The soil bulk density of undisturbed samples was evaluated using computed tomography and paraffin-sealed soil clod techniques, with the objective of identifying soil compaction processes and to compare the applied methodologies. Data were also used to complement a soil classification survey for irrigation purposes. Samples were collected from soil profiles of the semi-arid region of Petrolina (PE), Brazil, from the soil surface down to a depth of 1 m, in 10 cm layers. Two distinct areas were chosen: (1) native vegetation ("caatinga"), and (2) cultivated area under central pivot irrigation. Tomographies were obtained by a first generation tomograph, using a 137Cs gamma source, a NaI (Tl) scintillation crystal, and a standard electronic counting system linked to a sample moving system, controlled by a specific computational interface. Results suggest a density increase at greater depths (below 0.4 m) for the "caatinga" area. In the central pivot area, a compacted soil layer was detected between approximately 0 and 0.4 m, consisting of natural and/or dense layers, possibly due to machinery action during soil tillage.
dense layer; compaction; gamma radiation