A quantitative study on three-dimensional pore parameters and physical properties of sodic soils restored by FGD gypsum and leaching water.

The application of flue gas desulfurization (FGD) gypsum has been recognized as a feasible measure in enhancing the quality of sodic soils. Quantitative evaluation of the effects of FGD gypsum on three-dimension (3D) pore characteristics is beneficial for understanding the reclamation mechanism of FGD gypsum on sodic soils. We collected intact soil cores from a sodic field at four depths (0-10, 10-20, 20-40, and 40-60 cm) in northern China to reconstruct 3D pore structures using X-ray computed tomography (CT), thus quantifying the effects of FGD gypsum (10.1 and 14.5 t hm) and leaching water (1520 and 2200 t hm) on the 3D pore characteristics and related soil physical properties. The treatments using FGD gypsum with leaching water promoted the formation of new pores and significantly (p < 0.05) increased the 3D image-based macroporosity, mesoporosity, total pore length, and number of nodes at depths of 0-20 cm, improving the permeability of sodic soils investigated, which is validated by the enhanced saturated hydraulic conductivity (K). Irrigation water of 1520 t hm is demonstrated effective in assisting FGD gypsum dissolution and leaching, but excessive leaching water (2200 t hm) may reduce the permeability of 20-40 cm depth. The combined application of 14.5 t hm FGD gypsum and 1520 t hm leaching water is suggested to obtain the optimal result for the investigated sodic soils. This study offers an applicable strategy for sodic soils reclamation and provides a reference for revealing the improvement mechanism of sodic soils by FGD gypsum and leaching water.