Mobility, Availability and Reaction Products of MAP, DAP and APP Fertilizers.

The limited availability of phosphorus (P) in calcareous and acidic soils is a major factor that limits crop production.  It has been found that liquid P fertilizer is more mobile and available for plant uptake in highly calcareous soils than granular fertilizer products containing the same rate of phosphorus.  The objectives of this study were to investigate 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, on different soil types, and to examine the relationship between fertilizer reaction products and available phosphorus. All soils were incubated in petri dishes containing five replicates of each fertilizer treatment at the center for five weeks at 25^o C. At the end of the incubation period, four concentric sections of soil surrounding the fertilizer placement point from each dish were removed and individually analyzed. Measurements included soil pH, total P, resin extractable P, fractionation of P, scanning electron microscopy-energy dispersive x-ray analysis of granules and P reaction products using x-ray absorption near-edge structure spectroscopy.  Our data show enhanced diffusion and/or solubility of some P sources in some soils.  Conclusions are pending.