Phosphorous is used by plants largely for root growth, development and in the process of seed germination. And also in the formation of buds, flowers, fruits and vegetables. Flowers that are well fed with phosphorus will have more blooms, and fruits ripen better and faster. Phosphorus availability is of great importance especially at the beginning of the season (root activity). Phosphorus is efficiently absorbed when fertilized along with nitrogen.
In severe phosphorus deficiency the growth of the plant will be delayed. Dark green leaf color, with a purple tinge.
Leaves smaller than usual, They may thicken and curl and the damaged leaves will feel hard to human touch.
low flowering, increased flower loss
Very rare, almost impossible to happen. The plant will not absorb phosphorus beyond demand. But high levels of Phosphorous, (more than 55ppm) may create the unavailability of iron (CO) zinc (ZI) and magnesium (MG).
When preparing a new area for planting it is customary to add superphosphate, a solid, granular phosphorus fertilizer, as a foundation in order to raise the overall phosphorus level, when there is a deficiancy. The NPK of superphosphate is 0-45-0, 0-18-0 etc.
The first number of three numbers on the fertilizer package is Nitrogen (N), the second is Phosphoros (P) and the third is Potassium (K). The number represent the weight percentage of the nutrient in the fertilizer package.
A measurement reading of over 55ppm in the solution obtained from the soil water sampler or from the runoff in hydroponics, is too high, and points on phosphorous accomulation. If this happens, wash the soil/planting media with a lot of pure water in order to lower the level of the phosphorous.
If no phosphorous is added with the irrigation water, only sample the runoff solution if there is nothing ,or less than 10ppm, add more using fertilizer.
If phosphorous fertilizer is added to every irrigation, you need to test the concetration also there, and compare to the runoff solution test. If they are equal, you need to raise the phosphorous fertilizer given. If the runoff solution concentration is higher than the concentration of the irrigation water, (but not more than 55ppm) you are fine.