Comparing two methods for measuring soil bulk density and moisture content

Authors: Jabro, Jalal - Jay; Stevens, William - Bart; Iversen, William - Bill

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2020
Publication Date: 6/12/2020
Citation: Jabro, J.D., Stevens, W.B., Iversen, W.M. 2020. Comparing two methods for measuring soil bulk density and moisture content. Open Journal of Soil Science. 10(6):233-243. https://doi.org/10.4236/ojss.2020.106012.
DOI: https://doi.org/10.4236/ojss.2020.106012

Interpretive Summary: Soil bulk density is defined as the ratio of the mass of oven-dried soil to the bulk volume of the soil. It is also used to convert gravimetric measurements of soil water contents to volumetric basis and to calculate total soil porosity. Bulk density is an important soil property that can often be used as an indicator of soil compaction, affecting soil porosity, water movement, rooting depth, and water holding capacity. It is also affected by soil texture, total porosity, amount of organic matter, and land management practices. The core sampling method and the CPN MC-3 Elite™ radiation gauge method for measuring bulk density (BD) and moisture content (MC) in a clay loam soil were compared. Significant differences exist between two methods for both BD and MC measurements. Variations in BD and MC measurements between two methods could have resulted from differences in soil compaction and soil disturbance caused by the core and radiation techniques, respectively, as well as by other sources of error. Different methods for measuring BD and MC produce different results. These methods have advantages and disadvantage for measuring soil BD and MC which one can consider in selecting an appropriate method for particular goals, situations and conditions. To date, there is no ideal method for measuring soil BD and MC, though, the core sampling method is the most common one for measuring BD for many agricultural, hydrological and environmental investigations in most soils. The accuracy, performance labor and time requirements and cost of each method must be considered when choosing a method for a particular application.

Technical Abstract: Soil bulk density and moisture content are dynamic properties that vary with changes in soil and field conditions and have many agricultural, hydrological and environmental implications. The main objective of this study was to compare between a soil core sampling method (core) and the CPN MC-3 Elite™ nuclear gauge method (radiation) for measuring bulk density (BD) and volumetric moisture content (MC) in a clay loam soil. Soil BD and MC measurements were determined using the core and radiation methods at 0 - 10 and 10 - 20 cm soil depths. The mean values of soil BD obtained using the core method (1.454, 1.492 Mg m-3) were greater than those obtained using the radiation method (1.343, 1.476 Mg m-3) at the 0 - 10 and 10 - 20 cm depths, respectively. Mean BD and MC values averaged across both depths (referred to as the 0 - 20 cm depth) measured by the core method were 4.47% and 22.74% greater, respectively, than those obtained by the radiation method. The coefficients of variation (CV) of soil BD values measured by the core method were lower than the CV values of those measured by the radiation method at both depths; however, the CV’s of BD values for both methods were larger at the 0 - 10 cm depth than those measured at the 10 - 20 cm depth. Similarly, the CV values of soil MC values measured by the core method were lower than the CV values of those measured by the radiation method at both depths. There were significant differences between two methods in terms of BD and MC, with the core method generating greater values than the radiation method at the 0 - 20 cm depth. These discrepancies between the two methods could have resulted from soil compaction and soil disturbance caused by the core and radiation techniques, respectively, as well as by other sources of error. Nevertheless, the core sampling method is considered the most common one for measuring BD for many agricultural, hydrological and environmental investigations in most soils.