|ZHANG, MINGCHU - University Of Alaska|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/18/2015
Publication Date: 10/2/2015
Citation: He, Z., Zhang, M. 2015. Structural and functional comparison of mobile and recalcitrant humic fractions from agricultural soils. In: He, H, Wu, F., editors. Labile Organic Matter - Chemical Composition, Functions, and Significance in Soil and the Environment. SSSA Special Publication 62. Madison, WI:Soil Science Society of America. p. 79-98.
Interpretive Summary: Humification is the natural process that occurs in soil and other ecosystems by which organic material decompose and break down to humic matter. An extraction method separates humid acid into mobile humic acid (MHA) and recalcitrant Ca-bound humic acid (CaHA) fractions. This chapter reviews the advances in applying multiple spectroscopic techniques in characterizing the structural and functional groups in MHA and CaHA fractions from agricultural soils. The multiple sets of data allow comparison and correlation analysis of the structural and functional groups of the two types of humic fractions identified by these complementary techniques. Data reviewed in this chapter indicate that MHA is mainly associated with the soil silt fraction whereas CaHA could be associated with the clay fraction. Thus, soil type or location is more critical than cropping management practices to influence these spectral features of the two humic fractions.
Technical Abstract: Mobile humic acid (MHA) and calcium humate (CaHA) are humic fractions sequentially extracted from soil samples. MHA is extracted by dilute NaOH, and CaHA is subsequently extracted by dilute NaOH from the dilute HCl-washed soil residues of the first extraction. This chapter reviews the recent advance in characterization of the structural and functional groups of MHA and CaHA fractions of agricultural soils by sophistical instrumental techniques. Capillary electrophoresis (CE) separates MHA and CaHA fractions into three or two major peaks, mainly superimposed on a characteristic humic "hump". The greater difference in the CE profiles between soils than between cropping management practices reflects the distinct "finger-print" CE features of these soil humic fractions. Modeling analysis of fluorescence excitation-emission matrix spectral data reveals four general fluorophore components. Fourier Transform Infrared (FT-IR) spectral data reveal a linear correlationship between the aliphatic band (3020-2800 cm-1) and the carboxyl band (1720-1600 cm-1) in the same types (i. e. MHA or CaHA) of humic fractions from 10 agricultural soils, suggesting that these two functional groups may be associated with same backbone or matrix in these humic fractions. Correlation analysis of 13C nuclear magnetic resonance (NMR) peak area and intensity of fluorophore components of these humic samples suggests that the fluorophore component 4 is enriched with nonpolar alkyl, NCH and OCH3 functional groups. Comparison of 13C NMR and ultrahigh resolution mass spectral data reveals that proteinaceous material in these humic fractions is associated with the nonpolar alkyl groups, but competitively bound to the humic backbone structure against aromatic groups.