By Scout Nelson
Phosphorus (P) fertilizers play a vital role in supporting strong plant growth and improving crop yields. In Minnesota, the most common dry phosphorus fertilizers include mono-ammonium phosphate (MAP) and di-ammonium phosphate (DAP), while triple superphosphate (TSP) and Crystal Green (struvite) are available in select regions. Understanding the differences among these fertilizers helps farmers make better decisions for their soil and crop needs.
The main difference between MAP and DAP lies in their chemical makeup. MAP is NH₄H₂PO₄, and DAP is (NH₄)₂HPO₄. DAP contains two ammonium ions per phosphate, while MAP has one. When dissolved in water, MAP becomes acidic, while DAP is more basic.
Because of its acidifying nature, MAP provides slightly more available phosphorus in high-pH soils. However, research shows minimal performance differences between the two, meaning farmers can confidently use whichever product is available locally.
Triple superphosphate, with the formula Ca(H₂PO₄)₂, does not contain nitrogen. Despite including calcium, TSP forms an acidic solution (pH 1–3), even lower than that of MAP.
Although TSP has a smaller market share in Minnesota, it serves as a good option when fall nitrogen applications are not recommended. It offers a phosphorus concentration similar to DAP (46% P₂O₅) and blends well with other fertilizers containing nitrogen, potassium, or sulfur.
Another phosphorus source is Crystal Green (struvite), made of magnesium ammonium phosphate (MgNH₄PO₄·6H₂O). Struvite contains about 28% P₂O₅ and is less water-soluble than MAP or DAP.
It is often produced from wastewater treatment by-products. Though some claims suggest struvite performs better in high-pH soils, most research indicates similar or slightly lower phosphorus availability compared to MAP, resulting in comparable crop yields when applied at equal rates.
In summary, while these phosphorus fertilizers differ chemically, most perform similarly in field results. Choosing the best option depends on soil conditions, nutrient needs, and fertilizer availability.
Photo Credit:gettyimages-fotokostic
Categories: Minnesota, Crops, General