Soil Bulk Density Analysis in Three Dimensions by Computed Tomographic Scanning

Abstract

Abstract Current soil bulk densitometric techniques lack the precision to detect three‐dimensional changes in density in a nondestructive manner. The x‐ray transmission computed tomography (CT) scanner was evaluated as a tool to determine soil bulk density. This scanner is an advanced tool in diagnostic radiology used to obtain a nondestructive cross‐sectional representation of the human body. Typical accuracy and precision for CT scanners are known for materials like human tissue with a linear attenuation coefficient near water. Machine response was evaluated near the upper limit of the measurement range where denser materials, such as soil, are located. Scanner analyses of soil and glass bead‐air filled sphere samples that varied in bulk density from 0.14 to 1.64 g/cm 3 revealed that a positive linear response occurred with increasing density. For the Metea sandy loam soil (Arenic Hapludalfs), this CT scanner was found to have precision in the order of 19 mg/cm 3 . Spatial resolution or the ability to distinguish between two objects in the scanning plane was found to range from 1.25 by 1.25 by 2 mm 3 to 6.4 mm in diameter by 2 mm. The greater resolution was obtained when density within the sample varied greatly. Errors in data can occur as a result of certain machine artifacts; however, many of these can be avoided by relatively simple methods. It was concluded that the CT scanner can be used to determine soil bulk density with good three‐dimensional spatial resolution. This is a potentially promising tool for research in the areas of compaction, soil management, and cultivation.