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Table 1 Yield, ash content, and elemental composition of the humic fractions

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

Fraction Yield (g kg−1soil) Asha(g kg−1humic fraction) Elemental compositionb(g kg−1humic fraction) Molar ratio
    C H N O O/C
pH 1 Insoluble 83.9 247 541a 42a 43a 374a 0.5
Soluble 2.3 196 478bd 44a 43a 434bc 0.7
pH 3 Insoluble 88.0 267 525a 45a 42a 388ab 0.5
Soluble 7.2 127 493bc 41a 45a 421abc 0.6
pH 5 Insoluble 22.2 542 478bd 55b 40a 427bc 0.7
Soluble 60.3 225 518ac 49b 41a 392ab 0.6
pH 7 Insoluble 7.4 609 451d 52b 39a 459c 0.8
Soluble 67.3 283 534a 49b 42a 375a 0.5
  1. aValues are the means of three replicates, and the standard error values are < 10%; bon a moisture and ash-free basis. Within columns, values followed by the same letter are not significantly different (P < 0.05).