Compound fertilizers, which contain N, P, and K, can often be produced by mixing straight fertilizers. In some cases, chemical reactions occur between the two or more components. For example monoammonium and diammonium phosphates, which provide plants with both N and P, are produced by neutralizing phosphoric acid (from phosphate rock) and ammonia (from a Haber facility):
NH3 + H3PO4 ? (NH4)H2PO42
NH3 + H3PO4 ? (NH4)2HPO4