Insights into the accumulation and chemical composition of soil organic matter influenced by saltwater intrusion in agricultural areas

Abstract

Saltwater intrusion (SWI) poses a critical issue for agricultural systems and soil carbon (C) cycling. Although the central role of soil organic matter (SOM) as a terrestrial C reservoir, in-depth information on how SWI influences SOM accumulation and chemical composition in agricultural areas remains elusive. To address this gap, agricultural soils from areas unaffected by SWI (control, CT area) and those impacted by SWI (SWI area) were subjected to SOM fractionation into free particulate (fSOM), occluded light (oSOM), weakly bound (wSOM), and strongly bound (sSOM) fractions. ¹³C nuclear magnetic resonance (NMR) was employed for chemical characterization of bulk soil and SOM fractions. Total soil organic C (SOC) under the SWI area (31 ± 1 g C kg⁻¹) was lower than the CT area (37 ± 1 g C kg⁻¹), presumably attributable to depletion of the O-alkyl C and carboxy C. The SOC accumulated in fSOM and oSOM fractions under the SWI area (2.1 ± 0.2 and 2.5 ± 0.3 g C kg⁻¹ soil, respectively) was lower than the CT area (3.2 ± 0.2 and 3.4 ± 0.3 g C kg⁻¹ soil, respectively), possibly reflecting diminished O-alkyl C. Similarly, SOC stored in wSOM and sSOM was smaller in the SWI area (7.4 ± 0.6 and 18.2 ± 1.1 g C kg⁻¹ soil, respectively) than the CT area (9.1 ± 0.4 and 21.3 ± 0.6 g C kg⁻¹ soil, respectively), presumably due to reduced aromatic C. These findings highlight the SWI impacts on SOM accumulation forms in agricultural areas, linking them with chemical components.