Rapid Nondestructive Bulk Density and Soil‐Water Content Determination by Computed Tomography

Abstract

AbstractComputed tomography (Ct) is a promising tool that may help provide measurements needed to obtain finer resolution in soil‐water content and bulk density for water uptake studies or detailed investigation of root‐soil interactions. A need exists for a unified method to accurately predict soil bulk density and water content using output from CT. Research was conducted on soil collected from the A horizon of Mexico silt loam (Udollic Ochraqualfs) and the B2t horizon of Crider silt loam (Typic Paleudalfs) to evaluate the relationship between linear attenuation coefficients and volume fraction of soil solids and water. Air‐dry soil (<2 mm) was packed into polyvinyl chloride cylinders at densities between 1.2 and 1.6 Mg/m3 and CT slices or tomographs were taken before and after water was added. The relationship between attenuation coefficients and volume fraction of soil solids was linear for both of the soils evaluated. Parameter values for the Mexico soil compared favorably with those determined on previous data collected from Metea fine sandy loam (Arenic Hapludalfs). Differences in the parameter values for the Mexico and Crider soils were attributed to differences in Fe content. An experiment with Fe added to the Mexico soil was conducted that verified the effect of Fe content on the attenuation coefficients. Approximately 98% of the variation between the attenuation coefficients and volume fraction of soil water was accounted for by using linear regression relationships after correction for swelling. Results from this study indicate that it may be possible to develop a universal relationship for computed tomography data vs. soil bulk density and water content; however, more research is needed to characterize the influence of sample size on the calibration relationship.