#1 The question is how much nitrogen do you want in your soil?
Quoted from
Aquarium Science – The Science of Aquariums : "Most (but not all) rooted “vascular” plants have been shown by testing to absorb phosphorus and iron from their roots much better than from their leaves. Most (but not all) vascular rooted plants also absorb potassium and nitrogen much better through their leaves".
#2 So, if we would like to follow this "guideline" it would be vice to have a soil rich in carbon, iron, and phosphate, while the water layer should contain potassium and nitrogen, true or false?
#3 An organic carbon-rich soil mixed with bonemeal or fish meal to add phosphate combined with iron sulfate would do it or?