Quantitative evaluation of pore characteristics of sodic soils reclaimed by flue gas desulphurization gypsum using X‐ray computed tomography

Abstract

Flue gas desulphurization (FGD) gypsum can effectively remediate sodic soils through improving two‐dimensional/three‐dimensional (3D) soil pore characteristics, especially vertical macroporosity. Understanding the response pattern of pore characteristics of sodic soils with different textures to FGD gypsum reclamation measures is critical to formulating appropriate improvement strategies for addressing growing challenges of land degradation. The objectives of this study were (a) to quantify the effect of FGD gypsum on two‐dimensional/three‐dimensional pore characteristics of amended sodic soils using X‐ray computed tomography (CT); and (b) to investigate the response pattern of different sodic soils to reclamation measures. Three types of intact sodic soils (sandy loam, silty loam, and silt soil) were collected from different sodic fields in north China for X‐ray CT image scan, and soil pore characteristic parameters (including porosity, pore network density, pore length density, and tortuosity) were measured. The results indicate that the high proportion of horizontal pores and lower pore length density are typical features in the sodic soils investigated. The responses of three sodic soils to reclamation measures demonstrate obvious variations that the 3D macroporosity of silt sodic soils was significantly increased (p < .05) by 53.7%, showing more sensitive and better effect than that of sandy loam (52.9%) and silty loam (20%) sodic soils, in which the reclamation improved the vertical macroporosity of silt sodic soil by 164.6%. It is speculated that the higher clay and silt contents in the silt sodic soils and their interaction with gypsum contribute to the expansion of pore size, and the formed macropore promotes the vertical migration of clay and silt particles to further increase the vertical macroporosity. In addition, FGD gypsum is beneficial for the formation of new pores in silt loam soils. The findings of this study confirm the feasibility of quantifying pore characteristics of sodic soils with the help of X‐ray CT images and suggest that it is necessary to adopt specific reclamation strategies for different degraded sodic soils.

Pore structure alteration in a reclaimed saline–sodic soil identified by multiscale X‐ray tomography

“…The possible mechanisms of pore structure change following DSS application could be summarized as the following two aspects. Firstly, the application of DSS increased the soil aggregation, resulting in the increase of inter‐aggregate porosity, which is consistent with previous research (Liao et al., 2020; Tirado‐Corbala et al., 2019; Yu et al., 2014). Moreover, the DSS amendment enhanced the growth of the alfalfa roots and then increased the total porosity of 10–20 cm in T1 and T4 soil cores.…”

“…The restoration of saline and sodic soils can be achieved by adding soil amendments, including biochar, rice ( Oryza sativa L.) straw, and desulfurized gypsum (Chen et al., 2015; Fei et al., 2019; Sun et al., 2021; Zhang et al., 2020). Among them, the desulfurized gypsum is one of the most important amendments that has been widely applied in saline–sodic soils (Liao et al., 2020; Qadir et al., 2001; Wang et al., 2017). It is a powder‐like by‐product of wet flue gas desulfurization, in which lime or steel slag powder were used as a sorbent of SO 2 emitted from coal‐fired power plants (Baligar et al., 2011).…”

Soil salinity and sodicity changes after a one‐time application of flue gas desulphurization gypsum to paddy fields

“…The reclamation mechanism of FGD gypsum lies mainly in the supply of Ca 2+ . Released Ca 2+ can exchange for Na + in the soil colloids to compress colloidal electric double layers and make colloidal particles more hydrophobic, which enhances the flocculation and aggregation of soil colloids and improves soil permeability (Armstrong & Tanton, 1992; Ilyas et al, 1997; Liao et al, 2020; Qadir et al, 2000; Tirado‐Corbalá et al, 2013). In addition, Ca 2+ reacts with HCO 3 − and CO 3 2− in soil to form CaCO 3 , which is practically insoluble in water (Wang et al, 2017).…”