Why is calcium dihydrogen phosphate most widely used as phosphorus fertilizers, and not calcium hydrogen phosphate

Why is calcium dihydrogen phosphate most widely used as phosphorus fertilizers, and not calcium hydrogen phosphate or calcium orthophosphate? What substance in simple superphosphate is ballast?

Calcium dihydrogen phosphate is better soluble in water (1.5g / 100ml) than hydrogen phosphate (0.02g / 100ml), and calcium orthophosphate is completely insoluble in water, and the solubility of fertilizer in water is very important. Only soluble compounds dissociate into ions, which are then absorbed by plants, CaSO4 is a ballast in the production of simple superphosphate.

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