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Purpose <p>This study investigates how soil organic matter (SOM) affects iron (Fe) adsorption and desorption in an alkaline, iron-rich fluvo-aquic soil of Shandong Province, China. Understanding SOM–Fe interactions is critical for improving Fe bioavailability and crop productivity in such alkaline soils.[Materials and Methods] Soil samples with varying SOM were prepared by removing native SOM and adding organic fertilizer to create an SOM gradient. Fe adsorption–desorption was studied using batch equilibrium experiments. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray (SEM–EDS) were used to identify functional groups binding Fe and to observe Fe–SOM associations. Adsorption isotherms were fitted with Langmuir and Freundlich models, and adsorption kinetics were evaluated with pseudo-first-order and pseudo-second-order models.</p> Results and discussion <p>Removing SOM significantly decreased Fe adsorption capacity, leaving more Fe in residual and oxide-bound forms and less in SOM-bound form. Adsorption followed the Freundlich model more closely than Langmuir, indicating heterogeneous, multilayer sorption on SOM-provided sites. FTIR confirmed that SOM supplies active Fe-binding sites (carboxyl and hydroxyl groups). SEM–EDS mapping showed Fe co-localized with carbon-rich regions in high-SOM treatments, corroborating that added SOM promotes greater Fe accumulation on soil particles. Adsorption kinetics were best described by a pseudo-second-order model, suggesting chemisorption (strong Fe–SOM bonding) as the dominant mechanism. Desorption experiments indicated that Fe bound with SOM was not easily released (lower desorption rates after SOM removal), highlighting specific and partly irreversible retention mechanisms.</p> Conclusions <p>SOM plays a critical role in stabilizing Fe and improving its bioavailability in alkaline soil. Maintaining adequate SOM levels is crucial for enhancing Fe retention, reducing Fe leaching, and improving plant Fe nutrition and crop yields in such soils. Sustainable agricultural practices should therefore prioritize SOM conservation to ensure long-term Fe availability.</p>

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Effect of soil organic matter on iron adsorption and desorption in an alkaline, iron-rich fluvo-aquic soil (Shandong, China)

  • 期刊论文

  • 发表日期：

    2025年9月26日

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  • Guoliang Liu,
  • Suyan Li,
  • Xiangyang Sun

摘要

Purpose

This study investigates how soil organic matter (SOM) affects iron (Fe) adsorption and desorption in an alkaline, iron-rich fluvo-aquic soil of Shandong Province, China. Understanding SOM–Fe interactions is critical for improving Fe bioavailability and crop productivity in such alkaline soils.[Materials and Methods] Soil samples with varying SOM were prepared by removing native SOM and adding organic fertilizer to create an SOM gradient. Fe adsorption–desorption was studied using batch equilibrium experiments. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray (SEM–EDS) were used to identify functional groups binding Fe and to observe Fe–SOM associations. Adsorption isotherms were fitted with Langmuir and Freundlich models, and adsorption kinetics were evaluated with pseudo-first-order and pseudo-second-order models.

Results and discussion

Removing SOM significantly decreased Fe adsorption capacity, leaving more Fe in residual and oxide-bound forms and less in SOM-bound form. Adsorption followed the Freundlich model more closely than Langmuir, indicating heterogeneous, multilayer sorption on SOM-provided sites. FTIR confirmed that SOM supplies active Fe-binding sites (carboxyl and hydroxyl groups). SEM–EDS mapping showed Fe co-localized with carbon-rich regions in high-SOM treatments, corroborating that added SOM promotes greater Fe accumulation on soil particles. Adsorption kinetics were best described by a pseudo-second-order model, suggesting chemisorption (strong Fe–SOM bonding) as the dominant mechanism. Desorption experiments indicated that Fe bound with SOM was not easily released (lower desorption rates after SOM removal), highlighting specific and partly irreversible retention mechanisms.

Conclusions

SOM plays a critical role in stabilizing Fe and improving its bioavailability in alkaline soil. Maintaining adequate SOM levels is crucial for enhancing Fe retention, reducing Fe leaching, and improving plant Fe nutrition and crop yields in such soils. Sustainable agricultural practices should therefore prioritize SOM conservation to ensure long-term Fe availability.