Table 4 Procedure for fractionation of soil inorganic P.

From: Using zeolite, molasses, and PGP microorganisms to improve apatite solubility and increase phosphorus uptake by Sorghum bicolor L. (Speedfed cultivar)

Step

P form

Extractant

pH

Description

1

Ca2-P

0.25 M NaHCO3

7.5

1 h shaking

2

Ca8-P

0.5 M NH4Ac

4.2

4 h shaking; 1 h shaking

3

Al-P

0.5 M NH4F

8.2

1 h shaking

4

Fe–P

0.1 M NaOH- 0.1 N Na2CO3

-

2 h shaking; 1 h shaking; 2 h shaking

5

O-P

0.3 M Na3C6H5O7-Na2S2O4-NaOH

-

16 h shaking

6

Ca10-P

0.25 M H2SO4

-

1 h shaking

  1. Ca2-P, Dicalcium Phosphate; Ca8-P, Octacalcium Phosphate; Al-P, Aluminum Phosphate; Fe–P, Iron Phosphate; O-P, Occluded or Oxide-bounded P; Ca10-P, Apatite Phosphate.
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