Di-ammonium Phosphate popularly known as DAP is a preferred fertilizer in India because it contains both Nitrogen and Phosphorus which are primary macro-nutrients and part of 18 essential plant nutrients.

DAP (NH4)2HPO4: Fertilizer grade DAP Contains 18% Nitrogen and 46% Phosphorus (P2O5).. DAP is manufactured by reacting Ammonia with Phosphoric acid under controlled conditions in fertilizer plants.

• Soil Testing: For efficient use of this fertilizer, soil must be tested for nitrogen and phosphorus content in order to determine the required amount of DAP.
• Basal Dose: DAP is the best suited fertilizer for basal dose as through this we can apply full dose of phosphorus and one-third to half dose of nitrogen. Remaining dosage of nitrogen can be applied through splits of urea at other stages of crop . So DAP gives the best combination with urea fertilizer. DAP is also the best fertilizer for pulses where less nitrogen and higher phosphorus is needed as starter dose.
• Placement of DAP: Since phosphorus is immobile in soil, its source (DAP) should be placed at a distance where plant roots can easily reach. Improper application of DAP may cause seedling injury due to release of ammonia. DAP should be placed below seed, slightly to one side.
• Soil Amendments: Nitrogen as well as phosphorus, give best results in neutral soils. But in case of alkaline, volatilization losses of ammonia are higher. So nitrogen use efficiency is reduced. Similarly excessive presence of calcium in alkaline soils, makes complexes with phosphorus and ultimately results in poor phosphorus recovery. So bringing soil pH to neutral by adding gypsum and leaching can only improve N and P use efficiency of DAP.
  In acidic soils, problem ions like Fe, AI and Mn become more active and form complexes with phosphorus. Again P use efficiency is reduced. Nitrogen use is not affected much by acidity. Addition of lime (CaCo3) to acidic soils brings soil pH to neutral. Thus P use efficiency is improved.

It is a very popular fertilizer because of its excellent physical properties and nutrient content. It is free flowing, dust-free and does not normally give any storage problem. DAP is almost water-soluble and ultimately leaves acid effect on soils because of ammonia (NH₄) it contains. DAP on incorporation into soil, reacts with water and gets converted into HPO₄ and NH₄. Ammonium (NH₄) follows the same routes as in case of urea. Phosphorus in DAP is present in best available from (HPO₄). Depending upon the soil reaction (pH), phosphorus exists in 3 forms which can be absorbed by plant roots. These are HPO₄, H₂PO₄ and PO₄. Phosphorus, which is immobile in soil, is not subjected to leaching losses.