A Greenhouse Study Comparing Brushite, MAP, DAP, TSP, and Struvite Using a Phosphorus Deficient Prairie Soil.

Over recent decades, monoammonium phosphate (MAP) and diammonium phosphate (DAP) have increased in popularity as phosphorus fertilizers in the US; however, there have been relatively few studies comparing them to each other and to the previously popular fertilizer mineral, triple superphosphate (TSP), whose active ingredient is monocalcium phosphate. Recent advances in technologies for phosphorus recovery from wastewater may lead to production of the minerals struvite (magnesium ammonium phosphate hexahydrate) and brushite (dicalcium phosphate dihydrate), neither of which is commonly used in large-scale agriculture and for which there is little comparative data. Much can be inferred about the fertilizer implications of these minerals through current understanding of the soil chemistry of P. In noncalcareous, calcium-rich soils, it has long been known that phosphorus solubility is often controlled by brushite within hours of application of any phosphorus fertilizer. We hypothesized that although MAP, DAP, TSP, and struvite may be more soluble in water than brushite, they are unlikely to be a significantly better fertilizer than brushite. We conducted a simple comparative greenhouse study to examine the effects of these fertilizers on a noncalcareous, phosphorus-deficient remnant prairie soil (Plano Silt Loam), holding nitrogen and potassium fertilizer rates constant. Preliminary analysis of the data, including aboveground dry matter, P concentration in dry matter, and total aboveground P, confirms the initial hypothesis.