Particle+Density Balesdent

Description and working steps

  • 50 g dry soil in 150ml deionized water in 250ml plastic flask + 7 glass beads, agitation 50 rpm over night (16h)
  • Sieving at 200 µm
  • The fraction > 200 µm is flotated in water, to separate a light (POM) and a dense (mineral) fraction
  • The suspension < 200 µm is sieved at 50 µm
  • The fraction > 50 µm is flotated in water, to separate a light (POM) and a dense (mineral) fraction

The fraction < 50 µm is floculated with CaCl2 0.8 g L-1)

Note :

If soils are clayey and very rich in SOC (≥4%) HMP can be used in step 1 to ensure aggregate dispersion.

Initial Aim

Advantages

  • Fractions do not need to be rinsed before characterization. No C loss.
  • Cheap, relatively fast (2h /sample)
  • Dispersion of all aggregates > 50 µm easily checked with binoculars.
  • Use of glass beads instead of ultrasons avoids POM beakdown (as described in Balesdent et al. 1991 and Schmidt et al. 1997).
  • The fraction < 50 µm can be further fractionated (clay, fine silt, coarse silt, e.g. Balesdent et al 87, 98; Puget et al. 2000) after dispersion with ultrasonic.

Disadvantages

  • The flotation-panning requires some practice

Reference

Balesdent, J., 1987. The turnover of soil organic fractions estimated by radiocarbon dating. Science of the Total Environment 62, 405-408