Computed tomographic measurement of macroporosity in chisel-disk and no-tillage seedbeds

Methods for evaluating soil conditions as influenced by tillage are often limited to analysis of bulk samples. The application of medical computed tomography (CT) to the characterization of tillage effects on soil provides an alternative tool for measurement since it is at a more detailed scale. The objective of this study was to compare soils under conventional and no-tillage (NT) systems using X-ray CT. Chisel-disk-disk (CDD) conventional tillage and NT systems were compared for a Mexico silt loam (fine, smectitic, mesic Aeric Vertic Epiaqualfs) soil. Five replicate soil cores (75 mm long by 75 mm diameter) were collected from each treatment. Two CT systems were used in this study: a medical CT scanner (MCT, 1 mm thick scans) and an ultra-high resolution CT scanner (UHCT, 0.1 mm thick scans). Significantly higher soil density was found for the NT treatment using the MCT scanner (P=0.05). Data from the UHCT scanner were used to compare the effects of scan thickness and to evaluate macropore characteristics. Macropore area was significantly higher (P<0.001) for CDD as compared to the NT treatment: 11 versus 5%. The number of macropores in the CDD treatment were twice those in NT; their perimeter was 62% longer; and their circularity was 94% of that for pores from the NT tillage treatment. The macropore box-counting fractal dimension (D) was significantly greater (P<0.001) for CDD (D=1.44) as compared to the NT treatment (D=1.26), reflecting the greater space-filling behavior of the CDD treatment. This study shows that the UHCT scanner can characterize differences in soil macroporosity more precisely than standard MCT scanners. The use of ultra-high resolution tomography can aid in the discrimination of differences between seedbeds created by different tillage systems.