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Bulk Density

  • Soil Health

  • Physical


Bulk density constitutes a direct measurement of soil compaction (or loosening), serving as an essential tool for evaluating the total porosity. An adequate volume of pore space within the soil is essential for the sustainable use of soil resources, benefiting both productivity and environmental health (Merrington et al.,2006).

Bulk density can capture the impacts of soil use and management on the dynamics of water/air relationships within the soil (Cardoso et al., 2013).

Bulk density is the mass per unit volume, usually expressed as g/cm3 (Sparling et al., 2003; Merrington et al., 2006).

Dry weight bulk density is the generally accepted measure of bulk density (Merrington et al.,2006).

In order to ensure consistency and to obtain reliable data, it is important that sampling protocols for bulk density consider the timing, depth and specific location of sampling (Merrington et al., 2006).

Methodology summary

The FAO Soil Doctor guide provides a standardized methodology for soil bulk density:

  • Intact soil cores are collected and the known volume of soil in the cores is dried at 105 °C and weighed.
  • This method uses a metal core of a known volume, which represents the volume of the soil for the purpose of the calculation of the soil bulk density. The core should be of cylindrical shape to allow for easy determination of its volume.
  • The core sample is pushed into the soil to the desired depth and then gently removed without altering the contents of the core. After obtaining the soil using the core, the soil weight is measured, and using the known volume of the core (an estimation of soil volume), soil bulk density can be determined (FAO soil doctor).

Detailed methodology on the core method and calculation of soil bulk density can be found at Soil Testing Methods from FAO pg. 16-19.

Detailed information on soil sampling such as where to take the samples from, how many, the best time to sample, and depth of sampling, can be found at the Farm Carbon Toolkit.

Metric threshold or direction of change

In general lower bulk density is considered good for soil health as high bulk density can indicate compaction. Thresholds will depend on the type of habitat, vegetation cover, soil type. In general in the UK a low bulk density can range between 0.3-1.3 g/cm3 as benchmarked by the UKCEH (Feeney et al., 2023).

Technological innovations

Thermo–time domain reflectometry (thermo-TDR) technique for monitoring bulk density in situ is non-destructive and able to capture spatial and temporal variations. Less labour intensive than sampling methods. More expensive and less accurate than laboratory methods (Liu et al., 2008).

The radiation method is non-destructive, allowing for the measurement of soil bulk density without altering the physical structure of the soil. It can be a fast method which reduces the time and labour required for soil characterization. The measurements can be taken directly in the field, making it a practical method for on-site evaluations. Its limitations rely on the complex methodology and the accuracy of measurements decreases with soil depth, the need for an experienced operator (Abed et al., 2018).

Digital electrochemical system for measuring and recording dry and wet for soil at different soil depths and textures, remotely (Al Shammary et al, 2019).


  • Agricultural
  • Forest
  • Grassland
  • Peatland
  • Saltmarsh
  • Wetland


  • Community


  • Low


  • Tier 1

Technical expertise

  • Low

Standardised methodology

  • Yes