Soil Water Retention Estimated From Pore Size Distribution Measured by X-Ray Microtomography.

Soil water retention curve (SWRC) is fundamental for characterizing the hydraulic behavior of soils. It relates soil water content and matric potential, and traditionally is obtained using the tension table and the pressure chamber methods. For near saturation conditions, soil pore structure plays an important role in the soil water retention properties because capillarity is the physical effect that holds the water inside the soil. Soil pore structure is frequently modeled as a bunch of capillaries of different characteristic diameters. Due to the simplicity, this model do not account for important soil pore characteristics as, for instance, connectivity and tortuosity. X-ray microtomography is a powerful tool that allows a detailed description of the soil pore size distribution (PSD) and their connectivity. In the present study five brazilian oxisols were investigated using X-ray microtomography with image spatial resolutions between 30μm and 1μm and their pore size distributions were assessed using different approaches for their estimation. The integral of the pore size distribution were then computed to generate the soil water retention curve, which were compared with traditional SWRC obtained by the tension table and the pressure chamber methods.