Monopotassium phosphate (MKP)( Fertilizer Spreader ), (also, potassium dihydrogenphosphate, KDP, or monobasic potassium phosphate) is an inorganic compound with the formula KH 2 PO 4. Together with dipotassium phosphate (K 2 HPO 4. (H 2 O) x) it is often used as a fertilizer, food additive, and a buffering agent. Salt often crystallizes with potassium salt and phosphoric acid.