I've gotten a recommendation for amending my soil. It calls for 1 cup calphos (soft rock phosphate) which is 0-3-0. It says it has 3% available P with 15% or so total P. I've locally source an amendment called Phosul. It's labeled 0-16-0. But it says on the bag 16% total P and 6% available P. But it's labeled 0-16-0. So if I'm subbing out the phosul for the calphos I should do the math based on it having 6% available P and ignore that it's labeled 0-16-0. 1 cup of calphos at 3% available P would be .5 cup of phosul at 6% available P to equal the same amount of available P. If I do the math by the label 0-16-0 vs 0-3-0 it would be .2 cup of phosul (rounded up) to equal the same amount. I'm new at this. Is it just labeling differences between different manufacturers? I should trust the 6% available P, correct?

Here's a pic of the product

This article was the best I could come up with to explain the phosphorus in fertilizers.
https://extension.umn.edu/phos...
It appears the total, the available and the water soluble are dependent on the process used. I could never really get a grip on the differences in how the plant available and the water soluble differed when applied to the soil. I am not even sure if one cup of your 6 percent would even be closely equivalent to two cups of your 3 percent product. Are they both pretty much equal in particle size? Amazing how something that looks so simple on the surface can be so confusing when you start thinking about it. Let us know what you figure out.

Thanks for that link. I found a similar one last night but I'm excited to check this one out. Most of it is above my head but I try. I'm check that article out tonight and get back to you. Thanks for the reply.