acids (DNA-RNA) and adenosine triphosphate (ATP). It is from the process of using ATP that the plant draws the energy necessary to perform all vital functions, including chlorophyll photosynthesis.
Furthermore phosphorus is an activator of numerous enzymatic activities, it enters the composition of reserve substances and vitamins.
The effects that phosphorus determines on a plant are more evident with the stimulation of the formation of flowers and roots and in the greater elasticity of the shoots.
Phosphorus deficiency is manifested by a real deficiency of the element in the substrate or, more frequently, because there are situations that block its availability for the plant (the retrogradation we have already discussed).
The factors that limit the availability of phosphorus are the excessively clayey soil, which strongly retains the element, the alkaline pH and the high limestone that determine the formation of insoluble compounds (bi and tricalcium phosphate).
In these conditions the plants show clear symptoms of phosphate deficiency that generate a poor vegetative development of the buds (dwarfism) and of the roots (plants not well anchored in the soil), sparsely lignified and little erect branches (typical in the rose), small leaves, slender, with bronze coloring. Flowering occurs with a lower intensity and in a late way, as well as the ripening of the fruits. Some specific manifestations are found in the tomato, where there is a purple coloring of the underside of the leaves. Furthermore, among the flowers, particularly in the carnation, there is a reduced growth with thin, narrow, straight leaves and small flowers. In the composites (Astro, Margherita, Chrysanthemum) there is a stunted growth and later the older leaves turn yellow, brown and die. In bulbous plants there is little radical formation.
In the rose there is an early fall of the leaves without yellowing, with the buds appearing slightly lignified, weak and twisted.
In fertilizers, phosphorus is associated with nitrogen and potassium, forming the classic NPK fertilizers. On packages, Phosphorus is present in the composition section and is conventionally referred to as Phosphoric Anhydride, which has the symbol "P2O5".
The addition of fertilizers with a high phosphorus content are advisable in the initial and central phases of plant development, to favor root formation and flowering induction.
Usually the phosphorus, given the reduced mobility in the ground, comes at the time of preparation of the same before sowing or transplants, or, in potted plants, at the time of repottings and in the autumn-winter period.