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

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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