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

Figure 5

Total luminescence spectra of humic acids: topsoil (5–20 cm); subsoil (20–40 cm). 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). (a) Topsoil: CK. (b) Topsoil: St. (c) Topsoil: Ss. (d) Topsoil: Smt. (e) Topsoil: Sms. (f) Subsoil: CK. (g) Subsoil: St. (h) Subsoil: Ss. (i) Subsoil: Smt. (j) Subsoil: Smt.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)