Accuracy assessment of bulk density measurement methods across different soil management practices: sample volume- and paraffin temperature-related errors

Abstract

Soil bulk density (BD) serves as a crucial physical property for characterizing soils and assessing the quality of their management systems. Various methods, including the Core, Clod, and Jolly balance (JBM) methods, are employed for BD measurement. However, these methods can yield significantly different measurements due to analytical errors. This study aims to assess the accuracy of these methods in a clayey Oxisol under different management conditions, while also identifying primary experimental errors in BD determination and strategies for their mitigation. Different statistical approaches were employed to analyze the impacts of sample volume, paraffin temperature, and management systems on BD determination methods. Method accuracy exhibited variation among management systems, particularly notable in secondary forest (SF) areas. In these areas, Core-based BD measurements were 37% lower than those obtained by the Clod and JBM methods. This disparity can be attributed to the higher macroporosity observed in SF, leading to greater sample volume loss and smaller volumes analyzed by the Clod and JBM. A correlation between paraffin temperature for sample coating and clod volume was observed, with paraffin temperature affecting BD measurements only in clods larger than 69.9 cm3. The paraffin temperature inducing the lowest mean error for larger clods was 92°C. For clods smaller than 69.9 cm3, BD measurement errors arose due to inadequate sample volume. Representative elementary volume was identified as a means to mitigate BD overvaluation by the Clod method. A volume of 99 cm3 proved effective in reducing mean BD errors to 5%, making it suitable for both field sampling and laboratory analytical procedures.

Keywords

• Core method; Jolly balance method; paraffin-coated clod method; representative elementary volume; analysis of covariance.