Phosphorus chemistry and mineralogy in excessively fertilized soils: descriptions of phosphorus-rich particles
1990
Pierzynski, G.M. | Logan, T.J. | Traina, S.J. | Bigham, J.M.
Data is limited on the mineralogical characteristics and formation mechanisms of P-bearing solids that occur in soils due to P fertilization. This study was conducted to characterize, isolate, and infer formation mechanisms for P-rich particles found in two excessively fertilized soils. Phosphorus-rich particles were described in terms of morphology, elemental composition, and crystallinity using electron optical techniques. These particles were found in the < 2.2 Mg/m3 density separates from the clay fractions of a Plainfield loamy sand (mixed, mesic Typic Udipsamment) and Blount silt loam (fine, illitic, mesic Aeric Ochraqualf) that had been excessively fertilized for more than 20 y. Particle morphologies indicated that the P-rich materials exist as discrete particles as well as coatings on other particles. The elemental composition of the particles varied within as well as between particles. Phosphorus concentrations in the P-rich materials ranged from 5.6 to 27.2% per mole of cation (mole cation %). Aluminum and Si were the dominant elements associated with P, while Ca, Fe, and Mn generally were present at low concentrations. The P-rich materials were amorphous to electron diffraction and can generally be described as an amorphous mixed Al-Si-P substance. An analogy was made between the P-rich material, the amorphous analog of variscite, and allophane.
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