Structural Analysis of Humic Acid in Soil at Different Corn Straw Returning Modes through Fluorescence Spectroscopy and Infrared Spectroscopy

Table 4

Positions and intensities of peaks in total luminescence fluorescence spectra of soil humic acids.

Treatment	Depth (cm)	Peak L		Peak C
		EEWP (nm)	Intensity (a.u.)	EEWP (nm)	Intensity (a.u.)
CK	5–20	472/536	254.0	307/521	231.1
St		473/524	171.7	307/518	195.1
Ss		473/532	235.6	307/522	230.0
Smt		473/528	216.6	307/521	202.8
Sms		472/531	223.7	307/520	225.3
CK	20–40	473/531	220.4	307/528	225.9
St		473/533	188.9	307/523	208.7
Ss		473/536	243.6	307/530	243.0
Smt		472/538	231.2	307/533	232.0
Sms		473/536	226.2	307/520	213.9

Note: no straw was applied (CK), straw returning to topsoil (St), straw returning to subsoil (Ss), straw mixing with topsoil (Smt), and straw mixing with subsoil (Sms).