Elemental and Fourier Transform-Infrared Spectroscopic Analysis of Water- and Pyrophosphate-Extracted Soil Organic Matter

Soil organic matter (SOM) plays an important role in soil fertility and, thus, in sustaining potato production. To investigate the impact of crop rotation on SOM composition, we sequentially extracted SOM by water (WEOM) and sodium pyrophosphate solution (PEOM) from different 3-year potato crop rotations with or without irrigation and quantified its elemental compositions. Different contents of P, Ca, Al, and Fe were observed among the PEOM fractions from fields with different crop rotations. Elemental contents in PEOM from irrigated treatments were consistently lower than those from the corresponding rainfed treatments. The structural features of these WEOM and PEOM samples were further characterized by Fourier transform-infrared (FT-IR) spectroscopy. Generally, the impacts of rotation and irrigation practices reflected on the changes of FT-IR band intensities in 3,020-2,800 cm−1 (aliphatic groups) and 1,640-1,600 cm−1 (aromatic compounds) of WEOM samples. The FT-IR spectroscopic analysis indicated that PEOM was more enriched in aliphatic, carboxyl, and aromatic compounds than WEOM. However, neither crop rotation nor irrigation changed the relative abundance of these functional groups in PEOM. This research improves our understanding of how the properties of SOM may be impacted by crop management.