... (H2PO4) 2-H2O. Properties: colored particles. Available water-soluble fertilizer, weak acid. Uses: the supply of plant phosphorus, calcium, ... : dark gray, gray, loose Web results. Available water-soluble fertilizer, weak acid. Uses: the supply of plant phosphorus, calcium ... of alkaline soil. Can be used as base fertilizer, foliar application, foliar spray. And nitrogen mixed with nitrogen fixation, to ...