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Synthesis, Characterization, and Agronomic Evaluation of Iron Phosphate Impurities in Superphosphates

^a Dep. of Soil and Plant Nutrition, Univ. of São Paulo/ESALQ, C.P. 9, 13418-900, Piracicaba, Brazil
^b IFDC, P.O. Box 2040, Muscle Shoals, AL 35662
^c Dep. of Plant and Soil Sciences, Alabama A&M Univ., Normal, AL 35762

View larger version (31K): [in a new window]   Fig. 1. X-ray diffractogram and powder diffraction file (PDF) data for compounds H8-syn (A) and H14-syn (B).

View larger version (18K): [in a new window]   Fig. 2. Infrared spectra for compounds H8-syn (A) and H14-syn (B).

View larger version (44K): [in a new window]   Fig. 3. SEM photomicrograph of subsample of the H8-syn showing (A) rod crystals of Fe2.8K1.1H8(PO4)6·4.1H2O (scale = 15 µm) and (B) EDS analysis of the specific square area.

View larger version (46K): [in a new window]   Fig. 4. Scanning electron microsope (SEM) photomicrograph of subsample of the H14-syn showing (A) pseudohexagonal plates of Fe3.0K0.9H14(PO4)8.4.3H2O (scale = 15 µm) and (B) EDS analysis of the specific square area on top of the main crystal.

View larger version (14K): [in a new window]   Fig. 5. Phosphorus (% of total P) released at equilibrium from Patos phosphate rock, H8-syn, and H14-syn as related to pH of a 0.01 M KCl solution.

View larger version (24K): [in a new window]   Fig. 6. Dry-matter yield of upland rice (A) and flooded rice (B) as affected by P source and P rate applied. Models followed by the same letter indicate their slopes are not statistically different (p 0.05).

View larger version (24K): [in a new window]   Fig. 7. Uptake of P by upland rice (A) and flooded rice (B) as affected by P source and P rate applied. Models followed by the same letter indicate their slopes are not statistically different (p 0.05).