Estimating soil porosity and pore size distribution changes due to wetting-drying cycles by morphometric image analysis

Porous systems such as soils tend to present great complexity when analyzed at the micrometer-scale. Processes such as tillage and repeated wetting and drying (W-D) cycles tend to continuously alter the structure of the soil. X-ray computed microtomography (μCT) is one of the techniques that can be utilized for quantifying changes in the soil micrometer-scale structure. The objective of this study was to analyze the effect of W-D cycles in the soil porous system of core samples submitted to contrasting management practices (conventional tillage – CT, minimum tillage – MT, no-tillage – NT). An algorithm based on the Mercury intrusion porosimetry method (MIP) was utilized for this purpose. An area of secondary forest (F) was used as a reference. The results of the porosity and functionality of the pores showed that the W-D cycles altered the pore distribution in all management systems. MT was the management that showed the most significant changes in the soil physical properties, where the application of W-D cycles caused fractions of transmission pores to become fissures. In CT, a significant reduction of transmission pores was observed, which indicates the effect of harrowing and plowing operations. Our results show that, depending on the management system adopted, the soil will respond differently to the action of W-D cycles with a direct influence on water retention and movement due to the induced changes in the soil porous system.