Should Soil pH Influence Fertilizer P Source Selection?
Soil pH should not be an important factor in selecting fertilizer P sources. From an academic perspective, monoammonium phosphates (MAP) create a more acidic zone around each fertilizer granule, whereas diammonium phosphates (DAP) create a basic zone. Thus, in high pH soils, it can be theorized that using MAP-based fertilizers should be better than DAP because the acid-producing fertilizer would offset the calcareous soils. An additional concern regarding MAP or DAP selection, aside from soil pH, is potential ammonia toxicity to germinating seeds in dry soils. In applying the recommended amount of P in a drill-row or pop-up fertilizer placement, DAP will contain approximately 60% more N, which may be a potential injury risk. However, since agronomic studies and economic data indicate no crop yield differences, it can be concluded that fertilizer selection should be made on traditional factors such as nutrient content, price, availability, etc.
