玉米秸秆还田后土壤胡敏酸变化的谱学研究

Study on Humic Acids in the Soil Applied with Corn Stalk by Spectroscopy Measurements

采用红外示差光谱、13C-核磁共振波谱和激光解吸质谱对玉米秸秆施入土壤后土壤胡敏酸(HA)的谱学特征的动态变化进行了研究。结果表明,在玉米秸秆施入土壤后土壤HA的变化具有阶段性,在开始的60d,主要是以秸秆含有的类胡敏酸物质(秸秆HA)为基础,腐解产物发生聚合作用形成新的与秸秆HA相类似的HA,并且秸秆分解形成的小分子中间产物与土壤原有的HA发生作用而进入HA结构中。而在施入60d后,碳水化合物和酰胺化合物以木质素分解的残体为核心发生聚合作用形成新HA,且在90d后进入HA中的亚甲基成分发生了转化,并伴随有甲氧基和甲基的产生。玉米秸秆分解形成的中间产物与土壤HA发生聚合反应,一部分形成为亚稳态的聚合体。玉米秸秆施入土壤后,土壤HA的芳香度降低,芳香碳减少,而烷基碳和烷氧碳增加,HA的脂肪族特性增强,同时,羧基碳减少,土壤HA的氧化程度下降,HA的平均分子量降低。

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.