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Table 4 Total and DCB extractable Al and Fe in the humic fractions

From: Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Fraction Si Fe Al
Total Total DCB extractable Total DCB extractable
(mol kg−1) (mol kg−1) (mol kg−1) (%)a (mol kg−1) (mol kg−1) (%)a
pH 1 Insoluble 1.81a 0.47abe 0.30ab 64 1.02a 0.29ac 28
Soluble nd nd nd nd nd nd nd
pH 3 Insoluble 1.67ae 0.60ace 0.35ab 58 1.03a 0.33a 32
Soluble 0.87be 0.24bde 0.24a 100 0.08b 0.10b 125
pH 5 Insoluble 3.67c 0.73c 0.25a 34 2.33cd 0.09b 4
Soluble 0.84be 0.37de 0.28ab 76 0.46a 0.22c 48
pH 7 Insoluble 4.22d 0.83c 0.37b 46 2.74d 0.10b 4
Soluble 1.26e 0.38e 0.27ab 71 0.60a 0.26c 43
  1. aPercentage of the total. Within columns, values followed by the same letter are not significantly different (P < 0.05). nd, not determined.