If one were to encapsulate the chemical wisdom of nitrophosphate fertilizer in a single sentence, it would be this: let nitric acid become a "double-duty" versatile player. Traditional phosphate fertilizer production requires sulfuric acid to decompose phosphate rock. In that process, sulfuric acid serves only as a "chemical key" and does not itself provide any nutrient elements needed by crops. The nitrophosphate process, however, takes a different path - it uses nitric acid directly in place of sulfuric acid to digest the phosphate rock. Nitric acid acts both as the acidulating agent that decomposes the rock, converting insoluble fluorapatite into soluble phosphoric acid and calcium nitrate, while at the same time the nitrate ions are retained intact within the fertilizer system, becoming a direct source of nitrate nitrogen nutrition. A single acid simultaneously shoulders the two missions of "unlocking the phosphate rock structure" and "supplying nitrogen nutrients."
From the perspective of atom economy, this is undoubtedly an elegant chemical design: virtually every "nitrogen" in the nitric acid molecule stays in the fertilizer, with almost no superfluous chemical consumption. After freezing crystallization to separate a portion of the calcium nitrate, neutralization with ammonia, and the addition of potassium salts, a two-nutrient (NP) or three-nutrient (NPK) compound fertilizer is ultimately produced. Even better, because sulfuric acid is omitted, the medium and trace elements such as calcium, magnesium, and silicon from the phosphate rock are not largely converted into difficult-to-use calcium sulfate waste, but are retained in the product in active forms. A single nitric acid molecule sets in motion the release and recombination of nearly all the nutrients in phosphate rock - this is the door to compound fertilizers that nitrophosphate fertilizer has opened through chemical ingenuity.