Monopotassium phosphate (also potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate, MKP) -- KH₂PO₄ -- is a soluble salt which is used as a fertilizer, a food additive and a fungicide. It is a source of phosphorus and potassium. It is also a buffering agent. When used in fertilizer mixtures with urea and ammonium phosphates, it minimizes escape of ammonia by keeping the pH at a relatively low level.

Fertilizer grade MKP contains not less than the equivalent of 50% P₂O₅ and 33% K₂O, and is labeled 0-52-34. MKP is often used as a nutrient source in the greenhouse trade and in hydroponics.