Effect of Phosphorus Fertilizer Source On Fate and Transformations of Phosphorus in High P Fixing Soils.

Low phosphorus (P) availability in agricultural soils is a major factor that limits crop production in many areas of the world.  Two soil types, a highly calcareous soil from the Eyre Peninsula, Australia, and a volcanic soil from the Cotacachi region, Ecuador were used.  Both soils are used for crop production despite high P fixation capacity, making increased crop yields difficult without P fertilizer additions.  Objectives of the study were to investigate and understand the mobility and availability of P from monoammonium phosphate (MAP), diammonium phosphate (DAP) and ammonium polyphosphate (APP) fertilizers alone or plus a fertilizer enhancement product (FEP) on the two high-P fixing soils, and to closely examine the relationship between fertilizer reaction products found within the granule and immediately around the application point, and available P.  An equivalent amount of each P source was placed in the center of each dish.  Five replicates of each P treatment of both soils were incubated in petri dishes for five weeks at 25^o C.  At the end of the incubation period, concentric sections of soil surrounding the fertilizer placement point were removed and individually analyzed for total P, resin extractable P and soil pH.  In addition, scanning electron microscopy-energy dispersive x-ray analysis of remaining granules and P K-edge x-ray absorption near-edge structure spectroscopy (XANES) analysis of soils were performed to determine fertilizer reaction products.  Conclusions are pending.