When it comes to phosphate source selection, the menu is a good one. It contains liquid sources, such as the polyphosphates 10-34-0 and 11-37-0; and granular sources such as monoammonium phosphate (also called MAP, which is 11-52-0) and diammonium phosphate (also called DAP, which is 18-46-0).
The polyphosphates can sequester metallic cations such as zinc (Zn), a benefit that allows the fertilizer solution to retain a high concentration of the micronutrient. Of the granular sources, MAP is often the choice for two reasons. First is its higher concentration of phosphorus, and second is the very low risk of seedling injury from free ammonia coming near the germinating seed during MAP applications.
Agronomic benefits aren’t the only factors in phosphate source selection. When a dealer’s bin space is limited, MAP boosts the amount of phosphate that can be held in storage and made available to meet grower needs. Selection of a higher analysis phosphorus source also means growers make fewer stops to fill starter fertilizer hoppers. This can mean more acres of corn planted during the critical, narrow spring planting window.