Abstract: Spectroscopy measurements (Fourier transform infrared differential spectroscopy, Carbon-13 nuclear magnetic resonance spectrometry, Matrix-assisted laser desorption/ionization-time of flight mass spectrometry) were performed to study the humic acids in the soil applied with corn stalk. The results showed that after incorporation of corn stalks into the soil, the soil humic acid (HA) changed significantly at different stages. During the first 60 days, new HAs were formed by polymerization and seems to be similar to that of initial HAs from composting corn stalk, some little molecular organic matters also reacted with soil HAs and turned into parts of soil HAs. After 60 days of the corn stalk residue incorporation , new HAs were formed by polymerization of decomposed lignin molecules, some methylenes transformed into methyls and methoxyls since 90th day. Application of corn stalk resulted in the increase of aliphatic components in soil HAs, the decrease in aromatic components of soil HAs and the suppression in oxidation degree of soil HAs. The average molecular weight of soil HAs also declined due to the application of corn stalk.

Key words: Corn stalk, Soil humic acid, Spectroscopy measurement