Table 5 Organic P fractionation procedure according to Kovar and Pierzynski (2009).

1

Labile Po

0.5 M NaHCO₃, pH 8.5

16 h shaking, Centrifuge and filter

Aliquot

a

Labile inorganic P

Labile Po = a–b

b

Digestion/Persulfate; Total labile P

2

Moderately labile Po

1 M HCl, 0.5 M NaOH

3 h shaking; 3 h shaking, Centrifuge and filter

Aliquot

a

Moderately labile inorganic P

Moderately labile Po = a–b

b

Digestion/Persulfate; Total MLP

Humic and Fulvic acid Po

0.5 M NaOH

6 h shaking, Centrifuge and filter

Aliquot

a

Digestion/Persulfate; Total P

Humic acid Po = a–b

b

Adjust pH To 1–1.5, Centrifuge, digestion/Persulfate; Fulvic acid Po

3

Non labile R Po

0.1 M H₂SO₄

24 h shaking, Centrifuge and filter