X-ray computed tomography for assessing the effect of tillage systems on topsoil morphological attributes

Abstract

The sustainability and efficiency of crop production are sometimes dependent on the adopted tillage system. In Brazil, conservation systems such as no-tillage (NT) have been adopted as an alternative to conventional tillage (CT) method. Conservation tillage systems usually tend to minimize soil losses, water runoff, preserve soil moisture and reduce the disruption of the soil structure. Nevertheless, the influence of these managements in the soil porous system, in the micrometric point of view, is not presented in most of the published literature. Considering the importance of pores for the proper functioning of the soil, the main objective of this study was to analyze the effect of long-term NT and CT systems, in comparison to non-managed soil maintained under secondary forest (F) conditions on the pore system of a clay soil, using 3D X-ray computed tomography (μCT) images. To achieve this goal, 3D μCT images were obtained from samples of the surface soil (0.05-0.10 m and 0.10-0.15 m). Morphological attributes such as: macroporosity (MAP), number of macropores (NMAP), shape of pores, tortuosity (τ) and connectivity (C), estimated based on the Euler-Poincaré characteristic (EPC), were employed to characterize the soil porous system. In addition, saturated hydraulic conductivity (Ks) and soil water retention curve (SWRC) were analyzed. The forest was characterized by the highest MAP. However, when comparing the tillage systems, the CT MAP was larger than that of NT. Ks showed the same trends, which indicates that Ks was directly influenced by MAP. However, SWRC analyses showed a greater volume fraction of mesopores and micropores under NT than under CT. The macropore size distribution reveals that large well-connected macropores (volume >1000 mm3) were responsible for the major contribution to MAP. However, the highest contribution to NMAP was given by macropores with volume up to 0.1 mm3. Tortuosity results indicate less sinuous pores for F, when compared to CT and NT. EPC results present better connectivity of pores in the shallow layer 0.05-0.10 m for F, while the opposite was observed for CT. The present research showed that from 3D μCT images, associated with results of hydraulic properties, it is possible to characterize the macroporous system of undisturbed samples. Research like this is important to infer about the impacts of management systems on soil.