Phosphorus - Roots and Flowers.

So, This molecule is VERY important for root development, flowering and fruit development.

It is also a part of the ATP molecule, which is the molecule plants use to transfer energy internally.

Pretty important, uh...?

Lots of soils contain a big amount of it.

BUT, most of it (98%-99%) is not available to plants...

In most soils it splits at about:

2% available to plants.

10% attached to the soil particles (And can become available.)

40% fixed in the soil structure.

48% fixed in organic matter - now, this part most organisms can get some of it using "Phosphatases" - enzymes that part phosphorus from organic compounds.

Phosphorus gets attached to the soil very quickly, (As the soil is "heavier" it attaches P stronger.) and roots can absorb it only from the very near areas (About 1mm).

Even when fertilizing, most of the available phosphorus will be found in the first 5-10 cm of the ground.

Thus, fertilizing with phosphorus is critical in the early stages of vegetable's seedlings. After that phase of the plant it depends on the soil's state - how much P it has in it (Which can be known through examination of soil samples in a laboratory by the Olsen method or other P-soil methods),

if it has organic matter, did it receive compost in the last 1-2 years or a Mycorrhizae treatment this year.

The availability of P is the soil is affected by 3 main factors:

1. pH of the soil - Plants absorb P as H2PO4-, so pH affects the availability of hydrogen ions and by that the concentration of this molecule.

2. The "heaviness" of the soil, as we mentioned.

3. The quantity of lime in soil - though it rises pH, P sinks down with Calcium.

Of course, when growing in a pot, or soil-less growing, Phosphorus needs to be added all the time, in the right concentration. (Which diverts in different plants and different stages of growth of the plant, but is about 10%-20% of Nitrogen.

Foliage fertilization - is actually pretty efficient for P fertilization! At about 50% absorbance.

(The best combination for that was found in an experiment using PEAK (=Mono-Potassium-Phosphate) with potassium hydroxid.)