Ok direction change.
I'm curious how many people actually calculate how much macro and micro goes into their soil amendments. Either when starting new soil or amending existing.
Second question, are you simply using the % listed on the boxes/bags?
Third, and possibly the one that's going to hang most people up. When you are considering your P and K numbers, do you use what is listed on the package (say...3-4-4), or do you use the actual weight of the desired element?
Confused? Lets look at a bag of Gardentone. 3-4-4 is what it's analysis states. But look closer at what they (and all fert producers) are guaranteeing is in there. Potassium is presented as K
2O, or potassium oxide. Two potassium atoms and an oxygen. Working out the maths on the atomic weights...
2xK (atomic weight 19) = 38
1xO (atomic weight 8) = 8
Total weight = 46
38 (total K) divided by 46 (total weight)
we see that 82.6% (round to 83%) of available K
2O is actually K. So applying that 83% to the listed minimum qty of 4 and you get....3.32.
Not happy about that? Well then look at phosphorus. Presented as P
2O
5 or phosphorus pentoxide. Again the maths on molecular weight show that merely 43% is actually phosphorus. In our bag of 3-4-4, the actual available P is only 1.72.
The left over oxygen is used by soil life, not the plant.
Discuss.....
PS. Another pet peeve, I guess, is N sourced from ammonium. It reacts with lime agents and that available N just exits the soil as a gas.
The Gardentone has .2%. So in my mind the label should REALLY read
2.8-
1.72-
3.32. Sorry Espoma, you're getting picked on but all ferts are labeled like this.