Diammonium Phosphate (DAP)

About This Product

Diammonium phosphate, DAP, has the formula (NH4)2HPO4 and CAS number 7783-28-0. It is supplied as white to brown granules, freely water-soluble, and dissolves to give an alkaline solution at around pH 8. The difference from MAP is one ammonium ion, and it changes the behaviour in the soil. DAP carries more nitrogen at 18 percent and slightly less phosphorus at 46 percent P2O5, and its solution is alkaline rather than acidic. On acidic soils that alkalinity is helpful, but around a dissolving granule on an already alkaline soil it briefly raises pH high enough to release free ammonia, which can damage germinating seedlings if the granule is placed in direct contact with seed. MAP is the safer choice for seed-placed application for that reason. DAP is also widely used outside agriculture: as a yeast nutrient in winemaking and brewing, where it supplies assimilable nitrogen for fermentation, and as a flame retardant for timber, paper and textiles, where it decomposes to leave a char barrier. It is used in fertilisers and blends, fermentation and yeast nutrition, flame retardant treatments, fire-fighting foams and as a buffer. Bio Green Chem supplies DAP to specification on nitrogen and P2O5 content, water-soluble phosphorus, pH, moisture, particle size and heavy metals.