It's all in how you use the P sources.
Rock Phosphate is a slow release.
Alfalfa Meal is medium release
Guano's are fast release
liquid organic nutrients are delivered plant available. That means they are ready to be absorbed by the plant - just like synthetic nutrients.
I use plenty of it in (rock phosphate's) some soils (bloom) and less in those that run shorter.
Short to a little medium release is like guano's. You must be careful of it's use, as it can create P tox if over used.
Here is where I have to mention that I run all my soils at 6.5 for veg. and ambient room temps of an average of 75+ degrees F.
In bloom? I run at 6.7 - 6.8. Doing this is done by ignoring the soil's pH it's self and adding all ingoing set to those pH values
While I use several bloom rooms. They do have a temp difference of about 5-6 deg F between them. Average is 69-70, and LONG running sativa's up to 76F.
Why?
Because temp's of the soil are directly involved in P uptake. The higher the temp? The slower the availability for uptake.
The lower your temps? More available P for uptake. (By microbe actions in the soil)
Here comes the part about having an active healthy bio heard in your soil.
I have the blessing of running an all organic farm. In fact I'm the CEO of a 6 farm organic co-op. We run organic crops, raise organic animals, create organic dairy products and now (getting to be real big too) Raising organic brewing ingredients...
This allows me the freedom to employ farm byproducts in the building of my soils. here is where I get a vary broad spectrum of living bio's for my soil's.
NOTE: I like to run a fungal heavy spectrum soil for cannabis.
There is another note that can be critical to P uptake.
Ca will block P if over used or you make you soils to ca heavy.... It will slow it down at high rates of use to complete blocking.
This again will directly tie to Ph of the soil.
Always remember that when you water? The pH will swing over a point in one direction. as the soil dry's out? It swings back to the soil's "resting point".. Proper starting soil's allow the plant to grow into the soil in many ways. One is that the plant will "help" set the soil's pH at a spot the plant "likes".
Use a good proper soil when starting plants and up to the first real up potting to 1 gallons. It will help the plant with that pHing of the soil action.
I see folks doing "spikes" in bloom with some real odd choices for the P source. To me? This is just doing it the easy way AND increasing the chances of P and K issues! I don't "SPIKE" my soils at later bloom.
It takes time to hash out a good soil formula. Sometimes lots of time. Being able to "look" at a plant and "read" it? Is one of the biggest assets to being able to "build" a SS bloom formula...
That help some?
