LIBS and FTIR-ATR spectroscopy studies of mineral-organic associations
in salinized soil
Abstract
The direct characterization of the spatial distribution of elements and
compound binding of salt-organic associations in soil is imperative for
understanding the mechanisms of organic matter decomposition and
nutrient release in soil degradation and development processes. Modern
spectroscopic techniques provide a feasible method for analysis at the
microscale. In this study, mid-infrared attenuated total reflectance
spectroscopy (FTIR–ATR) was used to obtain molecular functional group
information, laser-induced breakdown spectroscopy (LIBS) was apply to
obtain micro-level distribution features of elements in soil, and
two-dimensional correlation spectroscopy (2DCOS) analysis was conducted
to illustrate the binding combination features of mineral-organic
associations in salinized from the Hetao Irrigation District in China.
The results showed that the distributions of Mg, Ca, Na, and K were
heterogeneous at the micro-level; the spatial distributions of Mg and Ca
showed a significant correlation (r = 0.90***), while K displayed a
negative correlation with the SOM contents. In soil with lower SOM
contents, the elements were distributed at the top of the ablation area
and enhanced with the increasing SOM content, which reflected the trends
of the SOM layer thickness outside the mineral–organic associations at
the micro-level. Furthermore, 2DCOS analysis suggested that the hydrogen
bonds in silicate groups were stronger than those of organic functional
groups, such as C=O/C=C, when combined with salt-related compounds, and
Mg, Ca, Na, and K did not originate from clay mineral compounds in
salinized soil, but partially originated from deposited organic
associations.