Phosphorus Fertilizer Sources: What Are the Differences and Which One Should You Use?

By Dan Kaiser

For most farmers, the source of dry phosphorus (P) fertilizer is limited to what local retailers have on hand. The most common sources sold in Minnesota are mono-ammonium phosphate (MAP) and di-ammonium phosphate (DAP). Triple superphosphate (TSP) and Crystal Green (struvite) are also available in some areas. What are the differences between these sources and how should growers decide which one to use?

What are the differences between MAP and DAP?

The chemical formulas for MAP and DAP are:

• MAP: NH4H2PO4
• DAP: (NH₄)₂HPO₄