X-ray microtomography analysis of lime application effects on soil porous system

Soil liming has demonstrated to be efficient to make acidic soils suitable to agriculture but little research has been done to evaluate its effect on soil structure in the microscale. X-ray microtomography (μCT) is a useful technique to obtain valuable information about the micromorphological characteristics of soil and, thus, can provide important insight into how liming affects such a porous system. In this study, μCT was used to evaluate changes on micromorphological and geometrical properties (porosity, number of pores, pore length, elongation, shape, connectivity and tortuosity) of a soil cultivated under no-tillage system (NTS) caused by the application of lime on the surface. A degraded pasture area representing soil conditions before the NTS implementation was also analyzed. Samples from two soil layers (0-10 cm, A, and 10-20 cm, B) were analyzed with a voxel size of 60 μm. Image visualization, processing and analysis were performed in the Avizo Fire software. Liming improved the soil chemical attributes only at layer A where it also produced positive effects on the soil porous system within a period of thirty months. We highlight the increase in soil porosity and number of pores into which the main soil pore was separated, as evidences of liming effects. At layer A, those pores were found to be more elongated and more connected for the limed site. However, changes in the pattern of the separated pores, with the formation of cylindrical pores in the horizontal orientation for the limed site, were observed at both soil layers, which can be attributed to stimulation of the soil fauna activity due to liming.