How much phosphorus do plants need?

What is the essence of Phosphorus in Plants?Phosphorus is used in several energy transfer compounds in plants. A very important function for P is its role in nucleic acids, the building blocks for the genetic code material in plant cells.
So, to get fruits, plants needs the blossom cells. To fight diseases, plants need immune cells. Phosphorus is essential, it is the nutrient needed to multiply cells in plants. Energy to produce fruits is transferred to various places via phosphorus.

How much phosphorus do plants need?
This is where most get it wrong. And organic farmers just use overdose. And fertigation with drip users apply phosphorus based fertilizers recklessly because sellers lied to them.

My approach is to look at plant tissue tests. Take a look at the attached picture. Look at cucumber, and check the adequate before blossom, during blossom, and after blossom. Phosphorus remain same. And funny enough, it has the lowest % of all major nutrients. Even plants needs more Mg and S than P. Hahaha! Dejavu! Miracle! LOL!

Check my nutrient solution up there and see. P is 50ppm, Mg is 50ppm, while A is 65ppm.
I may move Mg up later.


Now, let us look at NPK 15 15 15.
N = 15%
P2O5 = 15%, P= 15 × 0.43 = 6.45% (still very high if we use the ratio of the tissue test)
K2O= 15% ×0.83 = 12.45%

If I go through a long calculation which is not necessary for this thread, the right proportion for NPK is always 3 : 1: 2 before blossom, and 2 : 1 : 3 or 3 : 1 : 3 after blossom. Phosphorus need does not change.

How to apply Phosphorus and Calcium
Using soluble phosphorus of any brand in non hydroponic system (in open field) is waste of money. Sellers tell you that you need phosphorus, bla bla bla bla. Rubbish. Yeah! You need it, but not like how they want to sell.

Phosphorus and Calcium does not just escape from the soil. They bind well with soil. I can permit calcium nitrate since it is not that expensive like phosphorus, but better if you use lime. Apply lime during soil preparation. Apply it in a good quantity to get to the right PH. If you eventually need more calcium, it will be later part of the crop.
Then use Calcium Nitrate. For Phosphorus, apply as much SSP or TSP as
possible during soil preparation in accordance with what your plants need. It will bind with the soil and not evaporate.

The first nutrient plants need is phosphorus to build good roots. First the root cells must be formed. It is why you need it constantly in the soil but at lower rate than all major nutrients.

You only need to fertigate potassium and nitrogen. That is all you need to fertigate. During soil preparation, mix NPK inside soil too to put in potassium. For the first two weeks, use urea only to fertigate. Guys, if you need potassium, dissolve NPK in hot water and fertigate it. LOL. Not good practice but what can man do? I tried it once and it worked, and I have introduced many to it. The brown particles that don't dissolve is phosphorus.
Do not fertigate that as it will clog your emitters. Just take it and pour beside the roots of your plants.

After blossom, fertigate with potassium nitrate plus calcium nitrate, and if you need more nitrogen, add urea. Or you fertigate with urea and potassium chloride. Just be careful with the high salinity of potassium chloride. But the amount of potassium in it is extremely high. I think 63%. I always have it. And I use together with potassium nitrate. I interchange.

So, if you can calculate the total amount of Phosphorus needed for your plant from A to Z, add it to the soil from the start. That is the way to go. But if you find later you are phosphorus deficient, your first option is side dressing with NPK. And you may then consider soluble phosphorus fertilizer if you have the cash. I have not for once used soluble phosphorus on open field. And I do not think I will ever use it. Only for hydroponics.

For organic guys, it is a good practice to spray soluble phosphorus during blossom. Yeah! I encourage you to do it.
And I will be using it for my plants too. I am using it mainly because of enzymes I added to it, and not because of the phosphorus in it. You will be shocked how little quantity major nutrients are in those organic soluble fertilizers. lol. For me, they are insignificant, but if you hear how they promote the stuff like they are millions ppm inside. Ha! Ignorance has really ripped off many people.