Table 1 Percentages of different C functional groups in humic acid extracted from microaggregates (150–250 µm), determined by 13C nuclear magnetic resonance spectroscopy (Supplementary Fig. S7).

From: Sub-micron level investigation reveals the inaccessibility of stabilized carbon in soil microaggregates

 

Carboxyl

Aromatic

O-alkyl

Alkyl

HIL

HOB

HIL/HOB ratio

%

NTR

7.6

50.6

21.3

20.5

28.9

71.1

0.41

CTR

10.4

35.2

31.2

23.2

41.6

58.4

0.71

  1. Four regions: carboxyl C (220–160 ppm), aromatic C (160–100 ppm), O-alkyl C (110–45 ppm), and alkyl C (45–10 ppm). Aromatic and alkyl C represent hydrophobic (HOB) fraction. Carboxylic and O-alkyl represent hydrophilic (HIL) fraction. NTR represents no-till, complex crop rotation. CTR represents conventional till, complex crop rotation.
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