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Recommendations are written as kilograms of N, P2O5 and K2O per hectare, but fertiliser is bought as products. DAP carries 46% P2O5 and 18% N, so it is sized on the phosphate need first and the nitrogen it supplies is deducted before the urea (46% N) balance is worked out. Potash comes from MOP at 60% K2O.
Product from nutrient
DAP = P2O5 need / 0.46; urea = (N need - 0.18 x DAP) / 0.46; MOP = K2O need / 0.60
Follow your state soil-test-based recommendation and label instructions. Over-application of nitrogen and phosphate causes groundwater and surface water pollution and may breach nutrient management rules.
DAP is 18% nitrogen. Ignoring it over-applies N, which wastes money, encourages lodging and leaches to groundwater.
Phosphate and potash are usually applied as a basal dose. Nitrogen is normally split — around one third basal and the rest as two top dressings timed to tillering and panicle or flowering stages.