What Is DAP Fertilizer?
DAP (Diammonium Phosphate) is one of the world's most widely used phosphorus fertilizers with an NPK ratio of 18-46-0. It provides both nitrogen and a high concentration of phosphorus, making it ideal for root development, flowering, and new plantings. DAP is applied at 2 to 4 pounds per 1,000 square feet, worked into soil before planting. It is alkaline-reacting initially but becomes acidifying over time as nitrifying bacteria convert the ammonium to nitrate.
What DAP Stands For
DAP is diammonium phosphate, a granular fertilizer with an NPK ratio of 18-46-0. It is the world's most widely used phosphorus fertilizer and the primary source of phosphorus in commercial agriculture. Each granule contains 18% nitrogen and 46% phosphorus by weight, with no potassium.
How DAP Works in Soil
When DAP dissolves, it releases ammonium (NH4+) and phosphate (HPO4 2-) ions. The ammonium temporarily raises soil pH near the granule to around 8.0, which can suppress seedling emergence if placed too close to the seed. The phosphate is immediately plant-available but becomes less available over time as it binds with calcium in alkaline soils or iron/aluminum in acidic soils.
Application Rates
For gardens: apply 2-4 lbs per 100 sq ft and work into the top 4-6 inches before planting. For row crops: band 50-100 lbs per acre 2 inches below and 2 inches to the side of the seed row. For lawns: apply 4.3 lbs per 1,000 sq ft to deliver approximately 2 lbs of phosphorus (only if a soil test confirms phosphorus deficiency).
When to Use DAP
Use DAP when a soil test shows low phosphorus levels. It is ideal for pre-plant incorporation in new garden beds, transplanting trees and shrubs, and establishing new lawns. The nitrogen content provides a starter boost alongside the high phosphorus for root development.
DAP vs MAP (Monoammonium Phosphate)
MAP (11-52-0) is the alternative high-phosphorus fertilizer. MAP has a lower nitrogen content and produces a slightly acidic reaction in soil (pH ~3.5 near the granule), making it safer for seed placement and better for alkaline soils. DAP is cheaper per pound and more widely available but should be kept 2 inches from seed to avoid ammonia toxicity to germinating seedlings.
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