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

Chemical and Biological Technologies in Agriculture

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

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	1.81^a	0.47^abe	0.30^ab	64	1.02^a	0.29^ac	28
pH 1	Soluble	nd	nd	nd	nd	nd	nd	nd
pH 3	Insoluble	1.67^ae	0.60^ace	0.35^ab	58	1.03^a	0.33^a	32
pH 3	Soluble	0.87^be	0.24^bde	0.24^a	100	0.08^b	0.10^b	125
pH 5	Insoluble	3.67^c	0.73^c	0.25^a	34	2.33^cd	0.09^b	4
pH 5	Soluble	0.84^be	0.37^de	0.28^ab	76	0.46^a	0.22^c	48
pH 7	Insoluble	4.22^d	0.83^c	0.37^b	46	2.74^d	0.10^b	4
pH 7	Soluble	1.26^e	0.38^e	0.27^ab	71	0.60^a	0.26^c	43

^aPercentage of the total. Within columns, values followed by the same letter are not significantly different (P < 0.05). nd, not determined.